1 (* Title: HOL/Multivariate_Analysis/Convex_Euclidean_Space.thy
2 Author: Robert Himmelmann, TU Muenchen
3 Author: Bogdan Grechuk, University of Edinburgh
6 header {* Convex sets, functions and related things. *}
8 theory Convex_Euclidean_Space
9 imports Topology_Euclidean_Space Convex "~~/src/HOL/Library/Set_Algebras"
13 (* ------------------------------------------------------------------------- *)
14 (* To be moved elsewhere *)
15 (* ------------------------------------------------------------------------- *)
17 lemma linear_scaleR: "linear (%(x :: 'n::euclidean_space). scaleR c x)"
18 by (metis linear_conv_bounded_linear scaleR.bounded_linear_right)
20 lemma injective_scaleR:
21 assumes "(c :: real) ~= 0"
22 shows "inj (%(x :: 'n::euclidean_space). scaleR c x)"
23 by (metis assms injI real_vector.scale_cancel_left)
25 lemma linear_add_cmul:
26 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
28 shows "f(a *\<^sub>R x + b *\<^sub>R y) = a *\<^sub>R f x + b *\<^sub>R f y"
29 using linear_add[of f] linear_cmul[of f] assms by (simp)
32 assumes "convex S" "x : S" "y : S" "u>=0" "v>=0" "u+v=1"
33 shows "(u *\<^sub>R x + v *\<^sub>R y) : S"
34 using assms convex_def[of S] by auto
37 assumes "convex S" "x : S" "y : S" "u>=0" "v>=0" "u+v>0"
38 shows "((u/(u+v)) *\<^sub>R x + (v/(u+v)) *\<^sub>R y) : S"
39 apply (subst mem_convex_2)
40 using assms apply (auto simp add: algebra_simps zero_le_divide_iff)
41 using add_divide_distrib[of u v "u+v"] by auto
43 lemma card_ge1: assumes "d ~= {}" "finite d" shows "card d >= 1"
44 by (metis Suc_eq_plus1 assms(1) assms(2) card_eq_0_iff fact_ge_one_nat fact_num_eq_if_nat one_le_mult_iff plus_nat.add_0)
46 lemma inj_on_image_mem_iff: "inj_on f B ==> (A <= B) ==> (f a : f`A) ==> (a : B) ==> (a : A)"
47 by (blast dest: inj_onD)
49 lemma independent_injective_on_span_image:
50 assumes iS: "independent (S::(_::euclidean_space) set)"
51 and lf: "linear f" and fi: "inj_on f (span S)"
52 shows "independent (f ` S)"
54 {fix a assume a: "a : S" "f a : span (f ` S - {f a})"
55 have eq: "f ` S - {f a} = f ` (S - {a})" using fi a span_inc
56 by (auto simp add: inj_on_def)
57 from a have "f a : f ` span (S -{a})"
58 unfolding eq span_linear_image[OF lf, of "S - {a}"] by blast
59 moreover have "span (S -{a}) <= span S" using span_mono[of "S-{a}" S] by auto
60 ultimately have "a : span (S -{a})" using fi a span_inc by (auto simp add: inj_on_def)
61 with a(1) iS have False by (simp add: dependent_def) }
62 then show ?thesis unfolding dependent_def by blast
66 fixes f :: "'n::euclidean_space => 'm::euclidean_space"
67 assumes lf: "linear f" and fi: "inj_on f (span S)"
68 shows "dim (f ` S) = dim (S:: ('n::euclidean_space) set)"
70 obtain B where B_def: "B<=S & independent B & S <= span B & card B = dim S"
71 using basis_exists[of S] by auto
72 hence "span S = span B" using span_mono[of B S] span_mono[of S "span B"] span_span[of B] by auto
73 hence "independent (f ` B)" using independent_injective_on_span_image[of B f] B_def assms by auto
74 moreover have "card (f ` B) = card B" using assms card_image[of f B] subset_inj_on[of f "span S" B]
75 B_def span_inc by auto
76 moreover have "(f ` B) <= (f ` S)" using B_def by auto
77 ultimately have "dim (f ` S) >= dim S"
78 using independent_card_le_dim[of "f ` B" "f ` S"] B_def by auto
79 from this show ?thesis using dim_image_le[of f S] assms by auto
82 lemma linear_injective_on_subspace_0:
83 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
84 assumes lf: "linear f" and "subspace S"
85 shows "inj_on f S <-> (!x : S. f x = 0 --> x = 0)"
87 have "inj_on f S <-> (!x : S. !y : S. f x = f y --> x = y)" by (simp add: inj_on_def)
88 also have "... <-> (!x : S. !y : S. f x - f y = 0 --> x - y = 0)" by simp
89 also have "... <-> (!x : S. !y : S. f (x - y) = 0 --> x - y = 0)"
90 by (simp add: linear_sub[OF lf])
91 also have "... <-> (! x : S. f x = 0 --> x = 0)"
92 using `subspace S` subspace_def[of S] subspace_sub[of S] by auto
93 finally show ?thesis .
96 lemma subspace_Inter: "(!s : f. subspace s) ==> subspace (Inter f)"
97 unfolding subspace_def by auto
99 lemma span_eq[simp]: "(span s = s) <-> subspace s"
101 { fix f assume "f <= subspace"
102 hence "subspace (Inter f)" using subspace_Inter[of f] unfolding subset_eq mem_def by auto }
103 thus ?thesis using hull_eq[unfolded mem_def, of subspace s] span_def by auto
106 lemma basis_inj_on: "d \<subseteq> {..<DIM('n)} \<Longrightarrow> inj_on (basis :: nat => 'n::euclidean_space) d"
107 by(auto simp add: inj_on_def euclidean_eq[where 'a='n])
109 lemma finite_substdbasis: "finite {basis i ::'n::euclidean_space |i. i : (d:: nat set)}" (is "finite ?S")
111 have eq: "?S = basis ` d" by blast
112 show ?thesis unfolding eq apply(rule finite_subset[OF _ range_basis_finite]) by auto
115 lemma card_substdbasis: assumes "d \<subseteq> {..<DIM('n::euclidean_space)}"
116 shows "card {basis i ::'n::euclidean_space | i. i : d} = card d" (is "card ?S = _")
118 have eq: "?S = basis ` d" by blast
119 show ?thesis unfolding eq using card_image[OF basis_inj_on[of d]] assms by auto
122 lemma substdbasis_expansion_unique: assumes "d\<subseteq>{..<DIM('a::euclidean_space)}"
123 shows "setsum (%i. f i *\<^sub>R basis i) d = (x::'a::euclidean_space)
124 <-> (!i<DIM('a). (i:d --> f i = x$$i) & (i ~: d --> x $$ i = 0))"
125 proof- have *:"\<And>x a b P. x * (if P then a else b) = (if P then x*a else x*b)" by auto
126 have **:"finite d" apply(rule finite_subset[OF assms]) by fastsimp
127 have ***:"\<And>i. (setsum (%i. f i *\<^sub>R ((basis i)::'a)) d) $$ i = (\<Sum>x\<in>d. if x = i then f x else 0)"
128 unfolding euclidean_component.setsum euclidean_scaleR basis_component *
129 apply(rule setsum_cong2) using assms by auto
130 show ?thesis unfolding euclidean_eq[where 'a='a] *** setsum_delta[OF **] using assms by auto
133 lemma independent_substdbasis: assumes "d\<subseteq>{..<DIM('a::euclidean_space)}"
134 shows "independent {basis i ::'a::euclidean_space |i. i : (d :: nat set)}" (is "independent ?A")
136 have *: "{basis i |i. i < DIM('a)} = basis ` {..<DIM('a)}" by auto
138 apply(intro independent_mono[of "{basis i ::'a |i. i : {..<DIM('a::euclidean_space)}}" "?A"] )
139 using independent_basis[where 'a='a] assms by (auto simp: *)
144 shows "dim (cball (0 :: 'n::euclidean_space) e) = DIM('n)"
146 { fix x :: "'n::euclidean_space" def y == "(e/norm x) *\<^sub>R x"
147 hence "y : cball 0 e" using cball_def dist_norm[of 0 y] assms by auto
148 moreover have "x = (norm x/e) *\<^sub>R y" using y_def assms by simp
149 moreover hence "x = (norm x/e) *\<^sub>R y" by auto
150 ultimately have "x : span (cball 0 e)"
151 using span_mul[of y "cball 0 e" "norm x/e"] span_inc[of "cball 0 e"] by auto
152 } hence "span (cball 0 e) = (UNIV :: ('n::euclidean_space) set)" by auto
153 from this show ?thesis using dim_span[of "cball (0 :: 'n::euclidean_space) e"] by (auto simp add: dim_UNIV)
156 lemma indep_card_eq_dim_span:
157 fixes B :: "('n::euclidean_space) set"
158 assumes "independent B"
159 shows "finite B & card B = dim (span B)"
160 using assms basis_card_eq_dim[of B "span B"] span_inc by auto
162 lemma setsum_not_0: "setsum f A ~= 0 ==> EX a:A. f a ~= 0"
163 apply(rule ccontr) by auto
165 lemma translate_inj_on:
166 fixes A :: "('n::euclidean_space) set"
167 shows "inj_on (%x. a+x) A" unfolding inj_on_def by auto
169 lemma translation_assoc:
170 fixes a b :: "'a::ab_group_add"
171 shows "(\<lambda>x. b+x) ` ((\<lambda>x. a+x) ` S) = (\<lambda>x. (a+b)+x) ` S" by auto
173 lemma translation_invert:
174 fixes a :: "'a::ab_group_add"
175 assumes "(\<lambda>x. a+x) ` A = (\<lambda>x. a+x) ` B"
178 have "(%x. -a+x) ` ((%x. a+x) ` A) = (%x. -a+x) ` ((%x. a+x) ` B)" using assms by auto
179 from this show ?thesis using translation_assoc[of "-a" a A] translation_assoc[of "-a" a B] by auto
182 lemma translation_galois:
183 fixes a :: "'a::ab_group_add"
184 shows "T=((\<lambda>x. a+x) ` S) <-> S=((\<lambda>x. (-a)+x) ` T)"
185 using translation_assoc[of "-a" a S] apply auto
186 using translation_assoc[of a "-a" T] by auto
188 lemma translation_inverse_subset:
189 assumes "((%x. -a+x) ` V) <= (S :: 'n::ab_group_add set)"
190 shows "V <= ((%x. a+x) ` S)"
192 { fix x assume "x:V" hence "x-a : S" using assms by auto
193 hence "x : {a + v |v. v : S}" apply auto apply (rule exI[of _ "x-a"]) apply simp done
194 hence "x : ((%x. a+x) ` S)" by auto }
195 from this show ?thesis by auto
198 lemma basis_0[simp]:"(basis i::'a::euclidean_space) = 0 \<longleftrightarrow> i\<ge>DIM('a)"
199 using norm_basis[of i, where 'a='a] unfolding norm_eq_zero[where 'a='a,THEN sym] by auto
201 lemma basis_to_basis_subspace_isomorphism:
202 assumes s: "subspace (S:: ('n::euclidean_space) set)"
203 and t: "subspace (T :: ('m::euclidean_space) set)"
204 and d: "dim S = dim T"
205 and B: "B <= S" "independent B" "S <= span B" "card B = dim S"
206 and C: "C <= T" "independent C" "T <= span C" "card C = dim T"
207 shows "EX f. linear f & f ` B = C & f ` S = T & inj_on f S"
209 (* Proof is a modified copy of the proof of similar lemma subspace_isomorphism
211 from B independent_bound have fB: "finite B" by blast
212 from C independent_bound have fC: "finite C" by blast
213 from B(4) C(4) card_le_inj[of B C] d obtain f where
214 f: "f ` B \<subseteq> C" "inj_on f B" using `finite B` `finite C` by auto
215 from linear_independent_extend[OF B(2)] obtain g where
216 g: "linear g" "\<forall>x\<in> B. g x = f x" by blast
217 from inj_on_iff_eq_card[OF fB, of f] f(2)
218 have "card (f ` B) = card B" by simp
219 with B(4) C(4) have ceq: "card (f ` B) = card C" using d
221 have "g ` B = f ` B" using g(2)
222 by (auto simp add: image_iff)
223 also have "\<dots> = C" using card_subset_eq[OF fC f(1) ceq] .
224 finally have gBC: "g ` B = C" .
225 have gi: "inj_on g B" using f(2) g(2)
226 by (auto simp add: inj_on_def)
227 note g0 = linear_indep_image_lemma[OF g(1) fB, unfolded gBC, OF C(2) gi]
228 {fix x y assume x: "x \<in> S" and y: "y \<in> S" and gxy:"g x = g y"
229 from B(3) x y have x': "x \<in> span B" and y': "y \<in> span B" by blast+
230 from gxy have th0: "g (x - y) = 0" by (simp add: linear_sub[OF g(1)])
231 have th1: "x - y \<in> span B" using x' y' by (metis span_sub)
232 have "x=y" using g0[OF th1 th0] by simp }
233 then have giS: "inj_on g S"
234 unfolding inj_on_def by blast
235 from span_subspace[OF B(1,3) s]
236 have "g ` S = span (g ` B)" by (simp add: span_linear_image[OF g(1)])
237 also have "\<dots> = span C" unfolding gBC ..
238 also have "\<dots> = T" using span_subspace[OF C(1,3) t] .
239 finally have gS: "g ` S = T" .
240 from g(1) gS giS gBC show ?thesis by blast
243 lemma closure_linear_image:
244 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
246 shows "f ` (closure S) <= closure (f ` S)"
247 using image_closure_subset[of S f "closure (f ` S)"] assms linear_conv_bounded_linear[of f]
248 linear_continuous_on[of f "closure S"] closed_closure[of "f ` S"] closure_subset[of "f ` S"] by auto
250 lemma closure_injective_linear_image:
251 fixes f :: "('n::euclidean_space) => ('n::euclidean_space)"
252 assumes "linear f" "inj f"
253 shows "f ` (closure S) = closure (f ` S)"
255 obtain f' where f'_def: "linear f' & f o f' = id & f' o f = id"
256 using assms linear_injective_isomorphism[of f] isomorphism_expand by auto
257 hence "f' ` closure (f ` S) <= closure (S)"
258 using closure_linear_image[of f' "f ` S"] image_compose[of f' f] by auto
259 hence "f ` f' ` closure (f ` S) <= f ` closure (S)" by auto
260 hence "closure (f ` S) <= f ` closure (S)" using image_compose[of f f' "closure (f ` S)"] f'_def by auto
261 from this show ?thesis using closure_linear_image[of f S] assms by auto
264 lemma closure_direct_sum:
265 fixes S :: "('n::euclidean_space) set"
266 fixes T :: "('m::euclidean_space) set"
267 shows "closure (S <*> T) = closure S <*> closure T"
269 { fix x assume "x : closure S <*> closure T"
270 from this obtain xs xt where xst_def: "xs : closure S & xt : closure T & (xs,xt) = x" by auto
271 { fix ee assume ee_def: "(ee :: real) > 0"
272 def e == "ee/2" hence e_def: "(e :: real)>0 & 2*e=ee" using ee_def by auto
273 from this obtain e where e_def: "(e :: real)>0 & 2*e=ee" by auto
274 obtain ys where ys_def: "ys : S & (dist ys xs < e)"
275 using e_def xst_def closure_approachable[of xs S] by auto
276 obtain yt where yt_def: "yt : T & (dist yt xt < e)"
277 using e_def xst_def closure_approachable[of xt T] by auto
278 from ys_def yt_def have "dist (ys,yt) (xs,xt) < sqrt (2*e^2)"
279 unfolding dist_norm apply (auto simp add: norm_Pair)
280 using mult_strict_mono'[of "norm (ys - xs)" e "norm (ys - xs)" e] e_def
281 mult_strict_mono'[of "norm (yt - xt)" e "norm (yt - xt)" e] by (simp add: power2_eq_square)
282 hence "((ys,yt) : S <*> T) & (dist (ys,yt) x < 2*e)"
283 using e_def sqrt_add_le_add_sqrt[of "e^2" "e^2"] xst_def ys_def yt_def by auto
284 hence "EX y: S <*> T. dist y x < ee" using e_def by auto
285 } hence "x : closure (S <*> T)" using closure_approachable[of x "S <*> T"] by auto
287 hence "closure (S <*> T) >= closure S <*> closure T" by auto
288 moreover have "closed (closure S <*> closure T)" using closed_Times by auto
289 ultimately show ?thesis using closure_minimal[of "S <*> T" "closure S <*> closure T"]
290 closure_subset[of S] closure_subset[of T] by auto
293 lemma closure_scaleR:
294 fixes S :: "('n::euclidean_space) set"
295 shows "(op *\<^sub>R c) ` (closure S) = closure ((op *\<^sub>R c) ` S)"
297 { assume "c ~= 0" hence ?thesis using closure_injective_linear_image[of "(op *\<^sub>R c)" S]
298 linear_scaleR injective_scaleR by auto
301 { assume zero: "c=0 & S ~= {}"
302 hence "closure S ~= {}" using closure_subset by auto
303 hence "op *\<^sub>R c ` (closure S) = {0}" using zero by auto
304 moreover have "op *\<^sub>R 0 ` S = {0}" using zero by auto
305 ultimately have ?thesis using zero by auto
308 { assume "S={}" hence ?thesis by auto }
309 ultimately show ?thesis by blast
312 lemma fst_linear: "linear fst" unfolding linear_def by (simp add: algebra_simps)
314 lemma snd_linear: "linear snd" unfolding linear_def by (simp add: algebra_simps)
316 lemma fst_snd_linear: "linear (%(x,y). x + y)" unfolding linear_def by (simp add: algebra_simps)
319 fixes x :: "'a::real_vector"
320 shows "scaleR 2 x = x + x"
321 unfolding one_add_one_is_two [symmetric] scaleR_left_distrib by simp
323 declare euclidean_simps[simp]
325 lemma vector_choose_size: "0 <= c ==> \<exists>(x::'a::euclidean_space). norm x = c"
326 apply (rule exI[where x="c *\<^sub>R basis 0 ::'a"]) using DIM_positive[where 'a='a] by auto
328 lemma setsum_delta_notmem: assumes "x\<notin>s"
329 shows "setsum (\<lambda>y. if (y = x) then P x else Q y) s = setsum Q s"
330 "setsum (\<lambda>y. if (x = y) then P x else Q y) s = setsum Q s"
331 "setsum (\<lambda>y. if (y = x) then P y else Q y) s = setsum Q s"
332 "setsum (\<lambda>y. if (x = y) then P y else Q y) s = setsum Q s"
333 apply(rule_tac [!] setsum_cong2) using assms by auto
335 lemma setsum_delta'':
336 fixes s::"'a::real_vector set" assumes "finite s"
337 shows "(\<Sum>x\<in>s. (if y = x then f x else 0) *\<^sub>R x) = (if y\<in>s then (f y) *\<^sub>R y else 0)"
339 have *:"\<And>x y. (if y = x then f x else (0::real)) *\<^sub>R x = (if x=y then (f x) *\<^sub>R x else 0)" by auto
340 show ?thesis unfolding * using setsum_delta[OF assms, of y "\<lambda>x. f x *\<^sub>R x"] by auto
343 lemma if_smult:"(if P then x else (y::real)) *\<^sub>R v = (if P then x *\<^sub>R v else y *\<^sub>R v)" by auto
345 lemma image_smult_interval:"(\<lambda>x. m *\<^sub>R (x::'a::ordered_euclidean_space)) ` {a..b} =
346 (if {a..b} = {} then {} else if 0 \<le> m then {m *\<^sub>R a..m *\<^sub>R b} else {m *\<^sub>R b..m *\<^sub>R a})"
347 using image_affinity_interval[of m 0 a b] by auto
349 lemma dist_triangle_eq:
350 fixes x y z :: "'a::euclidean_space"
351 shows "dist x z = dist x y + dist y z \<longleftrightarrow> norm (x - y) *\<^sub>R (y - z) = norm (y - z) *\<^sub>R (x - y)"
352 proof- have *:"x - y + (y - z) = x - z" by auto
353 show ?thesis unfolding dist_norm norm_triangle_eq[of "x - y" "y - z", unfolded *]
354 by(auto simp add:norm_minus_commute) qed
356 lemma norm_minus_eqI:"x = - y \<Longrightarrow> norm x = norm y" by auto
358 lemma Min_grI: assumes "finite A" "A \<noteq> {}" "\<forall>a\<in>A. x < a" shows "x < Min A"
359 unfolding Min_gr_iff[OF assms(1,2)] using assms(3) by auto
361 lemma norm_lt: "norm x < norm y \<longleftrightarrow> inner x x < inner y y"
362 unfolding norm_eq_sqrt_inner by simp
364 lemma norm_le: "norm x \<le> norm y \<longleftrightarrow> inner x x \<le> inner y y"
365 unfolding norm_eq_sqrt_inner by simp
369 subsection {* Affine set and affine hull.*}
372 affine :: "'a::real_vector set \<Rightarrow> bool" where
373 "affine s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s)"
375 lemma affine_alt: "affine s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u::real. (1 - u) *\<^sub>R x + u *\<^sub>R y \<in> s)"
376 unfolding affine_def by(metis eq_diff_eq')
378 lemma affine_empty[intro]: "affine {}"
379 unfolding affine_def by auto
381 lemma affine_sing[intro]: "affine {x}"
382 unfolding affine_alt by (auto simp add: scaleR_left_distrib [symmetric])
384 lemma affine_UNIV[intro]: "affine UNIV"
385 unfolding affine_def by auto
387 lemma affine_Inter: "(\<forall>s\<in>f. affine s) \<Longrightarrow> affine (\<Inter> f)"
388 unfolding affine_def by auto
390 lemma affine_Int: "affine s \<Longrightarrow> affine t \<Longrightarrow> affine (s \<inter> t)"
391 unfolding affine_def by auto
393 lemma affine_affine_hull: "affine(affine hull s)"
394 unfolding hull_def using affine_Inter[of "{t \<in> affine. s \<subseteq> t}"]
395 unfolding mem_def by auto
397 lemma affine_hull_eq[simp]: "(affine hull s = s) \<longleftrightarrow> affine s"
398 by (metis affine_affine_hull hull_same mem_def)
400 lemma setsum_restrict_set'': assumes "finite A"
401 shows "setsum f {x \<in> A. P x} = (\<Sum>x\<in>A. if P x then f x else 0)"
402 unfolding mem_def[of _ P, symmetric] unfolding setsum_restrict_set'[OF assms] ..
404 subsection {* Some explicit formulations (from Lars Schewe). *}
406 lemma affine: fixes V::"'a::real_vector set"
407 shows "affine V \<longleftrightarrow> (\<forall>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> V \<and> setsum u s = 1 \<longrightarrow> (setsum (\<lambda>x. (u x) *\<^sub>R x)) s \<in> V)"
408 unfolding affine_def apply rule apply(rule, rule, rule) apply(erule conjE)+
409 defer apply(rule, rule, rule, rule, rule) proof-
410 fix x y u v assume as:"x \<in> V" "y \<in> V" "u + v = (1::real)"
411 "\<forall>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> V \<and> setsum u s = 1 \<longrightarrow> (\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V"
412 thus "u *\<^sub>R x + v *\<^sub>R y \<in> V" apply(cases "x=y")
413 using as(4)[THEN spec[where x="{x,y}"], THEN spec[where x="\<lambda>w. if w = x then u else v"]] and as(1-3)
414 by(auto simp add: scaleR_left_distrib[THEN sym])
416 fix s u assume as:"\<forall>x\<in>V. \<forall>y\<in>V. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> V"
417 "finite s" "s \<noteq> {}" "s \<subseteq> V" "setsum u s = (1::real)"
418 def n \<equiv> "card s"
419 have "card s = 0 \<or> card s = 1 \<or> card s = 2 \<or> card s > 2" by auto
420 thus "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V" proof(auto simp only: disjE)
421 assume "card s = 2" hence "card s = Suc (Suc 0)" by auto
422 then obtain a b where "s = {a, b}" unfolding card_Suc_eq by auto
423 thus ?thesis using as(1)[THEN bspec[where x=a], THEN bspec[where x=b]] using as(4,5)
424 by(auto simp add: setsum_clauses(2))
425 next assume "card s > 2" thus ?thesis using as and n_def proof(induct n arbitrary: u s)
426 case (Suc n) fix s::"'a set" and u::"'a \<Rightarrow> real"
427 assume IA:"\<And>u s. \<lbrakk>2 < card s; \<forall>x\<in>V. \<forall>y\<in>V. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> V; finite s;
428 s \<noteq> {}; s \<subseteq> V; setsum u s = 1; n = card s \<rbrakk> \<Longrightarrow> (\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V" and
429 as:"Suc n = card s" "2 < card s" "\<forall>x\<in>V. \<forall>y\<in>V. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> V"
430 "finite s" "s \<noteq> {}" "s \<subseteq> V" "setsum u s = 1"
431 have "\<exists>x\<in>s. u x \<noteq> 1" proof(rule_tac ccontr)
432 assume " \<not> (\<exists>x\<in>s. u x \<noteq> 1)" hence "setsum u s = real_of_nat (card s)" unfolding card_eq_setsum by auto
433 thus False using as(7) and `card s > 2` by (metis Numeral1_eq1_nat less_0_number_of less_int_code(15)
434 less_nat_number_of not_less_iff_gr_or_eq of_nat_1 of_nat_eq_iff pos2 rel_simps(4)) qed
435 then obtain x where x:"x\<in>s" "u x \<noteq> 1" by auto
437 have c:"card (s - {x}) = card s - 1" apply(rule card_Diff_singleton) using `x\<in>s` as(4) by auto
438 have *:"s = insert x (s - {x})" "finite (s - {x})" using `x\<in>s` and as(4) by auto
439 have **:"setsum u (s - {x}) = 1 - u x"
440 using setsum_clauses(2)[OF *(2), of u x, unfolded *(1)[THEN sym] as(7)] by auto
441 have ***:"inverse (1 - u x) * setsum u (s - {x}) = 1" unfolding ** using `u x \<noteq> 1` by auto
442 have "(\<Sum>xa\<in>s - {x}. (inverse (1 - u x) * u xa) *\<^sub>R xa) \<in> V" proof(cases "card (s - {x}) > 2")
443 case True hence "s - {x} \<noteq> {}" "card (s - {x}) = n" unfolding c and as(1)[symmetric] proof(rule_tac ccontr)
444 assume "\<not> s - {x} \<noteq> {}" hence "card (s - {x}) = 0" unfolding card_0_eq[OF *(2)] by simp
445 thus False using True by auto qed auto
446 thus ?thesis apply(rule_tac IA[of "s - {x}" "\<lambda>y. (inverse (1 - u x) * u y)"])
447 unfolding setsum_right_distrib[THEN sym] using as and *** and True by auto
448 next case False hence "card (s - {x}) = Suc (Suc 0)" using as(2) and c by auto
449 then obtain a b where "(s - {x}) = {a, b}" "a\<noteq>b" unfolding card_Suc_eq by auto
450 thus ?thesis using as(3)[THEN bspec[where x=a], THEN bspec[where x=b]]
451 using *** *(2) and `s \<subseteq> V` unfolding setsum_right_distrib by(auto simp add: setsum_clauses(2)) qed
452 hence "u x + (1 - u x) = 1 \<Longrightarrow> u x *\<^sub>R x + (1 - u x) *\<^sub>R ((\<Sum>xa\<in>s - {x}. u xa *\<^sub>R xa) /\<^sub>R (1 - u x)) \<in> V"
453 apply-apply(rule as(3)[rule_format])
454 unfolding RealVector.scaleR_right.setsum using x(1) as(6) by auto
455 thus "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V" unfolding scaleR_scaleR[THEN sym] and scaleR_right.setsum [symmetric]
456 apply(subst *) unfolding setsum_clauses(2)[OF *(2)]
457 using `u x \<noteq> 1` by auto
459 next assume "card s = 1" then obtain a where "s={a}" by(auto simp add: card_Suc_eq)
460 thus ?thesis using as(4,5) by simp
461 qed(insert `s\<noteq>{}` `finite s`, auto)
464 lemma affine_hull_explicit:
465 "affine hull p = {y. \<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> setsum u s = 1 \<and> setsum (\<lambda>v. (u v) *\<^sub>R v) s = y}"
466 apply(rule hull_unique) apply(subst subset_eq) prefer 3 apply rule unfolding mem_Collect_eq and mem_def[of _ affine]
467 apply (erule exE)+ apply(erule conjE)+ prefer 2 apply rule proof-
468 fix x assume "x\<in>p" thus "\<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
469 apply(rule_tac x="{x}" in exI, rule_tac x="\<lambda>x. 1" in exI) by auto
471 fix t x s u assume as:"p \<subseteq> t" "affine t" "finite s" "s \<noteq> {}" "s \<subseteq> p" "setsum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"
472 thus "x \<in> t" using as(2)[unfolded affine, THEN spec[where x=s], THEN spec[where x=u]] by auto
474 show "affine {y. \<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y}" unfolding affine_def
475 apply(rule,rule,rule,rule,rule) unfolding mem_Collect_eq proof-
476 fix u v ::real assume uv:"u + v = 1"
477 fix x assume "\<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
478 then obtain sx ux where x:"finite sx" "sx \<noteq> {}" "sx \<subseteq> p" "setsum ux sx = 1" "(\<Sum>v\<in>sx. ux v *\<^sub>R v) = x" by auto
479 fix y assume "\<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y"
480 then obtain sy uy where y:"finite sy" "sy \<noteq> {}" "sy \<subseteq> p" "setsum uy sy = 1" "(\<Sum>v\<in>sy. uy v *\<^sub>R v) = y" by auto
481 have xy:"finite (sx \<union> sy)" using x(1) y(1) by auto
482 have **:"(sx \<union> sy) \<inter> sx = sx" "(sx \<union> sy) \<inter> sy = sy" by auto
483 show "\<exists>s ua. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> setsum ua s = 1 \<and> (\<Sum>v\<in>s. ua v *\<^sub>R v) = u *\<^sub>R x + v *\<^sub>R y"
484 apply(rule_tac x="sx \<union> sy" in exI)
485 apply(rule_tac x="\<lambda>a. (if a\<in>sx then u * ux a else 0) + (if a\<in>sy then v * uy a else 0)" in exI)
486 unfolding scaleR_left_distrib setsum_addf if_smult scaleR_zero_left ** setsum_restrict_set[OF xy, THEN sym]
487 unfolding scaleR_scaleR[THEN sym] RealVector.scaleR_right.setsum [symmetric] and setsum_right_distrib[THEN sym]
488 unfolding x y using x(1-3) y(1-3) uv by simp qed qed
490 lemma affine_hull_finite:
492 shows "affine hull s = {y. \<exists>u. setsum u s = 1 \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = y}"
493 unfolding affine_hull_explicit and set_eq_iff and mem_Collect_eq apply (rule,rule)
494 apply(erule exE)+ apply(erule conjE)+ defer apply(erule exE) apply(erule conjE) proof-
495 fix x u assume "setsum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"
496 thus "\<exists>sa u. finite sa \<and> \<not> (\<forall>x. (x \<in> sa) = (x \<in> {})) \<and> sa \<subseteq> s \<and> setsum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = x"
497 apply(rule_tac x=s in exI, rule_tac x=u in exI) using assms by auto
499 fix x t u assume "t \<subseteq> s" hence *:"s \<inter> t = t" by auto
500 assume "finite t" "\<not> (\<forall>x. (x \<in> t) = (x \<in> {}))" "setsum u t = 1" "(\<Sum>v\<in>t. u v *\<^sub>R v) = x"
501 thus "\<exists>u. setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x" apply(rule_tac x="\<lambda>x. if x\<in>t then u x else 0" in exI)
502 unfolding if_smult scaleR_zero_left and setsum_restrict_set[OF assms, THEN sym] and * by auto qed
504 subsection {* Stepping theorems and hence small special cases. *}
506 lemma affine_hull_empty[simp]: "affine hull {} = {}"
507 apply(rule hull_unique) unfolding mem_def by auto
509 lemma affine_hull_finite_step:
510 fixes y :: "'a::real_vector"
511 shows "(\<exists>u. setsum u {} = w \<and> setsum (\<lambda>x. u x *\<^sub>R x) {} = y) \<longleftrightarrow> w = 0 \<and> y = 0" (is ?th1)
512 "finite s \<Longrightarrow> (\<exists>u. setsum u (insert a s) = w \<and> setsum (\<lambda>x. u x *\<^sub>R x) (insert a s) = y) \<longleftrightarrow>
513 (\<exists>v u. setsum u s = w - v \<and> setsum (\<lambda>x. u x *\<^sub>R x) s = y - v *\<^sub>R a)" (is "?as \<Longrightarrow> (?lhs = ?rhs)")
518 then obtain u where u:"setsum u (insert a s) = w \<and> (\<Sum>x\<in>insert a s. u x *\<^sub>R x) = y" by auto
519 have ?rhs proof(cases "a\<in>s")
520 case True hence *:"insert a s = s" by auto
521 show ?thesis using u[unfolded *] apply(rule_tac x=0 in exI) by auto
523 case False thus ?thesis apply(rule_tac x="u a" in exI) using u and `?as` by auto
526 then obtain v u where vu:"setsum u s = w - v" "(\<Sum>x\<in>s. u x *\<^sub>R x) = y - v *\<^sub>R a" by auto
527 have *:"\<And>x M. (if x = a then v else M) *\<^sub>R x = (if x = a then v *\<^sub>R x else M *\<^sub>R x)" by auto
528 have ?lhs proof(cases "a\<in>s")
529 case True thus ?thesis
530 apply(rule_tac x="\<lambda>x. (if x=a then v else 0) + u x" in exI)
531 unfolding setsum_clauses(2)[OF `?as`] apply simp
532 unfolding scaleR_left_distrib and setsum_addf
533 unfolding vu and * and scaleR_zero_left
534 by (auto simp add: setsum_delta[OF `?as`])
537 hence **:"\<And>x. x \<in> s \<Longrightarrow> u x = (if x = a then v else u x)"
538 "\<And>x. x \<in> s \<Longrightarrow> u x *\<^sub>R x = (if x = a then v *\<^sub>R x else u x *\<^sub>R x)" by auto
539 from False show ?thesis
540 apply(rule_tac x="\<lambda>x. if x=a then v else u x" in exI)
541 unfolding setsum_clauses(2)[OF `?as`] and * using vu
542 using setsum_cong2[of s "\<lambda>x. u x *\<^sub>R x" "\<lambda>x. if x = a then v *\<^sub>R x else u x *\<^sub>R x", OF **(2)]
543 using setsum_cong2[of s u "\<lambda>x. if x = a then v else u x", OF **(1)] by auto
545 ultimately show "?lhs = ?rhs" by blast
549 fixes a b :: "'a::real_vector"
550 shows "affine hull {a,b} = {u *\<^sub>R a + v *\<^sub>R b| u v. (u + v = 1)}" (is "?lhs = ?rhs")
552 have *:"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)"
553 "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto
554 have "?lhs = {y. \<exists>u. setsum u {a, b} = 1 \<and> (\<Sum>v\<in>{a, b}. u v *\<^sub>R v) = y}"
555 using affine_hull_finite[of "{a,b}"] by auto
556 also have "\<dots> = {y. \<exists>v u. u b = 1 - v \<and> u b *\<^sub>R b = y - v *\<^sub>R a}"
557 by(simp add: affine_hull_finite_step(2)[of "{b}" a])
558 also have "\<dots> = ?rhs" unfolding * by auto
559 finally show ?thesis by auto
563 fixes a b c :: "'a::real_vector"
564 shows "affine hull {a,b,c} = { u *\<^sub>R a + v *\<^sub>R b + w *\<^sub>R c| u v w. u + v + w = 1}" (is "?lhs = ?rhs")
566 have *:"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)"
567 "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto
568 show ?thesis apply(simp add: affine_hull_finite affine_hull_finite_step)
569 unfolding * apply auto
570 apply(rule_tac x=v in exI) apply(rule_tac x=va in exI) apply auto
571 apply(rule_tac x=u in exI) by(auto intro!: exI)
575 assumes "affine S" "x : S" "y : S" "u+v=1"
576 shows "(u *\<^sub>R x + v *\<^sub>R y) : S"
577 using assms affine_def[of S] by auto
580 assumes "affine S" "x : S" "y : S" "z : S" "u+v+w=1"
581 shows "(u *\<^sub>R x + v *\<^sub>R y + w *\<^sub>R z) : S"
583 have "(u *\<^sub>R x + v *\<^sub>R y + w *\<^sub>R z) : affine hull {x, y, z}"
584 using affine_hull_3[of x y z] assms by auto
585 moreover have " affine hull {x, y, z} <= affine hull S"
586 using hull_mono[of "{x, y, z}" "S"] assms by auto
587 moreover have "affine hull S = S"
588 using assms affine_hull_eq[of S] by auto
589 ultimately show ?thesis by auto
592 lemma mem_affine_3_minus:
593 assumes "affine S" "x : S" "y : S" "z : S"
594 shows "x + v *\<^sub>R (y-z) : S"
595 using mem_affine_3[of S x y z 1 v "-v"] assms by (simp add: algebra_simps)
598 subsection {* Some relations between affine hull and subspaces. *}
600 lemma affine_hull_insert_subset_span:
601 fixes a :: "'a::euclidean_space"
602 shows "affine hull (insert a s) \<subseteq> {a + v| v . v \<in> span {x - a | x . x \<in> s}}"
603 unfolding subset_eq Ball_def unfolding affine_hull_explicit span_explicit mem_Collect_eq
604 apply(rule,rule) apply(erule exE)+ apply(erule conjE)+ proof-
605 fix x t u assume as:"finite t" "t \<noteq> {}" "t \<subseteq> insert a s" "setsum u t = 1" "(\<Sum>v\<in>t. u v *\<^sub>R v) = x"
606 have "(\<lambda>x. x - a) ` (t - {a}) \<subseteq> {x - a |x. x \<in> s}" using as(3) by auto
607 thus "\<exists>v. x = a + v \<and> (\<exists>S u. finite S \<and> S \<subseteq> {x - a |x. x \<in> s} \<and> (\<Sum>v\<in>S. u v *\<^sub>R v) = v)"
608 apply(rule_tac x="x - a" in exI)
609 apply (rule conjI, simp)
610 apply(rule_tac x="(\<lambda>x. x - a) ` (t - {a})" in exI)
611 apply(rule_tac x="\<lambda>x. u (x + a)" in exI)
612 apply (rule conjI) using as(1) apply simp
615 apply (simp add: setsum_reindex[unfolded inj_on_def] scaleR_right_diff_distrib setsum_subtractf scaleR_left.setsum[THEN sym] setsum_diff1 scaleR_left_diff_distrib)
616 unfolding as by simp qed
618 lemma affine_hull_insert_span:
619 fixes a :: "'a::euclidean_space"
620 assumes "a \<notin> s"
621 shows "affine hull (insert a s) =
622 {a + v | v . v \<in> span {x - a | x. x \<in> s}}"
623 apply(rule, rule affine_hull_insert_subset_span) unfolding subset_eq Ball_def
624 unfolding affine_hull_explicit and mem_Collect_eq proof(rule,rule,erule exE,erule conjE)
625 fix y v assume "y = a + v" "v \<in> span {x - a |x. x \<in> s}"
626 then obtain t u where obt:"finite t" "t \<subseteq> {x - a |x. x \<in> s}" "a + (\<Sum>v\<in>t. u v *\<^sub>R v) = y" unfolding span_explicit by auto
627 def f \<equiv> "(\<lambda>x. x + a) ` t"
628 have f:"finite f" "f \<subseteq> s" "(\<Sum>v\<in>f. u (v - a) *\<^sub>R (v - a)) = y - a" unfolding f_def using obt
629 by(auto simp add: setsum_reindex[unfolded inj_on_def])
630 have *:"f \<inter> {a} = {}" "f \<inter> - {a} = f" using f(2) assms by auto
631 show "\<exists>sa u. finite sa \<and> sa \<noteq> {} \<and> sa \<subseteq> insert a s \<and> setsum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = y"
632 apply(rule_tac x="insert a f" in exI)
633 apply(rule_tac x="\<lambda>x. if x=a then 1 - setsum (\<lambda>x. u (x - a)) f else u (x - a)" in exI)
634 using assms and f unfolding setsum_clauses(2)[OF f(1)] and if_smult
635 unfolding setsum_cases[OF f(1), of "\<lambda>x. x = a"]
636 by (auto simp add: setsum_subtractf scaleR_left.setsum algebra_simps *) qed
638 lemma affine_hull_span:
639 fixes a :: "'a::euclidean_space"
641 shows "affine hull s = {a + v | v. v \<in> span {x - a | x. x \<in> s - {a}}}"
642 using affine_hull_insert_span[of a "s - {a}", unfolded insert_Diff[OF assms]] by auto
644 subsection{* Parallel Affine Sets *}
646 definition affine_parallel :: "'a::real_vector set => 'a::real_vector set => bool"
647 where "affine_parallel S T = (? a. T = ((%x. a + x) ` S))"
649 lemma affine_parallel_expl_aux:
650 fixes S T :: "'a::real_vector set"
651 assumes "!x. (x : S <-> (a+x) : T)"
652 shows "T = ((%x. a + x) ` S)"
654 { fix x assume "x : T" hence "(-a)+x : S" using assms by auto
655 hence " x : ((%x. a + x) ` S)" using imageI[of "-a+x" S "(%x. a+x)"] by auto}
656 moreover have "T >= ((%x. a + x) ` S)" using assms by auto
657 ultimately show ?thesis by auto
660 lemma affine_parallel_expl:
661 "affine_parallel S T = (? a. !x. (x : S <-> (a+x) : T))"
662 unfolding affine_parallel_def using affine_parallel_expl_aux[of S _ T] by auto
664 lemma affine_parallel_reflex: "affine_parallel S S" unfolding affine_parallel_def apply (rule exI[of _ "0"]) by auto
666 lemma affine_parallel_commut:
667 assumes "affine_parallel A B" shows "affine_parallel B A"
669 from assms obtain a where "B=((%x. a + x) ` A)" unfolding affine_parallel_def by auto
670 from this show ?thesis using translation_galois[of B a A] unfolding affine_parallel_def by auto
673 lemma affine_parallel_assoc:
674 assumes "affine_parallel A B" "affine_parallel B C"
675 shows "affine_parallel A C"
677 from assms obtain ab where "B=((%x. ab + x) ` A)" unfolding affine_parallel_def by auto
679 from assms obtain bc where "C=((%x. bc + x) ` B)" unfolding affine_parallel_def by auto
680 ultimately show ?thesis using translation_assoc[of bc ab A] unfolding affine_parallel_def by auto
683 lemma affine_translation_aux:
684 fixes a :: "'a::real_vector"
685 assumes "affine ((%x. a + x) ` S)" shows "affine S"
688 assume xy: "x : S" "y : S" "(u :: real)+v=1"
689 hence "(a+x):((%x. a + x) ` S)" "(a+y):((%x. a + x) ` S)" by auto
690 hence h1: "u *\<^sub>R (a+x) + v *\<^sub>R (a+y) : ((%x. a + x) ` S)" using xy assms unfolding affine_def by auto
691 have "u *\<^sub>R (a+x) + v *\<^sub>R (a+y) = (u+v) *\<^sub>R a + (u *\<^sub>R x + v *\<^sub>R y)" by (simp add:algebra_simps)
692 also have "...= a + (u *\<^sub>R x + v *\<^sub>R y)" using `u+v=1` by auto
693 ultimately have "a + (u *\<^sub>R x + v *\<^sub>R y) : ((%x. a + x) ` S)" using h1 by auto
694 hence "u *\<^sub>R x + v *\<^sub>R y : S" by auto
695 } from this show ?thesis unfolding affine_def by auto
698 lemma affine_translation:
699 fixes a :: "'a::real_vector"
700 shows "affine S <-> affine ((%x. a + x) ` S)"
702 have "affine S ==> affine ((%x. a + x) ` S)" using affine_translation_aux[of "-a" "((%x. a + x) ` S)"] using translation_assoc[of "-a" a S] by auto
703 from this show ?thesis using affine_translation_aux by auto
706 lemma parallel_is_affine:
707 fixes S T :: "'a::real_vector set"
708 assumes "affine S" "affine_parallel S T"
711 from assms obtain a where "T=((%x. a + x) ` S)" unfolding affine_parallel_def by auto
712 from this show ?thesis using affine_translation assms by auto
715 lemma subspace_imp_affine:
716 fixes s :: "(_::euclidean_space) set" shows "subspace s \<Longrightarrow> affine s"
717 unfolding subspace_def affine_def by auto
719 subsection{* Subspace Parallel to an Affine Set *}
721 lemma subspace_affine:
722 fixes S :: "('n::euclidean_space) set"
723 shows "subspace S <-> (affine S & 0 : S)"
725 have h0: "subspace S ==> (affine S & 0 : S)" using subspace_imp_affine[of S] subspace_0 by auto
726 { assume assm: "affine S & 0 : S"
728 fix x assume x_def: "x : S"
729 have "c *\<^sub>R x = (1-c) *\<^sub>R 0 + c *\<^sub>R x" by auto
730 moreover have "(1-c) *\<^sub>R 0 + c *\<^sub>R x : S" using affine_alt[of S] assm x_def by auto
731 ultimately have "c *\<^sub>R x : S" by auto
732 } hence h1: "!c. !x : S. c *\<^sub>R x : S" by auto
733 { fix x y assume xy_def: "x : S" "y : S"
734 def u == "(1 :: real)/2"
735 have "(1/2) *\<^sub>R (x+y) = (1/2) *\<^sub>R (x+y)" by auto
736 moreover have "(1/2) *\<^sub>R (x+y)=(1/2) *\<^sub>R x + (1-(1/2)) *\<^sub>R y" by (simp add: algebra_simps)
737 moreover have "(1-u) *\<^sub>R x + u *\<^sub>R y : S" using affine_alt[of S] assm xy_def by auto
738 ultimately have "(1/2) *\<^sub>R (x+y) : S" using u_def by auto
739 moreover have "(x+y) = 2 *\<^sub>R ((1/2) *\<^sub>R (x+y))" by auto
740 ultimately have "(x+y) : S" using h1[rule_format, of "(1/2) *\<^sub>R (x+y)" "2"] by auto
741 } hence "!x : S. !y : S. (x+y) : S" by auto
742 hence "subspace S" using h1 assm unfolding subspace_def by auto
743 } from this show ?thesis using h0 by metis
746 lemma affine_diffs_subspace:
747 fixes S :: "('n::euclidean_space) set"
748 assumes "affine S" "a : S"
749 shows "subspace ((%x. (-a)+x) ` S)"
751 have "affine ((%x. (-a)+x) ` S)" using affine_translation assms by auto
752 moreover have "0 : ((%x. (-a)+x) ` S)" using assms exI[of "(%x. x:S & -a+x=0)" a] by auto
753 ultimately show ?thesis using subspace_affine by auto
756 lemma parallel_subspace_explicit:
757 fixes a :: "'n::euclidean_space"
758 assumes "affine S" "a : S"
759 assumes "L == {y. ? x : S. (-a)+x=y}"
760 shows "subspace L & affine_parallel S L"
762 have par: "affine_parallel S L" unfolding affine_parallel_def using assms by auto
763 hence "affine L" using assms parallel_is_affine by auto
764 moreover have "0 : L" using assms apply auto using exI[of "(%x. x:S & -a+x=0)" a] by auto
765 ultimately show ?thesis using subspace_affine par by auto
768 lemma parallel_subspace_aux:
769 fixes A B :: "('n::euclidean_space) set"
770 assumes "subspace A" "subspace B" "affine_parallel A B"
773 from assms obtain a where a_def: "!x. (x : A <-> (a+x) : B)" using affine_parallel_expl[of A B] by auto
774 hence "-a : A" using assms subspace_0[of B] by auto
775 hence "a : A" using assms subspace_neg[of A "-a"] by auto
776 from this show ?thesis using assms a_def unfolding subspace_def by auto
779 lemma parallel_subspace:
780 fixes A B :: "('n::euclidean_space) set"
781 assumes "subspace A" "subspace B" "affine_parallel A B"
784 have "A>=B" using assms parallel_subspace_aux by auto
785 moreover have "A<=B" using assms parallel_subspace_aux[of B A] affine_parallel_commut by auto
786 ultimately show ?thesis by auto
789 lemma affine_parallel_subspace:
790 fixes S :: "('n::euclidean_space) set"
791 assumes "affine S" "S ~= {}"
792 shows "?!L. subspace L & affine_parallel S L"
794 have ex: "? L. subspace L & affine_parallel S L" using assms parallel_subspace_explicit by auto
795 { fix L1 L2 assume ass: "subspace L1 & affine_parallel S L1" "subspace L2 & affine_parallel S L2"
796 hence "affine_parallel L1 L2" using affine_parallel_commut[of S L1] affine_parallel_assoc[of L1 S L2] by auto
797 hence "L1=L2" using ass parallel_subspace by auto
798 } from this show ?thesis using ex by auto
801 subsection {* Cones. *}
804 cone :: "'a::real_vector set \<Rightarrow> bool" where
805 "cone s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>c\<ge>0. (c *\<^sub>R x) \<in> s)"
807 lemma cone_empty[intro, simp]: "cone {}"
808 unfolding cone_def by auto
810 lemma cone_univ[intro, simp]: "cone UNIV"
811 unfolding cone_def by auto
813 lemma cone_Inter[intro]: "(\<forall>s\<in>f. cone s) \<Longrightarrow> cone(\<Inter> f)"
814 unfolding cone_def by auto
816 subsection {* Conic hull. *}
818 lemma cone_cone_hull: "cone (cone hull s)"
819 unfolding hull_def using cone_Inter[of "{t \<in> conic. s \<subseteq> t}"]
820 by (auto simp add: mem_def)
822 lemma cone_hull_eq: "(cone hull s = s) \<longleftrightarrow> cone s"
823 apply(rule hull_eq[unfolded mem_def])
824 using cone_Inter unfolding subset_eq by (auto simp add: mem_def)
827 assumes "cone S" "x : S" "c>=0"
828 shows "c *\<^sub>R x : S"
829 using assms cone_def[of S] by auto
831 lemma cone_contains_0:
832 fixes S :: "('m::euclidean_space) set"
834 shows "(S ~= {}) <-> (0 : S)"
836 { assume "S ~= {}" from this obtain a where "a:S" by auto
837 hence "0 : S" using assms mem_cone[of S a 0] by auto
838 } from this show ?thesis by auto
842 shows "cone {(0 :: 'm::euclidean_space)}"
843 unfolding cone_def by auto
845 lemma cone_Union[intro]: "(!s:f. cone s) --> (cone (Union f))"
846 unfolding cone_def by blast
849 fixes S :: "('m::euclidean_space) set"
851 shows "cone S <-> 0:S & (!c. c>0 --> ((op *\<^sub>R c) ` S) = S)"
854 { fix c assume "(c :: real)>0"
855 { fix x assume "x : S" hence "x : (op *\<^sub>R c) ` S" unfolding image_def
856 using `cone S` `c>0` mem_cone[of S x "1/c"]
857 exI[of "(%t. t:S & x = c *\<^sub>R t)" "(1 / c) *\<^sub>R x"] by auto
860 { fix x assume "x : (op *\<^sub>R c) ` S"
861 (*from this obtain t where "t:S & x = c *\<^sub>R t" by auto*)
862 hence "x:S" using `cone S` `c>0` unfolding cone_def image_def `c>0` by auto
864 ultimately have "((op *\<^sub>R c) ` S) = S" by auto
865 } hence "0:S & (!c. c>0 --> ((op *\<^sub>R c) ` S) = S)" using `cone S` cone_contains_0[of S] assms by auto
868 { assume a: "0:S & (!c. c>0 --> ((op *\<^sub>R c) ` S) = S)"
870 fix c1 assume "(c1 :: real)>=0"
871 hence "(c1=0) | (c1>0)" by auto
872 hence "c1 *\<^sub>R x : S" using a `x:S` by auto
874 hence "cone S" unfolding cone_def by auto
875 } ultimately show ?thesis by blast
878 lemma cone_hull_empty:
880 by (metis cone_empty cone_hull_eq)
882 lemma cone_hull_empty_iff:
883 fixes S :: "('m::euclidean_space) set"
884 shows "(S = {}) <-> (cone hull S = {})"
885 by (metis bot_least cone_hull_empty hull_subset xtrans(5))
887 lemma cone_hull_contains_0:
888 fixes S :: "('m::euclidean_space) set"
889 shows "(S ~= {}) <-> (0 : cone hull S)"
890 using cone_cone_hull[of S] cone_contains_0[of "cone hull S"] cone_hull_empty_iff[of S] by auto
893 assumes "x : S" "c>=0"
894 shows "c *\<^sub>R x : cone hull S"
895 by (metis assms cone_cone_hull hull_inc mem_cone mem_def)
897 lemma cone_hull_expl:
898 fixes S :: "('m::euclidean_space) set"
899 shows "cone hull S = {c *\<^sub>R x | c x. c>=0 & x : S}" (is "?lhs = ?rhs")
901 { fix x assume "x : ?rhs"
902 from this obtain cx xx where x_def: "x= cx *\<^sub>R xx & (cx :: real)>=0 & xx : S" by auto
903 fix c assume c_def: "(c :: real)>=0"
904 hence "c *\<^sub>R x = (c*cx) *\<^sub>R xx" using x_def by (simp add: algebra_simps)
905 moreover have "(c*cx) >= 0" using c_def x_def using mult_nonneg_nonneg by auto
906 ultimately have "c *\<^sub>R x : ?rhs" using x_def by auto
907 } hence "cone ?rhs" unfolding cone_def by auto
908 hence "?rhs : cone" unfolding mem_def by auto
909 { fix x assume "x : S" hence "1 *\<^sub>R x : ?rhs" apply auto apply(rule_tac x="1" in exI) by auto
910 hence "x : ?rhs" by auto
911 } hence "S <= ?rhs" by auto
912 hence "?lhs <= ?rhs" using `?rhs : cone` hull_minimal[of S "?rhs" "cone"] by auto
914 { fix x assume "x : ?rhs"
915 from this obtain cx xx where x_def: "x= cx *\<^sub>R xx & (cx :: real)>=0 & xx : S" by auto
916 hence "xx : cone hull S" using hull_subset[of S] by auto
917 hence "x : ?lhs" using x_def cone_cone_hull[of S] cone_def[of "cone hull S"] by auto
918 } ultimately show ?thesis by auto
922 fixes S :: "('m::euclidean_space) set"
924 shows "cone (closure S)"
926 { assume "S = {}" hence ?thesis by auto }
928 { assume "S ~= {}" hence "0:S & (!c. c>0 --> op *\<^sub>R c ` S = S)" using cone_iff[of S] assms by auto
929 hence "0:(closure S) & (!c. c>0 --> op *\<^sub>R c ` (closure S) = (closure S))"
930 using closure_subset by (auto simp add: closure_scaleR)
931 hence ?thesis using cone_iff[of "closure S"] by auto
933 ultimately show ?thesis by blast
936 subsection {* Affine dependence and consequential theorems (from Lars Schewe). *}
939 affine_dependent :: "'a::real_vector set \<Rightarrow> bool" where
940 "affine_dependent s \<longleftrightarrow> (\<exists>x\<in>s. x \<in> (affine hull (s - {x})))"
942 lemma affine_dependent_explicit:
943 "affine_dependent p \<longleftrightarrow>
944 (\<exists>s u. finite s \<and> s \<subseteq> p \<and> setsum u s = 0 \<and>
945 (\<exists>v\<in>s. u v \<noteq> 0) \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = 0)"
946 unfolding affine_dependent_def affine_hull_explicit mem_Collect_eq apply(rule)
947 apply(erule bexE,erule exE,erule exE) apply(erule conjE)+ defer apply(erule exE,erule exE) apply(erule conjE)+ apply(erule bexE)
949 fix x s u assume as:"x \<in> p" "finite s" "s \<noteq> {}" "s \<subseteq> p - {x}" "setsum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"
950 have "x\<notin>s" using as(1,4) by auto
951 show "\<exists>s u. finite s \<and> s \<subseteq> p \<and> setsum u s = 0 \<and> (\<exists>v\<in>s. u v \<noteq> 0) \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = 0"
952 apply(rule_tac x="insert x s" in exI, rule_tac x="\<lambda>v. if v = x then - 1 else u v" in exI)
953 unfolding if_smult and setsum_clauses(2)[OF as(2)] and setsum_delta_notmem[OF `x\<notin>s`] and as using as by auto
955 fix s u v assume as:"finite s" "s \<subseteq> p" "setsum u s = 0" "(\<Sum>v\<in>s. u v *\<^sub>R v) = 0" "v \<in> s" "u v \<noteq> 0"
956 have "s \<noteq> {v}" using as(3,6) by auto
957 thus "\<exists>x\<in>p. \<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p - {x} \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
958 apply(rule_tac x=v in bexI, rule_tac x="s - {v}" in exI, rule_tac x="\<lambda>x. - (1 / u v) * u x" in exI)
959 unfolding scaleR_scaleR[THEN sym] and scaleR_right.setsum [symmetric] unfolding setsum_right_distrib[THEN sym] and setsum_diff1[OF as(1)] using as by auto
962 lemma affine_dependent_explicit_finite:
963 fixes s :: "'a::real_vector set" assumes "finite s"
964 shows "affine_dependent s \<longleftrightarrow> (\<exists>u. setsum u s = 0 \<and> (\<exists>v\<in>s. u v \<noteq> 0) \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = 0)"
967 have *:"\<And>vt u v. (if vt then u v else 0) *\<^sub>R v = (if vt then (u v) *\<^sub>R v else (0::'a))" by auto
969 then obtain t u v where "finite t" "t \<subseteq> s" "setsum u t = 0" "v\<in>t" "u v \<noteq> 0" "(\<Sum>v\<in>t. u v *\<^sub>R v) = 0"
970 unfolding affine_dependent_explicit by auto
971 thus ?rhs apply(rule_tac x="\<lambda>x. if x\<in>t then u x else 0" in exI)
972 apply auto unfolding * and setsum_restrict_set[OF assms, THEN sym]
973 unfolding Int_absorb1[OF `t\<subseteq>s`] by auto
976 then obtain u v where "setsum u s = 0" "v\<in>s" "u v \<noteq> 0" "(\<Sum>v\<in>s. u v *\<^sub>R v) = 0" by auto
977 thus ?lhs unfolding affine_dependent_explicit using assms by auto
980 subsection {* A general lemma. *}
982 lemma convex_connected:
983 fixes s :: "'a::real_normed_vector set"
984 assumes "convex s" shows "connected s"
986 { fix e1 e2 assume as:"open e1" "open e2" "e1 \<inter> e2 \<inter> s = {}" "s \<subseteq> e1 \<union> e2"
987 assume "e1 \<inter> s \<noteq> {}" "e2 \<inter> s \<noteq> {}"
988 then obtain x1 x2 where x1:"x1\<in>e1" "x1\<in>s" and x2:"x2\<in>e2" "x2\<in>s" by auto
989 hence n:"norm (x1 - x2) > 0" unfolding zero_less_norm_iff using as(3) by auto
991 { fix x e::real assume as:"0 \<le> x" "x \<le> 1" "0 < e"
992 { fix y have *:"(1 - x) *\<^sub>R x1 + x *\<^sub>R x2 - ((1 - y) *\<^sub>R x1 + y *\<^sub>R x2) = (y - x) *\<^sub>R x1 - (y - x) *\<^sub>R x2"
993 by (simp add: algebra_simps)
994 assume "\<bar>y - x\<bar> < e / norm (x1 - x2)"
995 hence "norm ((1 - x) *\<^sub>R x1 + x *\<^sub>R x2 - ((1 - y) *\<^sub>R x1 + y *\<^sub>R x2)) < e"
996 unfolding * and scaleR_right_diff_distrib[THEN sym]
997 unfolding less_divide_eq using n by auto }
998 hence "\<exists>d>0. \<forall>y. \<bar>y - x\<bar> < d \<longrightarrow> norm ((1 - x) *\<^sub>R x1 + x *\<^sub>R x2 - ((1 - y) *\<^sub>R x1 + y *\<^sub>R x2)) < e"
999 apply(rule_tac x="e / norm (x1 - x2)" in exI) using as
1000 apply auto unfolding zero_less_divide_iff using n by simp } note * = this
1002 have "\<exists>x\<ge>0. x \<le> 1 \<and> (1 - x) *\<^sub>R x1 + x *\<^sub>R x2 \<notin> e1 \<and> (1 - x) *\<^sub>R x1 + x *\<^sub>R x2 \<notin> e2"
1003 apply(rule connected_real_lemma) apply (simp add: `x1\<in>e1` `x2\<in>e2` dist_commute)+
1004 using * apply(simp add: dist_norm)
1005 using as(1,2)[unfolded open_dist] apply simp
1006 using as(1,2)[unfolded open_dist] apply simp
1007 using assms[unfolded convex_alt, THEN bspec[where x=x1], THEN bspec[where x=x2]] using x1 x2
1009 then obtain x where "x\<ge>0" "x\<le>1" "(1 - x) *\<^sub>R x1 + x *\<^sub>R x2 \<notin> e1" "(1 - x) *\<^sub>R x1 + x *\<^sub>R x2 \<notin> e2" by auto
1010 hence False using as(4)
1011 using assms[unfolded convex_alt, THEN bspec[where x=x1], THEN bspec[where x=x2]]
1012 using x1(2) x2(2) by auto }
1013 thus ?thesis unfolding connected_def by auto
1016 subsection {* One rather trivial consequence. *}
1018 lemma connected_UNIV[intro]: "connected (UNIV :: 'a::real_normed_vector set)"
1019 by(simp add: convex_connected convex_UNIV)
1021 subsection {* Balls, being convex, are connected. *}
1023 lemma convex_box: fixes a::"'a::euclidean_space"
1024 assumes "\<And>i. i<DIM('a) \<Longrightarrow> convex {x. P i x}"
1025 shows "convex {x. \<forall>i<DIM('a). P i (x$$i)}"
1026 using assms unfolding convex_def by(auto simp add:euclidean_simps)
1028 lemma convex_positive_orthant: "convex {x::'a::euclidean_space. (\<forall>i<DIM('a). 0 \<le> x$$i)}"
1029 by (rule convex_box) (simp add: atLeast_def[symmetric] convex_real_interval)
1031 lemma convex_local_global_minimum:
1032 fixes s :: "'a::real_normed_vector set"
1033 assumes "0<e" "convex_on s f" "ball x e \<subseteq> s" "\<forall>y\<in>ball x e. f x \<le> f y"
1034 shows "\<forall>y\<in>s. f x \<le> f y"
1036 have "x\<in>s" using assms(1,3) by auto
1037 assume "\<not> (\<forall>y\<in>s. f x \<le> f y)"
1038 then obtain y where "y\<in>s" and y:"f x > f y" by auto
1039 hence xy:"0 < dist x y" by (auto simp add: dist_nz[THEN sym])
1041 then obtain u where "0 < u" "u \<le> 1" and u:"u < e / dist x y"
1042 using real_lbound_gt_zero[of 1 "e / dist x y"] using xy `e>0` and divide_pos_pos[of e "dist x y"] by auto
1043 hence "f ((1-u) *\<^sub>R x + u *\<^sub>R y) \<le> (1-u) * f x + u * f y" using `x\<in>s` `y\<in>s`
1044 using assms(2)[unfolded convex_on_def, THEN bspec[where x=x], THEN bspec[where x=y], THEN spec[where x="1-u"]] by auto
1046 have *:"x - ((1 - u) *\<^sub>R x + u *\<^sub>R y) = u *\<^sub>R (x - y)" by (simp add: algebra_simps)
1047 have "(1 - u) *\<^sub>R x + u *\<^sub>R y \<in> ball x e" unfolding mem_ball dist_norm unfolding * and norm_scaleR and abs_of_pos[OF `0<u`] unfolding dist_norm[THEN sym]
1048 using u unfolding pos_less_divide_eq[OF xy] by auto
1049 hence "f x \<le> f ((1 - u) *\<^sub>R x + u *\<^sub>R y)" using assms(4) by auto
1050 ultimately show False using mult_strict_left_mono[OF y `u>0`] unfolding left_diff_distrib by auto
1054 fixes x :: "'a::real_normed_vector"
1055 shows "convex (ball x e)"
1056 proof(auto simp add: convex_def)
1057 fix y z assume yz:"dist x y < e" "dist x z < e"
1058 fix u v ::real assume uv:"0 \<le> u" "0 \<le> v" "u + v = 1"
1059 have "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> u * dist x y + v * dist x z" using uv yz
1060 using convex_distance[of "ball x e" x, unfolded convex_on_def, THEN bspec[where x=y], THEN bspec[where x=z]] by auto
1061 thus "dist x (u *\<^sub>R y + v *\<^sub>R z) < e" using convex_bound_lt[OF yz uv] by auto
1065 fixes x :: "'a::real_normed_vector"
1066 shows "convex(cball x e)"
1067 proof(auto simp add: convex_def Ball_def)
1068 fix y z assume yz:"dist x y \<le> e" "dist x z \<le> e"
1069 fix u v ::real assume uv:" 0 \<le> u" "0 \<le> v" "u + v = 1"
1070 have "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> u * dist x y + v * dist x z" using uv yz
1071 using convex_distance[of "cball x e" x, unfolded convex_on_def, THEN bspec[where x=y], THEN bspec[where x=z]] by auto
1072 thus "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> e" using convex_bound_le[OF yz uv] by auto
1075 lemma connected_ball:
1076 fixes x :: "'a::real_normed_vector"
1077 shows "connected (ball x e)"
1078 using convex_connected convex_ball by auto
1080 lemma connected_cball:
1081 fixes x :: "'a::real_normed_vector"
1082 shows "connected(cball x e)"
1083 using convex_connected convex_cball by auto
1085 subsection {* Convex hull. *}
1087 lemma convex_convex_hull: "convex(convex hull s)"
1088 unfolding hull_def using convex_Inter[of "{t\<in>convex. s\<subseteq>t}"]
1089 unfolding mem_def by auto
1091 lemma convex_hull_eq: "convex hull s = s \<longleftrightarrow> convex s"
1092 by (metis convex_convex_hull hull_same mem_def)
1094 lemma bounded_convex_hull:
1095 fixes s :: "'a::real_normed_vector set"
1096 assumes "bounded s" shows "bounded(convex hull s)"
1097 proof- from assms obtain B where B:"\<forall>x\<in>s. norm x \<le> B" unfolding bounded_iff by auto
1098 show ?thesis apply(rule bounded_subset[OF bounded_cball, of _ 0 B])
1099 unfolding subset_hull[unfolded mem_def, of convex, OF convex_cball]
1100 unfolding subset_eq mem_cball dist_norm using B by auto qed
1102 lemma finite_imp_bounded_convex_hull:
1103 fixes s :: "'a::real_normed_vector set"
1104 shows "finite s \<Longrightarrow> bounded(convex hull s)"
1105 using bounded_convex_hull finite_imp_bounded by auto
1107 subsection {* Convex hull is "preserved" by a linear function. *}
1109 lemma convex_hull_linear_image:
1110 assumes "bounded_linear f"
1111 shows "f ` (convex hull s) = convex hull (f ` s)"
1112 apply rule unfolding subset_eq ball_simps apply(rule_tac[!] hull_induct, rule hull_inc) prefer 3
1113 apply(erule imageE)apply(rule_tac x=xa in image_eqI) apply assumption
1114 apply(rule hull_subset[unfolded subset_eq, rule_format]) apply assumption
1116 interpret f: bounded_linear f by fact
1117 show "convex {x. f x \<in> convex hull f ` s}"
1118 unfolding convex_def by(auto simp add: f.scaleR f.add convex_convex_hull[unfolded convex_def, rule_format]) next
1119 interpret f: bounded_linear f by fact
1120 show "convex {x. x \<in> f ` (convex hull s)}" using convex_convex_hull[unfolded convex_def, of s]
1121 unfolding convex_def by (auto simp add: f.scaleR [symmetric] f.add [symmetric])
1124 lemma in_convex_hull_linear_image:
1125 assumes "bounded_linear f" "x \<in> convex hull s"
1126 shows "(f x) \<in> convex hull (f ` s)"
1127 using convex_hull_linear_image[OF assms(1)] assms(2) by auto
1129 subsection {* Stepping theorems for convex hulls of finite sets. *}
1131 lemma convex_hull_empty[simp]: "convex hull {} = {}"
1132 apply(rule hull_unique) unfolding mem_def by auto
1134 lemma convex_hull_singleton[simp]: "convex hull {a} = {a}"
1135 apply(rule hull_unique) unfolding mem_def by auto
1137 lemma convex_hull_insert:
1138 fixes s :: "'a::real_vector set"
1139 assumes "s \<noteq> {}"
1140 shows "convex hull (insert a s) = {x. \<exists>u\<ge>0. \<exists>v\<ge>0. \<exists>b. (u + v = 1) \<and>
1141 b \<in> (convex hull s) \<and> (x = u *\<^sub>R a + v *\<^sub>R b)}" (is "?xyz = ?hull")
1142 apply(rule,rule hull_minimal,rule) unfolding mem_def[of _ convex] and insert_iff prefer 3 apply rule proof-
1143 fix x assume x:"x = a \<or> x \<in> s"
1144 thus "x\<in>?hull" apply rule unfolding mem_Collect_eq apply(rule_tac x=1 in exI) defer
1145 apply(rule_tac x=0 in exI) using assms hull_subset[of s convex] by auto
1147 fix x assume "x\<in>?hull"
1148 then obtain u v b where obt:"u\<ge>0" "v\<ge>0" "u + v = 1" "b \<in> convex hull s" "x = u *\<^sub>R a + v *\<^sub>R b" by auto
1149 have "a\<in>convex hull insert a s" "b\<in>convex hull insert a s"
1150 using hull_mono[of s "insert a s" convex] hull_mono[of "{a}" "insert a s" convex] and obt(4) by auto
1151 thus "x\<in> convex hull insert a s" unfolding obt(5) using convex_convex_hull[of "insert a s", unfolded convex_def]
1152 apply(erule_tac x=a in ballE) apply(erule_tac x=b in ballE) apply(erule_tac x=u in allE) using obt by auto
1154 show "convex ?hull" unfolding convex_def apply(rule,rule,rule,rule,rule,rule,rule) proof-
1155 fix x y u v assume as:"(0::real) \<le> u" "0 \<le> v" "u + v = 1" "x\<in>?hull" "y\<in>?hull"
1156 from as(4) obtain u1 v1 b1 where obt1:"u1\<ge>0" "v1\<ge>0" "u1 + v1 = 1" "b1 \<in> convex hull s" "x = u1 *\<^sub>R a + v1 *\<^sub>R b1" by auto
1157 from as(5) obtain u2 v2 b2 where obt2:"u2\<ge>0" "v2\<ge>0" "u2 + v2 = 1" "b2 \<in> convex hull s" "y = u2 *\<^sub>R a + v2 *\<^sub>R b2" by auto
1158 have *:"\<And>(x::'a) s1 s2. x - s1 *\<^sub>R x - s2 *\<^sub>R x = ((1::real) - (s1 + s2)) *\<^sub>R x" by (auto simp add: algebra_simps)
1159 have "\<exists>b \<in> convex hull s. u *\<^sub>R x + v *\<^sub>R y = (u * u1) *\<^sub>R a + (v * u2) *\<^sub>R a + (b - (u * u1) *\<^sub>R b - (v * u2) *\<^sub>R b)"
1160 proof(cases "u * v1 + v * v2 = 0")
1161 have *:"\<And>(x::'a) s1 s2. x - s1 *\<^sub>R x - s2 *\<^sub>R x = ((1::real) - (s1 + s2)) *\<^sub>R x" by (auto simp add: algebra_simps)
1162 case True hence **:"u * v1 = 0" "v * v2 = 0"
1163 using mult_nonneg_nonneg[OF `u\<ge>0` `v1\<ge>0`] mult_nonneg_nonneg[OF `v\<ge>0` `v2\<ge>0`] by arith+
1164 hence "u * u1 + v * u2 = 1" using as(3) obt1(3) obt2(3) by auto
1165 thus ?thesis unfolding obt1(5) obt2(5) * using assms hull_subset[of s convex] by(auto simp add: ** scaleR_right_distrib)
1167 have "1 - (u * u1 + v * u2) = (u + v) - (u * u1 + v * u2)" using as(3) obt1(3) obt2(3) by (auto simp add: field_simps)
1168 also have "\<dots> = u * (v1 + u1 - u1) + v * (v2 + u2 - u2)" using as(3) obt1(3) obt2(3) by (auto simp add: field_simps)
1169 also have "\<dots> = u * v1 + v * v2" by simp finally have **:"1 - (u * u1 + v * u2) = u * v1 + v * v2" by auto
1170 case False have "0 \<le> u * v1 + v * v2" "0 \<le> u * v1" "0 \<le> u * v1 + v * v2" "0 \<le> v * v2" apply -
1171 apply(rule add_nonneg_nonneg) prefer 4 apply(rule add_nonneg_nonneg) apply(rule_tac [!] mult_nonneg_nonneg)
1172 using as(1,2) obt1(1,2) obt2(1,2) by auto
1173 thus ?thesis unfolding obt1(5) obt2(5) unfolding * and ** using False
1174 apply(rule_tac x="((u * v1) / (u * v1 + v * v2)) *\<^sub>R b1 + ((v * v2) / (u * v1 + v * v2)) *\<^sub>R b2" in bexI) defer
1175 apply(rule convex_convex_hull[of s, unfolded convex_def, rule_format]) using obt1(4) obt2(4)
1176 unfolding add_divide_distrib[THEN sym] and real_0_le_divide_iff
1177 by (auto simp add: scaleR_left_distrib scaleR_right_distrib)
1179 have u1:"u1 \<le> 1" unfolding obt1(3)[THEN sym] and not_le using obt1(2) by auto
1180 have u2:"u2 \<le> 1" unfolding obt2(3)[THEN sym] and not_le using obt2(2) by auto
1181 have "u1 * u + u2 * v \<le> (max u1 u2) * u + (max u1 u2) * v" apply(rule add_mono)
1182 apply(rule_tac [!] mult_right_mono) using as(1,2) obt1(1,2) obt2(1,2) by auto
1183 also have "\<dots> \<le> 1" unfolding mult.add_right[THEN sym] and as(3) using u1 u2 by auto
1185 show "u *\<^sub>R x + v *\<^sub>R y \<in> ?hull" unfolding mem_Collect_eq apply(rule_tac x="u * u1 + v * u2" in exI)
1186 apply(rule conjI) defer apply(rule_tac x="1 - u * u1 - v * u2" in exI) unfolding Bex_def
1187 using as(1,2) obt1(1,2) obt2(1,2) * by(auto intro!: mult_nonneg_nonneg add_nonneg_nonneg simp add: algebra_simps)
1192 subsection {* Explicit expression for convex hull. *}
1194 lemma convex_hull_indexed:
1195 fixes s :: "'a::real_vector set"
1196 shows "convex hull s = {y. \<exists>k u x. (\<forall>i\<in>{1::nat .. k}. 0 \<le> u i \<and> x i \<in> s) \<and>
1197 (setsum u {1..k} = 1) \<and>
1198 (setsum (\<lambda>i. u i *\<^sub>R x i) {1..k} = y)}" (is "?xyz = ?hull")
1199 apply(rule hull_unique) unfolding mem_def[of _ convex] apply(rule) defer
1200 apply(subst convex_def) apply(rule,rule,rule,rule,rule,rule,rule)
1202 fix x assume "x\<in>s"
1203 thus "x \<in> ?hull" unfolding mem_Collect_eq apply(rule_tac x=1 in exI, rule_tac x="\<lambda>x. 1" in exI) by auto
1205 fix t assume as:"s \<subseteq> t" "convex t"
1206 show "?hull \<subseteq> t" apply(rule) unfolding mem_Collect_eq apply(erule exE | erule conjE)+ proof-
1207 fix x k u y assume assm:"\<forall>i\<in>{1::nat..k}. 0 \<le> u i \<and> y i \<in> s" "setsum u {1..k} = 1" "(\<Sum>i = 1..k. u i *\<^sub>R y i) = x"
1208 show "x\<in>t" unfolding assm(3)[THEN sym] apply(rule as(2)[unfolded convex, rule_format])
1209 using assm(1,2) as(1) by auto qed
1211 fix x y u v assume uv:"0\<le>u" "0\<le>v" "u+v=(1::real)" and xy:"x\<in>?hull" "y\<in>?hull"
1212 from xy obtain k1 u1 x1 where x:"\<forall>i\<in>{1::nat..k1}. 0\<le>u1 i \<and> x1 i \<in> s" "setsum u1 {Suc 0..k1} = 1" "(\<Sum>i = Suc 0..k1. u1 i *\<^sub>R x1 i) = x" by auto
1213 from xy obtain k2 u2 x2 where y:"\<forall>i\<in>{1::nat..k2}. 0\<le>u2 i \<and> x2 i \<in> s" "setsum u2 {Suc 0..k2} = 1" "(\<Sum>i = Suc 0..k2. u2 i *\<^sub>R x2 i) = y" by auto
1214 have *:"\<And>P (x1::'a) x2 s1 s2 i.(if P i then s1 else s2) *\<^sub>R (if P i then x1 else x2) = (if P i then s1 *\<^sub>R x1 else s2 *\<^sub>R x2)"
1215 "{1..k1 + k2} \<inter> {1..k1} = {1..k1}" "{1..k1 + k2} \<inter> - {1..k1} = (\<lambda>i. i + k1) ` {1..k2}"
1216 prefer 3 apply(rule,rule) unfolding image_iff apply(rule_tac x="x - k1" in bexI) by(auto simp add: not_le)
1217 have inj:"inj_on (\<lambda>i. i + k1) {1..k2}" unfolding inj_on_def by auto
1218 show "u *\<^sub>R x + v *\<^sub>R y \<in> ?hull" apply(rule)
1219 apply(rule_tac x="k1 + k2" in exI, rule_tac x="\<lambda>i. if i \<in> {1..k1} then u * u1 i else v * u2 (i - k1)" in exI)
1220 apply(rule_tac x="\<lambda>i. if i \<in> {1..k1} then x1 i else x2 (i - k1)" in exI) apply(rule,rule) defer apply(rule)
1221 unfolding * and setsum_cases[OF finite_atLeastAtMost[of 1 "k1 + k2"]] and setsum_reindex[OF inj] and o_def Collect_mem_eq
1222 unfolding scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] setsum_right_distrib[THEN sym] proof-
1223 fix i assume i:"i \<in> {1..k1+k2}"
1224 show "0 \<le> (if i \<in> {1..k1} then u * u1 i else v * u2 (i - k1)) \<and> (if i \<in> {1..k1} then x1 i else x2 (i - k1)) \<in> s"
1225 proof(cases "i\<in>{1..k1}")
1226 case True thus ?thesis using mult_nonneg_nonneg[of u "u1 i"] and uv(1) x(1)[THEN bspec[where x=i]] by auto
1227 next def j \<equiv> "i - k1"
1228 case False with i have "j \<in> {1..k2}" unfolding j_def by auto
1229 thus ?thesis unfolding j_def[symmetric] using False
1230 using mult_nonneg_nonneg[of v "u2 j"] and uv(2) y(1)[THEN bspec[where x=j]] by auto qed
1231 qed(auto simp add: not_le x(2,3) y(2,3) uv(3))
1234 lemma convex_hull_finite:
1235 fixes s :: "'a::real_vector set"
1237 shows "convex hull s = {y. \<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and>
1238 setsum u s = 1 \<and> setsum (\<lambda>x. u x *\<^sub>R x) s = y}" (is "?HULL = ?set")
1239 proof(rule hull_unique, auto simp add: mem_def[of _ convex] convex_def[of ?set])
1240 fix x assume "x\<in>s" thus " \<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> (\<Sum>x\<in>s. u x *\<^sub>R x) = x"
1241 apply(rule_tac x="\<lambda>y. if x=y then 1 else 0" in exI) apply auto
1242 unfolding setsum_delta'[OF assms] and setsum_delta''[OF assms] by auto
1244 fix u v ::real assume uv:"0 \<le> u" "0 \<le> v" "u + v = 1"
1245 fix ux assume ux:"\<forall>x\<in>s. 0 \<le> ux x" "setsum ux s = (1::real)"
1246 fix uy assume uy:"\<forall>x\<in>s. 0 \<le> uy x" "setsum uy s = (1::real)"
1247 { fix x assume "x\<in>s"
1248 hence "0 \<le> u * ux x + v * uy x" using ux(1)[THEN bspec[where x=x]] uy(1)[THEN bspec[where x=x]] and uv(1,2)
1249 by (auto, metis add_nonneg_nonneg mult_nonneg_nonneg uv(1) uv(2)) }
1250 moreover have "(\<Sum>x\<in>s. u * ux x + v * uy x) = 1"
1251 unfolding setsum_addf and setsum_right_distrib[THEN sym] and ux(2) uy(2) using uv(3) by auto
1252 moreover have "(\<Sum>x\<in>s. (u * ux x + v * uy x) *\<^sub>R x) = u *\<^sub>R (\<Sum>x\<in>s. ux x *\<^sub>R x) + v *\<^sub>R (\<Sum>x\<in>s. uy x *\<^sub>R x)"
1253 unfolding scaleR_left_distrib and setsum_addf and scaleR_scaleR[THEN sym] and scaleR_right.setsum [symmetric] by auto
1254 ultimately show "\<exists>uc. (\<forall>x\<in>s. 0 \<le> uc x) \<and> setsum uc s = 1 \<and> (\<Sum>x\<in>s. uc x *\<^sub>R x) = u *\<^sub>R (\<Sum>x\<in>s. ux x *\<^sub>R x) + v *\<^sub>R (\<Sum>x\<in>s. uy x *\<^sub>R x)"
1255 apply(rule_tac x="\<lambda>x. u * ux x + v * uy x" in exI) by auto
1257 fix t assume t:"s \<subseteq> t" "convex t"
1258 fix u assume u:"\<forall>x\<in>s. 0 \<le> u x" "setsum u s = (1::real)"
1259 thus "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> t" using t(2)[unfolded convex_explicit, THEN spec[where x=s], THEN spec[where x=u]]
1260 using assms and t(1) by auto
1263 subsection {* Another formulation from Lars Schewe. *}
1265 lemma setsum_constant_scaleR:
1266 fixes y :: "'a::real_vector"
1267 shows "(\<Sum>x\<in>A. y) = of_nat (card A) *\<^sub>R y"
1268 apply (cases "finite A")
1269 apply (induct set: finite)
1270 apply (simp_all add: algebra_simps)
1273 lemma convex_hull_explicit:
1274 fixes p :: "'a::real_vector set"
1275 shows "convex hull p = {y. \<exists>s u. finite s \<and> s \<subseteq> p \<and>
1276 (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = y}" (is "?lhs = ?rhs")
1278 { fix x assume "x\<in>?lhs"
1279 then obtain k u y where obt:"\<forall>i\<in>{1::nat..k}. 0 \<le> u i \<and> y i \<in> p" "setsum u {1..k} = 1" "(\<Sum>i = 1..k. u i *\<^sub>R y i) = x"
1280 unfolding convex_hull_indexed by auto
1282 have fin:"finite {1..k}" by auto
1283 have fin':"\<And>v. finite {i \<in> {1..k}. y i = v}" by auto
1284 { fix j assume "j\<in>{1..k}"
1285 hence "y j \<in> p" "0 \<le> setsum u {i. Suc 0 \<le> i \<and> i \<le> k \<and> y i = y j}"
1286 using obt(1)[THEN bspec[where x=j]] and obt(2) apply simp
1287 apply(rule setsum_nonneg) using obt(1) by auto }
1289 have "(\<Sum>v\<in>y ` {1..k}. setsum u {i \<in> {1..k}. y i = v}) = 1"
1290 unfolding setsum_image_gen[OF fin, THEN sym] using obt(2) by auto
1291 moreover have "(\<Sum>v\<in>y ` {1..k}. setsum u {i \<in> {1..k}. y i = v} *\<^sub>R v) = x"
1292 using setsum_image_gen[OF fin, of "\<lambda>i. u i *\<^sub>R y i" y, THEN sym]
1293 unfolding scaleR_left.setsum using obt(3) by auto
1294 ultimately have "\<exists>s u. finite s \<and> s \<subseteq> p \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
1295 apply(rule_tac x="y ` {1..k}" in exI)
1296 apply(rule_tac x="\<lambda>v. setsum u {i\<in>{1..k}. y i = v}" in exI) by auto
1297 hence "x\<in>?rhs" by auto }
1299 { fix y assume "y\<in>?rhs"
1300 then obtain s u where obt:"finite s" "s \<subseteq> p" "\<forall>x\<in>s. 0 \<le> u x" "setsum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = y" by auto
1302 obtain f where f:"inj_on f {1..card s}" "f ` {1..card s} = s" using ex_bij_betw_nat_finite_1[OF obt(1)] unfolding bij_betw_def by auto
1304 { fix i::nat assume "i\<in>{1..card s}"
1305 hence "f i \<in> s" apply(subst f(2)[THEN sym]) by auto
1306 hence "0 \<le> u (f i)" "f i \<in> p" using obt(2,3) by auto }
1307 moreover have *:"finite {1..card s}" by auto
1308 { fix y assume "y\<in>s"
1309 then obtain i where "i\<in>{1..card s}" "f i = y" using f using image_iff[of y f "{1..card s}"] by auto
1310 hence "{x. Suc 0 \<le> x \<and> x \<le> card s \<and> f x = y} = {i}" apply auto using f(1)[unfolded inj_on_def] apply(erule_tac x=x in ballE) by auto
1311 hence "card {x. Suc 0 \<le> x \<and> x \<le> card s \<and> f x = y} = 1" by auto
1312 hence "(\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x)) = u y"
1313 "(\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x) *\<^sub>R f x) = u y *\<^sub>R y"
1314 by (auto simp add: setsum_constant_scaleR) }
1316 hence "(\<Sum>x = 1..card s. u (f x)) = 1" "(\<Sum>i = 1..card s. u (f i) *\<^sub>R f i) = y"
1317 unfolding setsum_image_gen[OF *(1), of "\<lambda>x. u (f x) *\<^sub>R f x" f] and setsum_image_gen[OF *(1), of "\<lambda>x. u (f x)" f]
1318 unfolding f using setsum_cong2[of s "\<lambda>y. (\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x) *\<^sub>R f x)" "\<lambda>v. u v *\<^sub>R v"]
1319 using setsum_cong2 [of s "\<lambda>y. (\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x))" u] unfolding obt(4,5) by auto
1321 ultimately have "\<exists>k u x. (\<forall>i\<in>{1..k}. 0 \<le> u i \<and> x i \<in> p) \<and> setsum u {1..k} = 1 \<and> (\<Sum>i::nat = 1..k. u i *\<^sub>R x i) = y"
1322 apply(rule_tac x="card s" in exI) apply(rule_tac x="u \<circ> f" in exI) apply(rule_tac x=f in exI) by fastsimp
1323 hence "y \<in> ?lhs" unfolding convex_hull_indexed by auto }
1324 ultimately show ?thesis unfolding set_eq_iff by blast
1327 subsection {* A stepping theorem for that expansion. *}
1329 lemma convex_hull_finite_step:
1330 fixes s :: "'a::real_vector set" assumes "finite s"
1331 shows "(\<exists>u. (\<forall>x\<in>insert a s. 0 \<le> u x) \<and> setsum u (insert a s) = w \<and> setsum (\<lambda>x. u x *\<^sub>R x) (insert a s) = y)
1332 \<longleftrightarrow> (\<exists>v\<ge>0. \<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = w - v \<and> setsum (\<lambda>x. u x *\<^sub>R x) s = y - v *\<^sub>R a)" (is "?lhs = ?rhs")
1333 proof(rule, case_tac[!] "a\<in>s")
1334 assume "a\<in>s" hence *:"insert a s = s" by auto
1335 assume ?lhs thus ?rhs unfolding * apply(rule_tac x=0 in exI) by auto
1337 assume ?lhs then obtain u where u:"\<forall>x\<in>insert a s. 0 \<le> u x" "setsum u (insert a s) = w" "(\<Sum>x\<in>insert a s. u x *\<^sub>R x) = y" by auto
1338 assume "a\<notin>s" thus ?rhs apply(rule_tac x="u a" in exI) using u(1)[THEN bspec[where x=a]] apply simp
1339 apply(rule_tac x=u in exI) using u[unfolded setsum_clauses(2)[OF assms]] and `a\<notin>s` by auto
1341 assume "a\<in>s" hence *:"insert a s = s" by auto
1342 have fin:"finite (insert a s)" using assms by auto
1343 assume ?rhs then obtain v u where uv:"v\<ge>0" "\<forall>x\<in>s. 0 \<le> u x" "setsum u s = w - v" "(\<Sum>x\<in>s. u x *\<^sub>R x) = y - v *\<^sub>R a" by auto
1344 show ?lhs apply(rule_tac x="\<lambda>x. (if a = x then v else 0) + u x" in exI) unfolding scaleR_left_distrib and setsum_addf and setsum_delta''[OF fin] and setsum_delta'[OF fin]
1345 unfolding setsum_clauses(2)[OF assms] using uv and uv(2)[THEN bspec[where x=a]] and `a\<in>s` by auto
1347 assume ?rhs then obtain v u where uv:"v\<ge>0" "\<forall>x\<in>s. 0 \<le> u x" "setsum u s = w - v" "(\<Sum>x\<in>s. u x *\<^sub>R x) = y - v *\<^sub>R a" by auto
1348 moreover assume "a\<notin>s" moreover have "(\<Sum>x\<in>s. if a = x then v else u x) = setsum u s" "(\<Sum>x\<in>s. (if a = x then v else u x) *\<^sub>R x) = (\<Sum>x\<in>s. u x *\<^sub>R x)"
1349 apply(rule_tac setsum_cong2) defer apply(rule_tac setsum_cong2) using `a\<notin>s` by auto
1350 ultimately show ?lhs apply(rule_tac x="\<lambda>x. if a = x then v else u x" in exI) unfolding setsum_clauses(2)[OF assms] by auto
1353 subsection {* Hence some special cases. *}
1355 lemma convex_hull_2:
1356 "convex hull {a,b} = {u *\<^sub>R a + v *\<^sub>R b | u v. 0 \<le> u \<and> 0 \<le> v \<and> u + v = 1}"
1357 proof- have *:"\<And>u. (\<forall>x\<in>{a, b}. 0 \<le> u x) \<longleftrightarrow> 0 \<le> u a \<and> 0 \<le> u b" by auto have **:"finite {b}" by auto
1358 show ?thesis apply(simp add: convex_hull_finite) unfolding convex_hull_finite_step[OF **, of a 1, unfolded * conj_assoc]
1359 apply auto apply(rule_tac x=v in exI) apply(rule_tac x="1 - v" in exI) apply simp
1360 apply(rule_tac x=u in exI) apply simp apply(rule_tac x="\<lambda>x. v" in exI) by simp qed
1362 lemma convex_hull_2_alt: "convex hull {a,b} = {a + u *\<^sub>R (b - a) | u. 0 \<le> u \<and> u \<le> 1}"
1363 unfolding convex_hull_2 unfolding Collect_def
1364 proof(rule ext) have *:"\<And>x y ::real. x + y = 1 \<longleftrightarrow> x = 1 - y" by auto
1365 fix x show "(\<exists>v u. x = v *\<^sub>R a + u *\<^sub>R b \<and> 0 \<le> v \<and> 0 \<le> u \<and> v + u = 1) = (\<exists>u. x = a + u *\<^sub>R (b - a) \<and> 0 \<le> u \<and> u \<le> 1)"
1366 unfolding * apply auto apply(rule_tac[!] x=u in exI) by (auto simp add: algebra_simps) qed
1368 lemma convex_hull_3:
1369 "convex hull {a,b,c} = { u *\<^sub>R a + v *\<^sub>R b + w *\<^sub>R c | u v w. 0 \<le> u \<and> 0 \<le> v \<and> 0 \<le> w \<and> u + v + w = 1}"
1371 have fin:"finite {a,b,c}" "finite {b,c}" "finite {c}" by auto
1372 have *:"\<And>x y z ::real. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z"
1373 "\<And>x y z ::_::euclidean_space. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z" by (auto simp add: field_simps)
1374 show ?thesis unfolding convex_hull_finite[OF fin(1)] and Collect_def and convex_hull_finite_step[OF fin(2)] and *
1375 unfolding convex_hull_finite_step[OF fin(3)] apply(rule ext) apply simp apply auto
1376 apply(rule_tac x=va in exI) apply (rule_tac x="u c" in exI) apply simp
1377 apply(rule_tac x="1 - v - w" in exI) apply simp apply(rule_tac x=v in exI) apply simp apply(rule_tac x="\<lambda>x. w" in exI) by simp qed
1379 lemma convex_hull_3_alt:
1380 "convex hull {a,b,c} = {a + u *\<^sub>R (b - a) + v *\<^sub>R (c - a) | u v. 0 \<le> u \<and> 0 \<le> v \<and> u + v \<le> 1}"
1381 proof- have *:"\<And>x y z ::real. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z" by auto
1382 show ?thesis unfolding convex_hull_3 apply (auto simp add: *) apply(rule_tac x=v in exI) apply(rule_tac x=w in exI) apply (simp add: algebra_simps)
1383 apply(rule_tac x=u in exI) apply(rule_tac x=v in exI) by (simp add: algebra_simps) qed
1385 subsection {* Relations among closure notions and corresponding hulls. *}
1387 text {* TODO: Generalize linear algebra concepts defined in @{text
1388 Euclidean_Space.thy} so that we can generalize these lemmas. *}
1390 lemma affine_imp_convex: "affine s \<Longrightarrow> convex s"
1391 unfolding affine_def convex_def by auto
1393 lemma subspace_imp_convex:
1394 fixes s :: "(_::euclidean_space) set" shows "subspace s \<Longrightarrow> convex s"
1395 using subspace_imp_affine affine_imp_convex by auto
1397 lemma affine_hull_subset_span:
1398 fixes s :: "(_::euclidean_space) set" shows "(affine hull s) \<subseteq> (span s)"
1399 by (metis hull_minimal mem_def span_inc subspace_imp_affine subspace_span)
1401 lemma convex_hull_subset_span:
1402 fixes s :: "(_::euclidean_space) set" shows "(convex hull s) \<subseteq> (span s)"
1403 by (metis hull_minimal mem_def span_inc subspace_imp_convex subspace_span)
1405 lemma convex_hull_subset_affine_hull: "(convex hull s) \<subseteq> (affine hull s)"
1406 by (metis affine_affine_hull affine_imp_convex hull_minimal hull_subset mem_def)
1409 lemma affine_dependent_imp_dependent:
1410 fixes s :: "(_::euclidean_space) set" shows "affine_dependent s \<Longrightarrow> dependent s"
1411 unfolding affine_dependent_def dependent_def
1412 using affine_hull_subset_span by auto
1414 lemma dependent_imp_affine_dependent:
1415 fixes s :: "(_::euclidean_space) set"
1416 assumes "dependent {x - a| x . x \<in> s}" "a \<notin> s"
1417 shows "affine_dependent (insert a s)"
1419 from assms(1)[unfolded dependent_explicit] obtain S u v
1420 where obt:"finite S" "S \<subseteq> {x - a |x. x \<in> s}" "v\<in>S" "u v \<noteq> 0" "(\<Sum>v\<in>S. u v *\<^sub>R v) = 0" by auto
1421 def t \<equiv> "(\<lambda>x. x + a) ` S"
1423 have inj:"inj_on (\<lambda>x. x + a) S" unfolding inj_on_def by auto
1424 have "0\<notin>S" using obt(2) assms(2) unfolding subset_eq by auto
1425 have fin:"finite t" and "t\<subseteq>s" unfolding t_def using obt(1,2) by auto
1427 hence "finite (insert a t)" and "insert a t \<subseteq> insert a s" by auto
1428 moreover have *:"\<And>P Q. (\<Sum>x\<in>t. (if x = a then P x else Q x)) = (\<Sum>x\<in>t. Q x)"
1429 apply(rule setsum_cong2) using `a\<notin>s` `t\<subseteq>s` by auto
1430 have "(\<Sum>x\<in>insert a t. if x = a then - (\<Sum>x\<in>t. u (x - a)) else u (x - a)) = 0"
1431 unfolding setsum_clauses(2)[OF fin] using `a\<notin>s` `t\<subseteq>s` apply auto unfolding * by auto
1432 moreover have "\<exists>v\<in>insert a t. (if v = a then - (\<Sum>x\<in>t. u (x - a)) else u (v - a)) \<noteq> 0"
1433 apply(rule_tac x="v + a" in bexI) using obt(3,4) and `0\<notin>S` unfolding t_def by auto
1434 moreover have *:"\<And>P Q. (\<Sum>x\<in>t. (if x = a then P x else Q x) *\<^sub>R x) = (\<Sum>x\<in>t. Q x *\<^sub>R x)"
1435 apply(rule setsum_cong2) using `a\<notin>s` `t\<subseteq>s` by auto
1436 have "(\<Sum>x\<in>t. u (x - a)) *\<^sub>R a = (\<Sum>v\<in>t. u (v - a) *\<^sub>R v)"
1437 unfolding scaleR_left.setsum unfolding t_def and setsum_reindex[OF inj] and o_def
1438 using obt(5) by (auto simp add: setsum_addf scaleR_right_distrib)
1439 hence "(\<Sum>v\<in>insert a t. (if v = a then - (\<Sum>x\<in>t. u (x - a)) else u (v - a)) *\<^sub>R v) = 0"
1440 unfolding setsum_clauses(2)[OF fin] using `a\<notin>s` `t\<subseteq>s` by (auto simp add: *)
1441 ultimately show ?thesis unfolding affine_dependent_explicit
1442 apply(rule_tac x="insert a t" in exI) by auto
1446 "convex s \<and> cone s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. (x + y) \<in> s) \<and> (\<forall>x\<in>s. \<forall>c\<ge>0. (c *\<^sub>R x) \<in> s)" (is "?lhs = ?rhs")
1448 { fix x y assume "x\<in>s" "y\<in>s" and ?lhs
1449 hence "2 *\<^sub>R x \<in>s" "2 *\<^sub>R y \<in> s" unfolding cone_def by auto
1450 hence "x + y \<in> s" using `?lhs`[unfolded convex_def, THEN conjunct1]
1451 apply(erule_tac x="2*\<^sub>R x" in ballE) apply(erule_tac x="2*\<^sub>R y" in ballE)
1452 apply(erule_tac x="1/2" in allE) apply simp apply(erule_tac x="1/2" in allE) by auto }
1453 thus ?thesis unfolding convex_def cone_def by blast
1456 lemma affine_dependent_biggerset: fixes s::"('a::euclidean_space) set"
1457 assumes "finite s" "card s \<ge> DIM('a) + 2"
1458 shows "affine_dependent s"
1460 have "s\<noteq>{}" using assms by auto then obtain a where "a\<in>s" by auto
1461 have *:"{x - a |x. x \<in> s - {a}} = (\<lambda>x. x - a) ` (s - {a})" by auto
1462 have "card {x - a |x. x \<in> s - {a}} = card (s - {a})" unfolding *
1463 apply(rule card_image) unfolding inj_on_def by auto
1464 also have "\<dots> > DIM('a)" using assms(2)
1465 unfolding card_Diff_singleton[OF assms(1) `a\<in>s`] by auto
1466 finally show ?thesis apply(subst insert_Diff[OF `a\<in>s`, THEN sym])
1467 apply(rule dependent_imp_affine_dependent)
1468 apply(rule dependent_biggerset) by auto qed
1470 lemma affine_dependent_biggerset_general:
1471 assumes "finite (s::('a::euclidean_space) set)" "card s \<ge> dim s + 2"
1472 shows "affine_dependent s"
1474 from assms(2) have "s \<noteq> {}" by auto
1475 then obtain a where "a\<in>s" by auto
1476 have *:"{x - a |x. x \<in> s - {a}} = (\<lambda>x. x - a) ` (s - {a})" by auto
1477 have **:"card {x - a |x. x \<in> s - {a}} = card (s - {a})" unfolding *
1478 apply(rule card_image) unfolding inj_on_def by auto
1479 have "dim {x - a |x. x \<in> s - {a}} \<le> dim s"
1480 apply(rule subset_le_dim) unfolding subset_eq
1481 using `a\<in>s` by (auto simp add:span_superset span_sub)
1482 also have "\<dots> < dim s + 1" by auto
1483 also have "\<dots> \<le> card (s - {a})" using assms
1484 using card_Diff_singleton[OF assms(1) `a\<in>s`] by auto
1485 finally show ?thesis apply(subst insert_Diff[OF `a\<in>s`, THEN sym])
1486 apply(rule dependent_imp_affine_dependent) apply(rule dependent_biggerset_general) unfolding ** by auto qed
1488 subsection {* Caratheodory's theorem. *}
1490 lemma convex_hull_caratheodory: fixes p::"('a::euclidean_space) set"
1491 shows "convex hull p = {y. \<exists>s u. finite s \<and> s \<subseteq> p \<and> card s \<le> DIM('a) + 1 \<and>
1492 (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = y}"
1493 unfolding convex_hull_explicit set_eq_iff mem_Collect_eq
1495 fix y let ?P = "\<lambda>n. \<exists>s u. finite s \<and> card s = n \<and> s \<subseteq> p \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y"
1496 assume "\<exists>s u. finite s \<and> s \<subseteq> p \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y"
1497 then obtain N where "?P N" by auto
1498 hence "\<exists>n\<le>N. (\<forall>k<n. \<not> ?P k) \<and> ?P n" apply(rule_tac ex_least_nat_le) by auto
1499 then obtain n where "?P n" and smallest:"\<forall>k<n. \<not> ?P k" by blast
1500 then obtain s u where obt:"finite s" "card s = n" "s\<subseteq>p" "\<forall>x\<in>s. 0 \<le> u x" "setsum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = y" by auto
1502 have "card s \<le> DIM('a) + 1" proof(rule ccontr, simp only: not_le)
1503 assume "DIM('a) + 1 < card s"
1504 hence "affine_dependent s" using affine_dependent_biggerset[OF obt(1)] by auto
1505 then obtain w v where wv:"setsum w s = 0" "v\<in>s" "w v \<noteq> 0" "(\<Sum>v\<in>s. w v *\<^sub>R v) = 0"
1506 using affine_dependent_explicit_finite[OF obt(1)] by auto
1507 def i \<equiv> "(\<lambda>v. (u v) / (- w v)) ` {v\<in>s. w v < 0}" def t \<equiv> "Min i"
1508 have "\<exists>x\<in>s. w x < 0" proof(rule ccontr, simp add: not_less)
1509 assume as:"\<forall>x\<in>s. 0 \<le> w x"
1510 hence "setsum w (s - {v}) \<ge> 0" apply(rule_tac setsum_nonneg) by auto
1511 hence "setsum w s > 0" unfolding setsum_diff1'[OF obt(1) `v\<in>s`]
1512 using as[THEN bspec[where x=v]] and `v\<in>s` using `w v \<noteq> 0` by auto
1513 thus False using wv(1) by auto
1514 qed hence "i\<noteq>{}" unfolding i_def by auto
1516 hence "t \<ge> 0" using Min_ge_iff[of i 0 ] and obt(1) unfolding t_def i_def
1517 using obt(4)[unfolded le_less] apply auto unfolding divide_le_0_iff by auto
1518 have t:"\<forall>v\<in>s. u v + t * w v \<ge> 0" proof
1519 fix v assume "v\<in>s" hence v:"0\<le>u v" using obt(4)[THEN bspec[where x=v]] by auto
1520 show"0 \<le> u v + t * w v" proof(cases "w v < 0")
1521 case False thus ?thesis apply(rule_tac add_nonneg_nonneg)
1522 using v apply simp apply(rule mult_nonneg_nonneg) using `t\<ge>0` by auto next
1523 case True hence "t \<le> u v / (- w v)" using `v\<in>s`
1524 unfolding t_def i_def apply(rule_tac Min_le) using obt(1) by auto
1525 thus ?thesis unfolding real_0_le_add_iff
1526 using pos_le_divide_eq[OF True[unfolded neg_0_less_iff_less[THEN sym]]] by auto
1529 obtain a where "a\<in>s" and "t = (\<lambda>v. (u v) / (- w v)) a" and "w a < 0"
1530 using Min_in[OF _ `i\<noteq>{}`] and obt(1) unfolding i_def t_def by auto
1531 hence a:"a\<in>s" "u a + t * w a = 0" by auto
1532 have *:"\<And>f. setsum f (s - {a}) = setsum f s - ((f a)::'b::ab_group_add)"
1533 unfolding setsum_diff1'[OF obt(1) `a\<in>s`] by auto
1534 have "(\<Sum>v\<in>s. u v + t * w v) = 1"
1535 unfolding setsum_addf wv(1) setsum_right_distrib[THEN sym] obt(5) by auto
1536 moreover have "(\<Sum>v\<in>s. u v *\<^sub>R v + (t * w v) *\<^sub>R v) - (u a *\<^sub>R a + (t * w a) *\<^sub>R a) = y"
1537 unfolding setsum_addf obt(6) scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] wv(4)
1538 using a(2) [THEN eq_neg_iff_add_eq_0 [THEN iffD2]] by simp
1539 ultimately have "?P (n - 1)" apply(rule_tac x="(s - {a})" in exI)
1540 apply(rule_tac x="\<lambda>v. u v + t * w v" in exI) using obt(1-3) and t and a
1541 by (auto simp add: * scaleR_left_distrib)
1542 thus False using smallest[THEN spec[where x="n - 1"]] by auto qed
1543 thus "\<exists>s u. finite s \<and> s \<subseteq> p \<and> card s \<le> DIM('a) + 1
1544 \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y" using obt by auto
1548 "convex hull p = {x::'a::euclidean_space. \<exists>s. finite s \<and> s \<subseteq> p \<and>
1549 card s \<le> DIM('a) + 1 \<and> x \<in> convex hull s}"
1550 unfolding set_eq_iff apply(rule, rule) unfolding mem_Collect_eq proof-
1551 fix x assume "x \<in> convex hull p"
1552 then obtain s u where "finite s" "s \<subseteq> p" "card s \<le> DIM('a) + 1"
1553 "\<forall>x\<in>s. 0 \<le> u x" "setsum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"unfolding convex_hull_caratheodory by auto
1554 thus "\<exists>s. finite s \<and> s \<subseteq> p \<and> card s \<le> DIM('a) + 1 \<and> x \<in> convex hull s"
1555 apply(rule_tac x=s in exI) using hull_subset[of s convex]
1556 using convex_convex_hull[unfolded convex_explicit, of s, THEN spec[where x=s], THEN spec[where x=u]] by auto
1558 fix x assume "\<exists>s. finite s \<and> s \<subseteq> p \<and> card s \<le> DIM('a) + 1 \<and> x \<in> convex hull s"
1559 then obtain s where "finite s" "s \<subseteq> p" "card s \<le> DIM('a) + 1" "x \<in> convex hull s" by auto
1560 thus "x \<in> convex hull p" using hull_mono[OF `s\<subseteq>p`] by auto
1564 subsection {* Some Properties of Affine Dependent Sets *}
1566 lemma affine_independent_empty: "~(affine_dependent {})"
1567 by (simp add: affine_dependent_def)
1569 lemma affine_independent_sing:
1570 fixes a :: "'n::euclidean_space"
1571 shows "~(affine_dependent {a})"
1572 by (simp add: affine_dependent_def)
1574 lemma affine_hull_translation:
1575 "affine hull ((%x. a + x) ` S) = (%x. a + x) ` (affine hull S)"
1577 have "affine ((%x. a + x) ` (affine hull S))" using affine_translation affine_affine_hull by auto
1578 moreover have "(%x. a + x) ` S <= (%x. a + x) ` (affine hull S)" using hull_subset[of S] by auto
1579 ultimately have h1: "affine hull ((%x. a + x) ` S) <= (%x. a + x) ` (affine hull S)" by (metis hull_minimal mem_def)
1580 have "affine((%x. -a + x) ` (affine hull ((%x. a + x) ` S)))" using affine_translation affine_affine_hull by auto
1581 moreover have "(%x. -a + x) ` (%x. a + x) ` S <= (%x. -a + x) ` (affine hull ((%x. a + x) ` S))" using hull_subset[of "(%x. a + x) ` S"] by auto
1582 moreover have "S=(%x. -a + x) ` (%x. a + x) ` S" using translation_assoc[of "-a" a] by auto
1583 ultimately have "(%x. -a + x) ` (affine hull ((%x. a + x) ` S)) >= (affine hull S)" by (metis hull_minimal mem_def)
1584 hence "affine hull ((%x. a + x) ` S) >= (%x. a + x) ` (affine hull S)" by auto
1585 from this show ?thesis using h1 by auto
1588 lemma affine_dependent_translation:
1589 assumes "affine_dependent S"
1590 shows "affine_dependent ((%x. a + x) ` S)"
1592 obtain x where x_def: "x : S & x : affine hull (S - {x})" using assms affine_dependent_def by auto
1593 have "op + a ` (S - {x}) = op + a ` S - {a + x}" by auto
1594 hence "a+x : affine hull ((%x. a + x) ` S - {a+x})" using affine_hull_translation[of a "S-{x}"] x_def by auto
1595 moreover have "a+x : (%x. a + x) ` S" using x_def by auto
1596 ultimately show ?thesis unfolding affine_dependent_def by auto
1599 lemma affine_dependent_translation_eq:
1600 "affine_dependent S <-> affine_dependent ((%x. a + x) ` S)"
1602 { assume "affine_dependent ((%x. a + x) ` S)"
1603 hence "affine_dependent S" using affine_dependent_translation[of "((%x. a + x) ` S)" "-a"] translation_assoc[of "-a" a] by auto
1604 } from this show ?thesis using affine_dependent_translation by auto
1607 lemma affine_hull_0_dependent:
1608 fixes S :: "('n::euclidean_space) set"
1609 assumes "0 : affine hull S"
1612 obtain s u where s_u_def: "finite s & s ~= {} & s <= S & setsum u s = 1 & (SUM v:s. u v *\<^sub>R v) = 0" using assms affine_hull_explicit[of S] by auto
1613 hence "EX v:s. u v ~= 0" using setsum_not_0[of "u" "s"] by auto
1614 hence "finite s & s <= S & (EX v:s. u v ~= 0 & (SUM v:s. u v *\<^sub>R v) = 0)" using s_u_def by auto
1615 from this show ?thesis unfolding dependent_explicit[of S] by auto
1618 lemma affine_dependent_imp_dependent2:
1619 fixes S :: "('n::euclidean_space) set"
1620 assumes "affine_dependent (insert 0 S)"
1623 obtain x where x_def: "x:insert 0 S & x : affine hull (insert 0 S - {x})" using affine_dependent_def[of "(insert 0 S)"] assms by blast
1624 hence "x : span (insert 0 S - {x})" using affine_hull_subset_span by auto
1625 moreover have "span (insert 0 S - {x}) = span (S - {x})" using insert_Diff_if[of "0" S "{x}"] span_insert_0[of "S-{x}"] by auto
1626 ultimately have "x : span (S - {x})" by auto
1627 hence "(x~=0) ==> dependent S" using x_def dependent_def by auto
1629 { assume "x=0" hence "0 : affine hull S" using x_def hull_mono[of "S - {0}" S] by auto
1630 hence "dependent S" using affine_hull_0_dependent by auto
1631 } ultimately show ?thesis by auto
1634 lemma affine_dependent_iff_dependent:
1635 fixes S :: "('n::euclidean_space) set"
1637 shows "affine_dependent (insert a S) <-> dependent ((%x. -a + x) ` S)"
1639 have "(op + (- a) ` S)={x - a| x . x : S}" by auto
1640 from this show ?thesis using affine_dependent_translation_eq[of "(insert a S)" "-a"]
1641 affine_dependent_imp_dependent2 assms
1642 dependent_imp_affine_dependent[of a S] by auto
1645 lemma affine_dependent_iff_dependent2:
1646 fixes S :: "('n::euclidean_space) set"
1648 shows "affine_dependent S <-> dependent ((%x. -a + x) ` (S-{a}))"
1650 have "insert a (S - {a})=S" using assms by auto
1651 from this show ?thesis using assms affine_dependent_iff_dependent[of a "S-{a}"] by auto
1654 lemma affine_hull_insert_span_gen:
1655 fixes a :: "_::euclidean_space"
1656 shows "affine hull (insert a s) = (%x. a+x) ` span ((%x. -a+x) ` s)"
1658 have h1: "{x - a |x. x : s}=((%x. -a+x) ` s)" by auto
1659 { assume "a ~: s" hence ?thesis using affine_hull_insert_span[of a s] h1 by auto}
1661 { assume a1: "a : s"
1662 have "EX x. x:s & -a+x=0" apply (rule exI[of _ a]) using a1 by auto
1663 hence "insert 0 ((%x. -a+x) ` (s - {a}))=(%x. -a+x) ` s" by auto
1664 hence "span ((%x. -a+x) ` (s - {a}))=span ((%x. -a+x) ` s)"
1665 using span_insert_0[of "op + (- a) ` (s - {a})"] by auto
1666 moreover have "{x - a |x. x : (s - {a})}=((%x. -a+x) ` (s - {a}))" by auto
1667 moreover have "insert a (s - {a})=(insert a s)" using assms by auto
1668 ultimately have ?thesis using assms affine_hull_insert_span[of "a" "s-{a}"] by auto
1670 ultimately show ?thesis by auto
1673 lemma affine_hull_span2:
1674 fixes a :: "_::euclidean_space"
1676 shows "affine hull s = (%x. a+x) ` span ((%x. -a+x) ` (s-{a}))"
1677 using affine_hull_insert_span_gen[of a "s - {a}", unfolded insert_Diff[OF assms]] by auto
1679 lemma affine_hull_span_gen:
1680 fixes a :: "_::euclidean_space"
1681 assumes "a : affine hull s"
1682 shows "affine hull s = (%x. a+x) ` span ((%x. -a+x) ` s)"
1684 have "affine hull (insert a s) = affine hull s" using hull_redundant[of a affine s] assms by auto
1685 from this show ?thesis using affine_hull_insert_span_gen[of a "s"] by auto
1688 lemma affine_hull_span_0:
1689 assumes "(0 :: _::euclidean_space) : affine hull S"
1690 shows "affine hull S = span S"
1691 using affine_hull_span_gen[of "0" S] assms by auto
1694 lemma extend_to_affine_basis:
1695 fixes S V :: "('n::euclidean_space) set"
1696 assumes "~(affine_dependent S)" "S <= V" "S~={}"
1697 shows "? T. ~(affine_dependent T) & S<=T & T<=V & affine hull T = affine hull V"
1699 obtain a where a_def: "a : S" using assms by auto
1700 hence h0: "independent ((%x. -a + x) ` (S-{a}))" using affine_dependent_iff_dependent2 assms by auto
1702 where B_def: "(%x. -a+x) ` (S - {a}) <= B & B <= (%x. -a+x) ` V & independent B & (%x. -a+x) ` V <= span B"
1703 using maximal_independent_subset_extend[of "(%x. -a+x) ` (S-{a})" "(%x. -a + x) ` V"] assms by blast
1704 def T == "(%x. a+x) ` (insert 0 B)" hence "T=insert a ((%x. a+x) ` B)" by auto
1705 hence "affine hull T = (%x. a+x) ` span B" using affine_hull_insert_span_gen[of a "((%x. a+x) ` B)"] translation_assoc[of "-a" a B] by auto
1706 hence "V <= affine hull T" using B_def assms translation_inverse_subset[of a V "span B"] by auto
1707 moreover have "T<=V" using T_def B_def a_def assms by auto
1708 ultimately have "affine hull T = affine hull V"
1709 by (metis Int_absorb1 Int_absorb2 Int_commute Int_lower2 assms hull_hull hull_mono)
1710 moreover have "S<=T" using T_def B_def translation_inverse_subset[of a "S-{a}" B] by auto
1711 moreover have "~(affine_dependent T)" using T_def affine_dependent_translation_eq[of "insert 0 B"] affine_dependent_imp_dependent2 B_def by auto
1712 ultimately show ?thesis using `T<=V` by auto
1715 lemma affine_basis_exists:
1716 fixes V :: "('n::euclidean_space) set"
1717 shows "? B. B <= V & ~(affine_dependent B) & affine hull V = affine hull B"
1719 { assume empt: "V={}" have "? B. B <= V & ~(affine_dependent B) & (affine hull V=affine hull B)" using empt affine_independent_empty by auto
1722 { assume nonempt: "V~={}" obtain x where "x:V" using nonempt by auto
1723 hence "? B. B <= V & ~(affine_dependent B) & (affine hull V=affine hull B)"
1724 using affine_dependent_def[of "{x}"] extend_to_affine_basis[of "{x}:: ('n::euclidean_space) set" V] by auto
1726 ultimately show ?thesis by auto
1729 subsection {* Affine Dimension of a Set *}
1731 definition "aff_dim V = (SOME d :: int. ? B. (affine hull B=affine hull V) & ~(affine_dependent B) & (of_nat(card B) = d+1))"
1733 lemma aff_dim_basis_exists:
1734 fixes V :: "('n::euclidean_space) set"
1735 shows "? B. (affine hull B=affine hull V) & ~(affine_dependent B) & (of_nat(card B) = aff_dim V+1)"
1737 obtain B where B_def: "~(affine_dependent B) & (affine hull B=affine hull V)" using affine_basis_exists[of V] by auto
1738 from this show ?thesis unfolding aff_dim_def some_eq_ex[of "%d. ? (B :: ('n::euclidean_space) set). (affine hull B=affine hull V) & ~(affine_dependent B) & (of_nat(card B) = d+1)"] apply auto apply (rule exI[of _ "int (card B)-(1 :: int)"]) apply (rule exI[of _ "B"]) by auto
1741 lemma affine_hull_nonempty: "(S ~= {}) <-> affine hull S ~= {}"
1743 fix S have "(S = {}) ==> affine hull S = {}"using affine_hull_empty by auto
1744 moreover have "affine hull S = {} ==> S = {}" unfolding hull_def by auto
1745 ultimately show "(S ~= {}) <-> affine hull S ~= {}" by blast
1748 lemma aff_dim_parallel_subspace_aux:
1749 fixes B :: "('n::euclidean_space) set"
1750 assumes "~(affine_dependent B)" "a:B"
1751 shows "finite B & ((card B) - 1 = dim (span ((%x. -a+x) ` (B-{a}))))"
1753 have "independent ((%x. -a + x) ` (B-{a}))" using affine_dependent_iff_dependent2 assms by auto
1754 hence fin: "dim (span ((%x. -a+x) ` (B-{a}))) = card ((%x. -a + x) ` (B-{a}))" "finite ((%x. -a + x) ` (B - {a}))" using indep_card_eq_dim_span[of "(%x. -a+x) ` (B-{a})"] by auto
1755 { assume emp: "(%x. -a + x) ` (B - {a}) = {}"
1756 have "B=insert a ((%x. a + x) ` (%x. -a + x) ` (B - {a}))" using translation_assoc[of "a" "-a" "(B - {a})"] assms by auto
1757 hence "B={a}" using emp by auto
1758 hence ?thesis using assms fin by auto
1761 { assume "(%x. -a + x) ` (B - {a}) ~= {}"
1762 hence "card ((%x. -a + x) ` (B - {a}))>0" using fin by auto
1763 moreover have h1: "card ((%x. -a + x) ` (B-{a})) = card (B-{a})"
1764 apply (rule card_image) using translate_inj_on by auto
1765 ultimately have "card (B-{a})>0" by auto
1766 hence "finite(B-{a})" using card_gt_0_iff[of "(B - {a})"] by auto
1767 moreover hence "(card (B-{a})= (card B) - 1)" using card_Diff_singleton assms by auto
1768 ultimately have ?thesis using fin h1 by auto
1769 } ultimately show ?thesis by auto
1772 lemma aff_dim_parallel_subspace:
1773 fixes V L :: "('n::euclidean_space) set"
1775 assumes "subspace L" "affine_parallel (affine hull V) L"
1776 shows "aff_dim V=int(dim L)"
1778 obtain B where B_def: "affine hull B = affine hull V & ~ affine_dependent B & int (card B) = aff_dim V + 1" using aff_dim_basis_exists by auto
1779 hence "B~={}" using assms B_def affine_hull_nonempty[of V] affine_hull_nonempty[of B] by auto
1780 from this obtain a where a_def: "a : B" by auto
1781 def Lb == "span ((%x. -a+x) ` (B-{a}))"
1782 moreover have "affine_parallel (affine hull B) Lb"
1783 using Lb_def B_def assms affine_hull_span2[of a B] a_def affine_parallel_commut[of "Lb" "(affine hull B)"] unfolding affine_parallel_def by auto
1784 moreover have "subspace Lb" using Lb_def subspace_span by auto
1785 moreover have "affine hull B ~= {}" using assms B_def affine_hull_nonempty[of V] by auto
1786 ultimately have "L=Lb" using assms affine_parallel_subspace[of "affine hull B"] affine_affine_hull[of B] B_def by auto
1787 hence "dim L=dim Lb" by auto
1788 moreover have "(card B) - 1 = dim Lb" "finite B" using Lb_def aff_dim_parallel_subspace_aux a_def B_def by auto
1789 (* hence "card B=dim Lb+1" using `B~={}` card_gt_0_iff[of B] by auto *)
1790 ultimately show ?thesis using B_def `B~={}` card_gt_0_iff[of B] by auto
1793 lemma aff_independent_finite:
1794 fixes B :: "('n::euclidean_space) set"
1795 assumes "~(affine_dependent B)"
1798 { assume "B~={}" from this obtain a where "a:B" by auto
1799 hence ?thesis using aff_dim_parallel_subspace_aux assms by auto
1800 } from this show ?thesis by auto
1803 lemma independent_finite:
1804 fixes B :: "('n::euclidean_space) set"
1805 assumes "independent B"
1807 using affine_dependent_imp_dependent[of B] aff_independent_finite[of B] assms by auto
1809 lemma subspace_dim_equal:
1810 assumes "subspace (S :: ('n::euclidean_space) set)" "subspace T" "S <= T" "dim S >= dim T"
1813 obtain B where B_def: "B <= S & independent B & S <= span B & (card B = dim S)" using basis_exists[of S] by auto
1814 hence "span B <= S" using span_mono[of B S] span_eq[of S] assms by metis
1815 hence "span B = S" using B_def by auto
1816 have "dim S = dim T" using assms dim_subset[of S T] by auto
1817 hence "T <= span B" using card_eq_dim[of B T] B_def independent_finite assms by auto
1818 from this show ?thesis using assms `span B=S` by auto
1821 lemma span_substd_basis: assumes "d\<subseteq>{..<DIM('a::euclidean_space)}"
1822 shows "(span {basis i | i. i : d}) = {x::'a::euclidean_space. (!i<DIM('a). i ~: d --> x$$i = 0)}"
1825 have "?A <= ?B" by auto
1826 moreover have s: "subspace ?B" using subspace_substandard[of "%i. i ~: d"] .
1827 ultimately have "span ?A <= ?B" using span_mono[of "?A" "?B"] span_eq[of "?B"] by blast
1828 moreover have "card d <= dim (span ?A)" using independent_card_le_dim[of "?A" "span ?A"]
1829 independent_substdbasis[OF assms] card_substdbasis[OF assms] span_inc[of "?A"] by auto
1830 moreover hence "dim ?B <= dim (span ?A)" using dim_substandard[OF assms] by auto
1831 ultimately show ?thesis using s subspace_dim_equal[of "span ?A" "?B"]
1832 subspace_span[of "?A"] by auto
1835 lemma basis_to_substdbasis_subspace_isomorphism:
1836 fixes B :: "('a::euclidean_space) set"
1837 assumes "independent B"
1838 shows "EX f d. card d = card B & linear f & f ` B = {basis i::'a |i. i : (d :: nat set)} &
1839 f ` span B = {x. ALL i<DIM('a). i ~: d --> x $$ i = (0::real)} & inj_on f (span B) \<and> d\<subseteq>{..<DIM('a)}"
1841 have B:"card B=dim B" using dim_unique[of B B "card B"] assms span_inc[of B] by auto
1842 def d \<equiv> "{..<dim B}" have t:"card d = dim B" unfolding d_def by auto
1843 have "dim B <= DIM('a)" using dim_subset_UNIV[of B] by auto
1844 hence d:"d\<subseteq>{..<DIM('a)}" unfolding d_def by auto
1845 let ?t = "{x::'a::euclidean_space. !i<DIM('a). i ~: d --> x$$i = 0}"
1846 have "EX f. linear f & f ` B = {basis i |i. i : d} &
1847 f ` span B = ?t & inj_on f (span B)"
1848 apply (rule basis_to_basis_subspace_isomorphism[of "span B" ?t B "{basis i |i. i : d}"])
1849 apply(rule subspace_span) apply(rule subspace_substandard) defer
1850 apply(rule span_inc) apply(rule assms) defer unfolding dim_span[of B] apply(rule B)
1851 unfolding span_substd_basis[OF d,THEN sym] card_substdbasis[OF d] apply(rule span_inc)
1852 apply(rule independent_substdbasis[OF d]) apply(rule,assumption)
1853 unfolding t[THEN sym] span_substd_basis[OF d] dim_substandard[OF d] by auto
1854 from this t `card B=dim B` show ?thesis using d by auto
1857 lemma aff_dim_empty:
1858 fixes S :: "('n::euclidean_space) set"
1859 shows "S = {} <-> aff_dim S = -1"
1861 obtain B where "affine hull B = affine hull S & ~ affine_dependent B & int (card B) = aff_dim S + 1" using aff_dim_basis_exists by auto
1862 moreover hence "S={} <-> B={}" using affine_hull_nonempty[of B] affine_hull_nonempty[of S] by auto
1863 ultimately show ?thesis using aff_independent_finite[of B] card_gt_0_iff[of B] by auto
1866 lemma aff_dim_affine_hull:
1867 fixes S :: "('n::euclidean_space) set"
1868 shows "aff_dim (affine hull S)=aff_dim S"
1869 unfolding aff_dim_def using hull_hull[of _ S] by auto
1871 lemma aff_dim_affine_hull2:
1872 fixes S T :: "('n::euclidean_space) set"
1873 assumes "affine hull S=affine hull T"
1874 shows "aff_dim S=aff_dim T" unfolding aff_dim_def using assms by auto
1876 lemma aff_dim_unique:
1877 fixes B V :: "('n::euclidean_space) set"
1878 assumes "(affine hull B=affine hull V) & ~(affine_dependent B)"
1879 shows "of_nat(card B) = aff_dim V+1"
1881 { assume "B={}" hence "V={}" using affine_hull_nonempty[of V] affine_hull_nonempty[of B] assms by auto
1882 hence "aff_dim V = (-1::int)" using aff_dim_empty by auto
1883 hence ?thesis using `B={}` by auto
1886 { assume "B~={}" from this obtain a where a_def: "a:B" by auto
1887 def Lb == "span ((%x. -a+x) ` (B-{a}))"
1888 have "affine_parallel (affine hull B) Lb"
1889 using Lb_def affine_hull_span2[of a B] a_def affine_parallel_commut[of "Lb" "(affine hull B)"]
1890 unfolding affine_parallel_def by auto
1891 moreover have "subspace Lb" using Lb_def subspace_span by auto
1892 ultimately have "aff_dim B=int(dim Lb)" using aff_dim_parallel_subspace[of B Lb] `B~={}` by auto
1893 moreover have "(card B) - 1 = dim Lb" "finite B" using Lb_def aff_dim_parallel_subspace_aux a_def assms by auto
1894 ultimately have "(of_nat(card B) = aff_dim B+1)" using `B~={}` card_gt_0_iff[of B] by auto
1895 hence ?thesis using aff_dim_affine_hull2 assms by auto
1896 } ultimately show ?thesis by blast
1899 lemma aff_dim_affine_independent:
1900 fixes B :: "('n::euclidean_space) set"
1901 assumes "~(affine_dependent B)"
1902 shows "of_nat(card B) = aff_dim B+1"
1903 using aff_dim_unique[of B B] assms by auto
1906 fixes a :: "'n::euclidean_space"
1907 shows "aff_dim {a}=0"
1908 using aff_dim_affine_independent[of "{a}"] affine_independent_sing by auto
1910 lemma aff_dim_inner_basis_exists:
1911 fixes V :: "('n::euclidean_space) set"
1912 shows "? B. B<=V & (affine hull B=affine hull V) & ~(affine_dependent B) & (of_nat(card B) = aff_dim V+1)"
1914 obtain B where B_def: "~(affine_dependent B) & B<=V & (affine hull B=affine hull V)" using affine_basis_exists[of V] by auto
1915 moreover hence "of_nat(card B) = aff_dim V+1" using aff_dim_unique by auto
1916 ultimately show ?thesis by auto
1919 lemma aff_dim_le_card:
1920 fixes V :: "('n::euclidean_space) set"
1922 shows "aff_dim V <= of_nat(card V) - 1"
1924 obtain B where B_def: "B<=V & (of_nat(card B) = aff_dim V+1)" using aff_dim_inner_basis_exists[of V] by auto
1925 moreover hence "card B <= card V" using assms card_mono by auto
1926 ultimately show ?thesis by auto
1929 lemma aff_dim_parallel_eq:
1930 fixes S T :: "('n::euclidean_space) set"
1931 assumes "affine_parallel (affine hull S) (affine hull T)"
1932 shows "aff_dim S=aff_dim T"
1934 { assume "T~={}" "S~={}"
1935 from this obtain L where L_def: "subspace L & affine_parallel (affine hull T) L"
1936 using affine_parallel_subspace[of "affine hull T"] affine_affine_hull[of T] affine_hull_nonempty by auto
1937 hence "aff_dim T = int(dim L)" using aff_dim_parallel_subspace `T~={}` by auto
1938 moreover have "subspace L & affine_parallel (affine hull S) L"
1939 using L_def affine_parallel_assoc[of "affine hull S" "affine hull T" L] assms by auto
1940 moreover hence "aff_dim S = int(dim L)" using aff_dim_parallel_subspace `S~={}` by auto
1941 ultimately have ?thesis by auto
1944 { assume "S={}" hence "S={} & T={}" using assms affine_hull_nonempty unfolding affine_parallel_def by auto
1945 hence ?thesis using aff_dim_empty by auto
1948 { assume "T={}" hence "S={} & T={}" using assms affine_hull_nonempty unfolding affine_parallel_def by auto
1949 hence ?thesis using aff_dim_empty by auto
1951 ultimately show ?thesis by blast
1954 lemma aff_dim_translation_eq:
1955 fixes a :: "'n::euclidean_space"
1956 shows "aff_dim ((%x. a + x) ` S)=aff_dim S"
1958 have "affine_parallel (affine hull S) (affine hull ((%x. a + x) ` S))" unfolding affine_parallel_def apply (rule exI[of _ "a"]) using affine_hull_translation[of a S] by auto
1959 from this show ?thesis using aff_dim_parallel_eq[of S "(%x. a + x) ` S"] by auto
1962 lemma aff_dim_affine:
1963 fixes S L :: "('n::euclidean_space) set"
1964 assumes "S ~= {}" "affine S"
1965 assumes "subspace L" "affine_parallel S L"
1966 shows "aff_dim S=int(dim L)"
1968 have 1: "(affine hull S) = S" using assms affine_hull_eq[of S] by auto
1969 hence "affine_parallel (affine hull S) L" using assms by (simp add:1)
1970 from this show ?thesis using assms aff_dim_parallel_subspace[of S L] by blast
1973 lemma dim_affine_hull:
1974 fixes S :: "('n::euclidean_space) set"
1975 shows "dim (affine hull S)=dim S"
1977 have "dim (affine hull S)>=dim S" using dim_subset by auto
1978 moreover have "dim(span S) >= dim (affine hull S)" using dim_subset affine_hull_subset_span by auto
1979 moreover have "dim(span S)=dim S" using dim_span by auto
1980 ultimately show ?thesis by auto
1983 lemma aff_dim_subspace:
1984 fixes S :: "('n::euclidean_space) set"
1985 assumes "S ~= {}" "subspace S"
1986 shows "aff_dim S=int(dim S)" using aff_dim_affine[of S S] assms subspace_imp_affine[of S] affine_parallel_reflex[of S] by auto
1989 fixes S :: "('n::euclidean_space) set"
1990 assumes "0 : affine hull S"
1991 shows "aff_dim S=int(dim S)"
1993 have "subspace(affine hull S)" using subspace_affine[of "affine hull S"] affine_affine_hull assms by auto
1994 hence "aff_dim (affine hull S) =int(dim (affine hull S))" using assms aff_dim_subspace[of "affine hull S"] by auto
1995 from this show ?thesis using aff_dim_affine_hull[of S] dim_affine_hull[of S] by auto
1998 lemma aff_dim_univ: "aff_dim (UNIV :: ('n::euclidean_space) set) = int(DIM('n))"
1999 using aff_dim_subspace[of "(UNIV :: ('n::euclidean_space) set)"]
2000 dim_UNIV[where 'a="'n::euclidean_space"] by auto
2003 fixes V :: "('n::euclidean_space) set"
2004 shows "aff_dim V >= -1"
2006 obtain B where B_def: "affine hull B = affine hull V & ~ affine_dependent B & int (card B) = aff_dim V + 1" using aff_dim_basis_exists by auto
2007 from this show ?thesis by auto
2010 lemma independent_card_le_aff_dim:
2011 assumes "(B::('n::euclidean_space) set) <= V"
2012 assumes "~(affine_dependent B)"
2013 shows "int(card B) <= aff_dim V+1"
2016 from this obtain T where T_def: "~(affine_dependent T) & B<=T & T<=V & affine hull T = affine hull V"
2017 using assms extend_to_affine_basis[of B V] by auto
2018 hence "of_nat(card T) = aff_dim V+1" using aff_dim_unique by auto
2019 hence ?thesis using T_def card_mono[of T B] aff_independent_finite[of T] by auto
2023 moreover have "-1<= aff_dim V" using aff_dim_geq by auto
2024 ultimately have ?thesis by auto
2025 } ultimately show ?thesis by blast
2028 lemma aff_dim_subset:
2029 fixes S T :: "('n::euclidean_space) set"
2031 shows "aff_dim S <= aff_dim T"
2033 obtain B where B_def: "~(affine_dependent B) & B<=S & (affine hull B=affine hull S) & of_nat(card B) = aff_dim S+1" using aff_dim_inner_basis_exists[of S] by auto
2034 moreover hence "int (card B) <= aff_dim T + 1" using assms independent_card_le_aff_dim[of B T] by auto
2035 ultimately show ?thesis by auto
2038 lemma aff_dim_subset_univ:
2039 fixes S :: "('n::euclidean_space) set"
2040 shows "aff_dim S <= int(DIM('n))"
2042 have "aff_dim (UNIV :: ('n::euclidean_space) set) = int(DIM('n))" using aff_dim_univ by auto
2043 from this show "aff_dim (S:: ('n::euclidean_space) set) <= int(DIM('n))" using assms aff_dim_subset[of S "(UNIV :: ('n::euclidean_space) set)"] subset_UNIV by auto
2046 lemma affine_dim_equal:
2047 assumes "affine (S :: ('n::euclidean_space) set)" "affine T" "S ~= {}" "S <= T" "aff_dim S = aff_dim T"
2050 obtain a where "a : S" using assms by auto
2051 hence "a : T" using assms by auto
2052 def LS == "{y. ? x : S. (-a)+x=y}"
2053 hence ls: "subspace LS & affine_parallel S LS" using assms parallel_subspace_explicit[of S a LS] `a : S` by auto
2054 hence h1: "int(dim LS) = aff_dim S" using assms aff_dim_affine[of S LS] by auto
2055 have "T ~= {}" using assms by auto
2056 def LT == "{y. ? x : T. (-a)+x=y}"
2057 hence lt: "subspace LT & affine_parallel T LT" using assms parallel_subspace_explicit[of T a LT] `a : T` by auto
2058 hence "int(dim LT) = aff_dim T" using assms aff_dim_affine[of T LT] `T ~= {}` by auto
2059 hence "dim LS = dim LT" using h1 assms by auto
2060 moreover have "LS <= LT" using LS_def LT_def assms by auto
2061 ultimately have "LS=LT" using subspace_dim_equal[of LS LT] ls lt by auto
2062 moreover have "S = {x. ? y : LS. a+y=x}" using LS_def by auto
2063 moreover have "T = {x. ? y : LT. a+y=x}" using LT_def by auto
2064 ultimately show ?thesis by auto
2067 lemma affine_hull_univ:
2068 fixes S :: "('n::euclidean_space) set"
2069 assumes "aff_dim S = int(DIM('n))"
2070 shows "affine hull S = (UNIV :: ('n::euclidean_space) set)"
2072 have "S ~= {}" using assms aff_dim_empty[of S] by auto
2073 have h0: "S <= affine hull S" using hull_subset[of S _] by auto
2074 have h1: "aff_dim (UNIV :: ('n::euclidean_space) set) = aff_dim S" using aff_dim_univ assms by auto
2075 hence h2: "aff_dim (affine hull S) <= aff_dim (UNIV :: ('n::euclidean_space) set)" using aff_dim_subset_univ[of "affine hull S"] assms h0 by auto
2076 have h3: "aff_dim S <= aff_dim (affine hull S)" using h0 aff_dim_subset[of S "affine hull S"] assms by auto
2077 hence h4: "aff_dim (affine hull S) = aff_dim (UNIV :: ('n::euclidean_space) set)" using h0 h1 h2 by auto
2078 from this show ?thesis using affine_dim_equal[of "affine hull S" "(UNIV :: ('n::euclidean_space) set)"] affine_affine_hull[of S] affine_UNIV assms h4 h0 `S ~= {}` by auto
2081 lemma aff_dim_convex_hull:
2082 fixes S :: "('n::euclidean_space) set"
2083 shows "aff_dim (convex hull S)=aff_dim S"
2084 using aff_dim_affine_hull[of S] convex_hull_subset_affine_hull[of S]
2085 hull_subset[of S "convex"] aff_dim_subset[of S "convex hull S"]
2086 aff_dim_subset[of "convex hull S" "affine hull S"] by auto
2088 lemma aff_dim_cball:
2089 fixes a :: "'n::euclidean_space"
2091 shows "aff_dim (cball a e) = int (DIM('n))"
2093 have "(%x. a + x) ` (cball 0 e)<=cball a e" unfolding cball_def dist_norm by auto
2094 hence "aff_dim (cball (0 :: 'n::euclidean_space) e) <= aff_dim (cball a e)"
2095 using aff_dim_translation_eq[of a "cball 0 e"]
2096 aff_dim_subset[of "op + a ` cball 0 e" "cball a e"] by auto
2097 moreover have "aff_dim (cball (0 :: 'n::euclidean_space) e) = int (DIM('n))"
2098 using hull_inc[of "(0 :: 'n::euclidean_space)" "cball 0 e"] centre_in_cball[of "(0 :: 'n::euclidean_space)"] assms
2099 by (simp add: dim_cball[of e] aff_dim_zero[of "cball 0 e"])
2100 ultimately show ?thesis using aff_dim_subset_univ[of "cball a e"] by auto
2104 fixes S :: "('n::euclidean_space) set"
2105 assumes "open S" "S ~= {}"
2106 shows "aff_dim S = int (DIM('n))"
2108 obtain x where "x:S" using assms by auto
2109 from this obtain e where e_def: "e>0 & cball x e <= S" using open_contains_cball[of S] assms by auto
2110 from this have "aff_dim (cball x e) <= aff_dim S" using aff_dim_subset by auto
2111 from this show ?thesis using aff_dim_cball[of e x] aff_dim_subset_univ[of S] e_def by auto
2114 lemma low_dim_interior:
2115 fixes S :: "('n::euclidean_space) set"
2116 assumes "~(aff_dim S = int (DIM('n)))"
2117 shows "interior S = {}"
2119 have "aff_dim(interior S) <= aff_dim S"
2120 using interior_subset aff_dim_subset[of "interior S" S] by auto
2121 from this show ?thesis using aff_dim_open[of "interior S"] aff_dim_subset_univ[of S] assms by auto
2124 subsection{* Relative Interior of a Set *}
2126 definition "rel_interior S = {x. ? T. openin (subtopology euclidean (affine hull S)) T & x : T & T <= S}"
2128 lemma rel_interior: "rel_interior S = {x : S. ? T. open T & x : T & (T Int (affine hull S)) <= S}"
2129 unfolding rel_interior_def[of S] openin_open[of "affine hull S"] apply auto
2131 fix x T assume a: "x:S" "open T" "x : T" "(T Int (affine hull S)) <= S"
2132 hence h1: "x : T Int affine hull S" using hull_inc by auto
2133 show "EX Tb. (EX Ta. open Ta & Tb = affine hull S Int Ta) & x : Tb & Tb <= S"
2134 apply (rule_tac x="T Int (affine hull S)" in exI)
2138 lemma mem_rel_interior:
2139 "x : rel_interior S <-> (? T. open T & x : (T Int S) & (T Int (affine hull S)) <= S)"
2140 by (auto simp add: rel_interior)
2142 lemma mem_rel_interior_ball: "x : rel_interior S <-> x : S & (? e. 0 < e & ((ball x e) Int (affine hull S)) <= S)"
2143 apply (simp add: rel_interior, safe)
2144 apply (force simp add: open_contains_ball)
2145 apply (rule_tac x="ball x e" in exI)
2146 apply (simp add: open_ball centre_in_ball)
2149 lemma rel_interior_ball:
2150 "rel_interior S = {x : S. ? e. e>0 & ((ball x e) Int (affine hull S)) <= S}"
2151 using mem_rel_interior_ball [of _ S] by auto
2153 lemma mem_rel_interior_cball: "x : rel_interior S <-> x : S & (? e. 0 < e & ((cball x e) Int (affine hull S)) <= S)"
2154 apply (simp add: rel_interior, safe)
2155 apply (force simp add: open_contains_cball)
2156 apply (rule_tac x="ball x e" in exI)
2157 apply (simp add: open_ball centre_in_ball subset_trans [OF ball_subset_cball])
2161 lemma rel_interior_cball: "rel_interior S = {x : S. ? e. e>0 & ((cball x e) Int (affine hull S)) <= S}" using mem_rel_interior_cball [of _ S] by auto
2163 lemma rel_interior_empty: "rel_interior {} = {}"
2164 by (auto simp add: rel_interior_def)
2166 lemma affine_hull_sing: "affine hull {a :: 'n::euclidean_space} = {a}"
2167 by (metis affine_hull_eq affine_sing)
2169 lemma rel_interior_sing: "rel_interior {a :: 'n::euclidean_space} = {a}"
2170 unfolding rel_interior_ball affine_hull_sing apply auto
2171 apply(rule_tac x="1 :: real" in exI) apply simp
2174 lemma subset_rel_interior:
2175 fixes S T :: "('n::euclidean_space) set"
2176 assumes "S<=T" "affine hull S=affine hull T"
2177 shows "rel_interior S <= rel_interior T"
2178 using assms by (auto simp add: rel_interior_def)
2180 lemma rel_interior_subset: "rel_interior S <= S"
2181 by (auto simp add: rel_interior_def)
2183 lemma rel_interior_subset_closure: "rel_interior S <= closure S"
2184 using rel_interior_subset by (auto simp add: closure_def)
2186 lemma interior_subset_rel_interior: "interior S <= rel_interior S"
2187 by (auto simp add: rel_interior interior_def)
2189 lemma interior_rel_interior:
2190 fixes S :: "('n::euclidean_space) set"
2191 assumes "aff_dim S = int(DIM('n))"
2192 shows "rel_interior S = interior S"
2194 have "affine hull S = UNIV" using assms affine_hull_univ[of S] by auto
2195 from this show ?thesis unfolding rel_interior interior_def by auto
2198 lemma rel_interior_open:
2199 fixes S :: "('n::euclidean_space) set"
2201 shows "rel_interior S = S"
2202 by (metis assms interior_eq interior_subset_rel_interior rel_interior_subset set_eq_subset)
2204 lemma interior_rel_interior_gen:
2205 fixes S :: "('n::euclidean_space) set"
2206 shows "interior S = (if aff_dim S = int(DIM('n)) then rel_interior S else {})"
2207 by (metis interior_rel_interior low_dim_interior)
2209 lemma rel_interior_univ:
2210 fixes S :: "('n::euclidean_space) set"
2211 shows "rel_interior (affine hull S) = affine hull S"
2213 have h1: "rel_interior (affine hull S) <= affine hull S" using rel_interior_subset by auto
2214 { fix x assume x_def: "x : affine hull S"
2215 obtain e :: real where "e=1" by auto
2216 hence "e>0 & ball x e Int affine hull (affine hull S) <= affine hull S" using hull_hull[of _ S] by auto
2217 hence "x : rel_interior (affine hull S)" using x_def rel_interior_ball[of "affine hull S"] by auto
2218 } from this show ?thesis using h1 by auto
2221 lemma rel_interior_univ2: "rel_interior (UNIV :: ('n::euclidean_space) set) = UNIV"
2222 by (metis open_UNIV rel_interior_open)
2224 lemma rel_interior_convex_shrink:
2225 fixes S :: "('a::euclidean_space) set"
2226 assumes "convex S" "c : rel_interior S" "x : S" "0 < e" "e <= 1"
2227 shows "x - e *\<^sub>R (x - c) : rel_interior S"
2229 (* Proof is a modified copy of the proof of similar lemma mem_interior_convex_shrink
2231 obtain d where "d>0" and d:"ball c d Int affine hull S <= S"
2232 using assms(2) unfolding mem_rel_interior_ball by auto
2233 { fix y assume as:"dist (x - e *\<^sub>R (x - c)) y < e * d & y : affine hull S"
2234 have *:"y = (1 - (1 - e)) *\<^sub>R ((1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x) + (1 - e) *\<^sub>R x" using `e>0` by (auto simp add: scaleR_left_diff_distrib scaleR_right_diff_distrib)
2235 have "x : affine hull S" using assms hull_subset[of S] by auto
2236 moreover have "1 / e + - ((1 - e) / e) = 1"
2237 using `e>0` mult_left.diff[of "1" "(1-e)" "1/e"] by auto
2238 ultimately have **: "(1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x : affine hull S"
2239 using as affine_affine_hull[of S] mem_affine[of "affine hull S" y x "(1 / e)" "-((1 - e) / e)"] by (simp add: algebra_simps)
2240 have "dist c ((1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x) = abs(1/e) * norm (e *\<^sub>R c - y + (1 - e) *\<^sub>R x)"
2241 unfolding dist_norm unfolding norm_scaleR[THEN sym] apply(rule arg_cong[where f=norm]) using `e>0`
2242 by(auto simp add:euclidean_eq[where 'a='a] field_simps)
2243 also have "... = abs(1/e) * norm (x - e *\<^sub>R (x - c) - y)" by(auto intro!:arg_cong[where f=norm] simp add: algebra_simps)
2244 also have "... < d" using as[unfolded dist_norm] and `e>0`
2245 by(auto simp add:pos_divide_less_eq[OF `e>0`] real_mult_commute)
2246 finally have "y : S" apply(subst *)
2247 apply(rule assms(1)[unfolded convex_alt,rule_format])
2248 apply(rule d[unfolded subset_eq,rule_format]) unfolding mem_ball using assms(3-5) ** by auto
2249 } hence "ball (x - e *\<^sub>R (x - c)) (e*d) Int affine hull S <= S" by auto
2250 moreover have "0 < e*d" using `0<e` `0<d` using real_mult_order by auto
2251 moreover have "c : S" using assms rel_interior_subset by auto
2252 moreover hence "x - e *\<^sub>R (x - c) : S"
2253 using mem_convex[of S x c e] apply (simp add: algebra_simps) using assms by auto
2254 ultimately show ?thesis
2255 using mem_rel_interior_ball[of "x - e *\<^sub>R (x - c)" S] `e>0` by auto
2258 lemma interior_real_semiline:
2260 shows "interior {a..} = {a<..}"
2262 { fix y assume "a<y" hence "y : interior {a..}"
2263 apply (simp add: mem_interior) apply (rule_tac x="(y-a)" in exI) apply (auto simp add: dist_norm)
2266 { fix y assume "y : interior {a..}" (*hence "a<=y" using interior_subset by auto*)
2267 from this obtain e where e_def: "e>0 & cball y e \<subseteq> {a..}"
2268 using mem_interior_cball[of y "{a..}"] by auto
2269 moreover hence "y-e : cball y e" by (auto simp add: cball_def dist_norm)
2270 ultimately have "a<=y-e" by auto
2271 hence "a<y" using e_def by auto
2272 } ultimately show ?thesis by auto
2275 lemma rel_interior_real_interval:
2276 fixes a b :: real assumes "a < b" shows "rel_interior {a..b} = {a<..<b}"
2278 have "{a<..<b} \<noteq> {}" using assms unfolding set_eq_iff by (auto intro!: exI[of _ "(a + b) / 2"])
2280 using interior_rel_interior_gen[of "{a..b}", symmetric]
2281 by (simp split: split_if_asm add: interior_closed_interval)
2284 lemma rel_interior_real_semiline:
2285 fixes a :: real shows "rel_interior {a..} = {a<..}"
2287 have *: "{a<..} \<noteq> {}" unfolding set_eq_iff by (auto intro!: exI[of _ "a + 1"])
2288 then show ?thesis using interior_real_semiline
2289 interior_rel_interior_gen[of "{a..}"]
2290 by (auto split: split_if_asm)
2293 subsection "Relative open"
2295 definition "rel_open S <-> (rel_interior S) = S"
2297 lemma rel_open: "rel_open S <-> openin (subtopology euclidean (affine hull S)) S"
2298 unfolding rel_open_def rel_interior_def apply auto
2299 using openin_subopen[of "subtopology euclidean (affine hull S)" S] by auto
2301 lemma opein_rel_interior:
2302 "openin (subtopology euclidean (affine hull S)) (rel_interior S)"
2303 apply (simp add: rel_interior_def)
2304 apply (subst openin_subopen) by blast
2306 lemma affine_rel_open:
2307 fixes S :: "('n::euclidean_space) set"
2308 assumes "affine S" shows "rel_open S"
2309 unfolding rel_open_def using assms rel_interior_univ[of S] affine_hull_eq[of S] by metis
2311 lemma affine_closed:
2312 fixes S :: "('n::euclidean_space) set"
2313 assumes "affine S" shows "closed S"
2316 from this obtain L where L_def: "subspace L & affine_parallel S L"
2317 using assms affine_parallel_subspace[of S] by auto
2318 from this obtain "a" where a_def: "S=(op + a ` L)"
2319 using affine_parallel_def[of L S] affine_parallel_commut by auto
2320 have "closed L" using L_def closed_subspace by auto
2321 hence "closed S" using closed_translation a_def by auto
2322 } from this show ?thesis by auto
2325 lemma closure_affine_hull:
2326 fixes S :: "('n::euclidean_space) set"
2327 shows "closure S <= affine hull S"
2329 have "closure S <= closure (affine hull S)" using subset_closure by auto
2330 moreover have "closure (affine hull S) = affine hull S"
2331 using affine_affine_hull affine_closed[of "affine hull S"] closure_eq by auto
2332 ultimately show ?thesis by auto
2335 lemma closure_same_affine_hull:
2336 fixes S :: "('n::euclidean_space) set"
2337 shows "affine hull (closure S) = affine hull S"
2339 have "affine hull (closure S) <= affine hull S"
2340 using hull_mono[of "closure S" "affine hull S" "affine"] closure_affine_hull[of S] hull_hull[of "affine" S] by auto
2341 moreover have "affine hull (closure S) >= affine hull S"
2342 using hull_mono[of "S" "closure S" "affine"] closure_subset by auto
2343 ultimately show ?thesis by auto
2346 lemma closure_aff_dim:
2347 fixes S :: "('n::euclidean_space) set"
2348 shows "aff_dim (closure S) = aff_dim S"
2350 have "aff_dim S <= aff_dim (closure S)" using aff_dim_subset closure_subset by auto
2351 moreover have "aff_dim (closure S) <= aff_dim (affine hull S)"
2352 using aff_dim_subset closure_affine_hull by auto
2353 moreover have "aff_dim (affine hull S) = aff_dim S" using aff_dim_affine_hull by auto
2354 ultimately show ?thesis by auto
2357 lemma rel_interior_closure_convex_shrink:
2358 fixes S :: "(_::euclidean_space) set"
2359 assumes "convex S" "c : rel_interior S" "x : closure S" "0 < e" "e <= 1"
2360 shows "x - e *\<^sub>R (x - c) : rel_interior S"
2362 (* Proof is a modified copy of the proof of similar lemma mem_interior_closure_convex_shrink
2364 obtain d where "d>0" and d:"ball c d Int affine hull S <= S"
2365 using assms(2) unfolding mem_rel_interior_ball by auto
2366 have "EX y : S. norm (y - x) * (1 - e) < e * d" proof(cases "x : S")
2367 case True thus ?thesis using `e>0` `d>0` by(rule_tac bexI[where x=x], auto intro!: mult_pos_pos) next
2368 case False hence x:"x islimpt S" using assms(3)[unfolded closure_def] by auto
2369 show ?thesis proof(cases "e=1")
2370 case True obtain y where "y : S" "y ~= x" "dist y x < 1"
2371 using x[unfolded islimpt_approachable,THEN spec[where x=1]] by auto
2372 thus ?thesis apply(rule_tac x=y in bexI) unfolding True using `d>0` by auto next
2373 case False hence "0 < e * d / (1 - e)" and *:"1 - e > 0"
2374 using `e<=1` `e>0` `d>0` by(auto intro!:mult_pos_pos divide_pos_pos)
2375 then obtain y where "y : S" "y ~= x" "dist y x < e * d / (1 - e)"
2376 using x[unfolded islimpt_approachable,THEN spec[where x="e*d / (1 - e)"]] by auto
2377 thus ?thesis apply(rule_tac x=y in bexI) unfolding dist_norm using pos_less_divide_eq[OF *] by auto qed qed
2378 then obtain y where "y : S" and y:"norm (y - x) * (1 - e) < e * d" by auto
2379 def z == "c + ((1 - e) / e) *\<^sub>R (x - y)"
2380 have *:"x - e *\<^sub>R (x - c) = y - e *\<^sub>R (y - z)" unfolding z_def using `e>0` by (auto simp add: scaleR_right_diff_distrib scaleR_right_distrib scaleR_left_diff_distrib)
2381 have zball: "z\<in>ball c d"
2382 using mem_ball z_def dist_norm[of c] using y and assms(4,5) by (auto simp add:field_simps norm_minus_commute)
2383 have "x : affine hull S" using closure_affine_hull assms by auto
2384 moreover have "y : affine hull S" using `y : S` hull_subset[of S] by auto
2385 moreover have "c : affine hull S" using assms rel_interior_subset hull_subset[of S] by auto
2386 ultimately have "z : affine hull S"
2387 using z_def affine_affine_hull[of S]
2388 mem_affine_3_minus [of "affine hull S" c x y "(1 - e) / e"]
2389 assms by (auto simp add: field_simps)
2390 hence "z : S" using d zball by auto
2391 obtain d1 where "d1>0" and d1:"ball z d1 <= ball c d"
2392 using zball open_ball[of c d] openE[of "ball c d" z] by auto
2393 hence "(ball z d1) Int (affine hull S) <= (ball c d) Int (affine hull S)" by auto
2394 hence "(ball z d1) Int (affine hull S) <= S" using d by auto
2395 hence "z : rel_interior S" using mem_rel_interior_ball using `d1>0` `z : S` by auto
2396 hence "y - e *\<^sub>R (y - z) : rel_interior S" using rel_interior_convex_shrink[of S z y e] assms`y : S` by auto
2397 thus ?thesis using * by auto
2400 subsection{* Relative interior preserves under linear transformations *}
2402 lemma rel_interior_translation_aux:
2403 fixes a :: "'n::euclidean_space"
2404 shows "((%x. a + x) ` rel_interior S) <= rel_interior ((%x. a + x) ` S)"
2406 { fix x assume x_def: "x : rel_interior S"
2407 from this obtain T where T_def: "open T & x : (T Int S) & (T Int (affine hull S)) <= S" using mem_rel_interior[of x S] by auto
2408 from this have "open ((%x. a + x) ` T)" and
2409 "(a + x) : (((%x. a + x) ` T) Int ((%x. a + x) ` S))" and
2410 "(((%x. a + x) ` T) Int (affine hull ((%x. a + x) ` S))) <= ((%x. a + x) ` S)"
2411 using affine_hull_translation[of a S] open_translation[of T a] x_def by auto
2412 from this have "(a+x) : rel_interior ((%x. a + x) ` S)"
2413 using mem_rel_interior[of "a+x" "((%x. a + x) ` S)"] by auto
2414 } from this show ?thesis by auto
2417 lemma rel_interior_translation:
2418 fixes a :: "'n::euclidean_space"
2419 shows "rel_interior ((%x. a + x) ` S) = ((%x. a + x) ` rel_interior S)"
2421 have "(%x. (-a) + x) ` rel_interior ((%x. a + x) ` S) <= rel_interior S"
2422 using rel_interior_translation_aux[of "-a" "(%x. a + x) ` S"]
2423 translation_assoc[of "-a" "a"] by auto
2424 hence "((%x. a + x) ` rel_interior S) >= rel_interior ((%x. a + x) ` S)"
2425 using translation_inverse_subset[of a "rel_interior (op + a ` S)" "rel_interior S"]
2427 from this show ?thesis using rel_interior_translation_aux[of a S] by auto
2431 lemma affine_hull_linear_image:
2432 assumes "bounded_linear f"
2433 shows "f ` (affine hull s) = affine hull f ` s"
2434 (* Proof is a modified copy of the proof of similar lemma convex_hull_linear_image
2436 apply rule unfolding subset_eq ball_simps apply(rule_tac[!] hull_induct, rule hull_inc) prefer 3
2437 apply(erule imageE)apply(rule_tac x=xa in image_eqI) apply assumption
2438 apply(rule hull_subset[unfolded subset_eq, rule_format]) apply assumption
2440 interpret f: bounded_linear f by fact
2441 show "affine {x. f x : affine hull f ` s}"
2442 unfolding affine_def by(auto simp add: f.scaleR f.add affine_affine_hull[unfolded affine_def, rule_format]) next
2443 interpret f: bounded_linear f by fact
2444 show "affine {x. x : f ` (affine hull s)}" using affine_affine_hull[unfolded affine_def, of s]
2445 unfolding affine_def by (auto simp add: f.scaleR [symmetric] f.add [symmetric])
2449 lemma rel_interior_injective_on_span_linear_image:
2450 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
2451 fixes S :: "('m::euclidean_space) set"
2452 assumes "bounded_linear f" and "inj_on f (span S)"
2453 shows "rel_interior (f ` S) = f ` (rel_interior S)"
2455 { fix z assume z_def: "z : rel_interior (f ` S)"
2456 have "z : f ` S" using z_def rel_interior_subset[of "f ` S"] by auto
2457 from this obtain x where x_def: "x : S & (f x = z)" by auto
2458 obtain e2 where e2_def: "e2>0 & cball z e2 Int affine hull (f ` S) <= (f ` S)"
2459 using z_def rel_interior_cball[of "f ` S"] by auto
2460 obtain K where K_def: "K>0 & (! x. norm (f x) <= norm x * K)"
2461 using assms RealVector.bounded_linear.pos_bounded[of f] by auto
2462 def e1 == "1/K" hence e1_def: "e1>0 & (! x. e1 * norm (f x) <= norm x)"
2463 using K_def pos_le_divide_eq[of e1] by auto
2464 def e == "e1 * e2" hence "e>0" using e1_def e2_def real_mult_order by auto
2465 { fix y assume y_def: "y : cball x e Int affine hull S"
2466 from this have h1: "f y : affine hull (f ` S)"
2467 using affine_hull_linear_image[of f S] assms by auto
2468 from y_def have "norm (x-y)<=e1 * e2"
2469 using cball_def[of x e] dist_norm[of x y] e_def by auto
2470 moreover have "(f x)-(f y)=f (x-y)"
2471 using assms linear_sub[of f x y] linear_conv_bounded_linear[of f] by auto
2472 moreover have "e1 * norm (f (x-y)) <= norm (x-y)" using e1_def by auto
2473 ultimately have "e1 * norm ((f x)-(f y)) <= e1 * e2" by auto
2474 hence "(f y) : (cball z e2)"
2475 using cball_def[of "f x" e2] dist_norm[of "f x" "f y"] e1_def x_def by auto
2476 hence "f y : (f ` S)" using y_def e2_def h1 by auto
2477 hence "y : S" using assms y_def hull_subset[of S] affine_hull_subset_span
2478 inj_on_image_mem_iff[of f "span S" S y] by auto
2480 hence "z : f ` (rel_interior S)" using mem_rel_interior_cball[of x S] `e>0` x_def by auto
2483 { fix x assume x_def: "x : rel_interior S"
2484 from this obtain e2 where e2_def: "e2>0 & cball x e2 Int affine hull S <= S"
2485 using rel_interior_cball[of S] by auto
2486 have "x : S" using x_def rel_interior_subset by auto
2487 hence *: "f x : f ` S" by auto
2488 have "! x:span S. f x = 0 --> x = 0"
2489 using assms subspace_span linear_conv_bounded_linear[of f]
2490 linear_injective_on_subspace_0[of f "span S"] by auto
2491 from this obtain e1 where e1_def: "e1>0 & (! x : span S. e1 * norm x <= norm (f x))"
2492 using assms injective_imp_isometric[of "span S" f]
2493 subspace_span[of S] closed_subspace[of "span S"] by auto
2494 def e == "e1 * e2" hence "e>0" using e1_def e2_def real_mult_order by auto
2495 { fix y assume y_def: "y : cball (f x) e Int affine hull (f ` S)"
2496 from this have "y : f ` (affine hull S)" using affine_hull_linear_image[of f S] assms by auto
2497 from this obtain xy where xy_def: "xy : affine hull S & (f xy = y)" by auto
2498 from this y_def have "norm ((f x)-(f xy))<=e1 * e2"
2499 using cball_def[of "f x" e] dist_norm[of "f x" y] e_def by auto
2500 moreover have "(f x)-(f xy)=f (x-xy)"
2501 using assms linear_sub[of f x xy] linear_conv_bounded_linear[of f] by auto
2502 moreover have "x-xy : span S"
2503 using subspace_sub[of "span S" x xy] subspace_span `x : S` xy_def
2504 affine_hull_subset_span[of S] span_inc by auto
2505 moreover hence "e1 * norm (x-xy) <= norm (f (x-xy))" using e1_def by auto
2506 ultimately have "e1 * norm (x-xy) <= e1 * e2" by auto
2507 hence "xy : (cball x e2)" using cball_def[of x e2] dist_norm[of x xy] e1_def by auto
2508 hence "y : (f ` S)" using xy_def e2_def by auto
2510 hence "(f x) : rel_interior (f ` S)"
2511 using mem_rel_interior_cball[of "(f x)" "(f ` S)"] * `e>0` by auto
2513 ultimately show ?thesis by auto
2516 lemma rel_interior_injective_linear_image:
2517 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
2518 assumes "bounded_linear f" and "inj f"
2519 shows "rel_interior (f ` S) = f ` (rel_interior S)"
2520 using assms rel_interior_injective_on_span_linear_image[of f S]
2521 subset_inj_on[of f "UNIV" "span S"] by auto
2523 subsection{* Some Properties of subset of standard basis *}
2525 lemma affine_hull_substd_basis: assumes "d\<subseteq>{..<DIM('a::euclidean_space)}"
2526 shows "affine hull (insert 0 {basis i | i. i : d}) =
2527 {x::'a::euclidean_space. (!i<DIM('a). i ~: d --> x$$i = 0)}"
2528 (is "affine hull (insert 0 ?A) = ?B")
2529 proof- have *:"\<And>A. op + (0\<Colon>'a) ` A = A" "\<And>A. op + (- (0\<Colon>'a)) ` A = A" by auto
2530 show ?thesis unfolding affine_hull_insert_span_gen span_substd_basis[OF assms,THEN sym] * ..
2533 lemma affine_hull_convex_hull: "affine hull (convex hull S) = affine hull S"
2534 by (metis Int_absorb1 Int_absorb2 convex_hull_subset_affine_hull hull_hull hull_mono hull_subset)
2536 subsection {* Openness and compactness are preserved by convex hull operation. *}
2538 lemma open_convex_hull[intro]:
2539 fixes s :: "'a::real_normed_vector set"
2541 shows "open(convex hull s)"
2542 unfolding open_contains_cball convex_hull_explicit unfolding mem_Collect_eq ball_simps(8)
2543 proof(rule, rule) fix a
2544 assume "\<exists>sa u. finite sa \<and> sa \<subseteq> s \<and> (\<forall>x\<in>sa. 0 \<le> u x) \<and> setsum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = a"
2545 then obtain t u where obt:"finite t" "t\<subseteq>s" "\<forall>x\<in>t. 0 \<le> u x" "setsum u t = 1" "(\<Sum>v\<in>t. u v *\<^sub>R v) = a" by auto
2547 from assms[unfolded open_contains_cball] obtain b where b:"\<forall>x\<in>s. 0 < b x \<and> cball x (b x) \<subseteq> s"
2548 using bchoice[of s "\<lambda>x e. e>0 \<and> cball x e \<subseteq> s"] by auto
2549 have "b ` t\<noteq>{}" unfolding i_def using obt by auto def i \<equiv> "b ` t"
2551 show "\<exists>e>0. cball a e \<subseteq> {y. \<exists>sa u. finite sa \<and> sa \<subseteq> s \<and> (\<forall>x\<in>sa. 0 \<le> u x) \<and> setsum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = y}"
2552 apply(rule_tac x="Min i" in exI) unfolding subset_eq apply rule defer apply rule unfolding mem_Collect_eq
2554 show "0 < Min i" unfolding i_def and Min_gr_iff[OF finite_imageI[OF obt(1)] `b \` t\<noteq>{}`]
2555 using b apply simp apply rule apply(erule_tac x=x in ballE) using `t\<subseteq>s` by auto
2556 next fix y assume "y \<in> cball a (Min i)"
2557 hence y:"norm (a - y) \<le> Min i" unfolding dist_norm[THEN sym] by auto
2558 { fix x assume "x\<in>t"
2559 hence "Min i \<le> b x" unfolding i_def apply(rule_tac Min_le) using obt(1) by auto
2560 hence "x + (y - a) \<in> cball x (b x)" using y unfolding mem_cball dist_norm by auto
2561 moreover from `x\<in>t` have "x\<in>s" using obt(2) by auto
2562 ultimately have "x + (y - a) \<in> s" using y and b[THEN bspec[where x=x]] unfolding subset_eq by fast }
2564 have *:"inj_on (\<lambda>v. v + (y - a)) t" unfolding inj_on_def by auto
2565 have "(\<Sum>v\<in>(\<lambda>v. v + (y - a)) ` t. u (v - (y - a))) = 1"
2566 unfolding setsum_reindex[OF *] o_def using obt(4) by auto
2567 moreover have "(\<Sum>v\<in>(\<lambda>v. v + (y - a)) ` t. u (v - (y - a)) *\<^sub>R v) = y"
2568 unfolding setsum_reindex[OF *] o_def using obt(4,5)
2569 by (simp add: setsum_addf setsum_subtractf scaleR_left.setsum[THEN sym] scaleR_right_distrib)
2570 ultimately show "\<exists>sa u. finite sa \<and> (\<forall>x\<in>sa. x \<in> s) \<and> (\<forall>x\<in>sa. 0 \<le> u x) \<and> setsum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = y"
2571 apply(rule_tac x="(\<lambda>v. v + (y - a)) ` t" in exI) apply(rule_tac x="\<lambda>v. u (v - (y - a))" in exI)
2572 using obt(1, 3) by auto
2576 lemma compact_convex_combinations:
2577 fixes s t :: "'a::real_normed_vector set"
2578 assumes "compact s" "compact t"
2579 shows "compact { (1 - u) *\<^sub>R x + u *\<^sub>R y | x y u. 0 \<le> u \<and> u \<le> 1 \<and> x \<in> s \<and> y \<in> t}"
2581 let ?X = "{0..1} \<times> s \<times> t"
2582 let ?h = "(\<lambda>z. (1 - fst z) *\<^sub>R fst (snd z) + fst z *\<^sub>R snd (snd z))"
2583 have *:"{ (1 - u) *\<^sub>R x + u *\<^sub>R y | x y u. 0 \<le> u \<and> u \<le> 1 \<and> x \<in> s \<and> y \<in> t} = ?h ` ?X"
2584 apply(rule set_eqI) unfolding image_iff mem_Collect_eq
2585 apply rule apply auto
2586 apply (rule_tac x=u in rev_bexI, simp)
2587 apply (erule rev_bexI, erule rev_bexI, simp)
2589 have "continuous_on ({0..1} \<times> s \<times> t)
2590 (\<lambda>z. (1 - fst z) *\<^sub>R fst (snd z) + fst z *\<^sub>R snd (snd z))"
2591 unfolding continuous_on by (rule ballI) (intro tendsto_intros)
2592 thus ?thesis unfolding *
2593 apply (rule compact_continuous_image)
2594 apply (intro compact_Times compact_interval assms)
2598 lemma compact_convex_hull: fixes s::"('a::euclidean_space) set"
2599 assumes "compact s" shows "compact(convex hull s)"
2601 case True thus ?thesis using compact_empty by simp
2603 case False then obtain w where "w\<in>s" by auto
2604 show ?thesis unfolding caratheodory[of s]
2605 proof(induct ("DIM('a) + 1"))
2606 have *:"{x.\<exists>sa. finite sa \<and> sa \<subseteq> s \<and> card sa \<le> 0 \<and> x \<in> convex hull sa} = {}"
2607 using compact_empty by auto
2608 case 0 thus ?case unfolding * by simp
2611 show ?case proof(cases "n=0")
2612 case True have "{x. \<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t} = s"
2613 unfolding set_eq_iff and mem_Collect_eq proof(rule, rule)
2614 fix x assume "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
2615 then obtain t where t:"finite t" "t \<subseteq> s" "card t \<le> Suc n" "x \<in> convex hull t" by auto
2616 show "x\<in>s" proof(cases "card t = 0")
2617 case True thus ?thesis using t(4) unfolding card_0_eq[OF t(1)] by simp
2619 case False hence "card t = Suc 0" using t(3) `n=0` by auto
2620 then obtain a where "t = {a}" unfolding card_Suc_eq by auto
2621 thus ?thesis using t(2,4) by simp
2624 fix x assume "x\<in>s"
2625 thus "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
2626 apply(rule_tac x="{x}" in exI) unfolding convex_hull_singleton by auto
2627 qed thus ?thesis using assms by simp
2629 case False have "{x. \<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t} =
2630 { (1 - u) *\<^sub>R x + u *\<^sub>R y | x y u.
2631 0 \<le> u \<and> u \<le> 1 \<and> x \<in> s \<and> y \<in> {x. \<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> n \<and> x \<in> convex hull t}}"
2632 unfolding set_eq_iff and mem_Collect_eq proof(rule,rule)
2633 fix x assume "\<exists>u v c. x = (1 - c) *\<^sub>R u + c *\<^sub>R v \<and>
2634 0 \<le> c \<and> c \<le> 1 \<and> u \<in> s \<and> (\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> n \<and> v \<in> convex hull t)"
2635 then obtain u v c t where obt:"x = (1 - c) *\<^sub>R u + c *\<^sub>R v"
2636 "0 \<le> c \<and> c \<le> 1" "u \<in> s" "finite t" "t \<subseteq> s" "card t \<le> n" "v \<in> convex hull t" by auto
2637 moreover have "(1 - c) *\<^sub>R u + c *\<^sub>R v \<in> convex hull insert u t"
2638 apply(rule mem_convex) using obt(2) and convex_convex_hull and hull_subset[of "insert u t" convex]
2639 using obt(7) and hull_mono[of t "insert u t"] by auto
2640 ultimately show "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
2641 apply(rule_tac x="insert u t" in exI) by (auto simp add: card_insert_if)
2643 fix x assume "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
2644 then obtain t where t:"finite t" "t \<subseteq> s" "card t \<le> Suc n" "x \<in> convex hull t" by auto
2645 let ?P = "\<exists>u v c. x = (1 - c) *\<^sub>R u + c *\<^sub>R v \<and>
2646 0 \<le> c \<and> c \<le> 1 \<and> u \<in> s \<and> (\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> n \<and> v \<in> convex hull t)"
2647 show ?P proof(cases "card t = Suc n")
2648 case False hence "card t \<le> n" using t(3) by auto
2649 thus ?P apply(rule_tac x=w in exI, rule_tac x=x in exI, rule_tac x=1 in exI) using `w\<in>s` and t
2650 by(auto intro!: exI[where x=t])
2652 case True then obtain a u where au:"t = insert a u" "a\<notin>u" apply(drule_tac card_eq_SucD) by auto
2653 show ?P proof(cases "u={}")
2654 case True hence "x=a" using t(4)[unfolded au] by auto
2655 show ?P unfolding `x=a` apply(rule_tac x=a in exI, rule_tac x=a in exI, rule_tac x=1 in exI)
2656 using t and `n\<noteq>0` unfolding au by(auto intro!: exI[where x="{a}"])
2658 case False obtain ux vx b where obt:"ux\<ge>0" "vx\<ge>0" "ux + vx = 1" "b \<in> convex hull u" "x = ux *\<^sub>R a + vx *\<^sub>R b"
2659 using t(4)[unfolded au convex_hull_insert[OF False]] by auto
2660 have *:"1 - vx = ux" using obt(3) by auto
2661 show ?P apply(rule_tac x=a in exI, rule_tac x=b in exI, rule_tac x=vx in exI)
2662 using obt and t(1-3) unfolding au and * using card_insert_disjoint[OF _ au(2)]
2663 by(auto intro!: exI[where x=u])
2667 thus ?thesis using compact_convex_combinations[OF assms Suc] by simp
2672 lemma finite_imp_compact_convex_hull:
2673 fixes s :: "('a::euclidean_space) set"
2674 shows "finite s \<Longrightarrow> compact(convex hull s)"
2675 by (metis compact_convex_hull finite_imp_compact)
2677 subsection {* Extremal points of a simplex are some vertices. *}
2679 lemma dist_increases_online:
2680 fixes a b d :: "'a::real_inner"
2681 assumes "d \<noteq> 0"
2682 shows "dist a (b + d) > dist a b \<or> dist a (b - d) > dist a b"
2683 proof(cases "inner a d - inner b d > 0")
2684 case True hence "0 < inner d d + (inner a d * 2 - inner b d * 2)"
2685 apply(rule_tac add_pos_pos) using assms by auto
2686 thus ?thesis apply(rule_tac disjI2) unfolding dist_norm and norm_eq_sqrt_inner and real_sqrt_less_iff
2687 by (simp add: algebra_simps inner_commute)
2689 case False hence "0 < inner d d + (inner b d * 2 - inner a d * 2)"
2690 apply(rule_tac add_pos_nonneg) using assms by auto
2691 thus ?thesis apply(rule_tac disjI1) unfolding dist_norm and norm_eq_sqrt_inner and real_sqrt_less_iff
2692 by (simp add: algebra_simps inner_commute)
2695 lemma norm_increases_online:
2696 fixes d :: "'a::real_inner"
2697 shows "d \<noteq> 0 \<Longrightarrow> norm(a + d) > norm a \<or> norm(a - d) > norm a"
2698 using dist_increases_online[of d a 0] unfolding dist_norm by auto
2700 lemma simplex_furthest_lt:
2701 fixes s::"'a::real_inner set" assumes "finite s"
2702 shows "\<forall>x \<in> (convex hull s). x \<notin> s \<longrightarrow> (\<exists>y\<in>(convex hull s). norm(x - a) < norm(y - a))"
2703 proof(induct_tac rule: finite_induct[of s])
2704 fix x s assume as:"finite s" "x\<notin>s" "\<forall>x\<in>convex hull s. x \<notin> s \<longrightarrow> (\<exists>y\<in>convex hull s. norm (x - a) < norm (y - a))"
2705 show "\<forall>xa\<in>convex hull insert x s. xa \<notin> insert x s \<longrightarrow> (\<exists>y\<in>convex hull insert x s. norm (xa - a) < norm (y - a))"
2706 proof(rule,rule,cases "s = {}")
2707 case False fix y assume y:"y \<in> convex hull insert x s" "y \<notin> insert x s"
2708 obtain u v b where obt:"u\<ge>0" "v\<ge>0" "u + v = 1" "b \<in> convex hull s" "y = u *\<^sub>R x + v *\<^sub>R b"
2709 using y(1)[unfolded convex_hull_insert[OF False]] by auto
2710 show "\<exists>z\<in>convex hull insert x s. norm (y - a) < norm (z - a)"
2711 proof(cases "y\<in>convex hull s")
2712 case True then obtain z where "z\<in>convex hull s" "norm (y - a) < norm (z - a)"
2713 using as(3)[THEN bspec[where x=y]] and y(2) by auto
2714 thus ?thesis apply(rule_tac x=z in bexI) unfolding convex_hull_insert[OF False] by auto
2716 case False show ?thesis using obt(3) proof(cases "u=0", case_tac[!] "v=0")
2717 assume "u=0" "v\<noteq>0" hence "y = b" using obt by auto
2718 thus ?thesis using False and obt(4) by auto
2720 assume "u\<noteq>0" "v=0" hence "y = x" using obt by auto
2721 thus ?thesis using y(2) by auto
2723 assume "u\<noteq>0" "v\<noteq>0"
2724 then obtain w where w:"w>0" "w<u" "w<v" using real_lbound_gt_zero[of u v] and obt(1,2) by auto
2725 have "x\<noteq>b" proof(rule ccontr)
2726 assume "\<not> x\<noteq>b" hence "y=b" unfolding obt(5)
2727 using obt(3) by(auto simp add: scaleR_left_distrib[THEN sym])
2728 thus False using obt(4) and False by simp qed
2729 hence *:"w *\<^sub>R (x - b) \<noteq> 0" using w(1) by auto
2730 show ?thesis using dist_increases_online[OF *, of a y]
2731 proof(erule_tac disjE)
2732 assume "dist a y < dist a (y + w *\<^sub>R (x - b))"
2733 hence "norm (y - a) < norm ((u + w) *\<^sub>R x + (v - w) *\<^sub>R b - a)"
2734 unfolding dist_commute[of a] unfolding dist_norm obt(5) by (simp add: algebra_simps)
2735 moreover have "(u + w) *\<^sub>R x + (v - w) *\<^sub>R b \<in> convex hull insert x s"
2736 unfolding convex_hull_insert[OF `s\<noteq>{}`] and mem_Collect_eq
2737 apply(rule_tac x="u + w" in exI) apply rule defer
2738 apply(rule_tac x="v - w" in exI) using `u\<ge>0` and w and obt(3,4) by auto
2739 ultimately show ?thesis by auto
2741 assume "dist a y < dist a (y - w *\<^sub>R (x - b))"
2742 hence "norm (y - a) < norm ((u - w) *\<^sub>R x + (v + w) *\<^sub>R b - a)"
2743 unfolding dist_commute[of a] unfolding dist_norm obt(5) by (simp add: algebra_simps)
2744 moreover have "(u - w) *\<^sub>R x + (v + w) *\<^sub>R b \<in> convex hull insert x s"
2745 unfolding convex_hull_insert[OF `s\<noteq>{}`] and mem_Collect_eq
2746 apply(rule_tac x="u - w" in exI) apply rule defer
2747 apply(rule_tac x="v + w" in exI) using `u\<ge>0` and w and obt(3,4) by auto
2748 ultimately show ?thesis by auto
2753 qed (auto simp add: assms)
2755 lemma simplex_furthest_le:
2756 fixes s :: "('a::euclidean_space) set"
2757 assumes "finite s" "s \<noteq> {}"
2758 shows "\<exists>y\<in>s. \<forall>x\<in>(convex hull s). norm(x - a) \<le> norm(y - a)"
2760 have "convex hull s \<noteq> {}" using hull_subset[of s convex] and assms(2) by auto
2761 then obtain x where x:"x\<in>convex hull s" "\<forall>y\<in>convex hull s. norm (y - a) \<le> norm (x - a)"
2762 using distance_attains_sup[OF finite_imp_compact_convex_hull[OF assms(1)], of a]
2763 unfolding dist_commute[of a] unfolding dist_norm by auto
2764 thus ?thesis proof(cases "x\<in>s")
2765 case False then obtain y where "y\<in>convex hull s" "norm (x - a) < norm (y - a)"
2766 using simplex_furthest_lt[OF assms(1), THEN bspec[where x=x]] and x(1) by auto
2767 thus ?thesis using x(2)[THEN bspec[where x=y]] by auto
2771 lemma simplex_furthest_le_exists:
2772 fixes s :: "('a::euclidean_space) set"
2773 shows "finite s \<Longrightarrow> (\<forall>x\<in>(convex hull s). \<exists>y\<in>s. norm(x - a) \<le> norm(y - a))"
2774 using simplex_furthest_le[of s] by (cases "s={}")auto
2776 lemma simplex_extremal_le:
2777 fixes s :: "('a::euclidean_space) set"
2778 assumes "finite s" "s \<noteq> {}"
2779 shows "\<exists>u\<in>s. \<exists>v\<in>s. \<forall>x\<in>convex hull s. \<forall>y \<in> convex hull s. norm(x - y) \<le> norm(u - v)"
2781 have "convex hull s \<noteq> {}" using hull_subset[of s convex] and assms(2) by auto
2782 then obtain u v where obt:"u\<in>convex hull s" "v\<in>convex hull s"
2783 "\<forall>x\<in>convex hull s. \<forall>y\<in>convex hull s. norm (x - y) \<le> norm (u - v)"
2784 using compact_sup_maxdistance[OF finite_imp_compact_convex_hull[OF assms(1)]] by auto
2785 thus ?thesis proof(cases "u\<notin>s \<or> v\<notin>s", erule_tac disjE)
2786 assume "u\<notin>s" then obtain y where "y\<in>convex hull s" "norm (u - v) < norm (y - v)"
2787 using simplex_furthest_lt[OF assms(1), THEN bspec[where x=u]] and obt(1) by auto
2788 thus ?thesis using obt(3)[THEN bspec[where x=y], THEN bspec[where x=v]] and obt(2) by auto
2790 assume "v\<notin>s" then obtain y where "y\<in>convex hull s" "norm (v - u) < norm (y - u)"
2791 using simplex_furthest_lt[OF assms(1), THEN bspec[where x=v]] and obt(2) by auto
2792 thus ?thesis using obt(3)[THEN bspec[where x=u], THEN bspec[where x=y]] and obt(1)
2793 by (auto simp add: norm_minus_commute)
2797 lemma simplex_extremal_le_exists:
2798 fixes s :: "('a::euclidean_space) set"
2799 shows "finite s \<Longrightarrow> x \<in> convex hull s \<Longrightarrow> y \<in> convex hull s
2800 \<Longrightarrow> (\<exists>u\<in>s. \<exists>v\<in>s. norm(x - y) \<le> norm(u - v))"
2801 using convex_hull_empty simplex_extremal_le[of s] by(cases "s={}")auto
2803 subsection {* Closest point of a convex set is unique, with a continuous projection. *}
2806 closest_point :: "'a::{real_inner,heine_borel} set \<Rightarrow> 'a \<Rightarrow> 'a" where
2807 "closest_point s a = (SOME x. x \<in> s \<and> (\<forall>y\<in>s. dist a x \<le> dist a y))"
2809 lemma closest_point_exists:
2810 assumes "closed s" "s \<noteq> {}"
2811 shows "closest_point s a \<in> s" "\<forall>y\<in>s. dist a (closest_point s a) \<le> dist a y"
2812 unfolding closest_point_def apply(rule_tac[!] someI2_ex)
2813 using distance_attains_inf[OF assms(1,2), of a] by auto
2815 lemma closest_point_in_set:
2816 "closed s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> (closest_point s a) \<in> s"
2817 by(meson closest_point_exists)
2819 lemma closest_point_le:
2820 "closed s \<Longrightarrow> x \<in> s \<Longrightarrow> dist a (closest_point s a) \<le> dist a x"
2821 using closest_point_exists[of s] by auto
2823 lemma closest_point_self:
2824 assumes "x \<in> s" shows "closest_point s x = x"
2825 unfolding closest_point_def apply(rule some1_equality, rule ex1I[of _ x])
2828 lemma closest_point_refl:
2829 "closed s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> (closest_point s x = x \<longleftrightarrow> x \<in> s)"
2830 using closest_point_in_set[of s x] closest_point_self[of x s] by auto
2832 lemma closer_points_lemma:
2833 assumes "inner y z > 0"
2834 shows "\<exists>u>0. \<forall>v>0. v \<le> u \<longrightarrow> norm(v *\<^sub>R z - y) < norm y"
2835 proof- have z:"inner z z > 0" unfolding inner_gt_zero_iff using assms by auto
2836 thus ?thesis using assms apply(rule_tac x="inner y z / inner z z" in exI) apply(rule) defer proof(rule+)
2837 fix v assume "0<v" "v \<le> inner y z / inner z z"
2838 thus "norm (v *\<^sub>R z - y) < norm y" unfolding norm_lt using z and assms
2839 by (simp add: field_simps inner_diff inner_commute mult_strict_left_mono[OF _ `0<v`])
2840 qed(rule divide_pos_pos, auto) qed
2842 lemma closer_point_lemma:
2843 assumes "inner (y - x) (z - x) > 0"
2844 shows "\<exists>u>0. u \<le> 1 \<and> dist (x + u *\<^sub>R (z - x)) y < dist x y"
2845 proof- obtain u where "u>0" and u:"\<forall>v>0. v \<le> u \<longrightarrow> norm (v *\<^sub>R (z - x) - (y - x)) < norm (y - x)"
2846 using closer_points_lemma[OF assms] by auto
2847 show ?thesis apply(rule_tac x="min u 1" in exI) using u[THEN spec[where x="min u 1"]] and `u>0`
2848 unfolding dist_norm by(auto simp add: norm_minus_commute field_simps) qed
2850 lemma any_closest_point_dot:
2851 assumes "convex s" "closed s" "x \<in> s" "y \<in> s" "\<forall>z\<in>s. dist a x \<le> dist a z"
2852 shows "inner (a - x) (y - x) \<le> 0"
2853 proof(rule ccontr) assume "\<not> inner (a - x) (y - x) \<le> 0"
2854 then obtain u where u:"u>0" "u\<le>1" "dist (x + u *\<^sub>R (y - x)) a < dist x a" using closer_point_lemma[of a x y] by auto
2855 let ?z = "(1 - u) *\<^sub>R x + u *\<^sub>R y" have "?z \<in> s" using mem_convex[OF assms(1,3,4), of u] using u by auto
2856 thus False using assms(5)[THEN bspec[where x="?z"]] and u(3) by (auto simp add: dist_commute algebra_simps) qed
2858 lemma any_closest_point_unique:
2859 fixes x :: "'a::real_inner"
2860 assumes "convex s" "closed s" "x \<in> s" "y \<in> s"
2861 "\<forall>z\<in>s. dist a x \<le> dist a z" "\<forall>z\<in>s. dist a y \<le> dist a z"
2862 shows "x = y" using any_closest_point_dot[OF assms(1-4,5)] and any_closest_point_dot[OF assms(1-2,4,3,6)]
2863 unfolding norm_pths(1) and norm_le_square
2864 by (auto simp add: algebra_simps)
2866 lemma closest_point_unique:
2867 assumes "convex s" "closed s" "x \<in> s" "\<forall>z\<in>s. dist a x \<le> dist a z"
2868 shows "x = closest_point s a"
2869 using any_closest_point_unique[OF assms(1-3) _ assms(4), of "closest_point s a"]
2870 using closest_point_exists[OF assms(2)] and assms(3) by auto
2872 lemma closest_point_dot:
2873 assumes "convex s" "closed s" "x \<in> s"
2874 shows "inner (a - closest_point s a) (x - closest_point s a) \<le> 0"
2875 apply(rule any_closest_point_dot[OF assms(1,2) _ assms(3)])
2876 using closest_point_exists[OF assms(2)] and assms(3) by auto
2878 lemma closest_point_lt:
2879 assumes "convex s" "closed s" "x \<in> s" "x \<noteq> closest_point s a"
2880 shows "dist a (closest_point s a) < dist a x"
2881 apply(rule ccontr) apply(rule_tac notE[OF assms(4)])
2882 apply(rule closest_point_unique[OF assms(1-3), of a])
2883 using closest_point_le[OF assms(2), of _ a] by fastsimp
2885 lemma closest_point_lipschitz:
2886 assumes "convex s" "closed s" "s \<noteq> {}"
2887 shows "dist (closest_point s x) (closest_point s y) \<le> dist x y"
2889 have "inner (x - closest_point s x) (closest_point s y - closest_point s x) \<le> 0"
2890 "inner (y - closest_point s y) (closest_point s x - closest_point s y) \<le> 0"
2891 apply(rule_tac[!] any_closest_point_dot[OF assms(1-2)])
2892 using closest_point_exists[OF assms(2-3)] by auto
2893 thus ?thesis unfolding dist_norm and norm_le
2894 using inner_ge_zero[of "(x - closest_point s x) - (y - closest_point s y)"]
2895 by (simp add: inner_add inner_diff inner_commute) qed
2897 lemma continuous_at_closest_point:
2898 assumes "convex s" "closed s" "s \<noteq> {}"
2899 shows "continuous (at x) (closest_point s)"
2900 unfolding continuous_at_eps_delta
2901 using le_less_trans[OF closest_point_lipschitz[OF assms]] by auto
2903 lemma continuous_on_closest_point:
2904 assumes "convex s" "closed s" "s \<noteq> {}"
2905 shows "continuous_on t (closest_point s)"
2906 by(metis continuous_at_imp_continuous_on continuous_at_closest_point[OF assms])
2908 subsection {* Various point-to-set separating/supporting hyperplane theorems. *}
2910 lemma supporting_hyperplane_closed_point:
2911 fixes z :: "'a::{real_inner,heine_borel}"
2912 assumes "convex s" "closed s" "s \<noteq> {}" "z \<notin> s"
2913 shows "\<exists>a b. \<exists>y\<in>s. inner a z < b \<and> (inner a y = b) \<and> (\<forall>x\<in>s. inner a x \<ge> b)"
2915 from distance_attains_inf[OF assms(2-3)] obtain y where "y\<in>s" and y:"\<forall>x\<in>s. dist z y \<le> dist z x" by auto
2916 show ?thesis apply(rule_tac x="y - z" in exI, rule_tac x="inner (y - z) y" in exI, rule_tac x=y in bexI)
2917 apply rule defer apply rule defer apply(rule, rule ccontr) using `y\<in>s` proof-
2918 show "inner (y - z) z < inner (y - z) y" apply(subst diff_less_iff(1)[THEN sym])
2919 unfolding inner_diff_right[THEN sym] and inner_gt_zero_iff using `y\<in>s` `z\<notin>s` by auto
2921 fix x assume "x\<in>s" have *:"\<forall>u. 0 \<le> u \<and> u \<le> 1 \<longrightarrow> dist z y \<le> dist z ((1 - u) *\<^sub>R y + u *\<^sub>R x)"
2922 using assms(1)[unfolded convex_alt] and y and `x\<in>s` and `y\<in>s` by auto
2923 assume "\<not> inner (y - z) y \<le> inner (y - z) x" then obtain v where
2924 "v>0" "v\<le>1" "dist (y + v *\<^sub>R (x - y)) z < dist y z" using closer_point_lemma[of z y x] apply - by (auto simp add: inner_diff)
2925 thus False using *[THEN spec[where x=v]] by(auto simp add: dist_commute algebra_simps)
2929 lemma separating_hyperplane_closed_point:
2930 fixes z :: "'a::{real_inner,heine_borel}"
2931 assumes "convex s" "closed s" "z \<notin> s"
2932 shows "\<exists>a b. inner a z < b \<and> (\<forall>x\<in>s. inner a x > b)"
2934 case True thus ?thesis apply(rule_tac x="-z" in exI, rule_tac x=1 in exI)
2935 using less_le_trans[OF _ inner_ge_zero[of z]] by auto
2937 case False obtain y where "y\<in>s" and y:"\<forall>x\<in>s. dist z y \<le> dist z x"
2938 using distance_attains_inf[OF assms(2) False] by auto
2939 show ?thesis apply(rule_tac x="y - z" in exI, rule_tac x="inner (y - z) z + (norm(y - z))\<twosuperior> / 2" in exI)
2940 apply rule defer apply rule proof-
2941 fix x assume "x\<in>s"
2942 have "\<not> 0 < inner (z - y) (x - y)" apply(rule_tac notI) proof(drule closer_point_lemma)
2943 assume "\<exists>u>0. u \<le> 1 \<and> dist (y + u *\<^sub>R (x - y)) z < dist y z"
2944 then obtain u where "u>0" "u\<le>1" "dist (y + u *\<^sub>R (x - y)) z < dist y z" by auto
2945 thus False using y[THEN bspec[where x="y + u *\<^sub>R (x - y)"]]
2946 using assms(1)[unfolded convex_alt, THEN bspec[where x=y]]
2947 using `x\<in>s` `y\<in>s` by (auto simp add: dist_commute algebra_simps) qed
2948 moreover have "0 < norm (y - z) ^ 2" using `y\<in>s` `z\<notin>s` by auto
2949 hence "0 < inner (y - z) (y - z)" unfolding power2_norm_eq_inner by simp
2950 ultimately show "inner (y - z) z + (norm (y - z))\<twosuperior> / 2 < inner (y - z) x"
2951 unfolding power2_norm_eq_inner and not_less by (auto simp add: field_simps inner_commute inner_diff)
2952 qed(insert `y\<in>s` `z\<notin>s`, auto)
2955 lemma separating_hyperplane_closed_0:
2956 assumes "convex (s::('a::euclidean_space) set)" "closed s" "0 \<notin> s"
2957 shows "\<exists>a b. a \<noteq> 0 \<and> 0 < b \<and> (\<forall>x\<in>s. inner a x > b)"
2959 case True have "norm ((basis 0)::'a) = 1" by auto
2960 hence "norm ((basis 0)::'a) = 1" "basis 0 \<noteq> (0::'a)" defer
2961 apply(subst norm_le_zero_iff[THEN sym]) by auto
2962 thus ?thesis apply(rule_tac x="basis 0" in exI, rule_tac x=1 in exI)
2963 using True using DIM_positive[where 'a='a] by auto
2964 next case False thus ?thesis using False using separating_hyperplane_closed_point[OF assms]
2965 apply - apply(erule exE)+ unfolding inner.zero_right apply(rule_tac x=a in exI, rule_tac x=b in exI) by auto qed
2967 subsection {* Now set-to-set for closed/compact sets. *}
2969 lemma separating_hyperplane_closed_compact:
2970 assumes "convex (s::('a::euclidean_space) set)" "closed s" "convex t" "compact t" "t \<noteq> {}" "s \<inter> t = {}"
2971 shows "\<exists>a b. (\<forall>x\<in>s. inner a x < b) \<and> (\<forall>x\<in>t. inner a x > b)"
2974 obtain b where b:"b>0" "\<forall>x\<in>t. norm x \<le> b" using compact_imp_bounded[OF assms(4)] unfolding bounded_pos by auto
2975 obtain z::"'a" where z:"norm z = b + 1" using vector_choose_size[of "b + 1"] and b(1) by auto
2976 hence "z\<notin>t" using b(2)[THEN bspec[where x=z]] by auto
2977 then obtain a b where ab:"inner a z < b" "\<forall>x\<in>t. b < inner a x"
2978 using separating_hyperplane_closed_point[OF assms(3) compact_imp_closed[OF assms(4)], of z] by auto
2979 thus ?thesis using True by auto
2981 case False then obtain y where "y\<in>s" by auto
2982 obtain a b where "0 < b" "\<forall>x\<in>{x - y |x y. x \<in> s \<and> y \<in> t}. b < inner a x"
2983 using separating_hyperplane_closed_point[OF convex_differences[OF assms(1,3)], of 0]
2984 using closed_compact_differences[OF assms(2,4)] using assms(6) by(auto, blast)
2985 hence ab:"\<forall>x\<in>s. \<forall>y\<in>t. b + inner a y < inner a x" apply- apply(rule,rule) apply(erule_tac x="x - y" in ballE) by (auto simp add: inner_diff)
2986 def k \<equiv> "Sup ((\<lambda>x. inner a x) ` t)"
2987 show ?thesis apply(rule_tac x="-a" in exI, rule_tac x="-(k + b / 2)" in exI)
2988 apply(rule,rule) defer apply(rule) unfolding inner_minus_left and neg_less_iff_less proof-
2989 from ab have "((\<lambda>x. inner a x) ` t) *<= (inner a y - b)"
2990 apply(erule_tac x=y in ballE) apply(rule setleI) using `y\<in>s` by auto
2991 hence k:"isLub UNIV ((\<lambda>x. inner a x) ` t) k" unfolding k_def apply(rule_tac Sup) using assms(5) by auto
2992 fix x assume "x\<in>t" thus "inner a x < (k + b / 2)" using `0<b` and isLubD2[OF k, of "inner a x"] by auto
2994 fix x assume "x\<in>s"
2995 hence "k \<le> inner a x - b" unfolding k_def apply(rule_tac Sup_least) using assms(5)
2996 using ab[THEN bspec[where x=x]] by auto
2997 thus "k + b / 2 < inner a x" using `0 < b` by auto
3001 lemma separating_hyperplane_compact_closed:
3002 fixes s :: "('a::euclidean_space) set"
3003 assumes "convex s" "compact s" "s \<noteq> {}" "convex t" "closed t" "s \<inter> t = {}"
3004 shows "\<exists>a b. (\<forall>x\<in>s. inner a x < b) \<and> (\<forall>x\<in>t. inner a x > b)"
3005 proof- obtain a b where "(\<forall>x\<in>t. inner a x < b) \<and> (\<forall>x\<in>s. b < inner a x)"
3006 using separating_hyperplane_closed_compact[OF assms(4-5,1-2,3)] and assms(6) by auto
3007 thus ?thesis apply(rule_tac x="-a" in exI, rule_tac x="-b" in exI) by auto qed
3009 subsection {* General case without assuming closure and getting non-strict separation. *}
3011 lemma separating_hyperplane_set_0:
3012 assumes "convex s" "(0::'a::euclidean_space) \<notin> s"
3013 shows "\<exists>a. a \<noteq> 0 \<and> (\<forall>x\<in>s. 0 \<le> inner a x)"
3014 proof- let ?k = "\<lambda>c. {x::'a. 0 \<le> inner c x}"
3015 have "frontier (cball 0 1) \<inter> (\<Inter> (?k ` s)) \<noteq> {}"
3016 apply(rule compact_imp_fip) apply(rule compact_frontier[OF compact_cball])
3017 defer apply(rule,rule,erule conjE) proof-
3018 fix f assume as:"f \<subseteq> ?k ` s" "finite f"
3019 obtain c where c:"f = ?k ` c" "c\<subseteq>s" "finite c" using finite_subset_image[OF as(2,1)] by auto
3020 then obtain a b where ab:"a \<noteq> 0" "0 < b" "\<forall>x\<in>convex hull c. b < inner a x"
3021 using separating_hyperplane_closed_0[OF convex_convex_hull, of c]
3022 using finite_imp_compact_convex_hull[OF c(3), THEN compact_imp_closed] and assms(2)
3023 using subset_hull[unfolded mem_def, of convex, OF assms(1), THEN sym, of c] by auto
3024 hence "\<exists>x. norm x = 1 \<and> (\<forall>y\<in>c. 0 \<le> inner y x)" apply(rule_tac x="inverse(norm a) *\<^sub>R a" in exI)
3025 using hull_subset[of c convex] unfolding subset_eq and inner_scaleR
3026 apply- apply rule defer apply rule apply(rule mult_nonneg_nonneg)
3027 by(auto simp add: inner_commute elim!: ballE)
3028 thus "frontier (cball 0 1) \<inter> \<Inter>f \<noteq> {}" unfolding c(1) frontier_cball dist_norm by auto
3029 qed(insert closed_halfspace_ge, auto)
3030 then obtain x where "norm x = 1" "\<forall>y\<in>s. x\<in>?k y" unfolding frontier_cball dist_norm by auto
3031 thus ?thesis apply(rule_tac x=x in exI) by(auto simp add: inner_commute) qed
3033 lemma separating_hyperplane_sets:
3034 assumes "convex s" "convex (t::('a::euclidean_space) set)" "s \<noteq> {}" "t \<noteq> {}" "s \<inter> t = {}"
3035 shows "\<exists>a b. a \<noteq> 0 \<and> (\<forall>x\<in>s. inner a x \<le> b) \<and> (\<forall>x\<in>t. inner a x \<ge> b)"
3036 proof- from separating_hyperplane_set_0[OF convex_differences[OF assms(2,1)]]
3037 obtain a where "a\<noteq>0" "\<forall>x\<in>{x - y |x y. x \<in> t \<and> y \<in> s}. 0 \<le> inner a x"
3038 using assms(3-5) by auto
3039 hence "\<forall>x\<in>t. \<forall>y\<in>s. inner a y \<le> inner a x"
3040 by (force simp add: inner_diff)
3042 apply(rule_tac x=a in exI, rule_tac x="Sup ((\<lambda>x. inner a x) ` s)" in exI) using `a\<noteq>0`
3044 apply (rule Sup[THEN isLubD2])
3046 apply (rule Sup_least)
3047 using assms(3-5) apply (auto simp add: setle_def)
3052 subsection {* More convexity generalities. *}
3054 lemma convex_closure:
3055 fixes s :: "'a::real_normed_vector set"
3056 assumes "convex s" shows "convex(closure s)"
3057 unfolding convex_def Ball_def closure_sequential
3058 apply(rule,rule,rule,rule,rule,rule,rule,rule,rule) apply(erule_tac exE)+
3059 apply(rule_tac x="\<lambda>n. u *\<^sub>R xb n + v *\<^sub>R xc n" in exI) apply(rule,rule)
3060 apply(rule assms[unfolded convex_def, rule_format]) prefer 6
3061 apply(rule Lim_add) apply(rule_tac [1-2] Lim_cmul) by auto
3063 lemma convex_interior:
3064 fixes s :: "'a::real_normed_vector set"
3065 assumes "convex s" shows "convex(interior s)"
3066 unfolding convex_alt Ball_def mem_interior apply(rule,rule,rule,rule,rule,rule) apply(erule exE | erule conjE)+ proof-
3067 fix x y u assume u:"0 \<le> u" "u \<le> (1::real)"
3068 fix e d assume ed:"ball x e \<subseteq> s" "ball y d \<subseteq> s" "0<d" "0<e"
3069 show "\<exists>e>0. ball ((1 - u) *\<^sub>R x + u *\<^sub>R y) e \<subseteq> s" apply(rule_tac x="min d e" in exI)
3070 apply rule unfolding subset_eq defer apply rule proof-
3071 fix z assume "z \<in> ball ((1 - u) *\<^sub>R x + u *\<^sub>R y) (min d e)"
3072 hence "(1- u) *\<^sub>R (z - u *\<^sub>R (y - x)) + u *\<^sub>R (z + (1 - u) *\<^sub>R (y - x)) \<in> s"
3073 apply(rule_tac assms[unfolded convex_alt, rule_format])
3074 using ed(1,2) and u unfolding subset_eq mem_ball Ball_def dist_norm by(auto simp add: algebra_simps)
3075 thus "z \<in> s" using u by (auto simp add: algebra_simps) qed(insert u ed(3-4), auto) qed
3077 lemma convex_hull_eq_empty[simp]: "convex hull s = {} \<longleftrightarrow> s = {}"
3078 using hull_subset[of s convex] convex_hull_empty by auto
3080 subsection {* Moving and scaling convex hulls. *}
3082 lemma convex_hull_translation_lemma:
3083 "convex hull ((\<lambda>x. a + x) ` s) \<subseteq> (\<lambda>x. a + x) ` (convex hull s)"
3084 by (metis convex_convex_hull convex_translation hull_minimal hull_subset image_mono mem_def)
3086 lemma convex_hull_bilemma: fixes neg
3087 assumes "(\<forall>s a. (convex hull (up a s)) \<subseteq> up a (convex hull s))"
3088 shows "(\<forall>s. up a (up (neg a) s) = s) \<and> (\<forall>s. up (neg a) (up a s) = s) \<and> (\<forall>s t a. s \<subseteq> t \<longrightarrow> up a s \<subseteq> up a t)
3089 \<Longrightarrow> \<forall>s. (convex hull (up a s)) = up a (convex hull s)"
3090 using assms by(metis subset_antisym)
3092 lemma convex_hull_translation:
3093 "convex hull ((\<lambda>x. a + x) ` s) = (\<lambda>x. a + x) ` (convex hull s)"
3094 apply(rule convex_hull_bilemma[rule_format, of _ _ "\<lambda>a. -a"], rule convex_hull_translation_lemma) unfolding image_image by auto
3096 lemma convex_hull_scaling_lemma:
3097 "(convex hull ((\<lambda>x. c *\<^sub>R x) ` s)) \<subseteq> (\<lambda>x. c *\<^sub>R x) ` (convex hull s)"
3098 by (metis convex_convex_hull convex_scaling hull_subset mem_def subset_hull subset_image_iff)
3100 lemma convex_hull_scaling:
3101 "convex hull ((\<lambda>x. c *\<^sub>R x) ` s) = (\<lambda>x. c *\<^sub>R x) ` (convex hull s)"
3102 apply(cases "c=0") defer apply(rule convex_hull_bilemma[rule_format, of _ _ inverse]) apply(rule convex_hull_scaling_lemma)
3103 unfolding image_image scaleR_scaleR by(auto simp add:image_constant_conv)
3105 lemma convex_hull_affinity:
3106 "convex hull ((\<lambda>x. a + c *\<^sub>R x) ` s) = (\<lambda>x. a + c *\<^sub>R x) ` (convex hull s)"
3107 by(simp only: image_image[THEN sym] convex_hull_scaling convex_hull_translation)
3109 subsection {* Convexity of cone hulls *}
3111 lemma convex_cone_hull:
3112 fixes S :: "('m::euclidean_space) set"
3114 shows "convex (cone hull S)"
3116 { fix x y assume xy_def: "x : cone hull S & y : cone hull S"
3117 hence "S ~= {}" using cone_hull_empty_iff[of S] by auto
3118 fix u v assume uv_def: "u>=0 & v>=0 & (u :: real)+v=1"
3119 hence *: "u *\<^sub>R x : cone hull S & v *\<^sub>R y : cone hull S"
3120 using cone_cone_hull[of S] xy_def cone_def[of "cone hull S"] by auto
3121 from * obtain cx xx where x_def: "u *\<^sub>R x = cx *\<^sub>R xx & (cx :: real)>=0 & xx : S"
3122 using cone_hull_expl[of S] by auto
3123 from * obtain cy yy where y_def: "v *\<^sub>R y = cy *\<^sub>R yy & (cy :: real)>=0 & yy : S"
3124 using cone_hull_expl[of S] by auto
3125 { assume "cx+cy<=0" hence "u *\<^sub>R x=0 & v *\<^sub>R y=0" using x_def y_def by auto
3126 hence "u *\<^sub>R x+ v *\<^sub>R y = 0" by auto
3127 hence "u *\<^sub>R x+ v *\<^sub>R y : cone hull S" using cone_hull_contains_0[of S] `S ~= {}` by auto
3131 hence "(cx/(cx+cy)) *\<^sub>R xx + (cy/(cx+cy)) *\<^sub>R yy : S"
3132 using assms mem_convex_alt[of S xx yy cx cy] x_def y_def by auto
3133 hence "cx *\<^sub>R xx + cy *\<^sub>R yy : cone hull S"
3134 using mem_cone_hull[of "(cx/(cx+cy)) *\<^sub>R xx + (cy/(cx+cy)) *\<^sub>R yy" S "cx+cy"]
3135 `cx+cy>0` by (auto simp add: scaleR_right_distrib)
3136 hence "u *\<^sub>R x+ v *\<^sub>R y : cone hull S" using x_def y_def by auto
3138 moreover have "(cx+cy<=0) | (cx+cy>0)" by auto
3139 ultimately have "u *\<^sub>R x+ v *\<^sub>R y : cone hull S" by blast
3140 } from this show ?thesis unfolding convex_def by auto
3143 lemma cone_convex_hull:
3144 fixes S :: "('m::euclidean_space) set"
3146 shows "cone (convex hull S)"
3148 { assume "S = {}" hence ?thesis by auto }
3150 { assume "S ~= {}" hence *: "0:S & (!c. c>0 --> op *\<^sub>R c ` S = S)" using cone_iff[of S] assms by auto
3151 { fix c assume "(c :: real)>0"
3152 hence "op *\<^sub>R c ` (convex hull S) = convex hull (op *\<^sub>R c ` S)"
3153 using convex_hull_scaling[of _ S] by auto
3154 also have "...=convex hull S" using * `c>0` by auto
3155 finally have "op *\<^sub>R c ` (convex hull S) = convex hull S" by auto
3157 hence "0 : convex hull S & (!c. c>0 --> (op *\<^sub>R c ` (convex hull S)) = (convex hull S))"
3158 using * hull_subset[of S convex] by auto
3159 hence ?thesis using `S ~= {}` cone_iff[of "convex hull S"] by auto
3161 ultimately show ?thesis by blast
3164 subsection {* Convex set as intersection of halfspaces. *}
3166 lemma convex_halfspace_intersection:
3167 fixes s :: "('a::euclidean_space) set"
3168 assumes "closed s" "convex s"
3169 shows "s = \<Inter> {h. s \<subseteq> h \<and> (\<exists>a b. h = {x. inner a x \<le> b})}"
3170 apply(rule set_eqI, rule) unfolding Inter_iff Ball_def mem_Collect_eq apply(rule,rule,erule conjE) proof-
3171 fix x assume "\<forall>xa. s \<subseteq> xa \<and> (\<exists>a b. xa = {x. inner a x \<le> b}) \<longrightarrow> x \<in> xa"
3172 hence "\<forall>a b. s \<subseteq> {x. inner a x \<le> b} \<longrightarrow> x \<in> {x. inner a x \<le> b}" by blast
3173 thus "x\<in>s" apply(rule_tac ccontr) apply(drule separating_hyperplane_closed_point[OF assms(2,1)])
3174 apply(erule exE)+ apply(erule_tac x="-a" in allE, erule_tac x="-b" in allE) by auto
3177 subsection {* Radon's theorem (from Lars Schewe). *}
3179 lemma radon_ex_lemma:
3180 assumes "finite c" "affine_dependent c"
3181 shows "\<exists>u. setsum u c = 0 \<and> (\<exists>v\<in>c. u v \<noteq> 0) \<and> setsum (\<lambda>v. u v *\<^sub>R v) c = 0"
3182 proof- from assms(2)[unfolded affine_dependent_explicit] guess s .. then guess u ..
3183 thus ?thesis apply(rule_tac x="\<lambda>v. if v\<in>s then u v else 0" in exI) unfolding if_smult scaleR_zero_left
3184 and setsum_restrict_set[OF assms(1), THEN sym] by(auto simp add: Int_absorb1) qed
3186 lemma radon_s_lemma:
3187 assumes "finite s" "setsum f s = (0::real)"
3188 shows "setsum f {x\<in>s. 0 < f x} = - setsum f {x\<in>s. f x < 0}"
3189 proof- have *:"\<And>x. (if f x < 0 then f x else 0) + (if 0 < f x then f x else 0) = f x" by auto
3190 show ?thesis unfolding real_add_eq_0_iff[THEN sym] and setsum_restrict_set''[OF assms(1)] and setsum_addf[THEN sym] and *
3191 using assms(2) by assumption qed
3193 lemma radon_v_lemma:
3194 assumes "finite s" "setsum f s = 0" "\<forall>x. g x = (0::real) \<longrightarrow> f x = (0::'a::euclidean_space)"
3195 shows "(setsum f {x\<in>s. 0 < g x}) = - setsum f {x\<in>s. g x < 0}"
3197 have *:"\<And>x. (if 0 < g x then f x else 0) + (if g x < 0 then f x else 0) = f x" using assms(3) by auto
3198 show ?thesis unfolding eq_neg_iff_add_eq_0 and setsum_restrict_set''[OF assms(1)] and setsum_addf[THEN sym] and *
3199 using assms(2) by assumption qed
3201 lemma radon_partition:
3202 assumes "finite c" "affine_dependent c"
3203 shows "\<exists>m p. m \<inter> p = {} \<and> m \<union> p = c \<and> (convex hull m) \<inter> (convex hull p) \<noteq> {}" proof-
3204 obtain u v where uv:"setsum u c = 0" "v\<in>c" "u v \<noteq> 0" "(\<Sum>v\<in>c. u v *\<^sub>R v) = 0" using radon_ex_lemma[OF assms] by auto
3205 have fin:"finite {x \<in> c. 0 < u x}" "finite {x \<in> c. 0 > u x}" using assms(1) by auto
3206 def z \<equiv> "(inverse (setsum u {x\<in>c. u x > 0})) *\<^sub>R setsum (\<lambda>x. u x *\<^sub>R x) {x\<in>c. u x > 0}"
3207 have "setsum u {x \<in> c. 0 < u x} \<noteq> 0" proof(cases "u v \<ge> 0")
3208 case False hence "u v < 0" by auto
3209 thus ?thesis proof(cases "\<exists>w\<in>{x \<in> c. 0 < u x}. u w > 0")
3210 case True thus ?thesis using setsum_nonneg_eq_0_iff[of _ u, OF fin(1)] by auto
3212 case False hence "setsum u c \<le> setsum (\<lambda>x. if x=v then u v else 0) c" apply(rule_tac setsum_mono) by auto
3213 thus ?thesis unfolding setsum_delta[OF assms(1)] using uv(2) and `u v < 0` and uv(1) by auto qed
3214 qed (insert setsum_nonneg_eq_0_iff[of _ u, OF fin(1)] uv(2-3), auto)
3216 hence *:"setsum u {x\<in>c. u x > 0} > 0" unfolding less_le apply(rule_tac conjI, rule_tac setsum_nonneg) by auto
3217 moreover have "setsum u ({x \<in> c. 0 < u x} \<union> {x \<in> c. u x < 0}) = setsum u c"
3218 "(\<Sum>x\<in>{x \<in> c. 0 < u x} \<union> {x \<in> c. u x < 0}. u x *\<^sub>R x) = (\<Sum>x\<in>c. u x *\<^sub>R x)"
3219 using assms(1) apply(rule_tac[!] setsum_mono_zero_left) by auto
3220 hence "setsum u {x \<in> c. 0 < u x} = - setsum u {x \<in> c. 0 > u x}"
3221 "(\<Sum>x\<in>{x \<in> c. 0 < u x}. u x *\<^sub>R x) = - (\<Sum>x\<in>{x \<in> c. 0 > u x}. u x *\<^sub>R x)"
3222 unfolding eq_neg_iff_add_eq_0 using uv(1,4) by (auto simp add: setsum_Un_zero[OF fin, THEN sym])
3223 moreover have "\<forall>x\<in>{v \<in> c. u v < 0}. 0 \<le> inverse (setsum u {x \<in> c. 0 < u x}) * - u x"
3224 apply (rule) apply (rule mult_nonneg_nonneg) using * by auto
3226 ultimately have "z \<in> convex hull {v \<in> c. u v \<le> 0}" unfolding convex_hull_explicit mem_Collect_eq
3227 apply(rule_tac x="{v \<in> c. u v < 0}" in exI, rule_tac x="\<lambda>y. inverse (setsum u {x\<in>c. u x > 0}) * - u y" in exI)
3228 using assms(1) unfolding scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] and z_def
3229 by(auto simp add: setsum_negf mult_right.setsum[THEN sym])
3230 moreover have "\<forall>x\<in>{v \<in> c. 0 < u v}. 0 \<le> inverse (setsum u {x \<in> c. 0 < u x}) * u x"
3231 apply (rule) apply (rule mult_nonneg_nonneg) using * by auto
3232 hence "z \<in> convex hull {v \<in> c. u v > 0}" unfolding convex_hull_explicit mem_Collect_eq
3233 apply(rule_tac x="{v \<in> c. 0 < u v}" in exI, rule_tac x="\<lambda>y. inverse (setsum u {x\<in>c. u x > 0}) * u y" in exI)
3234 using assms(1) unfolding scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] and z_def using *
3235 by(auto simp add: setsum_negf mult_right.setsum[THEN sym])
3236 ultimately show ?thesis apply(rule_tac x="{v\<in>c. u v \<le> 0}" in exI, rule_tac x="{v\<in>c. u v > 0}" in exI) by auto
3239 lemma radon: assumes "affine_dependent c"
3240 obtains m p where "m\<subseteq>c" "p\<subseteq>c" "m \<inter> p = {}" "(convex hull m) \<inter> (convex hull p) \<noteq> {}"
3241 proof- from assms[unfolded affine_dependent_explicit] guess s .. then guess u ..
3242 hence *:"finite s" "affine_dependent s" and s:"s \<subseteq> c" unfolding affine_dependent_explicit by auto
3243 from radon_partition[OF *] guess m .. then guess p ..
3244 thus ?thesis apply(rule_tac that[of p m]) using s by auto qed
3246 subsection {* Helly's theorem. *}
3248 lemma helly_induct: fixes f::"('a::euclidean_space) set set"
3249 assumes "card f = n" "n \<ge> DIM('a) + 1"
3250 "\<forall>s\<in>f. convex s" "\<forall>t\<subseteq>f. card t = DIM('a) + 1 \<longrightarrow> \<Inter> t \<noteq> {}"
3251 shows "\<Inter> f \<noteq> {}"
3252 using assms proof(induct n arbitrary: f)
3254 have "finite f" using `card f = Suc n` by (auto intro: card_ge_0_finite)
3255 show "\<Inter> f \<noteq> {}" apply(cases "n = DIM('a)") apply(rule Suc(5)[rule_format])
3256 unfolding `card f = Suc n` proof-
3257 assume ng:"n \<noteq> DIM('a)" hence "\<exists>X. \<forall>s\<in>f. X s \<in> \<Inter>(f - {s})" apply(rule_tac bchoice) unfolding ex_in_conv
3258 apply(rule, rule Suc(1)[rule_format]) unfolding card_Diff_singleton_if[OF `finite f`] `card f = Suc n`
3259 defer defer apply(rule Suc(4)[rule_format]) defer apply(rule Suc(5)[rule_format]) using Suc(3) `finite f` by auto
3260 then obtain X where X:"\<forall>s\<in>f. X s \<in> \<Inter>(f - {s})" by auto
3261 show ?thesis proof(cases "inj_on X f")
3262 case False then obtain s t where st:"s\<noteq>t" "s\<in>f" "t\<in>f" "X s = X t" unfolding inj_on_def by auto
3263 hence *:"\<Inter> f = \<Inter> (f - {s}) \<inter> \<Inter> (f - {t})" by auto
3264 show ?thesis unfolding * unfolding ex_in_conv[THEN sym] apply(rule_tac x="X s" in exI)
3265 apply(rule, rule X[rule_format]) using X st by auto
3266 next case True then obtain m p where mp:"m \<inter> p = {}" "m \<union> p = X ` f" "convex hull m \<inter> convex hull p \<noteq> {}"
3267 using radon_partition[of "X ` f"] and affine_dependent_biggerset[of "X ` f"]
3268 unfolding card_image[OF True] and `card f = Suc n` using Suc(3) `finite f` and ng by auto
3269 have "m \<subseteq> X ` f" "p \<subseteq> X ` f" using mp(2) by auto
3270 then obtain g h where gh:"m = X ` g" "p = X ` h" "g \<subseteq> f" "h \<subseteq> f" unfolding subset_image_iff by auto
3271 hence "f \<union> (g \<union> h) = f" by auto
3272 hence f:"f = g \<union> h" using inj_on_Un_image_eq_iff[of X f "g \<union> h"] and True
3273 unfolding mp(2)[unfolded image_Un[THEN sym] gh] by auto
3274 have *:"g \<inter> h = {}" using mp(1) unfolding gh using inj_on_image_Int[OF True gh(3,4)] by auto
3275 have "convex hull (X ` h) \<subseteq> \<Inter> g" "convex hull (X ` g) \<subseteq> \<Inter> h"
3276 apply(rule_tac [!] hull_minimal) using Suc gh(3-4) unfolding mem_def unfolding subset_eq
3277 apply(rule_tac [2] convex_Inter, rule_tac [4] convex_Inter) apply rule prefer 3 apply rule proof-
3278 fix x assume "x\<in>X ` g" then guess y unfolding image_iff ..
3279 thus "x\<in>\<Inter>h" using X[THEN bspec[where x=y]] using * f by auto next
3280 fix x assume "x\<in>X ` h" then guess y unfolding image_iff ..
3281 thus "x\<in>\<Inter>g" using X[THEN bspec[where x=y]] using * f by auto
3283 thus ?thesis unfolding f using mp(3)[unfolded gh] by blast qed
3286 lemma helly: fixes f::"('a::euclidean_space) set set"
3287 assumes "card f \<ge> DIM('a) + 1" "\<forall>s\<in>f. convex s"
3288 "\<forall>t\<subseteq>f. card t = DIM('a) + 1 \<longrightarrow> \<Inter> t \<noteq> {}"
3289 shows "\<Inter> f \<noteq>{}"
3290 apply(rule helly_induct) using assms by auto
3292 subsection {* Homeomorphism of all convex compact sets with nonempty interior. *}
3294 lemma compact_frontier_line_lemma:
3295 fixes s :: "('a::euclidean_space) set"
3296 assumes "compact s" "0 \<in> s" "x \<noteq> 0"
3297 obtains u where "0 \<le> u" "(u *\<^sub>R x) \<in> frontier s" "\<forall>v>u. (v *\<^sub>R x) \<notin> s"
3299 obtain b where b:"b>0" "\<forall>x\<in>s. norm x \<le> b" using compact_imp_bounded[OF assms(1), unfolded bounded_pos] by auto
3300 let ?A = "{y. \<exists>u. 0 \<le> u \<and> u \<le> b / norm(x) \<and> (y = u *\<^sub>R x)}"
3301 have A:"?A = (\<lambda>u. u *\<^sub>R x) ` {0 .. b / norm x}"
3303 have *:"\<And>x A B. x\<in>A \<Longrightarrow> x\<in>B \<Longrightarrow> A\<inter>B \<noteq> {}" by blast
3304 have "compact ?A" unfolding A apply(rule compact_continuous_image, rule continuous_at_imp_continuous_on)
3305 apply(rule, rule continuous_vmul)
3306 apply(rule continuous_at_id) by(rule compact_interval)
3307 moreover have "{y. \<exists>u\<ge>0. u \<le> b / norm x \<and> y = u *\<^sub>R x} \<inter> s \<noteq> {}" apply(rule *[OF _ assms(2)])
3308 unfolding mem_Collect_eq using `b>0` assms(3) by(auto intro!: divide_nonneg_pos)
3309 ultimately obtain u y where obt: "u\<ge>0" "u \<le> b / norm x" "y = u *\<^sub>R x"
3310 "y\<in>?A" "y\<in>s" "\<forall>z\<in>?A \<inter> s. dist 0 z \<le> dist 0 y" using distance_attains_sup[OF compact_inter[OF _ assms(1), of ?A], of 0] by auto
3312 have "norm x > 0" using assms(3)[unfolded zero_less_norm_iff[THEN sym]] by auto
3313 { fix v assume as:"v > u" "v *\<^sub>R x \<in> s"
3314 hence "v \<le> b / norm x" using b(2)[rule_format, OF as(2)]
3315 using `u\<ge>0` unfolding pos_le_divide_eq[OF `norm x > 0`] by auto
3316 hence "norm (v *\<^sub>R x) \<le> norm y" apply(rule_tac obt(6)[rule_format, unfolded dist_0_norm]) apply(rule IntI) defer
3317 apply(rule as(2)) unfolding mem_Collect_eq apply(rule_tac x=v in exI)
3318 using as(1) `u\<ge>0` by(auto simp add:field_simps)
3319 hence False unfolding obt(3) using `u\<ge>0` `norm x > 0` `v>u` by(auto simp add:field_simps)
3322 have "u *\<^sub>R x \<in> frontier s" unfolding frontier_straddle apply(rule,rule,rule) apply(rule_tac x="u *\<^sub>R x" in bexI) unfolding obt(3)[THEN sym]
3323 prefer 3 apply(rule_tac x="(u + (e / 2) / norm x) *\<^sub>R x" in exI) apply(rule, rule) proof-
3324 fix e assume "0 < e" and as:"(u + e / 2 / norm x) *\<^sub>R x \<in> s"
3325 hence "u + e / 2 / norm x > u" using`norm x > 0` by(auto simp del:zero_less_norm_iff intro!: divide_pos_pos)
3326 thus False using u_max[OF _ as] by auto
3327 qed(insert `y\<in>s`, auto simp add: dist_norm scaleR_left_distrib obt(3))
3328 thus ?thesis by(metis that[of u] u_max obt(1))
3331 lemma starlike_compact_projective:
3332 assumes "compact s" "cball (0::'a::euclidean_space) 1 \<subseteq> s "
3333 "\<forall>x\<in>s. \<forall>u. 0 \<le> u \<and> u < 1 \<longrightarrow> (u *\<^sub>R x) \<in> (s - frontier s )"
3334 shows "s homeomorphic (cball (0::'a::euclidean_space) 1)"
3336 have fs:"frontier s \<subseteq> s" apply(rule frontier_subset_closed) using compact_imp_closed[OF assms(1)] by simp
3337 def pi \<equiv> "\<lambda>x::'a. inverse (norm x) *\<^sub>R x"
3338 have "0 \<notin> frontier s" unfolding frontier_straddle apply(rule ccontr) unfolding not_not apply(erule_tac x=1 in allE)
3339 using assms(2)[unfolded subset_eq Ball_def mem_cball] by auto
3340 have injpi:"\<And>x y. pi x = pi y \<and> norm x = norm y \<longleftrightarrow> x = y" unfolding pi_def by auto
3342 have contpi:"continuous_on (UNIV - {0}) pi" apply(rule continuous_at_imp_continuous_on)
3343 apply rule unfolding pi_def
3344 apply (rule continuous_mul)
3345 apply (rule continuous_at_inv[unfolded o_def])
3346 apply (rule continuous_at_norm)
3348 apply (rule continuous_at_id)
3350 def sphere \<equiv> "{x::'a. norm x = 1}"
3351 have pi:"\<And>x. x \<noteq> 0 \<Longrightarrow> pi x \<in> sphere" "\<And>x u. u>0 \<Longrightarrow> pi (u *\<^sub>R x) = pi x" unfolding pi_def sphere_def by auto
3353 have "0\<in>s" using assms(2) and centre_in_cball[of 0 1] by auto
3354 have front_smul:"\<forall>x\<in>frontier s. \<forall>u\<ge>0. u *\<^sub>R x \<in> s \<longleftrightarrow> u \<le> 1" proof(rule,rule,rule)
3355 fix x u assume x:"x\<in>frontier s" and "(0::real)\<le>u"
3356 hence "x\<noteq>0" using `0\<notin>frontier s` by auto
3357 obtain v where v:"0 \<le> v" "v *\<^sub>R x \<in> frontier s" "\<forall>w>v. w *\<^sub>R x \<notin> s"
3358 using compact_frontier_line_lemma[OF assms(1) `0\<in>s` `x\<noteq>0`] by auto
3359 have "v=1" apply(rule ccontr) unfolding neq_iff apply(erule disjE) proof-
3360 assume "v<1" thus False using v(3)[THEN spec[where x=1]] using x and fs by auto next
3361 assume "v>1" thus False using assms(3)[THEN bspec[where x="v *\<^sub>R x"], THEN spec[where x="inverse v"]]
3362 using v and x and fs unfolding inverse_less_1_iff by auto qed
3363 show "u *\<^sub>R x \<in> s \<longleftrightarrow> u \<le> 1" apply rule using v(3)[unfolded `v=1`, THEN spec[where x=u]] proof-
3364 assume "u\<le>1" thus "u *\<^sub>R x \<in> s" apply(cases "u=1")
3365 using assms(3)[THEN bspec[where x=x], THEN spec[where x=u]] using `0\<le>u` and x and fs by auto qed auto qed
3367 have "\<exists>surf. homeomorphism (frontier s) sphere pi surf"
3368 apply(rule homeomorphism_compact) apply(rule compact_frontier[OF assms(1)])
3369 apply(rule continuous_on_subset[OF contpi]) defer apply(rule set_eqI,rule)
3370 unfolding inj_on_def prefer 3 apply(rule,rule,rule)
3371 proof- fix x assume "x\<in>pi ` frontier s" then obtain y where "y\<in>frontier s" "x = pi y" by auto
3372 thus "x \<in> sphere" using pi(1)[of y] and `0 \<notin> frontier s` by auto
3373 next fix x assume "x\<in>sphere" hence "norm x = 1" "x\<noteq>0" unfolding sphere_def by auto
3374 then obtain u where "0 \<le> u" "u *\<^sub>R x \<in> frontier s" "\<forall>v>u. v *\<^sub>R x \<notin> s"
3375 using compact_frontier_line_lemma[OF assms(1) `0\<in>s`, of x] by auto
3376 thus "x \<in> pi ` frontier s" unfolding image_iff le_less pi_def apply(rule_tac x="u *\<^sub>R x" in bexI) using `norm x = 1` `0\<notin>frontier s` by auto
3377 next fix x y assume as:"x \<in> frontier s" "y \<in> frontier s" "pi x = pi y"
3378 hence xys:"x\<in>s" "y\<in>s" using fs by auto
3379 from as(1,2) have nor:"norm x \<noteq> 0" "norm y \<noteq> 0" using `0\<notin>frontier s` by auto
3380 from nor have x:"x = norm x *\<^sub>R ((inverse (norm y)) *\<^sub>R y)" unfolding as(3)[unfolded pi_def, THEN sym] by auto
3381 from nor have y:"y = norm y *\<^sub>R ((inverse (norm x)) *\<^sub>R x)" unfolding as(3)[unfolded pi_def] by auto
3382 have "0 \<le> norm y * inverse (norm x)" "0 \<le> norm x * inverse (norm y)"
3383 unfolding divide_inverse[THEN sym] apply(rule_tac[!] divide_nonneg_pos) using nor by auto
3384 hence "norm x = norm y" apply(rule_tac ccontr) unfolding neq_iff
3385 using x y and front_smul[THEN bspec, OF as(1), THEN spec[where x="norm y * (inverse (norm x))"]]
3386 using front_smul[THEN bspec, OF as(2), THEN spec[where x="norm x * (inverse (norm y))"]]
3387 using xys nor by(auto simp add:field_simps divide_le_eq_1 divide_inverse[THEN sym])
3388 thus "x = y" apply(subst injpi[THEN sym]) using as(3) by auto
3389 qed(insert `0 \<notin> frontier s`, auto)
3390 then obtain surf where surf:"\<forall>x\<in>frontier s. surf (pi x) = x" "pi ` frontier s = sphere" "continuous_on (frontier s) pi"
3391 "\<forall>y\<in>sphere. pi (surf y) = y" "surf ` sphere = frontier s" "continuous_on sphere surf" unfolding homeomorphism_def by auto
3393 have cont_surfpi:"continuous_on (UNIV - {0}) (surf \<circ> pi)" apply(rule continuous_on_compose, rule contpi)
3394 apply(rule continuous_on_subset[of sphere], rule surf(6)) using pi(1) by auto
3396 { fix x assume as:"x \<in> cball (0::'a) 1"
3397 have "norm x *\<^sub>R surf (pi x) \<in> s" proof(cases "x=0 \<or> norm x = 1")
3398 case False hence "pi x \<in> sphere" "norm x < 1" using pi(1)[of x] as by(auto simp add: dist_norm)
3399 thus ?thesis apply(rule_tac assms(3)[rule_format, THEN DiffD1])
3400 apply(rule_tac fs[unfolded subset_eq, rule_format])
3401 unfolding surf(5)[THEN sym] by auto
3402 next case True thus ?thesis apply rule defer unfolding pi_def apply(rule fs[unfolded subset_eq, rule_format])
3403 unfolding surf(5)[unfolded sphere_def, THEN sym] using `0\<in>s` by auto qed } note hom = this
3405 { fix x assume "x\<in>s"
3406 hence "x \<in> (\<lambda>x. norm x *\<^sub>R surf (pi x)) ` cball 0 1" proof(cases "x=0")
3407 case True show ?thesis unfolding image_iff True apply(rule_tac x=0 in bexI) by auto
3408 next let ?a = "inverse (norm (surf (pi x)))"
3409 case False hence invn:"inverse (norm x) \<noteq> 0" by auto
3410 from False have pix:"pi x\<in>sphere" using pi(1) by auto
3411 hence "pi (surf (pi x)) = pi x" apply(rule_tac surf(4)[rule_format]) by assumption
3412 hence **:"norm x *\<^sub>R (?a *\<^sub>R surf (pi x)) = x" apply(rule_tac scaleR_left_imp_eq[OF invn]) unfolding pi_def using invn by auto
3413 hence *:"?a * norm x > 0" and"?a > 0" "?a \<noteq> 0" using surf(5) `0\<notin>frontier s` apply -
3414 apply(rule_tac mult_pos_pos) using False[unfolded zero_less_norm_iff[THEN sym]] by auto
3415 have "norm (surf (pi x)) \<noteq> 0" using ** False by auto
3416 hence "norm x = norm ((?a * norm x) *\<^sub>R surf (pi x))"
3417 unfolding norm_scaleR abs_mult abs_norm_cancel abs_of_pos[OF `?a > 0`] by auto
3418 moreover have "pi x = pi ((inverse (norm (surf (pi x))) * norm x) *\<^sub>R surf (pi x))"
3419 unfolding pi(2)[OF *] surf(4)[rule_format, OF pix] ..
3420 moreover have "surf (pi x) \<in> frontier s" using surf(5) pix by auto
3421 hence "dist 0 (inverse (norm (surf (pi x))) *\<^sub>R x) \<le> 1" unfolding dist_norm
3422 using ** and * using front_smul[THEN bspec[where x="surf (pi x)"], THEN spec[where x="norm x * ?a"]]
3423 using False `x\<in>s` by(auto simp add:field_simps)
3424 ultimately show ?thesis unfolding image_iff apply(rule_tac x="inverse (norm (surf(pi x))) *\<^sub>R x" in bexI)
3425 apply(subst injpi[THEN sym]) unfolding abs_mult abs_norm_cancel abs_of_pos[OF `?a > 0`]
3426 unfolding pi(2)[OF `?a > 0`] by auto
3427 qed } note hom2 = this
3429 show ?thesis apply(subst homeomorphic_sym) apply(rule homeomorphic_compact[where f="\<lambda>x. norm x *\<^sub>R surf (pi x)"])
3430 apply(rule compact_cball) defer apply(rule set_eqI, rule, erule imageE, drule hom)
3431 prefer 4 apply(rule continuous_at_imp_continuous_on, rule) apply(rule_tac [3] hom2) proof-
3432 fix x::"'a" assume as:"x \<in> cball 0 1"
3433 thus "continuous (at x) (\<lambda>x. norm x *\<^sub>R surf (pi x))" proof(cases "x=0")
3434 case False thus ?thesis apply(rule_tac continuous_mul, rule_tac continuous_at_norm)
3435 using cont_surfpi unfolding continuous_on_eq_continuous_at[OF open_delete[OF open_UNIV]] o_def by auto
3436 next obtain B where B:"\<forall>x\<in>s. norm x \<le> B" using compact_imp_bounded[OF assms(1)] unfolding bounded_iff by auto
3437 hence "B > 0" using assms(2) unfolding subset_eq apply(erule_tac x="basis 0" in ballE) defer
3438 apply(erule_tac x="basis 0" in ballE)
3439 unfolding Ball_def mem_cball dist_norm using DIM_positive[where 'a='a]
3440 by(auto simp add:norm_basis[unfolded One_nat_def])
3441 case True show ?thesis unfolding True continuous_at Lim_at apply(rule,rule) apply(rule_tac x="e / B" in exI)
3442 apply(rule) apply(rule divide_pos_pos) prefer 3 apply(rule,rule,erule conjE)
3443 unfolding norm_zero scaleR_zero_left dist_norm diff_0_right norm_scaleR abs_norm_cancel proof-
3444 fix e and x::"'a" assume as:"norm x < e / B" "0 < norm x" "0<e"
3445 hence "surf (pi x) \<in> frontier s" using pi(1)[of x] unfolding surf(5)[THEN sym] by auto
3446 hence "norm (surf (pi x)) \<le> B" using B fs by auto
3447 hence "norm x * norm (surf (pi x)) \<le> norm x * B" using as(2) by auto
3448 also have "\<dots> < e / B * B" apply(rule mult_strict_right_mono) using as(1) `B>0` by auto
3449 also have "\<dots> = e" using `B>0` by auto
3450 finally show "norm x * norm (surf (pi x)) < e" by assumption
3451 qed(insert `B>0`, auto) qed
3452 next { fix x assume as:"surf (pi x) = 0"
3453 have "x = 0" proof(rule ccontr)
3454 assume "x\<noteq>0" hence "pi x \<in> sphere" using pi(1) by auto
3455 hence "surf (pi x) \<in> frontier s" using surf(5) by auto
3456 thus False using `0\<notin>frontier s` unfolding as by simp qed
3457 } note surf_0 = this
3458 show "inj_on (\<lambda>x. norm x *\<^sub>R surf (pi x)) (cball 0 1)" unfolding inj_on_def proof(rule,rule,rule)
3459 fix x y assume as:"x \<in> cball 0 1" "y \<in> cball 0 1" "norm x *\<^sub>R surf (pi x) = norm y *\<^sub>R surf (pi y)"
3460 thus "x=y" proof(cases "x=0 \<or> y=0")
3461 case True thus ?thesis using as by(auto elim: surf_0) next
3463 hence "pi (surf (pi x)) = pi (surf (pi y))" using as(3)
3464 using pi(2)[of "norm x" "surf (pi x)"] pi(2)[of "norm y" "surf (pi y)"] by auto
3465 moreover have "pi x \<in> sphere" "pi y \<in> sphere" using pi(1) False by auto
3466 ultimately have *:"pi x = pi y" using surf(4)[THEN bspec[where x="pi x"]] surf(4)[THEN bspec[where x="pi y"]] by auto
3467 moreover have "norm x = norm y" using as(3)[unfolded *] using False by(auto dest:surf_0)
3468 ultimately show ?thesis using injpi by auto qed qed
3471 lemma homeomorphic_convex_compact_lemma: fixes s::"('a::euclidean_space) set"
3472 assumes "convex s" "compact s" "cball 0 1 \<subseteq> s"
3473 shows "s homeomorphic (cball (0::'a) 1)"
3474 apply(rule starlike_compact_projective[OF assms(2-3)]) proof(rule,rule,rule,erule conjE)
3475 fix x u assume as:"x \<in> s" "0 \<le> u" "u < (1::real)"
3476 hence "u *\<^sub>R x \<in> interior s" unfolding interior_def mem_Collect_eq
3477 apply(rule_tac x="ball (u *\<^sub>R x) (1 - u)" in exI) apply(rule, rule open_ball)
3478 unfolding centre_in_ball apply rule defer apply(rule) unfolding mem_ball proof-
3479 fix y assume "dist (u *\<^sub>R x) y < 1 - u"
3480 hence "inverse (1 - u) *\<^sub>R (y - u *\<^sub>R x) \<in> s"
3481 using assms(3) apply(erule_tac subsetD) unfolding mem_cball dist_commute dist_norm
3482 unfolding group_add_class.diff_0 group_add_class.diff_0_right norm_minus_cancel norm_scaleR
3483 apply (rule mult_left_le_imp_le[of "1 - u"])
3484 unfolding mult_assoc[symmetric] using `u<1` by auto
3485 thus "y \<in> s" using assms(1)[unfolded convex_def, rule_format, of "inverse(1 - u) *\<^sub>R (y - u *\<^sub>R x)" x "1 - u" u]
3486 using as unfolding scaleR_scaleR by auto qed auto
3487 thus "u *\<^sub>R x \<in> s - frontier s" using frontier_def and interior_subset by auto qed
3489 lemma homeomorphic_convex_compact_cball: fixes e::real and s::"('a::euclidean_space) set"
3490 assumes "convex s" "compact s" "interior s \<noteq> {}" "0 < e"
3491 shows "s homeomorphic (cball (b::'a) e)"
3492 proof- obtain a where "a\<in>interior s" using assms(3) by auto
3493 then obtain d where "d>0" and d:"cball a d \<subseteq> s" unfolding mem_interior_cball by auto
3494 let ?d = "inverse d" and ?n = "0::'a"
3495 have "cball ?n 1 \<subseteq> (\<lambda>x. inverse d *\<^sub>R (x - a)) ` s"
3496 apply(rule, rule_tac x="d *\<^sub>R x + a" in image_eqI) defer
3497 apply(rule d[unfolded subset_eq, rule_format]) using `d>0` unfolding mem_cball dist_norm
3498 by(auto simp add: mult_right_le_one_le)
3499 hence "(\<lambda>x. inverse d *\<^sub>R (x - a)) ` s homeomorphic cball ?n 1"
3500 using homeomorphic_convex_compact_lemma[of "(\<lambda>x. ?d *\<^sub>R -a + ?d *\<^sub>R x) ` s", OF convex_affinity compact_affinity]
3501 using assms(1,2) by(auto simp add: uminus_add_conv_diff scaleR_right_diff_distrib)
3502 thus ?thesis apply(rule_tac homeomorphic_trans[OF _ homeomorphic_balls(2)[of 1 _ ?n]])
3503 apply(rule homeomorphic_trans[OF homeomorphic_affinity[of "?d" s "?d *\<^sub>R -a"]])
3504 using `d>0` `e>0` by(auto simp add: uminus_add_conv_diff scaleR_right_diff_distrib) qed
3506 lemma homeomorphic_convex_compact: fixes s::"('a::euclidean_space) set" and t::"('a) set"
3507 assumes "convex s" "compact s" "interior s \<noteq> {}"
3508 "convex t" "compact t" "interior t \<noteq> {}"
3509 shows "s homeomorphic t"
3510 using assms by(meson zero_less_one homeomorphic_trans homeomorphic_convex_compact_cball homeomorphic_sym)
3512 subsection {* Epigraphs of convex functions. *}
3514 definition "epigraph s (f::_ \<Rightarrow> real) = {xy. fst xy \<in> s \<and> f (fst xy) \<le> snd xy}"
3516 lemma mem_epigraph: "(x, y) \<in> epigraph s f \<longleftrightarrow> x \<in> s \<and> f x \<le> y" unfolding epigraph_def by auto
3518 (** This might break sooner or later. In fact it did already once. **)
3519 lemma convex_epigraph:
3520 "convex(epigraph s f) \<longleftrightarrow> convex_on s f \<and> convex s"
3521 unfolding convex_def convex_on_def
3522 unfolding Ball_def split_paired_All epigraph_def
3523 unfolding mem_Collect_eq fst_conv snd_conv fst_add snd_add fst_scaleR snd_scaleR Ball_def[symmetric]
3524 apply safe defer apply(erule_tac x=x in allE,erule_tac x="f x" in allE) apply safe
3525 apply(erule_tac x=xa in allE,erule_tac x="f xa" in allE) prefer 3
3526 apply(rule_tac y="u * f a + v * f aa" in order_trans) defer by(auto intro!:mult_left_mono add_mono)
3528 lemma convex_epigraphI:
3529 "convex_on s f \<Longrightarrow> convex s \<Longrightarrow> convex(epigraph s f)"
3530 unfolding convex_epigraph by auto
3532 lemma convex_epigraph_convex:
3533 "convex s \<Longrightarrow> convex_on s f \<longleftrightarrow> convex(epigraph s f)"
3534 by(simp add: convex_epigraph)
3536 subsection {* Use this to derive general bound property of convex function. *}
3540 shows "convex_on s f \<longleftrightarrow> (\<forall>k u x. (\<forall>i\<in>{1..k::nat}. 0 \<le> u i \<and> x i \<in> s) \<and> setsum u {1..k} = 1 \<longrightarrow>
3541 f (setsum (\<lambda>i. u i *\<^sub>R x i) {1..k} ) \<le> setsum (\<lambda>i. u i * f(x i)) {1..k} ) "
3542 unfolding convex_epigraph_convex[OF assms] convex epigraph_def Ball_def mem_Collect_eq
3543 unfolding fst_setsum snd_setsum fst_scaleR snd_scaleR
3545 apply (drule_tac x=k in spec)
3546 apply (drule_tac x=u in spec)
3547 apply (drule_tac x="\<lambda>i. (x i, f (x i))" in spec)
3549 using assms[unfolded convex] apply simp
3550 apply(rule_tac y="\<Sum>i = 1..k. u i * f (fst (x i))" in order_trans)
3551 defer apply(rule setsum_mono) apply(erule_tac x=i in allE) unfolding real_scaleR_def
3552 apply(rule mult_left_mono)using assms[unfolded convex] by auto
3555 subsection {* Convexity of general and special intervals. *}
3557 lemma convexI: (* TODO: move to Library/Convex.thy *)
3558 assumes "\<And>x y u v. \<lbrakk>x \<in> s; y \<in> s; 0 \<le> u; 0 \<le> v; u + v = 1\<rbrakk> \<Longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s"
3560 using assms unfolding convex_def by fast
3562 lemma is_interval_convex:
3563 fixes s :: "('a::euclidean_space) set"
3564 assumes "is_interval s" shows "convex s"
3565 proof (rule convexI)
3566 fix x y u v assume as:"x \<in> s" "y \<in> s" "0 \<le> u" "0 \<le> v" "u + v = (1::real)"
3567 hence *:"u = 1 - v" "1 - v \<ge> 0" and **:"v = 1 - u" "1 - u \<ge> 0" by auto
3568 { fix a b assume "\<not> b \<le> u * a + v * b"
3569 hence "u * a < (1 - v) * b" unfolding not_le using as(4) by(auto simp add: field_simps)
3570 hence "a < b" unfolding * using as(4) *(2) apply(rule_tac mult_left_less_imp_less[of "1 - v"]) by(auto simp add: field_simps)
3571 hence "a \<le> u * a + v * b" unfolding * using as(4) by (auto simp add: field_simps intro!:mult_right_mono)
3573 { fix a b assume "\<not> u * a + v * b \<le> a"
3574 hence "v * b > (1 - u) * a" unfolding not_le using as(4) by(auto simp add: field_simps)
3575 hence "a < b" unfolding * using as(4) apply(rule_tac mult_left_less_imp_less) by(auto simp add: field_simps)
3576 hence "u * a + v * b \<le> b" unfolding ** using **(2) as(3) by(auto simp add: field_simps intro!:mult_right_mono) }
3577 ultimately show "u *\<^sub>R x + v *\<^sub>R y \<in> s" apply- apply(rule assms[unfolded is_interval_def, rule_format, OF as(1,2)])
3578 using as(3-) DIM_positive[where 'a='a] by(auto simp add:euclidean_simps) qed
3580 lemma is_interval_connected:
3581 fixes s :: "('a::euclidean_space) set"
3582 shows "is_interval s \<Longrightarrow> connected s"
3583 using is_interval_convex convex_connected by auto
3585 lemma convex_interval: "convex {a .. b}" "convex {a<..<b::'a::ordered_euclidean_space}"
3586 apply(rule_tac[!] is_interval_convex) using is_interval_interval by auto
3588 (* FIXME: rewrite these lemmas without using vec1
3589 subsection {* On @{text "real^1"}, @{text "is_interval"}, @{text "convex"} and @{text "connected"} are all equivalent. *}
3591 lemma is_interval_1:
3592 "is_interval s \<longleftrightarrow> (\<forall>a\<in>s. \<forall>b\<in>s. \<forall> x. dest_vec1 a \<le> dest_vec1 x \<and> dest_vec1 x \<le> dest_vec1 b \<longrightarrow> x \<in> s)"
3593 unfolding is_interval_def forall_1 by auto
3595 lemma is_interval_connected_1: "is_interval s \<longleftrightarrow> connected (s::(real^1) set)"
3596 apply(rule, rule is_interval_connected, assumption) unfolding is_interval_1
3597 apply(rule,rule,rule,rule,erule conjE,rule ccontr) proof-
3598 fix a b x assume as:"connected s" "a \<in> s" "b \<in> s" "dest_vec1 a \<le> dest_vec1 x" "dest_vec1 x \<le> dest_vec1 b" "x\<notin>s"
3599 hence *:"dest_vec1 a < dest_vec1 x" "dest_vec1 x < dest_vec1 b" apply(rule_tac [!] ccontr) unfolding not_less by auto
3600 let ?halfl = "{z. inner (basis 1) z < dest_vec1 x} " and ?halfr = "{z. inner (basis 1) z > dest_vec1 x} "
3601 { fix y assume "y \<in> s" have "y \<in> ?halfr \<union> ?halfl" apply(rule ccontr)
3602 using as(6) `y\<in>s` by (auto simp add: inner_vector_def) }
3603 moreover have "a\<in>?halfl" "b\<in>?halfr" using * by (auto simp add: inner_vector_def)
3604 hence "?halfl \<inter> s \<noteq> {}" "?halfr \<inter> s \<noteq> {}" using as(2-3) by auto
3605 ultimately show False apply(rule_tac notE[OF as(1)[unfolded connected_def]])
3606 apply(rule_tac x="?halfl" in exI, rule_tac x="?halfr" in exI)
3607 apply(rule, rule open_halfspace_lt, rule, rule open_halfspace_gt)
3608 by(auto simp add: field_simps) qed
3610 lemma is_interval_convex_1:
3611 "is_interval s \<longleftrightarrow> convex (s::(real^1) set)"
3612 by(metis is_interval_convex convex_connected is_interval_connected_1)
3614 lemma convex_connected_1:
3615 "connected s \<longleftrightarrow> convex (s::(real^1) set)"
3616 by(metis is_interval_convex convex_connected is_interval_connected_1)
3618 subsection {* Another intermediate value theorem formulation. *}
3620 lemma ivt_increasing_component_on_1: fixes f::"real \<Rightarrow> 'a::euclidean_space"
3621 assumes "a \<le> b" "continuous_on {a .. b} f" "(f a)$$k \<le> y" "y \<le> (f b)$$k"
3622 shows "\<exists>x\<in>{a..b}. (f x)$$k = y"
3623 proof- have "f a \<in> f ` {a..b}" "f b \<in> f ` {a..b}" apply(rule_tac[!] imageI)
3624 using assms(1) by auto
3625 thus ?thesis using connected_ivt_component[of "f ` {a..b}" "f a" "f b" k y]
3626 using connected_continuous_image[OF assms(2) convex_connected[OF convex_real_interval(5)]]
3627 using assms by(auto intro!: imageI) qed
3629 lemma ivt_increasing_component_1: fixes f::"real \<Rightarrow> 'a::euclidean_space"
3630 shows "a \<le> b \<Longrightarrow> \<forall>x\<in>{a .. b}. continuous (at x) f
3631 \<Longrightarrow> f a$$k \<le> y \<Longrightarrow> y \<le> f b$$k \<Longrightarrow> \<exists>x\<in>{a..b}. (f x)$$k = y"
3632 by(rule ivt_increasing_component_on_1)
3633 (auto simp add: continuous_at_imp_continuous_on)
3635 lemma ivt_decreasing_component_on_1: fixes f::"real \<Rightarrow> 'a::euclidean_space"
3636 assumes "a \<le> b" "continuous_on {a .. b} f" "(f b)$$k \<le> y" "y \<le> (f a)$$k"
3637 shows "\<exists>x\<in>{a..b}. (f x)$$k = y"
3638 apply(subst neg_equal_iff_equal[THEN sym])
3639 using ivt_increasing_component_on_1[of a b "\<lambda>x. - f x" k "- y"] using assms using continuous_on_neg
3640 by (auto simp add:euclidean_simps)
3642 lemma ivt_decreasing_component_1: fixes f::"real \<Rightarrow> 'a::euclidean_space"
3643 shows "a \<le> b \<Longrightarrow> \<forall>x\<in>{a .. b}. continuous (at x) f
3644 \<Longrightarrow> f b$$k \<le> y \<Longrightarrow> y \<le> f a$$k \<Longrightarrow> \<exists>x\<in>{a..b}. (f x)$$k = y"
3645 by(rule ivt_decreasing_component_on_1)
3646 (auto simp: continuous_at_imp_continuous_on)
3648 subsection {* A bound within a convex hull, and so an interval. *}
3650 lemma convex_on_convex_hull_bound:
3651 assumes "convex_on (convex hull s) f" "\<forall>x\<in>s. f x \<le> b"
3652 shows "\<forall>x\<in> convex hull s. f x \<le> b" proof
3653 fix x assume "x\<in>convex hull s"
3654 then obtain k u v where obt:"\<forall>i\<in>{1..k::nat}. 0 \<le> u i \<and> v i \<in> s" "setsum u {1..k} = 1" "(\<Sum>i = 1..k. u i *\<^sub>R v i) = x"
3655 unfolding convex_hull_indexed mem_Collect_eq by auto
3656 have "(\<Sum>i = 1..k. u i * f (v i)) \<le> b" using setsum_mono[of "{1..k}" "\<lambda>i. u i * f (v i)" "\<lambda>i. u i * b"]
3657 unfolding setsum_left_distrib[THEN sym] obt(2) mult_1 apply(drule_tac meta_mp) apply(rule mult_left_mono)
3658 using assms(2) obt(1) by auto
3659 thus "f x \<le> b" using assms(1)[unfolded convex_on[OF convex_convex_hull], rule_format, of k u v]
3660 unfolding obt(2-3) using obt(1) and hull_subset[unfolded subset_eq, rule_format, of _ s] by auto qed
3662 lemma unit_interval_convex_hull:
3663 "{0::'a::ordered_euclidean_space .. (\<chi>\<chi> i. 1)} = convex hull {x. \<forall>i<DIM('a). (x$$i = 0) \<or> (x$$i = 1)}"
3664 (is "?int = convex hull ?points")
3665 proof- have 01:"{0,(\<chi>\<chi> i. 1)} \<subseteq> convex hull ?points" apply rule apply(rule_tac hull_subset[unfolded subset_eq, rule_format]) by auto
3666 { fix n x assume "x\<in>{0::'a::ordered_euclidean_space .. \<chi>\<chi> i. 1}" "n \<le> DIM('a)" "card {i. i<DIM('a) \<and> x$$i \<noteq> 0} \<le> n"
3667 hence "x\<in>convex hull ?points" proof(induct n arbitrary: x)
3668 case 0 hence "x = 0" apply(subst euclidean_eq) apply rule by auto
3669 thus "x\<in>convex hull ?points" using 01 by auto
3671 case (Suc n) show "x\<in>convex hull ?points" proof(cases "{i. i<DIM('a) \<and> x$$i \<noteq> 0} = {}")
3672 case True hence "x = 0" apply(subst euclidean_eq) by auto
3673 thus "x\<in>convex hull ?points" using 01 by auto
3675 case False def xi \<equiv> "Min ((\<lambda>i. x$$i) ` {i. i<DIM('a) \<and> x$$i \<noteq> 0})"
3676 have "xi \<in> (\<lambda>i. x$$i) ` {i. i<DIM('a) \<and> x$$i \<noteq> 0}" unfolding xi_def apply(rule Min_in) using False by auto
3677 then obtain i where i':"x$$i = xi" "x$$i \<noteq> 0" "i<DIM('a)" by auto
3678 have i:"\<And>j. j<DIM('a) \<Longrightarrow> x$$j > 0 \<Longrightarrow> x$$i \<le> x$$j"
3679 unfolding i'(1) xi_def apply(rule_tac Min_le) unfolding image_iff
3680 defer apply(rule_tac x=j in bexI) using i' by auto
3681 have i01:"x$$i \<le> 1" "x$$i > 0" using Suc(2)[unfolded mem_interval,rule_format,of i]
3682 using i'(2-) `x$$i \<noteq> 0` by auto
3683 show ?thesis proof(cases "x$$i=1")
3684 case True have "\<forall>j\<in>{i. i<DIM('a) \<and> x$$i \<noteq> 0}. x$$j = 1" apply(rule, rule ccontr) unfolding mem_Collect_eq
3685 proof(erule conjE) fix j assume as:"x $$ j \<noteq> 0" "x $$ j \<noteq> 1" "j<DIM('a)"
3686 hence j:"x$$j \<in> {0<..<1}" using Suc(2) by(auto simp add: eucl_le[where 'a='a] elim!:allE[where x=j])
3687 hence "x$$j \<in> op $$ x ` {i. i<DIM('a) \<and> x $$ i \<noteq> 0}" using as(3) by auto
3688 hence "x$$j \<ge> x$$i" unfolding i'(1) xi_def apply(rule_tac Min_le) by auto
3689 thus False using True Suc(2) j by(auto simp add: elim!:ballE[where x=j]) qed
3690 thus "x\<in>convex hull ?points" apply(rule_tac hull_subset[unfolded subset_eq, rule_format])
3692 next let ?y = "\<lambda>j. if x$$j = 0 then 0 else (x$$j - x$$i) / (1 - x$$i)"
3693 case False hence *:"x = x$$i *\<^sub>R (\<chi>\<chi> j. if x$$j = 0 then 0 else 1) + (1 - x$$i) *\<^sub>R (\<chi>\<chi> j. ?y j)"
3694 apply(subst euclidean_eq) by(auto simp add: field_simps euclidean_simps)
3695 { fix j assume j:"j<DIM('a)"
3696 have "x$$j \<noteq> 0 \<Longrightarrow> 0 \<le> (x $$ j - x $$ i) / (1 - x $$ i)" "(x $$ j - x $$ i) / (1 - x $$ i) \<le> 1"
3697 apply(rule_tac divide_nonneg_pos) using i(1)[of j] using False i01
3698 using Suc(2)[unfolded mem_interval, rule_format, of j] using j
3699 by(auto simp add:field_simps euclidean_simps)
3700 hence "0 \<le> ?y j \<and> ?y j \<le> 1" by auto }
3701 moreover have "i\<in>{j. j<DIM('a) \<and> x$$j \<noteq> 0} - {j. j<DIM('a) \<and> ((\<chi>\<chi> j. ?y j)::'a) $$ j \<noteq> 0}"
3702 using i01 using i'(3) by auto
3703 hence "{j. j<DIM('a) \<and> x$$j \<noteq> 0} \<noteq> {j. j<DIM('a) \<and> ((\<chi>\<chi> j. ?y j)::'a) $$ j \<noteq> 0}" using i'(3) by blast
3704 hence **:"{j. j<DIM('a) \<and> ((\<chi>\<chi> j. ?y j)::'a) $$ j \<noteq> 0} \<subset> {j. j<DIM('a) \<and> x$$j \<noteq> 0}" apply - apply rule
3705 by( auto simp add:euclidean_simps)
3706 have "card {j. j<DIM('a) \<and> ((\<chi>\<chi> j. ?y j)::'a) $$ j \<noteq> 0} \<le> n"
3707 using less_le_trans[OF psubset_card_mono[OF _ **] Suc(4)] by auto
3708 ultimately show ?thesis apply(subst *) apply(rule convex_convex_hull[unfolded convex_def, rule_format])
3709 apply(rule_tac hull_subset[unfolded subset_eq, rule_format]) defer apply(rule Suc(1))
3710 unfolding mem_interval using i01 Suc(3) by auto
3711 qed qed qed } note * = this
3712 have **:"DIM('a) = card {..<DIM('a)}" by auto
3713 show ?thesis apply rule defer apply(rule hull_minimal) unfolding subset_eq prefer 3 apply rule
3714 apply(rule_tac n2="DIM('a)" in *) prefer 3 apply(subst(2) **)
3715 apply(rule card_mono) using 01 and convex_interval(1) prefer 5 apply - apply rule
3716 unfolding mem_interval apply rule unfolding mem_Collect_eq apply(erule_tac x=i in allE)
3717 by(auto simp add: mem_def[of _ convex]) qed
3719 subsection {* And this is a finite set of vertices. *}
3721 lemma unit_cube_convex_hull: obtains s where "finite s" "{0 .. (\<chi>\<chi> i. 1)::'a::ordered_euclidean_space} = convex hull s"
3722 apply(rule that[of "{x::'a. \<forall>i<DIM('a). x$$i=0 \<or> x$$i=1}"])
3723 apply(rule finite_subset[of _ "(\<lambda>s. (\<chi>\<chi> i. if i\<in>s then 1::real else 0)::'a) ` Pow {..<DIM('a)}"])
3724 prefer 3 apply(rule unit_interval_convex_hull) apply rule unfolding mem_Collect_eq proof-
3725 fix x::"'a" assume as:"\<forall>i<DIM('a). x $$ i = 0 \<or> x $$ i = 1"
3726 show "x \<in> (\<lambda>s. \<chi>\<chi> i. if i \<in> s then 1 else 0) ` Pow {..<DIM('a)}"
3727 apply(rule image_eqI[where x="{i. i<DIM('a) \<and> x$$i = 1}"])
3728 using as apply(subst euclidean_eq) by auto qed auto
3730 subsection {* Hence any cube (could do any nonempty interval). *}
3732 lemma cube_convex_hull:
3733 assumes "0 < d" obtains s::"('a::ordered_euclidean_space) set" where
3734 "finite s" "{x - (\<chi>\<chi> i. d) .. x + (\<chi>\<chi> i. d)} = convex hull s" proof-
3735 let ?d = "(\<chi>\<chi> i. d)::'a"
3736 have *:"{x - ?d .. x + ?d} = (\<lambda>y. x - ?d + (2 * d) *\<^sub>R y) ` {0 .. \<chi>\<chi> i. 1}" apply(rule set_eqI, rule)
3737 unfolding image_iff defer apply(erule bexE) proof-
3738 fix y assume as:"y\<in>{x - ?d .. x + ?d}"
3739 { fix i assume i:"i<DIM('a)" have "x $$ i \<le> d + y $$ i" "y $$ i \<le> d + x $$ i"
3740 using as[unfolded mem_interval, THEN spec[where x=i]] i
3741 by(auto simp add:euclidean_simps)
3742 hence "1 \<ge> inverse d * (x $$ i - y $$ i)" "1 \<ge> inverse d * (y $$ i - x $$ i)"
3743 apply(rule_tac[!] mult_left_le_imp_le[OF _ assms]) unfolding mult_assoc[THEN sym]
3744 using assms by(auto simp add: field_simps)
3745 hence "inverse d * (x $$ i * 2) \<le> 2 + inverse d * (y $$ i * 2)"
3746 "inverse d * (y $$ i * 2) \<le> 2 + inverse d * (x $$ i * 2)" by(auto simp add:field_simps) }
3747 hence "inverse (2 * d) *\<^sub>R (y - (x - ?d)) \<in> {0..\<chi>\<chi> i.1}" unfolding mem_interval using assms
3748 by(auto simp add: euclidean_simps field_simps)
3749 thus "\<exists>z\<in>{0..\<chi>\<chi> i.1}. y = x - ?d + (2 * d) *\<^sub>R z" apply- apply(rule_tac x="inverse (2 * d) *\<^sub>R (y - (x - ?d))" in bexI)
3752 fix y z assume as:"z\<in>{0..\<chi>\<chi> i.1}" "y = x - ?d + (2*d) *\<^sub>R z"
3753 have "\<And>i. i<DIM('a) \<Longrightarrow> 0 \<le> d * z $$ i \<and> d * z $$ i \<le> d"
3754 using assms as(1)[unfolded mem_interval] apply(erule_tac x=i in allE)
3755 apply rule apply(rule mult_nonneg_nonneg) prefer 3 apply(rule mult_right_le_one_le)
3757 thus "y \<in> {x - ?d..x + ?d}" unfolding as(2) mem_interval apply- apply rule using as(1)[unfolded mem_interval]
3758 apply(erule_tac x=i in allE) using assms by(auto simp add: euclidean_simps) qed
3759 obtain s where "finite s" "{0::'a..\<chi>\<chi> i.1} = convex hull s" using unit_cube_convex_hull by auto
3760 thus ?thesis apply(rule_tac that[of "(\<lambda>y. x - ?d + (2 * d) *\<^sub>R y)` s"]) unfolding * and convex_hull_affinity by auto qed
3762 subsection {* Bounded convex function on open set is continuous. *}
3764 lemma convex_on_bounded_continuous:
3765 fixes s :: "('a::real_normed_vector) set"
3766 assumes "open s" "convex_on s f" "\<forall>x\<in>s. abs(f x) \<le> b"
3767 shows "continuous_on s f"
3768 apply(rule continuous_at_imp_continuous_on) unfolding continuous_at_real_range proof(rule,rule,rule)
3769 fix x e assume "x\<in>s" "(0::real) < e"
3770 def B \<equiv> "abs b + 1"
3771 have B:"0 < B" "\<And>x. x\<in>s \<Longrightarrow> abs (f x) \<le> B"
3772 unfolding B_def defer apply(drule assms(3)[rule_format]) by auto
3773 obtain k where "k>0"and k:"cball x k \<subseteq> s" using assms(1)[unfolded open_contains_cball, THEN bspec[where x=x]] using `x\<in>s` by auto
3774 show "\<exists>d>0. \<forall>x'. norm (x' - x) < d \<longrightarrow> \<bar>f x' - f x\<bar> < e"
3775 apply(rule_tac x="min (k / 2) (e / (2 * B) * k)" in exI) apply rule defer proof(rule,rule)
3776 fix y assume as:"norm (y - x) < min (k / 2) (e / (2 * B) * k)"
3777 show "\<bar>f y - f x\<bar> < e" proof(cases "y=x")
3778 case False def t \<equiv> "k / norm (y - x)"
3779 have "2 < t" "0<t" unfolding t_def using as False and `k>0` by(auto simp add:field_simps)
3780 have "y\<in>s" apply(rule k[unfolded subset_eq,rule_format]) unfolding mem_cball dist_norm
3781 apply(rule order_trans[of _ "2 * norm (x - y)"]) using as by(auto simp add: field_simps norm_minus_commute)
3782 { def w \<equiv> "x + t *\<^sub>R (y - x)"
3783 have "w\<in>s" unfolding w_def apply(rule k[unfolded subset_eq,rule_format]) unfolding mem_cball dist_norm
3784 unfolding t_def using `k>0` by auto
3785 have "(1 / t) *\<^sub>R x + - x + ((t - 1) / t) *\<^sub>R x = (1 / t - 1 + (t - 1) / t) *\<^sub>R x" by (auto simp add: algebra_simps)
3786 also have "\<dots> = 0" using `t>0` by(auto simp add:field_simps)
3787 finally have w:"(1 / t) *\<^sub>R w + ((t - 1) / t) *\<^sub>R x = y" unfolding w_def using False and `t>0` by (auto simp add: algebra_simps)
3788 have "2 * B < e * t" unfolding t_def using `0<e` `0<k` `B>0` and as and False by (auto simp add:field_simps)
3789 hence "(f w - f x) / t < e"
3790 using B(2)[OF `w\<in>s`] and B(2)[OF `x\<in>s`] using `t>0` by(auto simp add:field_simps)
3791 hence th1:"f y - f x < e" apply- apply(rule le_less_trans) defer apply assumption
3792 using assms(2)[unfolded convex_on_def,rule_format,of w x "1/t" "(t - 1)/t", unfolded w]
3793 using `0<t` `2<t` and `x\<in>s` `w\<in>s` by(auto simp add:field_simps) }
3795 { def w \<equiv> "x - t *\<^sub>R (y - x)"
3796 have "w\<in>s" unfolding w_def apply(rule k[unfolded subset_eq,rule_format]) unfolding mem_cball dist_norm
3797 unfolding t_def using `k>0` by auto
3798 have "(1 / (1 + t)) *\<^sub>R x + (t / (1 + t)) *\<^sub>R x = (1 / (1 + t) + t / (1 + t)) *\<^sub>R x" by (auto simp add: algebra_simps)
3799 also have "\<dots>=x" using `t>0` by (auto simp add:field_simps)
3800 finally have w:"(1 / (1+t)) *\<^sub>R w + (t / (1 + t)) *\<^sub>R y = x" unfolding w_def using False and `t>0` by (auto simp add: algebra_simps)
3801 have "2 * B < e * t" unfolding t_def using `0<e` `0<k` `B>0` and as and False by (auto simp add:field_simps)
3802 hence *:"(f w - f y) / t < e" using B(2)[OF `w\<in>s`] and B(2)[OF `y\<in>s`] using `t>0` by(auto simp add:field_simps)
3803 have "f x \<le> 1 / (1 + t) * f w + (t / (1 + t)) * f y"
3804 using assms(2)[unfolded convex_on_def,rule_format,of w y "1/(1+t)" "t / (1+t)",unfolded w]
3805 using `0<t` `2<t` and `y\<in>s` `w\<in>s` by (auto simp add:field_simps)
3806 also have "\<dots> = (f w + t * f y) / (1 + t)" using `t>0` unfolding divide_inverse by (auto simp add:field_simps)
3807 also have "\<dots> < e + f y" using `t>0` * `e>0` by(auto simp add:field_simps)
3808 finally have "f x - f y < e" by auto }
3809 ultimately show ?thesis by auto
3810 qed(insert `0<e`, auto)
3811 qed(insert `0<e` `0<k` `0<B`, auto simp add:field_simps intro!:mult_pos_pos) qed
3813 subsection {* Upper bound on a ball implies upper and lower bounds. *}
3815 lemma convex_bounds_lemma:
3816 fixes x :: "'a::real_normed_vector"
3817 assumes "convex_on (cball x e) f" "\<forall>y \<in> cball x e. f y \<le> b"
3818 shows "\<forall>y \<in> cball x e. abs(f y) \<le> b + 2 * abs(f x)"
3819 apply(rule) proof(cases "0 \<le> e") case True
3820 fix y assume y:"y\<in>cball x e" def z \<equiv> "2 *\<^sub>R x - y"
3821 have *:"x - (2 *\<^sub>R x - y) = y - x" by (simp add: scaleR_2)
3822 have z:"z\<in>cball x e" using y unfolding z_def mem_cball dist_norm * by(auto simp add: norm_minus_commute)
3823 have "(1 / 2) *\<^sub>R y + (1 / 2) *\<^sub>R z = x" unfolding z_def by (auto simp add: algebra_simps)
3824 thus "\<bar>f y\<bar> \<le> b + 2 * \<bar>f x\<bar>" using assms(1)[unfolded convex_on_def,rule_format, OF y z, of "1/2" "1/2"]
3825 using assms(2)[rule_format,OF y] assms(2)[rule_format,OF z] by(auto simp add:field_simps)
3826 next case False fix y assume "y\<in>cball x e"
3827 hence "dist x y < 0" using False unfolding mem_cball not_le by (auto simp del: dist_not_less_zero)
3828 thus "\<bar>f y\<bar> \<le> b + 2 * \<bar>f x\<bar>" using zero_le_dist[of x y] by auto qed
3830 subsection {* Hence a convex function on an open set is continuous. *}
3832 lemma convex_on_continuous:
3833 assumes "open (s::('a::ordered_euclidean_space) set)" "convex_on s f"
3834 (* FIXME: generalize to euclidean_space *)
3835 shows "continuous_on s f"
3836 unfolding continuous_on_eq_continuous_at[OF assms(1)] proof
3837 note dimge1 = DIM_positive[where 'a='a]
3838 fix x assume "x\<in>s"
3839 then obtain e where e:"cball x e \<subseteq> s" "e>0" using assms(1) unfolding open_contains_cball by auto
3840 def d \<equiv> "e / real DIM('a)"
3841 have "0 < d" unfolding d_def using `e>0` dimge1 by(rule_tac divide_pos_pos, auto)
3842 let ?d = "(\<chi>\<chi> i. d)::'a"
3843 obtain c where c:"finite c" "{x - ?d..x + ?d} = convex hull c" using cube_convex_hull[OF `d>0`, of x] by auto
3844 have "x\<in>{x - ?d..x + ?d}" using `d>0` unfolding mem_interval by(auto simp add:euclidean_simps)
3845 hence "c\<noteq>{}" using c by auto
3846 def k \<equiv> "Max (f ` c)"
3847 have "convex_on {x - ?d..x + ?d} f" apply(rule convex_on_subset[OF assms(2)])
3848 apply(rule subset_trans[OF _ e(1)]) unfolding subset_eq mem_cball proof
3849 fix z assume z:"z\<in>{x - ?d..x + ?d}"
3850 have e:"e = setsum (\<lambda>i. d) {..<DIM('a)}" unfolding setsum_constant d_def using dimge1
3851 unfolding real_eq_of_nat by auto
3852 show "dist x z \<le> e" unfolding dist_norm e apply(rule_tac order_trans[OF norm_le_l1], rule setsum_mono)
3853 using z[unfolded mem_interval] apply(erule_tac x=i in allE) by(auto simp add:euclidean_simps) qed
3854 hence k:"\<forall>y\<in>{x - ?d..x + ?d}. f y \<le> k" unfolding c(2) apply(rule_tac convex_on_convex_hull_bound) apply assumption
3855 unfolding k_def apply(rule, rule Max_ge) using c(1) by auto
3856 have "d \<le> e" unfolding d_def apply(rule mult_imp_div_pos_le) using `e>0` dimge1 unfolding mult_le_cancel_left1 by auto
3857 hence dsube:"cball x d \<subseteq> cball x e" unfolding subset_eq Ball_def mem_cball by auto
3858 have conv:"convex_on (cball x d) f" apply(rule convex_on_subset, rule convex_on_subset[OF assms(2)]) apply(rule e(1)) using dsube by auto
3859 hence "\<forall>y\<in>cball x d. abs (f y) \<le> k + 2 * abs (f x)" apply(rule_tac convex_bounds_lemma) apply assumption proof
3860 fix y assume y:"y\<in>cball x d"
3861 { fix i assume "i<DIM('a)" hence "x $$ i - d \<le> y $$ i" "y $$ i \<le> x $$ i + d"
3862 using order_trans[OF component_le_norm y[unfolded mem_cball dist_norm], of i] by(auto simp add:euclidean_simps) }
3863 thus "f y \<le> k" apply(rule_tac k[rule_format]) unfolding mem_cball mem_interval dist_norm
3864 by(auto simp add:euclidean_simps) qed
3865 hence "continuous_on (ball x d) f" apply(rule_tac convex_on_bounded_continuous)
3866 apply(rule open_ball, rule convex_on_subset[OF conv], rule ball_subset_cball)
3869 thus "continuous (at x) f" unfolding continuous_on_eq_continuous_at[OF open_ball]
3873 subsection {* Line segments, Starlike Sets, etc.*}
3875 (* Use the same overloading tricks as for intervals, so that
3876 segment[a,b] is closed and segment(a,b) is open relative to affine hull. *)
3879 midpoint :: "'a::real_vector \<Rightarrow> 'a \<Rightarrow> 'a" where
3880 "midpoint a b = (inverse (2::real)) *\<^sub>R (a + b)"
3883 open_segment :: "'a::real_vector \<Rightarrow> 'a \<Rightarrow> 'a set" where
3884 "open_segment a b = {(1 - u) *\<^sub>R a + u *\<^sub>R b | u::real. 0 < u \<and> u < 1}"
3887 closed_segment :: "'a::real_vector \<Rightarrow> 'a \<Rightarrow> 'a set" where
3888 "closed_segment a b = {(1 - u) *\<^sub>R a + u *\<^sub>R b | u::real. 0 \<le> u \<and> u \<le> 1}"
3890 definition "between = (\<lambda> (a,b). closed_segment a b)"
3892 lemmas segment = open_segment_def closed_segment_def
3894 definition "starlike s \<longleftrightarrow> (\<exists>a\<in>s. \<forall>x\<in>s. closed_segment a x \<subseteq> s)"
3896 lemma midpoint_refl: "midpoint x x = x"
3897 unfolding midpoint_def unfolding scaleR_right_distrib unfolding scaleR_left_distrib[THEN sym] by auto
3899 lemma midpoint_sym: "midpoint a b = midpoint b a" unfolding midpoint_def by (auto simp add: scaleR_right_distrib)
3901 lemma midpoint_eq_iff: "midpoint a b = c \<longleftrightarrow> a + b = c + c"
3903 have "midpoint a b = c \<longleftrightarrow> scaleR 2 (midpoint a b) = scaleR 2 c"
3906 unfolding midpoint_def scaleR_2 [symmetric] by simp
3909 lemma dist_midpoint:
3910 fixes a b :: "'a::real_normed_vector" shows
3911 "dist a (midpoint a b) = (dist a b) / 2" (is ?t1)
3912 "dist b (midpoint a b) = (dist a b) / 2" (is ?t2)
3913 "dist (midpoint a b) a = (dist a b) / 2" (is ?t3)
3914 "dist (midpoint a b) b = (dist a b) / 2" (is ?t4)
3916 have *: "\<And>x y::'a. 2 *\<^sub>R x = - y \<Longrightarrow> norm x = (norm y) / 2" unfolding equation_minus_iff by auto
3917 have **:"\<And>x y::'a. 2 *\<^sub>R x = y \<Longrightarrow> norm x = (norm y) / 2" by auto
3918 note scaleR_right_distrib [simp]
3919 show ?t1 unfolding midpoint_def dist_norm apply (rule **)
3920 by (simp add: scaleR_right_diff_distrib, simp add: scaleR_2)
3921 show ?t2 unfolding midpoint_def dist_norm apply (rule *)
3922 by (simp add: scaleR_right_diff_distrib, simp add: scaleR_2)
3923 show ?t3 unfolding midpoint_def dist_norm apply (rule *)
3924 by (simp add: scaleR_right_diff_distrib, simp add: scaleR_2)
3925 show ?t4 unfolding midpoint_def dist_norm apply (rule **)
3926 by (simp add: scaleR_right_diff_distrib, simp add: scaleR_2)
3929 lemma midpoint_eq_endpoint:
3930 "midpoint a b = a \<longleftrightarrow> a = b"
3931 "midpoint a b = b \<longleftrightarrow> a = b"
3932 unfolding midpoint_eq_iff by auto
3934 lemma convex_contains_segment:
3935 "convex s \<longleftrightarrow> (\<forall>a\<in>s. \<forall>b\<in>s. closed_segment a b \<subseteq> s)"
3936 unfolding convex_alt closed_segment_def by auto
3938 lemma convex_imp_starlike:
3939 "convex s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> starlike s"
3940 unfolding convex_contains_segment starlike_def by auto
3942 lemma segment_convex_hull:
3943 "closed_segment a b = convex hull {a,b}" proof-
3944 have *:"\<And>x. {x} \<noteq> {}" by auto
3945 have **:"\<And>u v. u + v = 1 \<longleftrightarrow> u = 1 - (v::real)" by auto
3946 show ?thesis unfolding segment convex_hull_insert[OF *] convex_hull_singleton apply(rule set_eqI)
3947 unfolding mem_Collect_eq apply(rule,erule exE)
3948 apply(rule_tac x="1 - u" in exI) apply rule defer apply(rule_tac x=u in exI) defer
3949 apply(erule exE, (erule conjE)?)+ apply(rule_tac x="1 - u" in exI) unfolding ** by auto qed
3951 lemma convex_segment: "convex (closed_segment a b)"
3952 unfolding segment_convex_hull by(rule convex_convex_hull)
3954 lemma ends_in_segment: "a \<in> closed_segment a b" "b \<in> closed_segment a b"
3955 unfolding segment_convex_hull apply(rule_tac[!] hull_subset[unfolded subset_eq, rule_format]) by auto
3957 lemma segment_furthest_le:
3958 fixes a b x y :: "'a::euclidean_space"
3959 assumes "x \<in> closed_segment a b" shows "norm(y - x) \<le> norm(y - a) \<or> norm(y - x) \<le> norm(y - b)" proof-
3960 obtain z where "z\<in>{a, b}" "norm (x - y) \<le> norm (z - y)" using simplex_furthest_le[of "{a, b}" y]
3961 using assms[unfolded segment_convex_hull] by auto
3962 thus ?thesis by(auto simp add:norm_minus_commute) qed
3964 lemma segment_bound:
3965 fixes x a b :: "'a::euclidean_space"
3966 assumes "x \<in> closed_segment a b"
3967 shows "norm(x - a) \<le> norm(b - a)" "norm(x - b) \<le> norm(b - a)"
3968 using segment_furthest_le[OF assms, of a]
3969 using segment_furthest_le[OF assms, of b]
3970 by (auto simp add:norm_minus_commute)
3972 lemma segment_refl:"closed_segment a a = {a}" unfolding segment by (auto simp add: algebra_simps)
3974 lemma between_mem_segment: "between (a,b) x \<longleftrightarrow> x \<in> closed_segment a b"
3975 unfolding between_def mem_def by auto
3977 lemma between:"between (a,b) (x::'a::euclidean_space) \<longleftrightarrow> dist a b = (dist a x) + (dist x b)"
3978 proof(cases "a = b")
3979 case True thus ?thesis unfolding between_def split_conv mem_def[of x, symmetric]
3980 by(auto simp add:segment_refl dist_commute) next
3981 case False hence Fal:"norm (a - b) \<noteq> 0" and Fal2: "norm (a - b) > 0" by auto
3982 have *:"\<And>u. a - ((1 - u) *\<^sub>R a + u *\<^sub>R b) = u *\<^sub>R (a - b)" by (auto simp add: algebra_simps)
3983 show ?thesis unfolding between_def split_conv mem_def[of x, symmetric] closed_segment_def mem_Collect_eq
3984 apply rule apply(erule exE, (erule conjE)+) apply(subst dist_triangle_eq) proof-
3985 fix u assume as:"x = (1 - u) *\<^sub>R a + u *\<^sub>R b" "0 \<le> u" "u \<le> 1"
3986 hence *:"a - x = u *\<^sub>R (a - b)" "x - b = (1 - u) *\<^sub>R (a - b)"
3987 unfolding as(1) by(auto simp add:algebra_simps)
3988 show "norm (a - x) *\<^sub>R (x - b) = norm (x - b) *\<^sub>R (a - x)"
3989 unfolding norm_minus_commute[of x a] * using as(2,3)
3990 by(auto simp add: field_simps)
3991 next assume as:"dist a b = dist a x + dist x b"
3992 have "norm (a - x) / norm (a - b) \<le> 1" unfolding divide_le_eq_1_pos[OF Fal2]
3993 unfolding as[unfolded dist_norm] norm_ge_zero by auto
3994 thus "\<exists>u. x = (1 - u) *\<^sub>R a + u *\<^sub>R b \<and> 0 \<le> u \<and> u \<le> 1" apply(rule_tac x="dist a x / dist a b" in exI)
3995 unfolding dist_norm apply(subst euclidean_eq) apply rule defer apply(rule, rule divide_nonneg_pos) prefer 4
3996 proof(rule,rule) fix i assume i:"i<DIM('a)"
3997 have "((1 - norm (a - x) / norm (a - b)) *\<^sub>R a + (norm (a - x) / norm (a - b)) *\<^sub>R b) $$ i =
3998 ((norm (a - b) - norm (a - x)) * (a $$ i) + norm (a - x) * (b $$ i)) / norm (a - b)"
3999 using Fal by(auto simp add: field_simps euclidean_simps)
4000 also have "\<dots> = x$$i" apply(rule divide_eq_imp[OF Fal])
4001 unfolding as[unfolded dist_norm] using as[unfolded dist_triangle_eq] apply-
4002 apply(subst (asm) euclidean_eq) using i apply(erule_tac x=i in allE) by(auto simp add:field_simps euclidean_simps)
4003 finally show "x $$ i = ((1 - norm (a - x) / norm (a - b)) *\<^sub>R a + (norm (a - x) / norm (a - b)) *\<^sub>R b) $$ i"
4005 qed(insert Fal2, auto) qed qed
4007 lemma between_midpoint: fixes a::"'a::euclidean_space" shows
4008 "between (a,b) (midpoint a b)" (is ?t1)
4009 "between (b,a) (midpoint a b)" (is ?t2)
4010 proof- have *:"\<And>x y z. x = (1/2::real) *\<^sub>R z \<Longrightarrow> y = (1/2) *\<^sub>R z \<Longrightarrow> norm z = norm x + norm y" by auto
4011 show ?t1 ?t2 unfolding between midpoint_def dist_norm apply(rule_tac[!] *)
4012 unfolding euclidean_eq[where 'a='a]
4013 by(auto simp add:field_simps euclidean_simps) qed
4015 lemma between_mem_convex_hull:
4016 "between (a,b) x \<longleftrightarrow> x \<in> convex hull {a,b}"
4017 unfolding between_mem_segment segment_convex_hull ..
4019 subsection {* Shrinking towards the interior of a convex set. *}
4021 lemma mem_interior_convex_shrink:
4022 fixes s :: "('a::euclidean_space) set"
4023 assumes "convex s" "c \<in> interior s" "x \<in> s" "0 < e" "e \<le> 1"
4024 shows "x - e *\<^sub>R (x - c) \<in> interior s"
4025 proof- obtain d where "d>0" and d:"ball c d \<subseteq> s" using assms(2) unfolding mem_interior by auto
4026 show ?thesis unfolding mem_interior apply(rule_tac x="e*d" in exI)
4027 apply(rule) defer unfolding subset_eq Ball_def mem_ball proof(rule,rule)
4028 fix y assume as:"dist (x - e *\<^sub>R (x - c)) y < e * d"
4029 have *:"y = (1 - (1 - e)) *\<^sub>R ((1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x) + (1 - e) *\<^sub>R x" using `e>0` by (auto simp add: scaleR_left_diff_distrib scaleR_right_diff_distrib)
4030 have "dist c ((1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x) = abs(1/e) * norm (e *\<^sub>R c - y + (1 - e) *\<^sub>R x)"
4031 unfolding dist_norm unfolding norm_scaleR[THEN sym] apply(rule arg_cong[where f=norm]) using `e>0`
4032 by(auto simp add: euclidean_simps euclidean_eq[where 'a='a] field_simps)
4033 also have "\<dots> = abs(1/e) * norm (x - e *\<^sub>R (x - c) - y)" by(auto intro!:arg_cong[where f=norm] simp add: algebra_simps)
4034 also have "\<dots> < d" using as[unfolded dist_norm] and `e>0`
4035 by(auto simp add:pos_divide_less_eq[OF `e>0`] mult_commute)
4036 finally show "y \<in> s" apply(subst *) apply(rule assms(1)[unfolded convex_alt,rule_format])
4037 apply(rule d[unfolded subset_eq,rule_format]) unfolding mem_ball using assms(3-5) by auto
4038 qed(rule mult_pos_pos, insert `e>0` `d>0`, auto) qed
4040 lemma mem_interior_closure_convex_shrink:
4041 fixes s :: "('a::euclidean_space) set"
4042 assumes "convex s" "c \<in> interior s" "x \<in> closure s" "0 < e" "e \<le> 1"
4043 shows "x - e *\<^sub>R (x - c) \<in> interior s"
4044 proof- obtain d where "d>0" and d:"ball c d \<subseteq> s" using assms(2) unfolding mem_interior by auto
4045 have "\<exists>y\<in>s. norm (y - x) * (1 - e) < e * d" proof(cases "x\<in>s")
4046 case True thus ?thesis using `e>0` `d>0` by(rule_tac bexI[where x=x], auto intro!: mult_pos_pos) next
4047 case False hence x:"x islimpt s" using assms(3)[unfolded closure_def] by auto
4048 show ?thesis proof(cases "e=1")
4049 case True obtain y where "y\<in>s" "y \<noteq> x" "dist y x < 1"
4050 using x[unfolded islimpt_approachable,THEN spec[where x=1]] by auto
4051 thus ?thesis apply(rule_tac x=y in bexI) unfolding True using `d>0` by auto next
4052 case False hence "0 < e * d / (1 - e)" and *:"1 - e > 0"
4053 using `e\<le>1` `e>0` `d>0` by(auto intro!:mult_pos_pos divide_pos_pos)
4054 then obtain y where "y\<in>s" "y \<noteq> x" "dist y x < e * d / (1 - e)"
4055 using x[unfolded islimpt_approachable,THEN spec[where x="e*d / (1 - e)"]] by auto
4056 thus ?thesis apply(rule_tac x=y in bexI) unfolding dist_norm using pos_less_divide_eq[OF *] by auto qed qed
4057 then obtain y where "y\<in>s" and y:"norm (y - x) * (1 - e) < e * d" by auto
4058 def z \<equiv> "c + ((1 - e) / e) *\<^sub>R (x - y)"
4059 have *:"x - e *\<^sub>R (x - c) = y - e *\<^sub>R (y - z)" unfolding z_def using `e>0` by (auto simp add: scaleR_right_diff_distrib scaleR_right_distrib scaleR_left_diff_distrib)
4060 have "z\<in>interior s" apply(rule subset_interior[OF d,unfolded subset_eq,rule_format])
4061 unfolding interior_open[OF open_ball] mem_ball z_def dist_norm using y and assms(4,5)
4062 by(auto simp add:field_simps norm_minus_commute)
4063 thus ?thesis unfolding * apply - apply(rule mem_interior_convex_shrink)
4064 using assms(1,4-5) `y\<in>s` by auto qed
4066 subsection {* Some obvious but surprisingly hard simplex lemmas. *}
4069 assumes "finite s" "0 \<notin> s"
4070 shows "convex hull (insert 0 s) = { y. (\<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s \<le> 1 \<and> setsum (\<lambda>x. u x *\<^sub>R x) s = y)}"
4071 unfolding convex_hull_finite[OF finite.insertI[OF assms(1)]] apply(rule set_eqI, rule) unfolding mem_Collect_eq
4072 apply(erule_tac[!] exE) apply(erule_tac[!] conjE)+ unfolding setsum_clauses(2)[OF assms(1)]
4073 apply(rule_tac x=u in exI) defer apply(rule_tac x="\<lambda>x. if x = 0 then 1 - setsum u s else u x" in exI) using assms(2)
4074 unfolding if_smult and setsum_delta_notmem[OF assms(2)] by auto
4076 lemma substd_simplex: assumes "d\<subseteq>{..<DIM('a::euclidean_space)}"
4077 shows "convex hull (insert 0 { basis i | i. i : d}) =
4078 {x::'a::euclidean_space . (!i<DIM('a). 0 <= x$$i) & setsum (%i. x$$i) d <= 1 &
4079 (!i<DIM('a). i ~: d --> x$$i = 0)}"
4080 (is "convex hull (insert 0 ?p) = ?s")
4081 (* Proof is a modified copy of the proof of similar lemma std_simplex in Convex_Euclidean_Space.thy *)
4082 proof- let ?D = d (*"{..<DIM('a::euclidean_space)}"*)
4083 have "0 ~: ?p" using assms by (auto simp: image_def)
4084 have "{(basis i)::'n::euclidean_space |i. i \<in> ?D} = basis ` ?D" by auto
4085 note sumbas = this setsum_reindex[OF basis_inj_on[of d], unfolded o_def, OF assms]
4086 show ?thesis unfolding simplex[OF finite_substdbasis `0 ~: ?p`]
4087 apply(rule set_eqI) unfolding mem_Collect_eq apply rule
4088 apply(erule exE, (erule conjE)+) apply(erule_tac[2] conjE)+ proof-
4089 fix x::"'a::euclidean_space" and u assume as: "\<forall>x\<in>{basis i |i. i \<in>?D}. 0 \<le> u x"
4090 "setsum u {basis i |i. i \<in> ?D} \<le> 1" "(\<Sum>x\<in>{basis i |i. i \<in>?D}. u x *\<^sub>R x) = x"
4091 have *:"\<forall>i<DIM('a). i:d --> u (basis i) = x$$i" and "(!i<DIM('a). i ~: d --> x $$ i = 0)" using as(3)
4092 unfolding sumbas unfolding substdbasis_expansion_unique[OF assms] by auto
4093 hence **:"setsum u {basis i |i. i \<in> ?D} = setsum (op $$ x) ?D" unfolding sumbas
4094 apply-apply(rule setsum_cong2) using assms by auto
4095 have " (\<forall>i<DIM('a). 0 \<le> x$$i) \<and> setsum (op $$ x) ?D \<le> 1"
4096 apply - proof(rule,rule,rule)
4097 fix i assume i:"i<DIM('a)" have "i : d ==> 0 \<le> x$$i" unfolding *[rule_format,OF i,THEN sym]
4098 apply(rule_tac as(1)[rule_format]) by auto
4099 moreover have "i ~: d ==> 0 \<le> x$$i"
4100 using `(!i<DIM('a). i ~: d --> x $$ i = 0)`[rule_format, OF i] by auto
4101 ultimately show "0 \<le> x$$i" by auto
4102 qed(insert as(2)[unfolded **], auto)
4103 from this show " (\<forall>i<DIM('a). 0 \<le> x$$i) \<and> setsum (op $$ x) ?D \<le> 1 & (!i<DIM('a). i ~: d --> x $$ i = 0)"
4104 using `(!i<DIM('a). i ~: d --> x $$ i = 0)` by auto
4105 next fix x::"'a::euclidean_space" assume as:"\<forall>i<DIM('a). 0 \<le> x $$ i" "setsum (op $$ x) ?D \<le> 1"
4106 "(!i<DIM('a). i ~: d --> x $$ i = 0)"
4107 show "\<exists>u. (\<forall>x\<in>{basis i |i. i \<in> ?D}. 0 \<le> u x) \<and>
4108 setsum u {basis i |i. i \<in> ?D} \<le> 1 \<and> (\<Sum>x\<in>{basis i |i. i \<in> ?D}. u x *\<^sub>R x) = x"
4109 apply(rule_tac x="\<lambda>y. inner y x" in exI) apply(rule,rule) unfolding mem_Collect_eq apply(erule exE)
4110 using as(1) apply(erule_tac x=i in allE) unfolding sumbas apply safe unfolding not_less basis_zero
4111 unfolding substdbasis_expansion_unique[OF assms] euclidean_component_def[THEN sym]
4112 using as(2,3) by(auto simp add:dot_basis not_less basis_zero)
4116 "convex hull (insert 0 { basis i | i. i<DIM('a)}) =
4117 {x::'a::euclidean_space . (\<forall>i<DIM('a). 0 \<le> x$$i) \<and> setsum (\<lambda>i. x$$i) {..<DIM('a)} \<le> 1 }"
4118 using substd_simplex[of "{..<DIM('a)}"] by auto
4120 lemma interior_std_simplex:
4121 "interior (convex hull (insert 0 { basis i| i. i<DIM('a)})) =
4122 {x::'a::euclidean_space. (\<forall>i<DIM('a). 0 < x$$i) \<and> setsum (\<lambda>i. x$$i) {..<DIM('a)} < 1 }"
4123 apply(rule set_eqI) unfolding mem_interior std_simplex unfolding subset_eq mem_Collect_eq Ball_def mem_ball
4124 unfolding Ball_def[symmetric] apply rule apply(erule exE, (erule conjE)+) defer apply(erule conjE) proof-
4125 fix x::"'a" and e assume "0<e" and as:"\<forall>xa. dist x xa < e \<longrightarrow> (\<forall>x<DIM('a). 0 \<le> xa $$ x) \<and> setsum (op $$ xa) {..<DIM('a)} \<le> 1"
4126 show "(\<forall>xa<DIM('a). 0 < x $$ xa) \<and> setsum (op $$ x) {..<DIM('a)} < 1" apply(safe) proof-
4127 fix i assume i:"i<DIM('a)" thus "0 < x $$ i" using as[THEN spec[where x="x - (e / 2) *\<^sub>R basis i"]] and `e>0`
4128 unfolding dist_norm by(auto simp add: inner_simps euclidean_component_def dot_basis elim!:allE[where x=i])
4129 next have **:"dist x (x + (e / 2) *\<^sub>R basis 0) < e" using `e>0`
4130 unfolding dist_norm by(auto intro!: mult_strict_left_mono)
4131 have "\<And>i. i<DIM('a) \<Longrightarrow> (x + (e / 2) *\<^sub>R basis 0) $$ i = x$$i + (if i = 0 then e/2 else 0)"
4132 unfolding euclidean_component_def by(auto simp add:inner_simps dot_basis)
4133 hence *:"setsum (op $$ (x + (e / 2) *\<^sub>R basis 0)) {..<DIM('a)} = setsum (\<lambda>i. x$$i + (if 0 = i then e/2 else 0)) {..<DIM('a)}"
4134 apply(rule_tac setsum_cong) by auto
4135 have "setsum (op $$ x) {..<DIM('a)} < setsum (op $$ (x + (e / 2) *\<^sub>R basis 0)) {..<DIM('a)}" unfolding * setsum_addf
4136 using `0<e` DIM_positive[where 'a='a] apply(subst setsum_delta') by auto
4137 also have "\<dots> \<le> 1" using ** apply(drule_tac as[rule_format]) by auto
4138 finally show "setsum (op $$ x) {..<DIM('a)} < 1" by auto qed
4139 next fix x::"'a" assume as:"\<forall>i<DIM('a). 0 < x $$ i" "setsum (op $$ x) {..<DIM('a)} < 1"
4140 guess a using UNIV_witness[where 'a='b] ..
4141 let ?d = "(1 - setsum (op $$ x) {..<DIM('a)}) / real (DIM('a))"
4142 have "Min ((op $$ x) ` {..<DIM('a)}) > 0" apply(rule Min_grI) using as(1) by auto
4143 moreover have"?d > 0" apply(rule divide_pos_pos) using as(2) by(auto simp add: Suc_le_eq)
4144 ultimately show "\<exists>e>0. \<forall>y. dist x y < e \<longrightarrow> (\<forall>i<DIM('a). 0 \<le> y $$ i) \<and> setsum (op $$ y) {..<DIM('a)} \<le> 1"
4145 apply(rule_tac x="min (Min ((op $$ x) ` {..<DIM('a)})) ?D" in exI) apply rule defer apply(rule,rule) proof-
4146 fix y assume y:"dist x y < min (Min (op $$ x ` {..<DIM('a)})) ?d"
4147 have "setsum (op $$ y) {..<DIM('a)} \<le> setsum (\<lambda>i. x$$i + ?d) {..<DIM('a)}" proof(rule setsum_mono)
4148 fix i assume "i\<in>{..<DIM('a)}" hence "abs (y$$i - x$$i) < ?d" apply-apply(rule le_less_trans)
4149 using component_le_norm[of "y - x" i]
4150 using y[unfolded min_less_iff_conj dist_norm, THEN conjunct2] by(auto simp add: norm_minus_commute)
4151 thus "y $$ i \<le> x $$ i + ?d" by auto qed
4152 also have "\<dots> \<le> 1" unfolding setsum_addf setsum_constant card_enum real_eq_of_nat by(auto simp add: Suc_le_eq)
4153 finally show "(\<forall>i<DIM('a). 0 \<le> y $$ i) \<and> setsum (op $$ y) {..<DIM('a)} \<le> 1"
4154 proof safe fix i assume i:"i<DIM('a)"
4155 have "norm (x - y) < x$$i" apply(rule less_le_trans)
4156 apply(rule y[unfolded min_less_iff_conj dist_norm, THEN conjunct1]) using i by auto
4157 thus "0 \<le> y$$i" using component_le_norm[of "x - y" i] and as(1)[rule_format, of i] by auto
4160 lemma interior_std_simplex_nonempty: obtains a::"'a::euclidean_space" where
4161 "a \<in> interior(convex hull (insert 0 {basis i | i . i<DIM('a)}))" proof-
4162 let ?D = "{..<DIM('a)}" let ?a = "setsum (\<lambda>b::'a. inverse (2 * real DIM('a)) *\<^sub>R b) {(basis i) | i. i<DIM('a)}"
4163 have *:"{basis i :: 'a | i. i<DIM('a)} = basis ` ?D" by auto
4164 { fix i assume i:"i<DIM('a)" have "?a $$ i = inverse (2 * real DIM('a))"
4165 unfolding euclidean_component.setsum * and setsum_reindex[OF basis_inj] and o_def
4166 apply(rule trans[of _ "setsum (\<lambda>j. if i = j then inverse (2 * real DIM('a)) else 0) ?D"]) apply(rule setsum_cong2)
4167 defer apply(subst setsum_delta') unfolding euclidean_component_def using i by(auto simp add:dot_basis) }
4169 show ?thesis apply(rule that[of ?a]) unfolding interior_std_simplex mem_Collect_eq proof safe
4170 fix i assume i:"i<DIM('a)" show "0 < ?a $$ i" unfolding **[OF i] by(auto simp add: Suc_le_eq)
4171 next have "setsum (op $$ ?a) ?D = setsum (\<lambda>i. inverse (2 * real DIM('a))) ?D" apply(rule setsum_cong2, rule **) by auto
4172 also have "\<dots> < 1" unfolding setsum_constant card_enum real_eq_of_nat divide_inverse[THEN sym] by (auto simp add:field_simps)
4173 finally show "setsum (op $$ ?a) ?D < 1" by auto qed qed
4175 lemma rel_interior_substd_simplex: assumes "d\<subseteq>{..<DIM('a::euclidean_space)}"
4176 shows "rel_interior (convex hull (insert 0 { basis i| i. i : d})) =
4177 {x::'a::euclidean_space. (\<forall>i\<in>d. 0 < x$$i) & setsum (%i. x$$i) d < 1 & (!i<DIM('a). i ~: d --> x$$i = 0)}"
4178 (is "rel_interior (convex hull (insert 0 ?p)) = ?s")
4179 (* Proof is a modified copy of the proof of similar lemma interior_std_simplex in Convex_Euclidean_Space.thy *)
4181 have "finite d" apply(rule finite_subset) using assms by auto
4182 { assume "d={}" hence ?thesis using rel_interior_sing using euclidean_eq[of _ 0] by auto }
4185 have h0: "affine hull (convex hull (insert 0 ?p))={x::'a::euclidean_space. (!i<DIM('a). i ~: d --> x$$i = 0)}"
4186 using affine_hull_convex_hull affine_hull_substd_basis assms by auto
4187 have aux: "!x::'n::euclidean_space. !i. ((! i:d. 0 <= x$$i) & (!i. i ~: d --> x$$i = 0))--> 0 <= x$$i" by auto
4188 { fix x::"'a::euclidean_space" assume x_def: "x : rel_interior (convex hull (insert 0 ?p))"
4189 from this obtain e where e0: "e>0" and
4190 "ball x e Int {xa. (!i<DIM('a). i ~: d --> xa$$i = 0)} <= convex hull (insert 0 ?p)"
4191 using mem_rel_interior_ball[of x "convex hull (insert 0 ?p)"] h0 by auto
4192 hence as: "ALL xa. (dist x xa < e & (!i<DIM('a). i ~: d --> xa$$i = 0)) -->
4193 (!i : d. 0 <= xa $$ i) & setsum (op $$ xa) d <= 1"
4194 unfolding ball_def unfolding substd_simplex[OF assms] using assms by auto
4195 have x0: "(!i<DIM('a). i ~: d --> x$$i = 0)"
4196 using x_def rel_interior_subset substd_simplex[OF assms] by auto
4197 have "(!i : d. 0 < x $$ i) & setsum (op $$ x) d < 1 & (!i<DIM('a). i ~: d --> x$$i = 0)" apply(rule,rule)
4199 fix i::nat assume "i:d"
4200 hence "\<forall>ia\<in>d. 0 \<le> (x - (e / 2) *\<^sub>R basis i) $$ ia" apply-apply(rule as[rule_format,THEN conjunct1])
4201 unfolding dist_norm using assms `e>0` x0 by auto
4202 thus "0 < x $$ i" apply(erule_tac x=i in ballE) using `e>0` `i\<in>d` assms by auto
4203 next obtain a where a:"a:d" using `d ~= {}` by auto
4204 have **:"dist x (x + (e / 2) *\<^sub>R basis a) < e"
4205 using `e>0` and Euclidean_Space.norm_basis[of a]
4206 unfolding dist_norm by auto
4207 have "\<And>i. (x + (e / 2) *\<^sub>R basis a) $$ i = x$$i + (if i = a then e/2 else 0)"
4208 unfolding euclidean_simps using a assms by auto
4209 hence *:"setsum (op $$ (x + (e / 2) *\<^sub>R basis a)) d =
4210 setsum (\<lambda>i. x$$i + (if a = i then e/2 else 0)) d" by(rule_tac setsum_cong, auto)
4211 have h1: "(ALL i<DIM('a). i ~: d --> (x + (e / 2) *\<^sub>R basis a) $$ i = 0)"
4212 using as[THEN spec[where x="x + (e / 2) *\<^sub>R basis a"]] `a:d` using x0
4213 by(auto simp add: norm_basis elim:allE[where x=a])
4214 have "setsum (op $$ x) d < setsum (op $$ (x + (e / 2) *\<^sub>R basis a)) d" unfolding * setsum_addf
4215 using `0<e` `a:d` using `finite d` by(auto simp add: setsum_delta')
4216 also have "\<dots> \<le> 1" using ** h1 as[rule_format, of "x + (e / 2) *\<^sub>R basis a"] by auto
4217 finally show "setsum (op $$ x) d < 1 & (!i<DIM('a). i ~: d --> x$$i = 0)" using x0 by auto
4222 fix x::"'a::euclidean_space" assume as: "x : ?s"
4223 have "!i. ((0<x$$i) | (0=x$$i) --> 0<=x$$i)" by auto
4224 moreover have "!i. (i:d) | (i ~: d)" by auto
4226 have "!i. ( (ALL i:d. 0 < x$$i) & (ALL i. i ~: d --> x$$i = 0) ) --> 0 <= x$$i" by metis
4227 hence h2: "x : convex hull (insert 0 ?p)" using as assms
4228 unfolding substd_simplex[OF assms] by fastsimp
4229 obtain a where a:"a:d" using `d ~= {}` by auto
4230 let ?d = "(1 - setsum (op $$ x) d) / real (card d)"
4231 have "card d >= 1" using `d ~={}` card_ge1[of d] using `finite d` by auto
4232 have "Min ((op $$ x) ` d) > 0" apply(rule Min_grI) using as `card d >= 1` `finite d` by auto
4233 moreover have "?d > 0" apply(rule divide_pos_pos) using as using `card d >= 1` by(auto simp add: Suc_le_eq)
4234 ultimately have h3: "min (Min ((op $$ x) ` d)) ?d > 0" by auto
4236 have "x : rel_interior (convex hull (insert 0 ?p))"
4237 unfolding rel_interior_ball mem_Collect_eq h0 apply(rule,rule h2)
4238 unfolding substd_simplex[OF assms]
4239 apply(rule_tac x="min (Min ((op $$ x) ` d)) ?d" in exI) apply(rule,rule h3) apply safe unfolding mem_ball
4240 proof- fix y::'a assume y:"dist x y < min (Min (op $$ x ` d)) ?d" and y2:"(!i<DIM('a). i ~: d --> y$$i = 0)"
4241 have "setsum (op $$ y) d \<le> setsum (\<lambda>i. x$$i + ?d) d" proof(rule setsum_mono)
4242 fix i assume i:"i\<in>d"
4243 have "abs (y$$i - x$$i) < ?d" apply(rule le_less_trans) using component_le_norm[of "y - x" i]
4244 using y[unfolded min_less_iff_conj dist_norm, THEN conjunct2]
4245 by(auto simp add: norm_minus_commute)
4246 thus "y $$ i \<le> x $$ i + ?d" by auto qed
4247 also have "\<dots> \<le> 1" unfolding setsum_addf setsum_constant card_enum real_eq_of_nat
4248 using `card d >= 1` by(auto simp add: Suc_le_eq)
4249 finally show "setsum (op $$ y) d \<le> 1" .
4251 fix i assume "i<DIM('a)" thus "0 \<le> y$$i"
4252 proof(cases "i\<in>d") case True
4253 have "norm (x - y) < x$$i" using y[unfolded min_less_iff_conj dist_norm, THEN conjunct1]
4254 using Min_gr_iff[of "op $$ x ` d" "norm (x - y)"] `card d >= 1` `i:d`
4255 apply auto by (metis Suc_n_not_le_n True card_eq_0_iff finite_imageI)
4256 thus "0 \<le> y$$i" using component_le_norm[of "x - y" i] and as(1)[rule_format] by auto
4257 qed(insert y2, auto)
4260 "!!x :: 'a::euclidean_space. (x : rel_interior (convex hull insert 0 {basis i |i. i : d})) =
4261 (x : {x. (ALL i:d. 0 < x $$ i) &
4262 setsum (op $$ x) d < 1 & (ALL i<DIM('a). i ~: d --> x $$ i = 0)})" by blast
4263 from this have ?thesis by (rule set_eqI)
4264 } ultimately show ?thesis by blast
4267 lemma rel_interior_substd_simplex_nonempty: assumes "d ~={}" "d\<subseteq>{..<DIM('a::euclidean_space)}"
4268 obtains a::"'a::euclidean_space" where
4269 "a : rel_interior(convex hull (insert 0 {basis i | i . i : d}))" proof-
4270 (* Proof is a modified copy of the proof of similar lemma interior_std_simplex_nonempty in Convex_Euclidean_Space.thy *)
4271 let ?D = d let ?a = "setsum (\<lambda>b::'a::euclidean_space. inverse (2 * real (card d)) *\<^sub>R b) {(basis i) | i. i \<in> ?D}"
4272 have *:"{basis i :: 'a | i. i \<in> ?D} = basis ` ?D" by auto
4273 have "finite d" apply(rule finite_subset) using assms(2) by auto
4274 hence d1: "real(card d) >= 1" using `d ~={}` card_ge1[of d] by auto
4275 { fix i assume "i:d" have "?a $$ i = inverse (2 * real (card d))"
4276 unfolding * setsum_reindex[OF basis_inj_on, OF assms(2)] o_def
4277 apply(rule trans[of _ "setsum (\<lambda>j. if i = j then inverse (2 * real (card d)) else 0) ?D"])
4278 unfolding euclidean_component.setsum
4279 apply(rule setsum_cong2)
4280 using `i:d` `finite d` setsum_delta'[of d i "(%k. inverse (2 * real (card d)))"] d1 assms(2)
4281 by (auto simp add: Euclidean_Space.basis_component[of i])}
4283 show ?thesis apply(rule that[of ?a]) unfolding rel_interior_substd_simplex[OF assms(2)] mem_Collect_eq
4284 proof safe fix i assume "i:d"
4285 have "0 < inverse (2 * real (card d))" using d1 by(auto simp add: Suc_le_eq)
4286 also have "...=?a $$ i" using **[of i] `i:d` by auto
4287 finally show "0 < ?a $$ i" by auto
4288 next have "setsum (op $$ ?a) ?D = setsum (\<lambda>i. inverse (2 * real (card d))) ?D"
4289 by(rule setsum_cong2, rule **)
4290 also have "\<dots> < 1" unfolding setsum_constant card_enum real_eq_of_nat real_divide_def[THEN sym]
4291 by (auto simp add:field_simps)
4292 finally show "setsum (op $$ ?a) ?D < 1" by auto
4293 next fix i assume "i<DIM('a)" and "i~:d"
4294 have "?a : (span {basis i | i. i : d})"
4295 apply (rule span_setsum[of "{basis i |i. i : d}" "(%b. b /\<^sub>R (2 * real (card d)))" "{basis i |i. i : d}"])
4296 using finite_substdbasis[of d] apply blast
4298 { fix x assume "(x :: 'a::euclidean_space): {basis i |i. i : d}"
4299 hence "x : span {basis i |i. i : d}"
4300 using span_superset[of _ "{basis i |i. i : d}"] by auto
4301 hence "(x /\<^sub>R (2 * real (card d))) : (span {basis i |i. i : d})"
4302 using span_mul[of x "{basis i |i. i : d}" "(inverse (real (card d)) / 2)"] by auto
4303 } thus "\<forall>x\<in>{basis i |i. i \<in> d}. x /\<^sub>R (2 * real (card d)) \<in> span {basis i ::'a |i. i \<in> d}" by auto
4305 thus "?a $$ i = 0 " using `i~:d` unfolding span_substd_basis[OF assms(2)] using `i<DIM('a)` by auto
4309 subsection{* Relative Interior of Convex Set *}
4311 lemma rel_interior_convex_nonempty_aux:
4312 fixes S :: "('n::euclidean_space) set"
4313 assumes "convex S" and "0 : S"
4314 shows "rel_interior S ~= {}"
4316 { assume "S = {0}" hence ?thesis using rel_interior_sing by auto }
4319 obtain B where B_def: "independent B & B<=S & (S <= span B) & card B = dim S" using basis_exists[of S] by auto
4320 hence "B~={}" using B_def assms `S ~= {0}` span_empty by auto
4321 have "insert 0 B <= span B" using subspace_span[of B] subspace_0[of "span B"] span_inc by auto
4322 hence "span (insert 0 B) <= span B"
4323 using span_span[of B] span_mono[of "insert 0 B" "span B"] by blast
4324 hence "convex hull insert 0 B <= span B"
4325 using convex_hull_subset_span[of "insert 0 B"] by auto
4326 hence "span (convex hull insert 0 B) <= span B"
4327 using span_span[of B] span_mono[of "convex hull insert 0 B" "span B"] by blast
4328 hence *: "span (convex hull insert 0 B) = span B"
4329 using span_mono[of B "convex hull insert 0 B"] hull_subset[of "insert 0 B"] by auto
4330 hence "span (convex hull insert 0 B) = span S"
4331 using B_def span_mono[of B S] span_mono[of S "span B"] span_span[of B] by auto
4332 moreover have "0 : affine hull (convex hull insert 0 B)"
4333 using hull_subset[of "convex hull insert 0 B"] hull_subset[of "insert 0 B"] by auto
4334 ultimately have **: "affine hull (convex hull insert 0 B) = affine hull S"
4335 using affine_hull_span_0[of "convex hull insert 0 B"] affine_hull_span_0[of "S"]
4336 assms hull_subset[of S] by auto
4337 obtain d and f::"'n=>'n" where fd: "card d = card B & linear f & f ` B = {basis i |i. i : (d :: nat set)} &
4338 f ` span B = {x. ALL i<DIM('n). i ~: d --> x $$ i = (0::real)} & inj_on f (span B)" and d:"d\<subseteq>{..<DIM('n)}"
4339 using basis_to_substdbasis_subspace_isomorphism[of B,OF _ ] B_def by auto
4340 hence "bounded_linear f" using linear_conv_bounded_linear by auto
4341 have "d ~={}" using fd B_def `B ~={}` by auto
4342 have "(insert 0 {basis i |i. i : d}) = f ` (insert 0 B)" using fd linear_0 by auto
4343 hence "(convex hull (insert 0 {basis i |i. i : d})) = f ` (convex hull (insert 0 B))"
4344 using convex_hull_linear_image[of f "(insert 0 {basis i |i. i : d})"]
4345 convex_hull_linear_image[of f "(insert 0 B)"] `bounded_linear f` by auto
4346 moreover have "rel_interior (f ` (convex hull insert 0 B)) =
4347 f ` rel_interior (convex hull insert 0 B)"
4348 apply (rule rel_interior_injective_on_span_linear_image[of f "(convex hull insert 0 B)"])
4349 using `bounded_linear f` fd * by auto
4350 ultimately have "rel_interior (convex hull insert 0 B) ~= {}"
4351 using rel_interior_substd_simplex_nonempty[OF `d~={}` d] apply auto by blast
4352 moreover have "convex hull (insert 0 B) <= S"
4353 using B_def assms hull_mono[of "insert 0 B" "S" "convex"] convex_hull_eq by auto
4354 ultimately have ?thesis using subset_rel_interior[of "convex hull insert 0 B" S] ** by auto
4355 } ultimately show ?thesis by auto
4358 lemma rel_interior_convex_nonempty:
4359 fixes S :: "('n::euclidean_space) set"
4361 shows "rel_interior S = {} <-> S = {}"
4363 { assume "S ~= {}" from this obtain a where "a : S" by auto
4364 hence "0 : op + (-a) ` S" using assms exI[of "(%x. x:S & -a+x=0)" a] by auto
4365 hence "rel_interior (op + (-a) ` S) ~= {}"
4366 using rel_interior_convex_nonempty_aux[of "op + (-a) ` S"]
4367 convex_translation[of S "-a"] assms by auto
4368 hence "rel_interior S ~= {}" using rel_interior_translation by auto
4369 } from this show ?thesis using rel_interior_empty by auto
4372 lemma convex_rel_interior:
4373 fixes S :: "(_::euclidean_space) set"
4375 shows "convex (rel_interior S)"
4378 assume assm: "x:rel_interior S" "y:rel_interior S" "0<=u" "(u :: real) <= 1"
4379 hence "x:S" using rel_interior_subset by auto
4380 have "x - u *\<^sub>R (x-y) : rel_interior S"
4382 case False hence "0<u" using assm by auto
4384 using assm rel_interior_convex_shrink[of S y x u] assms `x:S` by auto
4386 case True thus ?thesis using assm by auto
4388 hence "(1-u) *\<^sub>R x + u *\<^sub>R y : rel_interior S" by (simp add: algebra_simps)
4389 } from this show ?thesis unfolding convex_alt by auto
4392 lemma convex_closure_rel_interior:
4393 fixes S :: "('n::euclidean_space) set"
4395 shows "closure(rel_interior S) = closure S"
4397 have h1: "closure(rel_interior S) <= closure S"
4398 using subset_closure[of "rel_interior S" S] rel_interior_subset[of S] by auto
4399 { assume "S ~= {}" from this obtain a where a_def: "a : rel_interior S"
4400 using rel_interior_convex_nonempty assms by auto
4401 { fix x assume x_def: "x : closure S"
4402 { assume "x=a" hence "x : closure(rel_interior S)" using a_def unfolding closure_def by auto }
4405 { fix e :: real assume e_def: "e>0"
4406 def e1 == "min 1 (e/norm (x - a))" hence e1_def: "e1>0 & e1<=1 & e1*norm(x-a)<=e"
4407 using `x ~= a` `e>0` divide_pos_pos[of e] le_divide_eq[of e1 e "norm(x-a)"] by simp
4408 hence *: "x - e1 *\<^sub>R (x - a) : rel_interior S"
4409 using rel_interior_closure_convex_shrink[of S a x e1] assms x_def a_def e1_def by auto
4410 have "EX y. y:rel_interior S & y ~= x & (dist y x) <= e"
4411 apply (rule_tac x="x - e1 *\<^sub>R (x - a)" in exI)
4412 using * e1_def dist_norm[of "x - e1 *\<^sub>R (x - a)" x] `x ~= a` by simp
4413 } hence "x islimpt rel_interior S" unfolding islimpt_approachable_le by auto
4414 hence "x : closure(rel_interior S)" unfolding closure_def by auto
4415 } ultimately have "x : closure(rel_interior S)" by auto
4416 } hence ?thesis using h1 by auto
4419 { assume "S = {}" hence "rel_interior S = {}" using rel_interior_empty by auto
4420 hence "closure(rel_interior S) = {}" using closure_empty by auto
4421 hence ?thesis using `S={}` by auto
4422 } ultimately show ?thesis by blast
4425 lemma rel_interior_same_affine_hull:
4426 fixes S :: "('n::euclidean_space) set"
4428 shows "affine hull (rel_interior S) = affine hull S"
4429 by (metis assms closure_same_affine_hull convex_closure_rel_interior)
4431 lemma rel_interior_aff_dim:
4432 fixes S :: "('n::euclidean_space) set"
4434 shows "aff_dim (rel_interior S) = aff_dim S"
4435 by (metis aff_dim_affine_hull2 assms rel_interior_same_affine_hull)
4437 lemma rel_interior_rel_interior:
4438 fixes S :: "('n::euclidean_space) set"
4440 shows "rel_interior (rel_interior S) = rel_interior S"
4442 have "openin (subtopology euclidean (affine hull (rel_interior S))) (rel_interior S)"
4443 using opein_rel_interior[of S] rel_interior_same_affine_hull[of S] assms by auto
4444 from this show ?thesis using rel_interior_def by auto
4447 lemma rel_interior_rel_open:
4448 fixes S :: "('n::euclidean_space) set"
4450 shows "rel_open (rel_interior S)"
4451 unfolding rel_open_def using rel_interior_rel_interior assms by auto
4453 lemma convex_rel_interior_closure_aux:
4454 fixes x y z :: "_::euclidean_space"
4455 assumes "0 < a" "0 < b" "(a+b) *\<^sub>R z = a *\<^sub>R x + b *\<^sub>R y"
4456 obtains e where "0 < e" "e <= 1" "z = y - e *\<^sub>R (y-x)"
4459 have "z = (1 / (a + b)) *\<^sub>R ((a + b) *\<^sub>R z)" apply auto using assms by simp
4460 also have "... = (1 / (a + b)) *\<^sub>R (a *\<^sub>R x + b *\<^sub>R y)" using assms
4461 scaleR_cancel_left[of "1/(a+b)" "(a + b) *\<^sub>R z" "a *\<^sub>R x + b *\<^sub>R y"] by auto
4462 also have "... = y - e *\<^sub>R (y-x)" using e_def apply (simp add: algebra_simps)
4463 using scaleR_left_distrib[of "a/(a+b)" "b/(a+b)" y] assms add_divide_distrib[of a b "a+b"] by auto
4464 finally have "z = y - e *\<^sub>R (y-x)" by auto
4465 moreover have "0<e" using e_def assms divide_pos_pos[of a "a+b"] by auto
4466 moreover have "e<=1" using e_def assms by auto
4467 ultimately show ?thesis using that[of e] by auto
4470 lemma convex_rel_interior_closure:
4471 fixes S :: "('n::euclidean_space) set"
4473 shows "rel_interior (closure S) = rel_interior S"
4475 { assume "S={}" hence ?thesis using assms rel_interior_convex_nonempty by auto }
4478 have "rel_interior (closure S) >= rel_interior S"
4479 using subset_rel_interior[of S "closure S"] closure_same_affine_hull closure_subset by auto
4481 { fix z assume z_def: "z : rel_interior (closure S)"
4482 obtain x where x_def: "x : rel_interior S"
4483 using `S ~= {}` assms rel_interior_convex_nonempty by auto
4484 { assume "x=z" hence "z : rel_interior S" using x_def by auto }
4487 obtain e where e_def: "e > 0 & cball z e Int affine hull closure S <= closure S"
4488 using z_def rel_interior_cball[of "closure S"] by auto
4489 hence *: "0 < e/norm(z-x)" using e_def `x ~= z` divide_pos_pos[of e "norm(z-x)"] by auto
4490 def y == "z + (e/norm(z-x)) *\<^sub>R (z-x)"
4491 have yball: "y : cball z e"
4492 using mem_cball y_def dist_norm[of z y] e_def by auto
4493 have "x : affine hull closure S"
4494 using x_def rel_interior_subset_closure hull_inc[of x "closure S"] by auto
4495 moreover have "z : affine hull closure S"
4496 using z_def rel_interior_subset hull_subset[of "closure S"] by auto
4497 ultimately have "y : affine hull closure S"
4498 using y_def affine_affine_hull[of "closure S"]
4499 mem_affine_3_minus [of "affine hull closure S" z z x "e/norm(z-x)"] by auto
4500 hence "y : closure S" using e_def yball by auto
4501 have "(1+(e/norm(z-x))) *\<^sub>R z = (e/norm(z-x)) *\<^sub>R x + y"
4502 using y_def by (simp add: algebra_simps)
4503 from this obtain e1 where "0 < e1 & e1 <= 1 & z = y - e1 *\<^sub>R (y - x)"
4504 using * convex_rel_interior_closure_aux[of "e / norm (z - x)" 1 z x y]
4505 by (auto simp add: algebra_simps)
4506 hence "z : rel_interior S"
4507 using rel_interior_closure_convex_shrink assms x_def `y : closure S` by auto
4508 } ultimately have "z : rel_interior S" by auto
4509 } ultimately have ?thesis by auto
4510 } ultimately show ?thesis by blast
4513 lemma convex_interior_closure:
4514 fixes S :: "('n::euclidean_space) set"
4516 shows "interior (closure S) = interior S"
4517 using closure_aff_dim[of S] interior_rel_interior_gen[of S] interior_rel_interior_gen[of "closure S"]
4518 convex_rel_interior_closure[of S] assms by auto
4520 lemma closure_eq_rel_interior_eq:
4521 fixes S1 S2 :: "('n::euclidean_space) set"
4522 assumes "convex S1" "convex S2"
4523 shows "(closure S1 = closure S2) <-> (rel_interior S1 = rel_interior S2)"
4524 by (metis convex_rel_interior_closure convex_closure_rel_interior assms)
4527 lemma closure_eq_between:
4528 fixes S1 S2 :: "('n::euclidean_space) set"
4529 assumes "convex S1" "convex S2"
4530 shows "(closure S1 = closure S2) <->
4531 ((rel_interior S1 <= S2) & (S2 <= closure S1))" (is "?A <-> ?B")
4533 have "?A --> ?B" by (metis assms closure_subset convex_rel_interior_closure rel_interior_subset)
4534 moreover have "?B --> (closure S1 <= closure S2)"
4535 by (metis assms(1) convex_closure_rel_interior subset_closure)
4536 moreover have "?B --> (closure S1 >= closure S2)" by (metis closed_closure closure_minimal)
4537 ultimately show ?thesis by blast
4540 lemma open_inter_closure_rel_interior:
4541 fixes S A :: "('n::euclidean_space) set"
4542 assumes "convex S" "open A"
4543 shows "((A Int closure S) = {}) <-> ((A Int rel_interior S) = {})"
4544 by (metis assms convex_closure_rel_interior open_inter_closure_eq_empty)
4546 definition "rel_frontier S = closure S - rel_interior S"
4548 lemma closed_affine_hull: "closed (affine hull ((S :: ('n::euclidean_space) set)))"
4549 by (metis affine_affine_hull affine_closed)
4551 lemma closed_rel_frontier: "closed(rel_frontier (S :: ('n::euclidean_space) set))"
4553 have *: "closedin (subtopology euclidean (affine hull S)) (closure S - rel_interior S)"
4554 apply (rule closedin_diff[of "subtopology euclidean (affine hull S)""closure S" "rel_interior S"]) using closed_closedin_trans[of "affine hull S" "closure S"] closed_affine_hull[of S]
4555 closure_affine_hull[of S] opein_rel_interior[of S] by auto
4556 show ?thesis apply (rule closedin_closed_trans[of "affine hull S" "rel_frontier S"])
4557 unfolding rel_frontier_def using * closed_affine_hull by auto
4561 lemma convex_rel_frontier_aff_dim:
4562 fixes S1 S2 :: "('n::euclidean_space) set"
4563 assumes "convex S1" "convex S2" "S2 ~= {}"
4564 assumes "S1 <= rel_frontier S2"
4565 shows "aff_dim S1 < aff_dim S2"
4567 have "S1 <= closure S2" using assms unfolding rel_frontier_def by auto
4568 hence *: "affine hull S1 <= affine hull S2"
4569 using hull_mono[of "S1" "closure S2"] closure_same_affine_hull[of S2] by auto
4570 hence "aff_dim S1 <= aff_dim S2" using * aff_dim_affine_hull[of S1] aff_dim_affine_hull[of S2]
4571 aff_dim_subset[of "affine hull S1" "affine hull S2"] by auto
4573 { assume eq: "aff_dim S1 = aff_dim S2"
4574 hence "S1 ~= {}" using aff_dim_empty[of S1] aff_dim_empty[of S2] `S2 ~= {}` by auto
4575 have **: "affine hull S1 = affine hull S2"
4576 apply (rule affine_dim_equal) using * affine_affine_hull apply auto
4577 using `S1 ~= {}` hull_subset[of S1] apply auto
4578 using eq aff_dim_affine_hull[of S1] aff_dim_affine_hull[of S2] by auto
4579 obtain a where a_def: "a : rel_interior S1"
4580 using `S1 ~= {}` rel_interior_convex_nonempty assms by auto
4581 obtain T where T_def: "open T & a : T Int S1 & T Int affine hull S1 <= S1"
4582 using mem_rel_interior[of a S1] a_def by auto
4583 hence "a : T Int closure S2" using a_def assms unfolding rel_frontier_def by auto
4584 from this obtain b where b_def: "b : T Int rel_interior S2"
4585 using open_inter_closure_rel_interior[of S2 T] assms T_def by auto
4586 hence "b : affine hull S1" using rel_interior_subset hull_subset[of S2] ** by auto
4587 hence "b : S1" using T_def b_def by auto
4588 hence False using b_def assms unfolding rel_frontier_def by auto
4589 } ultimately show ?thesis using zless_le by auto
4593 lemma convex_rel_interior_if:
4594 fixes S :: "('n::euclidean_space) set"
4596 assumes "z : rel_interior S"
4597 shows "(!x:affine hull S. EX m. m>1 & (!e. (e>1 & e<=m) --> (1-e)*\<^sub>R x+ e *\<^sub>R z : S ))"
4599 obtain e1 where e1_def: "e1>0 & cball z e1 Int affine hull S <= S"
4600 using mem_rel_interior_cball[of z S] assms by auto
4601 { fix x assume x_def: "x:affine hull S"
4603 def m == "1+e1/norm(x-z)"
4604 hence "m>1" using e1_def `x ~= z` divide_pos_pos[of e1 "norm (x - z)"] by auto
4605 { fix e assume e_def: "e>1 & e<=m"
4606 have "z : affine hull S" using assms rel_interior_subset hull_subset[of S] by auto
4607 hence *: "(1-e)*\<^sub>R x+ e *\<^sub>R z : affine hull S"
4608 using mem_affine[of "affine hull S" x z "(1-e)" e] affine_affine_hull[of S] x_def by auto
4609 have "norm (z + e *\<^sub>R x - (x + e *\<^sub>R z)) = norm ((e - 1) *\<^sub>R (x-z))" by (simp add: algebra_simps)
4610 also have "...= (e - 1) * norm(x-z)" using norm_scaleR e_def by auto
4611 also have "...<=(m - 1) * norm(x-z)" using e_def mult_right_mono[of _ _ "norm(x-z)"] by auto
4612 also have "...= (e1 / norm (x - z)) * norm (x - z)" using m_def by auto
4613 also have "...=e1" using `x ~= z` e1_def by simp
4614 finally have **: "norm (z + e *\<^sub>R x - (x + e *\<^sub>R z)) <= e1" by auto
4615 have "(1-e)*\<^sub>R x+ e *\<^sub>R z : cball z e1"
4616 using m_def ** unfolding cball_def dist_norm by (auto simp add: algebra_simps)
4617 hence "(1-e)*\<^sub>R x+ e *\<^sub>R z : S" using e_def * e1_def by auto
4618 } hence "EX m. m>1 & (!e. (e>1 & e<=m) --> (1-e)*\<^sub>R x+ e *\<^sub>R z : S )" using `m>1` by auto
4621 { assume "x=z" def m == "1+e1" hence "m>1" using e1_def by auto
4622 { fix e assume e_def: "e>1 & e<=m"
4623 hence "(1-e)*\<^sub>R x+ e *\<^sub>R z : S"
4624 using e1_def x_def `x=z` by (auto simp add: algebra_simps)
4625 hence "(1-e)*\<^sub>R x+ e *\<^sub>R z : S" using e_def by auto
4626 } hence "EX m. m>1 & (!e. (e>1 & e<=m) --> (1-e)*\<^sub>R x+ e *\<^sub>R z : S )" using `m>1` by auto
4627 } ultimately have "EX m. m>1 & (!e. (e>1 & e<=m) --> (1-e)*\<^sub>R x+ e *\<^sub>R z : S )" by auto
4628 } from this show ?thesis by auto
4631 lemma convex_rel_interior_if2:
4632 fixes S :: "('n::euclidean_space) set"
4634 assumes "z : rel_interior S"
4635 shows "(!x:affine hull S. EX e. e>1 & (1-e)*\<^sub>R x+ e *\<^sub>R z : S)"
4636 using convex_rel_interior_if[of S z] assms by auto
4638 lemma convex_rel_interior_only_if:
4639 fixes S :: "('n::euclidean_space) set"
4640 assumes "convex S" "S ~= {}"
4641 assumes "(!x:S. EX e. e>1 & (1-e)*\<^sub>R x+ e *\<^sub>R z : S)"
4642 shows "z : rel_interior S"
4644 obtain x where x_def: "x : rel_interior S" using rel_interior_convex_nonempty assms by auto
4645 hence "x:S" using rel_interior_subset by auto
4646 from this obtain e where e_def: "e>1 & (1 - e) *\<^sub>R x + e *\<^sub>R z : S" using assms by auto
4647 def y == "(1 - e) *\<^sub>R x + e *\<^sub>R z" hence "y:S" using e_def by auto
4648 def e1 == "1/e" hence "0<e1 & e1<1" using e_def by auto
4649 hence "z=y-(1-e1)*\<^sub>R (y-x)" using e1_def y_def by (auto simp add: algebra_simps)
4650 from this show ?thesis
4651 using rel_interior_convex_shrink[of S x y "1-e1"] `0<e1 & e1<1` `y:S` x_def assms by auto
4654 lemma convex_rel_interior_iff:
4655 fixes S :: "('n::euclidean_space) set"
4656 assumes "convex S" "S ~= {}"
4657 shows "z : rel_interior S <-> (!x:S. EX e. e>1 & (1-e)*\<^sub>R x+ e *\<^sub>R z : S)"
4658 using assms hull_subset[of S "affine"]
4659 convex_rel_interior_if[of S z] convex_rel_interior_only_if[of S z] by auto
4661 lemma convex_rel_interior_iff2:
4662 fixes S :: "('n::euclidean_space) set"
4663 assumes "convex S" "S ~= {}"
4664 shows "z : rel_interior S <-> (!x:affine hull S. EX e. e>1 & (1-e)*\<^sub>R x+ e *\<^sub>R z : S)"
4665 using assms hull_subset[of S]
4666 convex_rel_interior_if2[of S z] convex_rel_interior_only_if[of S z] by auto
4669 lemma convex_interior_iff:
4670 fixes S :: "('n::euclidean_space) set"
4672 shows "z : interior S <-> (!x. EX e. e>0 & z+ e *\<^sub>R x : S)"
4674 { assume a: "~(aff_dim S = int DIM('n))"
4675 { assume "z : interior S"
4676 hence False using a interior_rel_interior_gen[of S] by auto
4679 { assume r: "!x. EX e. e>0 & z+ e *\<^sub>R x : S"
4680 { fix x obtain e1 where e1_def: "e1>0 & z+ e1 *\<^sub>R (x-z) : S" using r by auto
4681 obtain e2 where e2_def: "e2>0 & z+ e2 *\<^sub>R (z-x) : S" using r by auto
4682 def x1 == "z+ e1 *\<^sub>R (x-z)"
4683 hence x1: "x1 : affine hull S" using e1_def hull_subset[of S] by auto
4684 def x2 == "z+ e2 *\<^sub>R (z-x)"
4685 hence x2: "x2 : affine hull S" using e2_def hull_subset[of S] by auto
4686 have *: "e1/(e1+e2) + e2/(e1+e2) = 1" using divide.add[of e1 e2 "e1+e2"] e1_def e2_def by simp
4687 hence "z = (e2/(e1+e2)) *\<^sub>R x1 + (e1/(e1+e2)) *\<^sub>R x2"
4688 using x1_def x2_def apply (auto simp add: algebra_simps)
4689 using scaleR_left_distrib[of "e1/(e1+e2)" "e2/(e1+e2)" z] by auto
4690 hence z: "z : affine hull S"
4691 using mem_affine[of "affine hull S" x1 x2 "e2/(e1+e2)" "e1/(e1+e2)"]
4692 x1 x2 affine_affine_hull[of S] * by auto
4693 have "x1-x2 = (e1+e2) *\<^sub>R (x-z)"
4694 using x1_def x2_def by (auto simp add: algebra_simps)
4695 hence "x=z+(1/(e1+e2)) *\<^sub>R (x1-x2)" using e1_def e2_def by simp
4696 hence "x : affine hull S" using mem_affine_3_minus[of "affine hull S" z x1 x2 "1/(e1+e2)"]
4697 x1 x2 z affine_affine_hull[of S] by auto
4698 } hence "affine hull S = UNIV" by auto
4699 hence "aff_dim S = int DIM('n)" using aff_dim_affine_hull[of S] by (simp add: aff_dim_univ)
4700 hence False using a by auto
4701 } ultimately have ?thesis by auto
4704 { assume a: "aff_dim S = int DIM('n)"
4705 hence "S ~= {}" using aff_dim_empty[of S] by auto
4706 have *: "affine hull S=UNIV" using a affine_hull_univ by auto
4707 { assume "z : interior S"
4708 hence "z : rel_interior S" using a interior_rel_interior_gen[of S] by auto
4709 hence **: "(!x. EX e. e>1 & (1-e)*\<^sub>R x+ e *\<^sub>R z : S)"
4710 using convex_rel_interior_iff2[of S z] assms `S~={}` * by auto
4711 fix x obtain e1 where e1_def: "e1>1 & (1-e1)*\<^sub>R (z-x)+ e1 *\<^sub>R z : S"
4712 using **[rule_format, of "z-x"] by auto
4714 hence "(1-e1)*\<^sub>R (z-x)+ e1 *\<^sub>R z = z+ e *\<^sub>R x" by (simp add: algebra_simps)
4715 hence "e>0 & z+ e *\<^sub>R x : S" using e1_def e_def by auto
4716 hence "EX e. e>0 & z+ e *\<^sub>R x : S" by auto
4719 { assume r: "(!x. EX e. e>0 & z+ e *\<^sub>R x : S)"
4720 { fix x obtain e1 where e1_def: "e1>0 & z + e1*\<^sub>R (z-x) : S"
4721 using r[rule_format, of "z-x"] by auto
4723 hence "z + e1*\<^sub>R (z-x) = (1-e)*\<^sub>R x+ e *\<^sub>R z" by (simp add: algebra_simps)
4724 hence "e > 1 & (1-e)*\<^sub>R x+ e *\<^sub>R z : S" using e1_def e_def by auto
4725 hence "EX e. e>1 & (1-e)*\<^sub>R x+ e *\<^sub>R z : S" by auto
4727 hence "z : rel_interior S" using convex_rel_interior_iff2[of S z] assms `S~={}` by auto
4728 hence "z : interior S" using a interior_rel_interior_gen[of S] by auto
4729 } ultimately have ?thesis by auto
4730 } ultimately show ?thesis by auto
4733 subsection{* Relative interior and closure under commom operations *}
4735 lemma rel_interior_inter_aux: "Inter {rel_interior S |S. S : I} <= Inter I"
4737 { fix y assume "y : Inter {rel_interior S |S. S : I}"
4738 hence y_def: "!S : I. y : rel_interior S" by auto
4739 { fix S assume "S : I" hence "y : S" using rel_interior_subset y_def by auto }
4740 hence "y : Inter I" by auto
4741 } thus ?thesis by auto
4744 lemma closure_inter: "closure (Inter I) <= Inter {closure S |S. S : I}"
4746 { fix y assume "y : Inter I" hence y_def: "!S : I. y : S" by auto
4747 { fix S assume "S : I" hence "y : closure S" using closure_subset y_def by auto }
4748 hence "y : Inter {closure S |S. S : I}" by auto
4749 } hence "Inter I <= Inter {closure S |S. S : I}" by auto
4750 moreover have "Inter {closure S |S. S : I} : closed"
4751 unfolding mem_def closed_Inter closed_closure by auto
4752 ultimately show ?thesis using closure_hull[of "Inter I"]
4753 hull_minimal[of "Inter I" "Inter {closure S |S. S : I}" "closed"] by auto
4756 lemma convex_closure_rel_interior_inter:
4757 assumes "!S : I. convex (S :: ('n::euclidean_space) set)"
4758 assumes "Inter {rel_interior S |S. S : I} ~= {}"
4759 shows "Inter {closure S |S. S : I} <= closure (Inter {rel_interior S |S. S : I})"
4761 obtain x where x_def: "!S : I. x : rel_interior S" using assms by auto
4762 { fix y assume "y : Inter {closure S |S. S : I}" hence y_def: "!S : I. y : closure S" by auto
4764 hence "y : closure (Inter {rel_interior S |S. S : I})"
4765 using x_def closure_subset[of "Inter {rel_interior S |S. S : I}"] by auto
4769 { fix e :: real assume e_def: "0 < e"
4770 def e1 == "min 1 (e/norm (y - x))" hence e1_def: "e1>0 & e1<=1 & e1*norm(y-x)<=e"
4771 using `y ~= x` `e>0` divide_pos_pos[of e] le_divide_eq[of e1 e "norm(y-x)"] by simp
4772 def z == "y - e1 *\<^sub>R (y - x)"
4773 { fix S assume "S : I"
4774 hence "z : rel_interior S" using rel_interior_closure_convex_shrink[of S x y e1]
4775 assms x_def y_def e1_def z_def by auto
4776 } hence *: "z : Inter {rel_interior S |S. S : I}" by auto
4777 have "EX z. z:Inter {rel_interior S |S. S : I} & z ~= y & (dist z y) <= e"
4778 apply (rule_tac x="z" in exI) using `y ~= x` z_def * e1_def e_def dist_norm[of z y] by simp
4779 } hence "y islimpt Inter {rel_interior S |S. S : I}" unfolding islimpt_approachable_le by blast
4780 hence "y : closure (Inter {rel_interior S |S. S : I})" unfolding closure_def by auto
4781 } ultimately have "y : closure (Inter {rel_interior S |S. S : I})" by auto
4782 } from this show ?thesis by auto
4786 lemma convex_closure_inter:
4787 assumes "!S : I. convex (S :: ('n::euclidean_space) set)"
4788 assumes "Inter {rel_interior S |S. S : I} ~= {}"
4789 shows "closure (Inter I) = Inter {closure S |S. S : I}"
4791 have "Inter {closure S |S. S : I} <= closure (Inter {rel_interior S |S. S : I})"
4792 using convex_closure_rel_interior_inter assms by auto
4793 moreover have "closure (Inter {rel_interior S |S. S : I}) <= closure (Inter I)"
4794 using rel_interior_inter_aux
4795 subset_closure[of "Inter {rel_interior S |S. S : I}" "Inter I"] by auto
4796 ultimately show ?thesis using closure_inter[of I] by auto
4799 lemma convex_inter_rel_interior_same_closure:
4800 assumes "!S : I. convex (S :: ('n::euclidean_space) set)"
4801 assumes "Inter {rel_interior S |S. S : I} ~= {}"
4802 shows "closure (Inter {rel_interior S |S. S : I}) = closure (Inter I)"
4804 have "Inter {closure S |S. S : I} <= closure (Inter {rel_interior S |S. S : I})"
4805 using convex_closure_rel_interior_inter assms by auto
4806 moreover have "closure (Inter {rel_interior S |S. S : I}) <= closure (Inter I)"
4807 using rel_interior_inter_aux
4808 subset_closure[of "Inter {rel_interior S |S. S : I}" "Inter I"] by auto
4809 ultimately show ?thesis using closure_inter[of I] by auto
4812 lemma convex_rel_interior_inter:
4813 assumes "!S : I. convex (S :: ('n::euclidean_space) set)"
4814 assumes "Inter {rel_interior S |S. S : I} ~= {}"
4815 shows "rel_interior (Inter I) <= Inter {rel_interior S |S. S : I}"
4817 have "convex(Inter I)" using assms convex_Inter by auto
4818 moreover have "convex(Inter {rel_interior S |S. S : I})" apply (rule convex_Inter)
4819 using assms convex_rel_interior by auto
4820 ultimately have "rel_interior (Inter {rel_interior S |S. S : I}) = rel_interior (Inter I)"
4821 using convex_inter_rel_interior_same_closure assms
4822 closure_eq_rel_interior_eq[of "Inter {rel_interior S |S. S : I}" "Inter I"] by blast
4823 from this show ?thesis using rel_interior_subset[of "Inter {rel_interior S |S. S : I}"] by auto
4826 lemma convex_rel_interior_finite_inter:
4827 assumes "!S : I. convex (S :: ('n::euclidean_space) set)"
4828 assumes "Inter {rel_interior S |S. S : I} ~= {}"
4830 shows "rel_interior (Inter I) = Inter {rel_interior S |S. S : I}"
4832 have "Inter I ~= {}" using assms rel_interior_inter_aux[of I] by auto
4833 have "convex (Inter I)" using convex_Inter assms by auto
4834 { assume "I={}" hence ?thesis using Inter_empty rel_interior_univ2 by auto }
4837 { fix z assume z_def: "z : Inter {rel_interior S |S. S : I}"
4838 { fix x assume x_def: "x : Inter I"
4839 { fix S assume S_def: "S : I" hence "z : rel_interior S" "x : S" using z_def x_def by auto
4840 (*from this obtain e where e_def: "e>1 & (1 - e) *\<^sub>R x + e *\<^sub>R z : S"*)
4841 hence "EX m. m>1 & (!e. (e>1 & e<=m) --> (1-e)*\<^sub>R x+ e *\<^sub>R z : S )"
4842 using convex_rel_interior_if[of S z] S_def assms hull_subset[of S] by auto
4843 } from this obtain mS where mS_def: "!S : I. (mS(S) > (1 :: real) &
4844 (!e. (e>1 & e<=mS(S)) --> (1-e)*\<^sub>R x+ e *\<^sub>R z : S))" by metis
4845 obtain e where e_def: "e=Min (mS ` I)" by auto
4846 have "e : (mS ` I)" using e_def assms `I ~= {}` by (simp add: Min_in)
4847 hence "e>(1 :: real)" using mS_def by auto
4848 moreover have "!S : I. e<=mS(S)" using e_def assms by auto
4849 ultimately have "EX e>1. (1 - e) *\<^sub>R x + e *\<^sub>R z : Inter I" using mS_def by auto
4850 } hence "z : rel_interior (Inter I)" using convex_rel_interior_iff[of "Inter I" z]
4851 `Inter I ~= {}` `convex (Inter I)` by auto
4852 } from this have ?thesis using convex_rel_interior_inter[of I] assms by auto
4853 } ultimately show ?thesis by blast
4856 lemma convex_closure_inter_two:
4857 fixes S T :: "('n::euclidean_space) set"
4858 assumes "convex S" "convex T"
4859 assumes "(rel_interior S) Int (rel_interior T) ~= {}"
4860 shows "closure (S Int T) = (closure S) Int (closure T)"
4861 using convex_closure_inter[of "{S,T}"] assms by auto
4863 lemma convex_rel_interior_inter_two:
4864 fixes S T :: "('n::euclidean_space) set"
4865 assumes "convex S" "convex T"
4866 assumes "(rel_interior S) Int (rel_interior T) ~= {}"
4867 shows "rel_interior (S Int T) = (rel_interior S) Int (rel_interior T)"
4868 using convex_rel_interior_finite_inter[of "{S,T}"] assms by auto
4871 lemma convex_affine_closure_inter:
4872 fixes S T :: "('n::euclidean_space) set"
4873 assumes "convex S" "affine T"
4874 assumes "(rel_interior S) Int T ~= {}"
4875 shows "closure (S Int T) = (closure S) Int T"
4877 have "affine hull T = T" using assms by auto
4878 hence "rel_interior T = T" using rel_interior_univ[of T] by metis
4879 moreover have "closure T = T" using assms affine_closed[of T] by auto
4880 ultimately show ?thesis using convex_closure_inter_two[of S T] assms affine_imp_convex by auto
4883 lemma convex_affine_rel_interior_inter:
4884 fixes S T :: "('n::euclidean_space) set"
4885 assumes "convex S" "affine T"
4886 assumes "(rel_interior S) Int T ~= {}"
4887 shows "rel_interior (S Int T) = (rel_interior S) Int T"
4889 have "affine hull T = T" using assms by auto
4890 hence "rel_interior T = T" using rel_interior_univ[of T] by metis
4891 moreover have "closure T = T" using assms affine_closed[of T] by auto
4892 ultimately show ?thesis using convex_rel_interior_inter_two[of S T] assms affine_imp_convex by auto
4895 lemma subset_rel_interior_convex:
4896 fixes S T :: "('n::euclidean_space) set"
4897 assumes "convex S" "convex T"
4898 assumes "S <= closure T"
4899 assumes "~(S <= rel_frontier T)"
4900 shows "rel_interior S <= rel_interior T"
4902 have *: "S Int closure T = S" using assms by auto
4903 have "~(rel_interior S <= rel_frontier T)"
4904 using subset_closure[of "rel_interior S" "rel_frontier T"] closed_rel_frontier[of T]
4905 closure_closed convex_closure_rel_interior[of S] closure_subset[of S] assms by auto
4906 hence "(rel_interior S) Int (rel_interior (closure T)) ~= {}"
4907 using assms rel_frontier_def[of T] rel_interior_subset convex_rel_interior_closure[of T] by auto
4908 hence "rel_interior S Int rel_interior T = rel_interior (S Int closure T)" using assms convex_closure
4909 convex_rel_interior_inter_two[of S "closure T"] convex_rel_interior_closure[of T] by auto
4910 also have "...=rel_interior (S)" using * by auto
4911 finally show ?thesis by auto
4915 lemma rel_interior_convex_linear_image:
4916 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
4919 shows "f ` (rel_interior S) = rel_interior (f ` S)"
4921 { assume "S = {}" hence ?thesis using assms rel_interior_empty rel_interior_convex_nonempty by auto }
4924 have *: "f ` (rel_interior S) <= f ` S" unfolding image_mono using rel_interior_subset by auto
4925 have "f ` S <= f ` (closure S)" unfolding image_mono using closure_subset by auto
4926 also have "... = f ` (closure (rel_interior S))" using convex_closure_rel_interior assms by auto
4927 also have "... <= closure (f ` (rel_interior S))" using closure_linear_image assms by auto
4928 finally have "closure (f ` S) = closure (f ` rel_interior S)"
4929 using subset_closure[of "f ` S" "closure (f ` rel_interior S)"] closure_closure
4930 subset_closure[of "f ` rel_interior S" "f ` S"] * by auto
4931 hence "rel_interior (f ` S) = rel_interior (f ` rel_interior S)" using assms convex_rel_interior
4932 linear_conv_bounded_linear[of f] convex_linear_image[of S] convex_linear_image[of "rel_interior S"]
4933 closure_eq_rel_interior_eq[of "f ` S" "f ` rel_interior S"] by auto
4934 hence "rel_interior (f ` S) <= f ` rel_interior S" using rel_interior_subset by auto
4936 { fix z assume z_def: "z : f ` rel_interior S"
4937 from this obtain z1 where z1_def: "z1 : rel_interior S & (f z1 = z)" by auto
4938 { fix x assume "x : f ` S"
4939 from this obtain x1 where x1_def: "x1 : S & (f x1 = x)" by auto
4940 from this obtain e where e_def: "e>1 & (1 - e) *\<^sub>R x1 + e *\<^sub>R z1 : S"
4941 using convex_rel_interior_iff[of S z1] `convex S` x1_def z1_def by auto
4942 moreover have "f ((1 - e) *\<^sub>R x1 + e *\<^sub>R z1) = (1 - e) *\<^sub>R x + e *\<^sub>R z"
4943 using x1_def z1_def `linear f` by (simp add: linear_add_cmul)
4944 ultimately have "(1 - e) *\<^sub>R x + e *\<^sub>R z : f ` S"
4945 using imageI[of "(1 - e) *\<^sub>R x1 + e *\<^sub>R z1" S f] by auto
4946 hence "EX e. (e>1 & (1 - e) *\<^sub>R x + e *\<^sub>R z : f ` S)" using e_def by auto
4947 } from this have "z : rel_interior (f ` S)" using convex_rel_interior_iff[of "f ` S" z] `convex S`
4948 `linear f` `S ~= {}` convex_linear_image[of S f] linear_conv_bounded_linear[of f] by auto
4949 } ultimately have ?thesis by auto
4950 } ultimately show ?thesis by blast
4954 lemma convex_linear_preimage:
4955 assumes c:"convex S" and l:"bounded_linear f"
4956 shows "convex(f -` S)"
4957 proof(auto simp add: convex_def)
4958 interpret f: bounded_linear f by fact
4959 fix x y assume xy:"f x : S" "f y : S"
4960 fix u v ::real assume uv:"0 <= u" "0 <= v" "u + v = 1"
4961 show "f (u *\<^sub>R x + v *\<^sub>R y) : S" unfolding image_iff
4962 using bexI[of _ "u *\<^sub>R x + v *\<^sub>R y"] f.add f.scaleR
4963 c[unfolded convex_def] xy uv by auto
4967 lemma rel_interior_convex_linear_preimage:
4968 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
4971 assumes "f -` (rel_interior S) ~= {}"
4972 shows "rel_interior (f -` S) = f -` (rel_interior S)"
4974 have "S ~= {}" using assms rel_interior_empty by auto
4975 have nonemp: "f -` S ~= {}" by (metis assms(3) rel_interior_subset subset_empty vimage_mono)
4976 hence "S Int (range f) ~= {}" by auto
4977 have conv: "convex (f -` S)" using convex_linear_preimage assms linear_conv_bounded_linear by auto
4978 hence "convex (S Int (range f))"
4979 by (metis assms(1) assms(2) convex_Int subspace_UNIV subspace_imp_convex subspace_linear_image)
4980 { fix z assume "z : f -` (rel_interior S)"
4981 hence z_def: "f z : rel_interior S" by auto
4982 { fix x assume "x : f -` S" from this have x_def: "f x : S" by auto
4983 from this obtain e where e_def: "e>1 & (1-e)*\<^sub>R (f x)+ e *\<^sub>R (f z) : S"
4984 using convex_rel_interior_iff[of S "f z"] z_def assms `S ~= {}` by auto
4985 moreover have "(1-e)*\<^sub>R (f x)+ e *\<^sub>R (f z) = f ((1-e)*\<^sub>R x + e *\<^sub>R z)"
4986 using `linear f` by (simp add: linear_def)
4987 ultimately have "EX e. e>1 & (1-e)*\<^sub>R x + e *\<^sub>R z : f -` S" using e_def by auto
4988 } hence "z : rel_interior (f -` S)"
4989 using convex_rel_interior_iff[of "f -` S" z] conv nonemp by auto
4992 { fix z assume z_def: "z : rel_interior (f -` S)"
4993 { fix x assume x_def: "x: S Int (range f)"
4994 from this obtain y where y_def: "(f y = x) & (y : f -` S)" by auto
4995 from this obtain e where e_def: "e>1 & (1-e)*\<^sub>R y+ e *\<^sub>R z : f -` S"
4996 using convex_rel_interior_iff[of "f -` S" z] z_def conv by auto
4997 moreover have "(1-e)*\<^sub>R x+ e *\<^sub>R (f z) = f ((1-e)*\<^sub>R y + e *\<^sub>R z)"
4998 using `linear f` y_def by (simp add: linear_def)
4999 ultimately have "EX e. e>1 & (1-e)*\<^sub>R x + e *\<^sub>R (f z) : S Int (range f)"
5001 } hence "f z : rel_interior (S Int (range f))" using `convex (S Int (range f))`
5002 `S Int (range f) ~= {}` convex_rel_interior_iff[of "S Int (range f)" "f z"] by auto
5003 moreover have "affine (range f)"
5004 by (metis assms(1) subspace_UNIV subspace_imp_affine subspace_linear_image)
5005 ultimately have "f z : rel_interior S"
5006 using convex_affine_rel_interior_inter[of S "range f"] assms by auto
5007 hence "z : f -` (rel_interior S)" by auto
5009 ultimately show ?thesis by auto
5013 lemma convex_direct_sum:
5014 fixes S :: "('n::euclidean_space) set"
5015 fixes T :: "('m::euclidean_space) set"
5016 assumes "convex S" "convex T"
5017 shows "convex (S <*> T)"
5020 fix x assume "x : S <*> T"
5021 from this obtain xs xt where xst_def: "xs : S & xt : T & (xs,xt) = x" by auto
5022 fix y assume "y : S <*> T"
5023 from this obtain ys yt where yst_def: "ys : S & yt : T & (ys,yt) = y" by auto
5024 fix u v assume uv_def: "(u :: real)>=0 & (v :: real)>=0 & u+v=1"
5025 have "u *\<^sub>R x + v *\<^sub>R y = (u *\<^sub>R xs + v *\<^sub>R ys, u *\<^sub>R xt + v *\<^sub>R yt)" using xst_def yst_def by auto
5026 moreover have "u *\<^sub>R xs + v *\<^sub>R ys : S"
5027 using uv_def xst_def yst_def convex_def[of S] assms by auto
5028 moreover have "u *\<^sub>R xt + v *\<^sub>R yt : T"
5029 using uv_def xst_def yst_def convex_def[of T] assms by auto
5030 ultimately have "u *\<^sub>R x + v *\<^sub>R y : S <*> T" by auto
5031 } from this show ?thesis unfolding convex_def by auto
5035 lemma convex_hull_direct_sum:
5036 fixes S :: "('n::euclidean_space) set"
5037 fixes T :: "('m::euclidean_space) set"
5038 shows "convex hull (S <*> T) = (convex hull S) <*> (convex hull T)"
5040 { fix x assume "x : (convex hull S) <*> (convex hull T)"
5041 from this obtain xs xt where xst_def: "xs : convex hull S & xt : convex hull T & (xs,xt) = x" by auto
5042 from xst_def obtain sI su where s: "finite sI & sI <= S & (ALL x:sI. 0 <= su x) & setsum su sI = 1
5043 & (SUM v:sI. su v *\<^sub>R v) = xs" using convex_hull_explicit[of S] by auto
5044 from xst_def obtain tI tu where t: "finite tI & tI <= T & (ALL x:tI. 0 <= tu x) & setsum tu tI = 1
5045 & (SUM v:tI. tu v *\<^sub>R v) = xt" using convex_hull_explicit[of T] by auto
5046 def I == "(sI <*> tI)"
5047 def u == "(%i. (su (fst i))*(tu(snd i)))"
5048 have "fst (SUM v:sI <*> tI. (su (fst v) * tu (snd v)) *\<^sub>R v)=
5049 (SUM vs:sI. SUM vt:tI. (su vs * tu vt) *\<^sub>R vs)"
5050 using fst_setsum[of "(%v. (su (fst v) * tu (snd v)) *\<^sub>R v)" "sI <*> tI"]
5051 by (simp add: split_def scaleR_prod_def setsum_cartesian_product)
5052 also have "...=(SUM vt:tI. tu vt *\<^sub>R (SUM vs:sI. su vs *\<^sub>R vs))"
5053 using setsum_commute[of "(%vt vs. (su vs * tu vt) *\<^sub>R vs)" sI tI]
5054 by (simp add: mult_commute scaleR_right.setsum)
5055 also have "...=(SUM vt:tI. tu vt *\<^sub>R xs)" using s by auto
5056 also have "...=(SUM vt:tI. tu vt) *\<^sub>R xs" by (simp add: scaleR_left.setsum)
5057 also have "...=xs" using t by auto
5058 finally have h1: "fst (SUM v:sI <*> tI. (su (fst v) * tu (snd v)) *\<^sub>R v)=xs" by auto
5059 have "snd (SUM v:sI <*> tI. (su (fst v) * tu (snd v)) *\<^sub>R v)=
5060 (SUM vs:sI. SUM vt:tI. (su vs * tu vt) *\<^sub>R vt)"
5061 using snd_setsum[of "(%v. (su (fst v) * tu (snd v)) *\<^sub>R v)" "sI <*> tI"]
5062 by (simp add: split_def scaleR_prod_def setsum_cartesian_product)
5063 also have "...=(SUM vs:sI. su vs *\<^sub>R (SUM vt:tI. tu vt *\<^sub>R vt))"
5064 by (simp add: mult_commute scaleR_right.setsum)
5065 also have "...=(SUM vs:sI. su vs *\<^sub>R xt)" using t by auto
5066 also have "...=(SUM vs:sI. su vs) *\<^sub>R xt" by (simp add: scaleR_left.setsum)
5067 also have "...=xt" using s by auto
5068 finally have h2: "snd (SUM v:sI <*> tI. (su (fst v) * tu (snd v)) *\<^sub>R v)=xt" by auto
5069 from h1 h2 have "(SUM v:sI <*> tI. (su (fst v) * tu (snd v)) *\<^sub>R v) = x" using xst_def by auto
5071 moreover have "finite I & (I <= S <*> T)" using s t I_def by auto
5072 moreover have "!i:I. 0 <= u i" using s t I_def u_def by (simp add: mult_nonneg_nonneg)
5073 moreover have "setsum u I = 1" using u_def I_def setsum_cartesian_product[of "(% x y. (su x)*(tu y))"]
5074 s t setsum_product[of su sI tu tI] by (auto simp add: split_def)
5075 ultimately have "x : convex hull (S <*> T)"
5076 apply (subst convex_hull_explicit[of "S <*> T"]) apply rule
5077 apply (rule_tac x="I" in exI) apply (rule_tac x="u" in exI)
5078 using I_def u_def by auto
5080 hence "convex hull (S <*> T) >= (convex hull S) <*> (convex hull T)" by auto
5081 moreover have "(convex hull S) <*> (convex hull T) : convex"
5082 unfolding mem_def by (simp add: convex_direct_sum convex_convex_hull)
5083 ultimately show ?thesis
5084 using hull_minimal[of "S <*> T" "(convex hull S) <*> (convex hull T)" "convex"]
5085 hull_subset[of S convex] hull_subset[of T convex] by auto
5088 lemma rel_interior_direct_sum:
5089 fixes S :: "('n::euclidean_space) set"
5090 fixes T :: "('m::euclidean_space) set"
5091 assumes "convex S" "convex T"
5092 shows "rel_interior (S <*> T) = rel_interior S <*> rel_interior T"
5094 { assume "S={}" hence ?thesis apply auto using rel_interior_empty by auto }
5096 { assume "T={}" hence ?thesis apply auto using rel_interior_empty by auto }
5098 assume "S ~={}" "T ~={}"
5099 hence ri: "rel_interior S ~= {}" "rel_interior T ~= {}" using rel_interior_convex_nonempty assms by auto
5100 hence "fst -` rel_interior S ~= {}" using fst_vimage_eq_Times[of "rel_interior S"] by auto
5101 hence "rel_interior ((fst :: 'n * 'm => 'n) -` S) = fst -` rel_interior S"
5102 using fst_linear `convex S` rel_interior_convex_linear_preimage[of fst S] by auto
5103 hence s: "rel_interior (S <*> (UNIV :: 'm set)) = rel_interior S <*> UNIV" by (simp add: fst_vimage_eq_Times)
5104 from ri have "snd -` rel_interior T ~= {}" using snd_vimage_eq_Times[of "rel_interior T"] by auto
5105 hence "rel_interior ((snd :: 'n * 'm => 'm) -` T) = snd -` rel_interior T"
5106 using snd_linear `convex T` rel_interior_convex_linear_preimage[of snd T] by auto
5107 hence t: "rel_interior ((UNIV :: 'n set) <*> T) = UNIV <*> rel_interior T" by (simp add: snd_vimage_eq_Times)
5108 from s t have *: "rel_interior (S <*> (UNIV :: 'm set)) Int rel_interior ((UNIV :: 'n set) <*> T)
5109 = rel_interior S <*> rel_interior T" by auto
5110 have "(S <*> T) = (S <*> (UNIV :: 'm set)) Int ((UNIV :: 'n set) <*> T)" by auto
5111 hence "rel_interior (S <*> T) = rel_interior ((S <*> (UNIV :: 'm set)) Int ((UNIV :: 'n set) <*> T))" by auto
5112 also have "...=rel_interior (S <*> (UNIV :: 'm set)) Int rel_interior ((UNIV :: 'n set) <*> T)"
5113 apply (subst convex_rel_interior_inter_two[of "S <*> (UNIV :: 'm set)" "(UNIV :: 'n set) <*> T"])
5114 using * ri assms convex_direct_sum by auto
5115 finally have ?thesis using * by auto
5117 ultimately show ?thesis by blast
5120 lemma rel_interior_scaleR:
5121 fixes S :: "('n::euclidean_space) set"
5123 shows "(op *\<^sub>R c) ` (rel_interior S) = rel_interior ((op *\<^sub>R c) ` S)"
5124 using rel_interior_injective_linear_image[of "(op *\<^sub>R c)" S]
5125 linear_conv_bounded_linear[of "op *\<^sub>R c"] linear_scaleR injective_scaleR[of c] assms by auto
5127 lemma rel_interior_convex_scaleR:
5128 fixes S :: "('n::euclidean_space) set"
5130 shows "(op *\<^sub>R c) ` (rel_interior S) = rel_interior ((op *\<^sub>R c) ` S)"
5131 by (metis assms linear_scaleR rel_interior_convex_linear_image)
5133 lemma convex_rel_open_scaleR:
5134 fixes S :: "('n::euclidean_space) set"
5135 assumes "convex S" "rel_open S"
5136 shows "convex ((op *\<^sub>R c) ` S) & rel_open ((op *\<^sub>R c) ` S)"
5137 by (metis assms convex_scaling rel_interior_convex_scaleR rel_open_def)
5140 lemma convex_rel_open_finite_inter:
5141 assumes "!S : I. (convex (S :: ('n::euclidean_space) set) & rel_open S)"
5143 shows "convex (Inter I) & rel_open (Inter I)"
5145 { assume "Inter {rel_interior S |S. S : I} = {}"
5146 hence "Inter I = {}" using assms unfolding rel_open_def by auto
5147 hence ?thesis unfolding rel_open_def using rel_interior_empty by auto
5150 { assume "Inter {rel_interior S |S. S : I} ~= {}"
5151 hence "rel_open (Inter I)" using assms unfolding rel_open_def
5152 using convex_rel_interior_finite_inter[of I] by auto
5153 hence ?thesis using convex_Inter assms by auto
5154 } ultimately show ?thesis by auto
5157 lemma convex_rel_open_linear_image:
5158 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
5160 assumes "convex S" "rel_open S"
5161 shows "convex (f ` S) & rel_open (f ` S)"
5162 by (metis assms convex_linear_image rel_interior_convex_linear_image
5163 linear_conv_bounded_linear rel_open_def)
5165 lemma convex_rel_open_linear_preimage:
5166 fixes f :: "('m::euclidean_space) => ('n::euclidean_space)"
5168 assumes "convex S" "rel_open S"
5169 shows "convex (f -` S) & rel_open (f -` S)"
5171 { assume "f -` (rel_interior S) = {}"
5172 hence "f -` S = {}" using assms unfolding rel_open_def by auto
5173 hence ?thesis unfolding rel_open_def using rel_interior_empty by auto
5176 { assume "f -` (rel_interior S) ~= {}"
5177 hence "rel_open (f -` S)" using assms unfolding rel_open_def
5178 using rel_interior_convex_linear_preimage[of f S] by auto
5179 hence ?thesis using convex_linear_preimage assms linear_conv_bounded_linear by auto
5180 } ultimately show ?thesis by auto
5183 lemma rel_interior_projection:
5184 fixes S :: "('m::euclidean_space*'n::euclidean_space) set"
5185 fixes f :: "'m::euclidean_space => ('n::euclidean_space) set"
5187 assumes "f = (%y. {z. (y,z) : S})"
5188 shows "(y,z) : rel_interior S <-> (y : rel_interior {y. (f y ~= {})} & z : rel_interior (f y))"
5190 { fix y assume "y : {y. (f y ~= {})}" from this obtain z where "(y,z) : S" using assms by auto
5191 hence "EX x. x : S & y = fst x" apply (rule_tac x="(y,z)" in exI) by auto
5192 from this obtain x where "x : S & y = fst x" by blast
5193 hence "y : fst ` S" unfolding image_def by auto
5195 hence "fst ` S = {y. (f y ~= {})}" unfolding fst_def using assms by auto
5196 hence h1: "fst ` rel_interior S = rel_interior {y. (f y ~= {})}"
5197 using rel_interior_convex_linear_image[of fst S] assms fst_linear by auto
5198 { fix y assume "y : rel_interior {y. (f y ~= {})}"
5199 hence "y : fst ` rel_interior S" using h1 by auto
5200 hence *: "rel_interior S Int fst -` {y} ~= {}" by auto
5201 moreover have aff: "affine (fst -` {y})" unfolding affine_alt by (simp add: algebra_simps)
5202 ultimately have **: "rel_interior (S Int fst -` {y}) = rel_interior S Int fst -` {y}"
5203 using convex_affine_rel_interior_inter[of S "fst -` {y}"] assms by auto
5204 have conv: "convex (S Int fst -` {y})" using convex_Int assms aff affine_imp_convex by auto
5205 { fix x assume "x : f y"
5206 hence "(y,x) : S Int (fst -` {y})" using assms by auto
5207 moreover have "x = snd (y,x)" by auto
5208 ultimately have "x : snd ` (S Int fst -` {y})" by blast
5210 hence "snd ` (S Int fst -` {y}) = f y" using assms by auto
5211 hence ***: "rel_interior (f y) = snd ` rel_interior (S Int fst -` {y})"
5212 using rel_interior_convex_linear_image[of snd "S Int fst -` {y}"] snd_linear conv by auto
5213 { fix z assume "z : rel_interior (f y)"
5214 hence "z : snd ` rel_interior (S Int fst -` {y})" using *** by auto
5215 moreover have "{y} = fst ` rel_interior (S Int fst -` {y})" using * ** rel_interior_subset by auto
5216 ultimately have "(y,z) : rel_interior (S Int fst -` {y})" by force
5217 hence "(y,z) : rel_interior S" using ** by auto
5220 { fix z assume "(y,z) : rel_interior S"
5221 hence "(y,z) : rel_interior (S Int fst -` {y})" using ** by auto
5222 hence "z : snd ` rel_interior (S Int fst -` {y})" by (metis Range_iff snd_eq_Range)
5223 hence "z : rel_interior (f y)" using *** by auto
5225 ultimately have "!!z. (y,z) : rel_interior S <-> z : rel_interior (f y)" by auto
5227 hence h2: "!!y z. y : rel_interior {t. f t ~= {}} ==> ((y, z) : rel_interior S) = (z : rel_interior (f y))"
5229 { fix y z assume asm: "(y, z) : rel_interior S"
5230 hence "y : fst ` rel_interior S" by (metis Domain_iff fst_eq_Domain)
5231 hence "y : rel_interior {t. f t ~= {}}" using h1 by auto
5232 hence "y : rel_interior {t. f t ~= {}} & (z : rel_interior (f y))" using h2 asm by auto
5233 } from this show ?thesis using h2 by blast
5236 subsection{* Relative interior of convex cone *}
5238 lemma cone_rel_interior:
5239 fixes S :: "('m::euclidean_space) set"
5241 shows "cone ({0} Un (rel_interior S))"
5243 { assume "S = {}" hence ?thesis by (simp add: rel_interior_empty cone_0) }
5245 { assume "S ~= {}" hence *: "0:S & (!c. c>0 --> op *\<^sub>R c ` S = S)" using cone_iff[of S] assms by auto
5246 hence *: "0:({0} Un (rel_interior S)) &
5247 (!c. c>0 --> op *\<^sub>R c ` ({0} Un rel_interior S) = ({0} Un rel_interior S))"
5248 by (auto simp add: rel_interior_scaleR)
5249 hence ?thesis using cone_iff[of "{0} Un rel_interior S"] by auto
5251 ultimately show ?thesis by blast
5254 lemma rel_interior_convex_cone_aux:
5255 fixes S :: "('m::euclidean_space) set"
5257 shows "(c,x) : rel_interior (cone hull ({(1 :: real)} <*> S)) <->
5258 c>0 & x : ((op *\<^sub>R c) ` (rel_interior S))"
5260 { assume "S={}" hence ?thesis by (simp add: rel_interior_empty cone_hull_empty) }
5262 { assume "S ~= {}" from this obtain s where "s : S" by auto
5263 have conv: "convex ({(1 :: real)} <*> S)" using convex_direct_sum[of "{(1 :: real)}" S]
5264 assms convex_singleton[of "1 :: real"] by auto
5265 def f == "(%y. {z. (y,z) : cone hull ({(1 :: real)} <*> S)})"
5266 hence *: "(c, x) : rel_interior (cone hull ({(1 :: real)} <*> S)) =
5267 (c : rel_interior {y. f y ~= {}} & x : rel_interior (f c))"
5268 apply (subst rel_interior_projection[of "cone hull ({(1 :: real)} <*> S)" f c x])
5269 using convex_cone_hull[of "{(1 :: real)} <*> S"] conv by auto
5270 { fix y assume "(y :: real)>=0"
5271 hence "y *\<^sub>R (1,s) : cone hull ({(1 :: real)} <*> S)"
5272 using cone_hull_expl[of "{(1 :: real)} <*> S"] `s:S` by auto
5273 hence "f y ~= {}" using f_def by auto
5275 hence "{y. f y ~= {}} = {0..}" using f_def cone_hull_expl[of "{(1 :: real)} <*> S"] by auto
5276 hence **: "rel_interior {y. f y ~= {}} = {0<..}" using rel_interior_real_semiline by auto
5277 { fix c assume "c>(0 :: real)"
5278 hence "f c = (op *\<^sub>R c ` S)" using f_def cone_hull_expl[of "{(1 :: real)} <*> S"] by auto
5279 hence "rel_interior (f c)= (op *\<^sub>R c ` rel_interior S)"
5280 using rel_interior_convex_scaleR[of S c] assms by auto
5282 hence ?thesis using * ** by auto
5283 } ultimately show ?thesis by blast
5287 lemma rel_interior_convex_cone:
5288 fixes S :: "('m::euclidean_space) set"
5290 shows "rel_interior (cone hull ({(1 :: real)} <*> S)) =
5291 {(c,c *\<^sub>R x) |c x. c>0 & x : (rel_interior S)}"
5294 { fix z assume "z:?lhs"
5295 have *: "z=(fst z,snd z)" by auto
5296 have "z:?rhs" using rel_interior_convex_cone_aux[of S "fst z" "snd z"] assms `z:?lhs` apply auto
5297 apply (rule_tac x="fst z" in exI) apply (rule_tac x="x" in exI) using * by auto
5300 { fix z assume "z:?rhs" hence "z:?lhs"
5301 using rel_interior_convex_cone_aux[of S "fst z" "snd z"] assms by auto
5303 ultimately show ?thesis by blast
5306 lemma convex_hull_finite_union:
5308 assumes "!i:I. (convex (S i) & (S i) ~= {})"
5309 shows "convex hull (Union (S ` I)) =
5310 {setsum (%i. c i *\<^sub>R s i) I |c s. (!i:I. c i >= 0) & (setsum c I = 1) & (!i:I. s i : S i)}"
5313 { fix x assume "x : ?rhs"
5314 from this obtain c s
5315 where *: "setsum (%i. c i *\<^sub>R s i) I=x" "(setsum c I = 1)"
5316 "(!i:I. c i >= 0) & (!i:I. s i : S i)" by auto
5317 hence "!i:I. s i : convex hull (Union (S ` I))" using hull_subset[of "Union (S ` I)" convex] by auto
5318 hence "x : ?lhs" unfolding *(1)[THEN sym]
5319 apply (subst convex_setsum[of I "convex hull Union (S ` I)" c s])
5320 using * assms convex_convex_hull by auto
5321 } hence "?lhs >= ?rhs" by auto
5323 { fix i assume "i:I"
5324 from this assms have "EX p. p : S i" by auto
5326 from this obtain p where p_def: "!i:I. p i : S i" by metis
5328 { fix i assume "i:I"
5329 { fix x assume "x : S i"
5330 def c == "(%j. if (j=i) then (1::real) else 0)"
5331 hence *: "setsum c I = 1" using `finite I` `i:I` setsum_delta[of I i "(%(j::'a). (1::real))"] by auto
5332 def s == "(%j. if (j=i) then x else p j)"
5333 hence "!j. c j *\<^sub>R s j = (if (j=i) then x else 0)" using c_def by (auto simp add: algebra_simps)
5334 hence "x = setsum (%i. c i *\<^sub>R s i) I"
5335 using s_def c_def `finite I` `i:I` setsum_delta[of I i "(%(j::'a). x)"] by auto
5336 hence "x : ?rhs" apply auto
5337 apply (rule_tac x="c" in exI)
5338 apply (rule_tac x="s" in exI) using * c_def s_def p_def `x : S i` by auto
5339 } hence "?rhs >= S i" by auto
5340 } hence *: "?rhs >= Union (S ` I)" by auto
5342 { fix u v assume uv: "(u :: real)>=0 & v>=0 & u+v=1"
5343 fix x y assume xy: "(x : ?rhs) & (y : ?rhs)"
5344 from xy obtain c s where xc: "x=setsum (%i. c i *\<^sub>R s i) I &
5345 (!i:I. c i >= 0) & (setsum c I = 1) & (!i:I. s i : S i)" by auto
5346 from xy obtain d t where yc: "y=setsum (%i. d i *\<^sub>R t i) I &
5347 (!i:I. d i >= 0) & (setsum d I = 1) & (!i:I. t i : S i)" by auto
5348 def e == "(%i. u * (c i)+v * (d i))"
5349 have ge0: "!i:I. e i >= 0" using e_def xc yc uv by (simp add: mult_nonneg_nonneg)
5350 have "setsum (%i. u * c i) I = u * setsum c I" by (simp add: setsum_right_distrib)
5351 moreover have "setsum (%i. v * d i) I = v * setsum d I" by (simp add: setsum_right_distrib)
5352 ultimately have sum1: "setsum e I = 1" using e_def xc yc uv by (simp add: setsum_addf)
5353 def q == "(%i. if (e i = 0) then (p i)
5354 else (u * (c i)/(e i))*\<^sub>R (s i)+(v * (d i)/(e i))*\<^sub>R (t i))"
5355 { fix i assume "i:I"
5356 { assume "e i = 0" hence "q i : S i" using `i:I` p_def q_def by auto }
5359 hence "q i : S i" using mem_convex_alt[of "S i" "s i" "t i" "u * (c i)" "v * (d i)"]
5360 mult_nonneg_nonneg[of u "c i"] mult_nonneg_nonneg[of v "d i"]
5361 assms q_def e_def `i:I` `e i ~= 0` xc yc uv by auto
5362 } ultimately have "q i : S i" by auto
5363 } hence qs: "!i:I. q i : S i" by auto
5364 { fix i assume "i:I"
5366 have ge: "u * (c i) >= 0 & v * (d i) >= 0" using xc yc uv `i:I` by (simp add: mult_nonneg_nonneg)
5367 moreover hence "u * (c i) <= 0 & v * (d i) <= 0" using `e i = 0` e_def `i:I` by simp
5368 ultimately have "u * (c i) = 0 & v * (d i) = 0" by auto
5369 hence "(u * (c i))*\<^sub>R (s i)+(v * (d i))*\<^sub>R (t i) = (e i) *\<^sub>R (q i)"
5370 using `e i = 0` by auto
5374 hence "(u * (c i)/(e i))*\<^sub>R (s i)+(v * (d i)/(e i))*\<^sub>R (t i) = q i"
5376 hence "e i *\<^sub>R ((u * (c i)/(e i))*\<^sub>R (s i)+(v * (d i)/(e i))*\<^sub>R (t i))
5377 = (e i) *\<^sub>R (q i)" by auto
5378 hence "(u * (c i))*\<^sub>R (s i)+(v * (d i))*\<^sub>R (t i) = (e i) *\<^sub>R (q i)"
5379 using `e i ~= 0` by (simp add: algebra_simps)
5381 "(u * (c i))*\<^sub>R (s i)+(v * (d i))*\<^sub>R (t i) = (e i) *\<^sub>R (q i)" by blast
5383 (u * (c i))*\<^sub>R (s i)+(v * (d i))*\<^sub>R (t i) = (e i) *\<^sub>R (q i)" by auto
5384 have "u *\<^sub>R x + v *\<^sub>R y =
5385 setsum (%i. (u * (c i))*\<^sub>R (s i)+(v * (d i))*\<^sub>R (t i)) I"
5386 using xc yc by (simp add: algebra_simps scaleR_right.setsum setsum_addf)
5387 also have "...=setsum (%i. (e i) *\<^sub>R (q i)) I" using * by auto
5388 finally have "u *\<^sub>R x + v *\<^sub>R y = setsum (%i. (e i) *\<^sub>R (q i)) I" by auto
5389 hence "u *\<^sub>R x + v *\<^sub>R y : ?rhs" using ge0 sum1 qs by auto
5390 } hence "convex ?rhs" unfolding convex_def by auto
5391 hence "?rhs : convex" unfolding mem_def by auto
5392 from this show ?thesis using `?lhs >= ?rhs` *
5393 hull_minimal[of "Union (S ` I)" "?rhs" "convex"] by blast
5396 lemma convex_hull_union_two:
5397 fixes S T :: "('m::euclidean_space) set"
5398 assumes "convex S" "S ~= {}" "convex T" "T ~= {}"
5399 shows "convex hull (S Un T) = {u *\<^sub>R s + v *\<^sub>R t |u v s t. u>=0 & v>=0 & u+v=1 & s:S & t:T}"
5402 def I == "{(1::nat),2}"
5403 def s == "(%i. (if i=(1::nat) then S else T))"
5404 have "Union (s ` I) = S Un T" using s_def I_def by auto
5405 hence "convex hull (Union (s ` I)) = convex hull (S Un T)" by auto
5406 moreover have "convex hull Union (s ` I) =
5407 {SUM i:I. c i *\<^sub>R sa i |c sa. (ALL i:I. 0 <= c i) & setsum c I = 1 & (ALL i:I. sa i : s i)}"
5408 apply (subst convex_hull_finite_union[of I s]) using assms s_def I_def by auto
5410 "{SUM i:I. c i *\<^sub>R sa i |c sa. (ALL i:I. 0 <= c i) & setsum c I = 1 & (ALL i:I. sa i : s i)} <=
5412 using s_def I_def by auto
5413 ultimately have "?lhs<=?rhs" by auto
5414 { fix x assume "x : ?rhs"
5415 from this obtain u v s t
5416 where *: "x=u *\<^sub>R s + v *\<^sub>R t & u>=0 & v>=0 & u+v=1 & s:S & t:T" by auto
5417 hence "x : convex hull {s,t}" using convex_hull_2[of s t] by auto
5418 hence "x : convex hull (S Un T)" using * hull_mono[of "{s, t}" "S Un T"] by auto
5419 } hence "?lhs >= ?rhs" by blast
5420 from this show ?thesis using `?lhs<=?rhs` by auto
5423 subsection {* Convexity on direct sums *}
5426 fixes S T :: "('n::euclidean_space) set"
5427 shows "closure S \<oplus> closure T \<subseteq> closure (S \<oplus> T)"
5429 have "(closure S) \<oplus> (closure T) = (\<lambda>(x,y). x + y) ` (closure S \<times> closure T)"
5430 by (simp add: set_plus_image)
5431 also have "... = (\<lambda>(x,y). x + y) ` closure (S \<times> T)"
5432 using closure_direct_sum by auto
5433 also have "... \<subseteq> closure (S \<oplus> T)"
5434 using fst_snd_linear closure_linear_image[of "(\<lambda>(x,y). x + y)" "S \<times> T"]
5435 by (auto simp: set_plus_image)
5436 finally show ?thesis
5441 fixes S T :: "('n::euclidean_space) set"
5442 assumes "convex S" "convex T"
5443 shows "convex (S \<oplus> T)"
5445 have "{x + y |x y. x : S & y : T} = {c. EX a:S. EX b:T. c = a + b}" by auto
5446 thus ?thesis unfolding set_plus_def using convex_sums[of S T] assms by auto
5449 lemma convex_hull_sum:
5450 fixes S T :: "('n::euclidean_space) set"
5451 shows "convex hull (S \<oplus> T) = (convex hull S) \<oplus> (convex hull T)"
5453 have "(convex hull S) \<oplus> (convex hull T) =
5454 (%(x,y). x + y) ` ((convex hull S) <*> (convex hull T))"
5455 by (simp add: set_plus_image)
5456 also have "... = (%(x,y). x + y) ` (convex hull (S <*> T))" using convex_hull_direct_sum by auto
5457 also have "...= convex hull (S \<oplus> T)" using fst_snd_linear linear_conv_bounded_linear
5458 convex_hull_linear_image[of "(%(x,y). x + y)" "S <*> T"] by (auto simp add: set_plus_image)
5459 finally show ?thesis by auto
5462 lemma rel_interior_sum:
5463 fixes S T :: "('n::euclidean_space) set"
5464 assumes "convex S" "convex T"
5465 shows "rel_interior (S \<oplus> T) = (rel_interior S) \<oplus> (rel_interior T)"
5467 have "(rel_interior S) \<oplus> (rel_interior T) = (%(x,y). x + y) ` (rel_interior S <*> rel_interior T)"
5468 by (simp add: set_plus_image)
5469 also have "... = (%(x,y). x + y) ` rel_interior (S <*> T)" using rel_interior_direct_sum assms by auto
5470 also have "...= rel_interior (S \<oplus> T)" using fst_snd_linear convex_direct_sum assms
5471 rel_interior_convex_linear_image[of "(%(x,y). x + y)" "S <*> T"] by (auto simp add: set_plus_image)
5472 finally show ?thesis by auto
5475 lemma convex_sum_gen:
5476 fixes S :: "'a \<Rightarrow> 'n::euclidean_space set"
5477 assumes "\<And>i. i \<in> I \<Longrightarrow> (convex (S i))"
5478 shows "convex (setsum_set S I)"
5480 assume "finite I" from this assms show ?thesis
5481 by induct (auto simp: convex_oplus)
5484 lemma convex_hull_sum_gen:
5485 fixes S :: "'a => ('n::euclidean_space) set"
5486 shows "convex hull (setsum_set S I) = setsum_set (%i. (convex hull (S i))) I"
5487 apply (subst setsum_set_linear) using convex_hull_sum convex_hull_singleton by auto
5490 lemma rel_interior_sum_gen:
5491 fixes S :: "'a => ('n::euclidean_space) set"
5492 assumes "!i:I. (convex (S i))"
5493 shows "rel_interior (setsum_set S I) = setsum_set (%i. (rel_interior (S i))) I"
5494 apply (subst setsum_set_cond_linear[of convex])
5495 using rel_interior_sum rel_interior_sing[of "0"] assms by (auto simp add: convex_oplus)
5497 lemma convex_rel_open_direct_sum:
5498 fixes S T :: "('n::euclidean_space) set"
5499 assumes "convex S" "rel_open S" "convex T" "rel_open T"
5500 shows "convex (S <*> T) & rel_open (S <*> T)"
5501 by (metis assms convex_direct_sum rel_interior_direct_sum rel_open_def)
5503 lemma convex_rel_open_sum:
5504 fixes S T :: "('n::euclidean_space) set"
5505 assumes "convex S" "rel_open S" "convex T" "rel_open T"
5506 shows "convex (S \<oplus> T) & rel_open (S \<oplus> T)"
5507 by (metis assms convex_oplus rel_interior_sum rel_open_def)
5509 lemma convex_hull_finite_union_cones:
5510 assumes "finite I" "I ~= {}"
5511 assumes "!i:I. (convex (S i) & cone (S i) & (S i) ~= {})"
5512 shows "convex hull (Union (S ` I)) = setsum_set S I"
5515 { fix x assume "x : ?lhs"
5516 from this obtain c xs where x_def: "x=setsum (%i. c i *\<^sub>R xs i) I &
5517 (!i:I. c i >= 0) & (setsum c I = 1) & (!i:I. xs i : S i)"
5518 using convex_hull_finite_union[of I S] assms by auto
5519 def s == "(%i. c i *\<^sub>R xs i)"
5520 { fix i assume "i:I"
5521 hence "s i : S i" using s_def x_def assms mem_cone[of "S i" "xs i" "c i"] by auto
5522 } hence "!i:I. s i : S i" by auto
5523 moreover have "x = setsum s I" using x_def s_def by auto
5524 ultimately have "x : ?rhs" using set_setsum_alt[of I S] assms by auto
5527 { fix x assume "x : ?rhs"
5528 from this obtain s where x_def: "x=setsum s I & (!i:I. s i : S i)"
5529 using set_setsum_alt[of I S] assms by auto
5530 def xs == "(%i. of_nat(card I) *\<^sub>R s i)"
5531 hence "x=setsum (%i. ((1 :: real)/of_nat(card I)) *\<^sub>R xs i) I" using x_def assms by auto
5532 moreover have "!i:I. xs i : S i" using x_def xs_def assms by (simp add: cone_def)
5533 moreover have "(!i:I. (1 :: real)/of_nat(card I) >= 0)" by auto
5534 moreover have "setsum (%i. (1 :: real)/of_nat(card I)) I = 1" using assms by auto
5535 ultimately have "x : ?lhs" apply (subst convex_hull_finite_union[of I S])
5536 using assms apply blast
5537 using assms apply blast
5538 apply rule apply (rule_tac x="(%i. (1 :: real)/of_nat(card I))" in exI) by auto
5539 } ultimately show ?thesis by auto
5542 lemma convex_hull_union_cones_two:
5543 fixes S T :: "('m::euclidean_space) set"
5544 assumes "convex S" "cone S" "S ~= {}"
5545 assumes "convex T" "cone T" "T ~= {}"
5546 shows "convex hull (S Un T) = S \<oplus> T"
5548 def I == "{(1::nat),2}"
5549 def A == "(%i. (if i=(1::nat) then S else T))"
5550 have "Union (A ` I) = S Un T" using A_def I_def by auto
5551 hence "convex hull (Union (A ` I)) = convex hull (S Un T)" by auto
5552 moreover have "convex hull Union (A ` I) = setsum_set A I"
5553 apply (subst convex_hull_finite_union_cones[of I A]) using assms A_def I_def by auto
5555 "setsum_set A I = S \<oplus> T" using A_def I_def
5556 unfolding set_plus_def apply auto unfolding set_plus_def by auto
5557 ultimately show ?thesis by auto
5560 lemma rel_interior_convex_hull_union:
5561 fixes S :: "'a => ('n::euclidean_space) set"
5563 assumes "!i:I. convex (S i) & (S i) ~= {}"
5564 shows "rel_interior (convex hull (Union (S ` I))) = {setsum (%i. c i *\<^sub>R s i) I
5565 |c s. (!i:I. c i > 0) & (setsum c I = 1) & (!i:I. s i : rel_interior(S i))}"
5568 { assume "I={}" hence ?thesis using convex_hull_empty rel_interior_empty by auto }
5571 def C0 == "convex hull (Union (S ` I))"
5572 have "!i:I. C0 >= S i" unfolding C0_def using hull_subset[of "Union (S ` I)"] by auto
5573 def K0 == "cone hull ({(1 :: real)} <*> C0)"
5574 def K == "(%i. cone hull ({(1 :: real)} <*> (S i)))"
5575 have "!i:I. K i ~= {}" unfolding K_def using assms by (simp add: cone_hull_empty_iff[symmetric])
5576 { fix i assume "i:I"
5577 hence "convex (K i)" unfolding K_def apply (subst convex_cone_hull) apply (subst convex_direct_sum)
5580 hence convK: "!i:I. convex (K i)" by auto
5581 { fix i assume "i:I"
5582 hence "K0 >= K i" unfolding K0_def K_def apply (subst hull_mono) using `!i:I. C0 >= S i` by auto
5584 hence "K0 >= Union (K ` I)" by auto
5585 moreover have "K0 : convex" unfolding mem_def K0_def
5586 apply (subst convex_cone_hull) apply (subst convex_direct_sum)
5587 unfolding C0_def using convex_convex_hull by auto
5588 ultimately have geq: "K0 >= convex hull (Union (K ` I))" using hull_minimal[of _ "K0" "convex"] by blast
5589 have "!i:I. K i >= {(1 :: real)} <*> (S i)" using K_def by (simp add: hull_subset)
5590 hence "Union (K ` I) >= {(1 :: real)} <*> Union (S ` I)" by auto
5591 hence "convex hull Union (K ` I) >= convex hull ({(1 :: real)} <*> Union (S ` I))" by (simp add: hull_mono)
5592 hence "convex hull Union (K ` I) >= {(1 :: real)} <*> C0" unfolding C0_def
5593 using convex_hull_direct_sum[of "{(1 :: real)}" "Union (S ` I)"] convex_hull_singleton by auto
5594 moreover have "convex hull(Union (K ` I)) : cone" unfolding mem_def apply (subst cone_convex_hull)
5595 using cone_Union[of "K ` I"] apply auto unfolding K_def using cone_cone_hull by auto
5596 ultimately have "convex hull (Union (K ` I)) >= K0"
5597 unfolding K0_def using hull_minimal[of _ "convex hull (Union (K ` I))" "cone"] by blast
5598 hence "K0 = convex hull (Union (K ` I))" using geq by auto
5599 also have "...=setsum_set K I"
5600 apply (subst convex_hull_finite_union_cones[of I K])
5601 using assms apply blast
5602 using `I ~= {}` apply blast
5603 unfolding K_def apply rule
5604 apply (subst convex_cone_hull) apply (subst convex_direct_sum)
5605 using assms cone_cone_hull `!i:I. K i ~= {}` K_def by auto
5606 finally have "K0 = setsum_set K I" by auto
5607 hence *: "rel_interior K0 = setsum_set (%i. (rel_interior (K i))) I"
5608 using rel_interior_sum_gen[of I K] convK by auto
5609 { fix x assume "x : ?lhs"
5610 hence "((1::real),x) : rel_interior K0" using K0_def C0_def
5611 rel_interior_convex_cone_aux[of C0 "(1::real)" x] convex_convex_hull by auto
5612 from this obtain k where k_def: "((1::real),x) = setsum k I & (!i:I. k i : rel_interior (K i))"
5613 using `finite I` * set_setsum_alt[of I "(%i. rel_interior (K i))"] by auto
5614 { fix i assume "i:I"
5615 hence "(convex (S i)) & k i : rel_interior (cone hull {1} <*> S i)" using k_def K_def assms by auto
5616 hence "EX ci si. k i = (ci, ci *\<^sub>R si) & 0 < ci & si : rel_interior (S i)"
5617 using rel_interior_convex_cone[of "S i"] by auto
5619 from this obtain c s where cs_def: "!i:I. (k i = (c i, c i *\<^sub>R s i) & 0 < c i
5620 & s i : rel_interior (S i))" by metis
5621 hence "x = (SUM i:I. c i *\<^sub>R s i) & setsum c I = 1" using k_def by (simp add: setsum_prod)
5622 hence "x : ?rhs" using k_def apply auto
5623 apply (rule_tac x="c" in exI) apply (rule_tac x="s" in exI) using cs_def by auto
5626 { fix x assume "x : ?rhs"
5627 from this obtain c s where cs_def: "x=setsum (%i. c i *\<^sub>R s i) I &
5628 (!i:I. c i > 0) & (setsum c I = 1) & (!i:I. s i : rel_interior(S i))" by auto
5629 def k == "(%i. (c i, c i *\<^sub>R s i))"
5630 { fix i assume "i:I"
5631 hence "k i : rel_interior (K i)"
5632 using k_def K_def assms cs_def rel_interior_convex_cone[of "S i"] by auto
5634 hence "((1::real),x) : rel_interior K0"
5635 using K0_def * set_setsum_alt[of I "(%i. rel_interior (K i))"] assms k_def cs_def
5636 apply auto apply (rule_tac x="k" in exI) by (simp add: setsum_prod)
5637 hence "x : ?lhs" using K0_def C0_def
5638 rel_interior_convex_cone_aux[of C0 "(1::real)" x] by (auto simp add: convex_convex_hull)
5640 ultimately have ?thesis by blast
5641 } ultimately show ?thesis by blast