|
1 (* Title: HOL/Library/Convex_Euclidean_Space.thy |
|
2 Author: Robert Himmelmann, TU Muenchen |
|
3 *) |
|
4 |
|
5 header {* Convex sets, functions and related things. *} |
|
6 |
|
7 theory Convex_Euclidean_Space |
|
8 imports Topology_Euclidean_Space |
|
9 begin |
|
10 |
|
11 |
|
12 (* ------------------------------------------------------------------------- *) |
|
13 (* To be moved elsewhere *) |
|
14 (* ------------------------------------------------------------------------- *) |
|
15 |
|
16 declare vector_add_ldistrib[simp] vector_ssub_ldistrib[simp] vector_smult_assoc[simp] vector_smult_rneg[simp] |
|
17 declare vector_sadd_rdistrib[simp] vector_sub_rdistrib[simp] |
|
18 declare dot_ladd[simp] dot_radd[simp] dot_lsub[simp] dot_rsub[simp] |
|
19 declare dot_lmult[simp] dot_rmult[simp] dot_lneg[simp] dot_rneg[simp] |
|
20 declare UNIV_1[simp] |
|
21 |
|
22 term "(x::real^'n \<Rightarrow> real) 0" |
|
23 |
|
24 lemma dim1in[intro]:"Suc 0 \<in> {1::nat .. CARD(1)}" by auto |
|
25 |
|
26 lemmas vector_component_simps = vector_minus_component vector_smult_component vector_add_component vector_less_eq_def Cart_lambda_beta dest_vec1_def basis_component vector_uminus_component |
|
27 |
|
28 lemmas continuous_intros = continuous_add continuous_vmul continuous_cmul continuous_const continuous_sub continuous_at_id continuous_within_id |
|
29 |
|
30 lemmas continuous_on_intros = continuous_on_add continuous_on_const continuous_on_id continuous_on_compose continuous_on_cmul continuous_on_neg continuous_on_sub |
|
31 uniformly_continuous_on_add uniformly_continuous_on_const uniformly_continuous_on_id uniformly_continuous_on_compose uniformly_continuous_on_cmul uniformly_continuous_on_neg uniformly_continuous_on_sub |
|
32 |
|
33 lemma dest_vec1_simps[simp]: fixes a::"real^1" |
|
34 shows "a$1 = 0 \<longleftrightarrow> a = 0" (*"a \<le> 1 \<longleftrightarrow> dest_vec1 a \<le> 1" "0 \<le> a \<longleftrightarrow> 0 \<le> dest_vec1 a"*) |
|
35 "a \<le> b \<longleftrightarrow> dest_vec1 a \<le> dest_vec1 b" "dest_vec1 (1::real^1) = 1" |
|
36 by(auto simp add:vector_component_simps all_1 Cart_eq) |
|
37 |
|
38 lemma nequals0I:"x\<in>A \<Longrightarrow> A \<noteq> {}" by auto |
|
39 |
|
40 lemma norm_not_0:"(x::real^'n::finite)\<noteq>0 \<Longrightarrow> norm x \<noteq> 0" by auto |
|
41 |
|
42 lemma setsum_delta_notmem: assumes "x\<notin>s" |
|
43 shows "setsum (\<lambda>y. if (y = x) then P x else Q y) s = setsum Q s" |
|
44 "setsum (\<lambda>y. if (x = y) then P x else Q y) s = setsum Q s" |
|
45 "setsum (\<lambda>y. if (y = x) then P y else Q y) s = setsum Q s" |
|
46 "setsum (\<lambda>y. if (x = y) then P y else Q y) s = setsum Q s" |
|
47 apply(rule_tac [!] setsum_cong2) using assms by auto |
|
48 |
|
49 lemma setsum_delta'': |
|
50 fixes s::"'a::real_vector set" assumes "finite s" |
|
51 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)" |
|
52 proof- |
|
53 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 |
|
54 show ?thesis unfolding * using setsum_delta[OF assms, of y "\<lambda>x. f x *\<^sub>R x"] by auto |
|
55 qed |
|
56 |
|
57 lemma not_disjointI:"x\<in>A \<Longrightarrow> x\<in>B \<Longrightarrow> A \<inter> B \<noteq> {}" by blast |
|
58 |
|
59 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 |
|
60 |
|
61 lemma mem_interval_1: fixes x :: "real^1" shows |
|
62 "(x \<in> {a .. b} \<longleftrightarrow> dest_vec1 a \<le> dest_vec1 x \<and> dest_vec1 x \<le> dest_vec1 b)" |
|
63 "(x \<in> {a<..<b} \<longleftrightarrow> dest_vec1 a < dest_vec1 x \<and> dest_vec1 x < dest_vec1 b)" |
|
64 by(simp_all add: Cart_eq vector_less_def vector_less_eq_def dest_vec1_def all_1) |
|
65 |
|
66 lemma image_smult_interval:"(\<lambda>x. m *\<^sub>R (x::real^'n::finite)) ` {a..b} = |
|
67 (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})" |
|
68 using image_affinity_interval[of m 0 a b] by auto |
|
69 |
|
70 lemma dest_vec1_inverval: |
|
71 "dest_vec1 ` {a .. b} = {dest_vec1 a .. dest_vec1 b}" |
|
72 "dest_vec1 ` {a<.. b} = {dest_vec1 a<.. dest_vec1 b}" |
|
73 "dest_vec1 ` {a ..<b} = {dest_vec1 a ..<dest_vec1 b}" |
|
74 "dest_vec1 ` {a<..<b} = {dest_vec1 a<..<dest_vec1 b}" |
|
75 apply(rule_tac [!] equalityI) |
|
76 unfolding subset_eq Ball_def Bex_def mem_interval_1 image_iff |
|
77 apply(rule_tac [!] allI)apply(rule_tac [!] impI) |
|
78 apply(rule_tac[2] x="vec1 x" in exI)apply(rule_tac[4] x="vec1 x" in exI) |
|
79 apply(rule_tac[6] x="vec1 x" in exI)apply(rule_tac[8] x="vec1 x" in exI) |
|
80 by (auto simp add: vector_less_def vector_less_eq_def all_1 dest_vec1_def |
|
81 vec1_dest_vec1[unfolded dest_vec1_def One_nat_def]) |
|
82 |
|
83 lemma dest_vec1_setsum: assumes "finite S" |
|
84 shows " dest_vec1 (setsum f S) = setsum (\<lambda>x. dest_vec1 (f x)) S" |
|
85 using dest_vec1_sum[OF assms] by auto |
|
86 |
|
87 lemma dist_triangle_eq: |
|
88 fixes x y z :: "real ^ _" |
|
89 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)" |
|
90 proof- have *:"x - y + (y - z) = x - z" by auto |
|
91 show ?thesis unfolding dist_norm norm_triangle_eq[of "x - y" "y - z", unfolded smult_conv_scaleR *] |
|
92 by(auto simp add:norm_minus_commute) qed |
|
93 |
|
94 lemma norm_eqI:"x = y \<Longrightarrow> norm x = norm y" by auto |
|
95 lemma norm_minus_eqI:"(x::real^'n::finite) = - y \<Longrightarrow> norm x = norm y" by auto |
|
96 |
|
97 lemma Min_grI: assumes "finite A" "A \<noteq> {}" "\<forall>a\<in>A. x < a" shows "x < Min A" |
|
98 unfolding Min_gr_iff[OF assms(1,2)] using assms(3) by auto |
|
99 |
|
100 lemma dimindex_ge_1:"CARD(_::finite) \<ge> 1" |
|
101 using one_le_card_finite by auto |
|
102 |
|
103 lemma real_dimindex_ge_1:"real (CARD('n::finite)) \<ge> 1" |
|
104 by(metis dimindex_ge_1 linorder_not_less real_eq_of_nat real_le_trans real_of_nat_1 real_of_nat_le_iff) |
|
105 |
|
106 lemma real_dimindex_gt_0:"real (CARD('n::finite)) > 0" apply(rule less_le_trans[OF _ real_dimindex_ge_1]) by auto |
|
107 |
|
108 subsection {* Affine set and affine hull.*} |
|
109 |
|
110 definition |
|
111 affine :: "'a::real_vector set \<Rightarrow> bool" where |
|
112 "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)" |
|
113 |
|
114 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)" |
|
115 proof- have *:"\<And>u v ::real. u + v = 1 \<longleftrightarrow> v = 1 - u" by auto |
|
116 { fix x y assume "x\<in>s" "y\<in>s" |
|
117 hence "(\<forall>u v::real. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s) \<longleftrightarrow> (\<forall>u::real. (1 - u) *\<^sub>R x + u *\<^sub>R y \<in> s)" apply auto |
|
118 apply(erule_tac[!] x="1 - u" in allE) unfolding * by auto } |
|
119 thus ?thesis unfolding affine_def by auto qed |
|
120 |
|
121 lemma affine_empty[intro]: "affine {}" |
|
122 unfolding affine_def by auto |
|
123 |
|
124 lemma affine_sing[intro]: "affine {x}" |
|
125 unfolding affine_alt by (auto simp add: scaleR_left_distrib [symmetric]) |
|
126 |
|
127 lemma affine_UNIV[intro]: "affine UNIV" |
|
128 unfolding affine_def by auto |
|
129 |
|
130 lemma affine_Inter: "(\<forall>s\<in>f. affine s) \<Longrightarrow> affine (\<Inter> f)" |
|
131 unfolding affine_def by auto |
|
132 |
|
133 lemma affine_Int: "affine s \<Longrightarrow> affine t \<Longrightarrow> affine (s \<inter> t)" |
|
134 unfolding affine_def by auto |
|
135 |
|
136 lemma affine_affine_hull: "affine(affine hull s)" |
|
137 unfolding hull_def using affine_Inter[of "{t \<in> affine. s \<subseteq> t}"] |
|
138 unfolding mem_def by auto |
|
139 |
|
140 lemma affine_hull_eq[simp]: "(affine hull s = s) \<longleftrightarrow> affine s" |
|
141 proof- |
|
142 { fix f assume "f \<subseteq> affine" |
|
143 hence "affine (\<Inter>f)" using affine_Inter[of f] unfolding subset_eq mem_def by auto } |
|
144 thus ?thesis using hull_eq[unfolded mem_def, of affine s] by auto |
|
145 qed |
|
146 |
|
147 lemma setsum_restrict_set'': assumes "finite A" |
|
148 shows "setsum f {x \<in> A. P x} = (\<Sum>x\<in>A. if P x then f x else 0)" |
|
149 unfolding mem_def[of _ P, symmetric] unfolding setsum_restrict_set'[OF assms] .. |
|
150 |
|
151 subsection {* Some explicit formulations (from Lars Schewe). *} |
|
152 |
|
153 lemma affine: fixes V::"'a::real_vector set" |
|
154 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)" |
|
155 unfolding affine_def apply rule apply(rule, rule, rule) apply(erule conjE)+ |
|
156 defer apply(rule, rule, rule, rule, rule) proof- |
|
157 fix x y u v assume as:"x \<in> V" "y \<in> V" "u + v = (1::real)" |
|
158 "\<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" |
|
159 thus "u *\<^sub>R x + v *\<^sub>R y \<in> V" apply(cases "x=y") |
|
160 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) |
|
161 by(auto simp add: scaleR_left_distrib[THEN sym]) |
|
162 next |
|
163 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" |
|
164 "finite s" "s \<noteq> {}" "s \<subseteq> V" "setsum u s = (1::real)" |
|
165 def n \<equiv> "card s" |
|
166 have "card s = 0 \<or> card s = 1 \<or> card s = 2 \<or> card s > 2" by auto |
|
167 thus "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V" proof(auto simp only: disjE) |
|
168 assume "card s = 2" hence "card s = Suc (Suc 0)" by auto |
|
169 then obtain a b where "s = {a, b}" unfolding card_Suc_eq by auto |
|
170 thus ?thesis using as(1)[THEN bspec[where x=a], THEN bspec[where x=b]] using as(4,5) |
|
171 by(auto simp add: setsum_clauses(2)) |
|
172 next assume "card s > 2" thus ?thesis using as and n_def proof(induct n arbitrary: u s) |
|
173 case (Suc n) fix s::"'a set" and u::"'a \<Rightarrow> real" |
|
174 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; |
|
175 s \<noteq> {}; s \<subseteq> V; setsum u s = 1; n \<equiv> card s \<rbrakk> \<Longrightarrow> (\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V" and |
|
176 as:"Suc n \<equiv> 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" |
|
177 "finite s" "s \<noteq> {}" "s \<subseteq> V" "setsum u s = 1" |
|
178 have "\<exists>x\<in>s. u x \<noteq> 1" proof(rule_tac ccontr) |
|
179 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 |
|
180 thus False using as(7) and `card s > 2` by (metis Numeral1_eq1_nat less_0_number_of less_int_code(15) |
|
181 less_nat_number_of not_less_iff_gr_or_eq of_nat_1 of_nat_eq_iff pos2 rel_simps(4)) qed |
|
182 then obtain x where x:"x\<in>s" "u x \<noteq> 1" by auto |
|
183 |
|
184 have c:"card (s - {x}) = card s - 1" apply(rule card_Diff_singleton) using `x\<in>s` as(4) by auto |
|
185 have *:"s = insert x (s - {x})" "finite (s - {x})" using `x\<in>s` and as(4) by auto |
|
186 have **:"setsum u (s - {x}) = 1 - u x" |
|
187 using setsum_clauses(2)[OF *(2), of u x, unfolded *(1)[THEN sym] as(7)] by auto |
|
188 have ***:"inverse (1 - u x) * setsum u (s - {x}) = 1" unfolding ** using `u x \<noteq> 1` by auto |
|
189 have "(\<Sum>xa\<in>s - {x}. (inverse (1 - u x) * u xa) *\<^sub>R xa) \<in> V" proof(cases "card (s - {x}) > 2") |
|
190 case True hence "s - {x} \<noteq> {}" "card (s - {x}) = n" unfolding c and as(1)[symmetric] proof(rule_tac ccontr) |
|
191 assume "\<not> s - {x} \<noteq> {}" hence "card (s - {x}) = 0" unfolding card_0_eq[OF *(2)] by simp |
|
192 thus False using True by auto qed auto |
|
193 thus ?thesis apply(rule_tac IA[of "s - {x}" "\<lambda>y. (inverse (1 - u x) * u y)"]) |
|
194 unfolding setsum_right_distrib[THEN sym] using as and *** and True by auto |
|
195 next case False hence "card (s - {x}) = Suc (Suc 0)" using as(2) and c by auto |
|
196 then obtain a b where "(s - {x}) = {a, b}" "a\<noteq>b" unfolding card_Suc_eq by auto |
|
197 thus ?thesis using as(3)[THEN bspec[where x=a], THEN bspec[where x=b]] |
|
198 using *** *(2) and `s \<subseteq> V` unfolding setsum_right_distrib by(auto simp add: setsum_clauses(2)) qed |
|
199 thus "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V" unfolding scaleR_scaleR[THEN sym] and scaleR_right.setsum [symmetric] |
|
200 apply(subst *) unfolding setsum_clauses(2)[OF *(2)] |
|
201 using as(3)[THEN bspec[where x=x], THEN bspec[where x="(inverse (1 - u x)) *\<^sub>R (\<Sum>xa\<in>s - {x}. u xa *\<^sub>R xa)"], |
|
202 THEN spec[where x="u x"], THEN spec[where x="1 - u x"]] and rev_subsetD[OF `x\<in>s` `s\<subseteq>V`] and `u x \<noteq> 1` by auto |
|
203 qed auto |
|
204 next assume "card s = 1" then obtain a where "s={a}" by(auto simp add: card_Suc_eq) |
|
205 thus ?thesis using as(4,5) by simp |
|
206 qed(insert `s\<noteq>{}` `finite s`, auto) |
|
207 qed |
|
208 |
|
209 lemma affine_hull_explicit: |
|
210 "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}" |
|
211 apply(rule hull_unique) apply(subst subset_eq) prefer 3 apply rule unfolding mem_Collect_eq and mem_def[of _ affine] |
|
212 apply (erule exE)+ apply(erule conjE)+ prefer 2 apply rule proof- |
|
213 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" |
|
214 apply(rule_tac x="{x}" in exI, rule_tac x="\<lambda>x. 1" in exI) by auto |
|
215 next |
|
216 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" |
|
217 thus "x \<in> t" using as(2)[unfolded affine, THEN spec[where x=s], THEN spec[where x=u]] by auto |
|
218 next |
|
219 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 |
|
220 apply(rule,rule,rule,rule,rule) unfolding mem_Collect_eq proof- |
|
221 fix u v ::real assume uv:"u + v = 1" |
|
222 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" |
|
223 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 |
|
224 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" |
|
225 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 |
|
226 have xy:"finite (sx \<union> sy)" using x(1) y(1) by auto |
|
227 have **:"(sx \<union> sy) \<inter> sx = sx" "(sx \<union> sy) \<inter> sy = sy" by auto |
|
228 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" |
|
229 apply(rule_tac x="sx \<union> sy" in exI) |
|
230 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) |
|
231 unfolding scaleR_left_distrib setsum_addf if_smult scaleR_zero_left ** setsum_restrict_set[OF xy, THEN sym] |
|
232 unfolding scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] and setsum_right_distrib[THEN sym] |
|
233 unfolding x y using x(1-3) y(1-3) uv by simp qed qed |
|
234 |
|
235 lemma affine_hull_finite: |
|
236 assumes "finite s" |
|
237 shows "affine hull s = {y. \<exists>u. setsum u s = 1 \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = y}" |
|
238 unfolding affine_hull_explicit and expand_set_eq and mem_Collect_eq apply (rule,rule) |
|
239 apply(erule exE)+ apply(erule conjE)+ defer apply(erule exE) apply(erule conjE) proof- |
|
240 fix x u assume "setsum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x" |
|
241 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" |
|
242 apply(rule_tac x=s in exI, rule_tac x=u in exI) using assms by auto |
|
243 next |
|
244 fix x t u assume "t \<subseteq> s" hence *:"s \<inter> t = t" by auto |
|
245 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" |
|
246 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) |
|
247 unfolding if_smult scaleR_zero_left and setsum_restrict_set[OF assms, THEN sym] and * by auto qed |
|
248 |
|
249 subsection {* Stepping theorems and hence small special cases. *} |
|
250 |
|
251 lemma affine_hull_empty[simp]: "affine hull {} = {}" |
|
252 apply(rule hull_unique) unfolding mem_def by auto |
|
253 |
|
254 lemma affine_hull_finite_step: |
|
255 fixes y :: "'a::real_vector" |
|
256 shows "(\<exists>u. setsum u {} = w \<and> setsum (\<lambda>x. u x *\<^sub>R x) {} = y) \<longleftrightarrow> w = 0 \<and> y = 0" (is ?th1) |
|
257 "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> |
|
258 (\<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)") |
|
259 proof- |
|
260 show ?th1 by simp |
|
261 assume ?as |
|
262 { assume ?lhs |
|
263 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 |
|
264 have ?rhs proof(cases "a\<in>s") |
|
265 case True hence *:"insert a s = s" by auto |
|
266 show ?thesis using u[unfolded *] apply(rule_tac x=0 in exI) by auto |
|
267 next |
|
268 case False thus ?thesis apply(rule_tac x="u a" in exI) using u and `?as` by auto |
|
269 qed } moreover |
|
270 { assume ?rhs |
|
271 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 |
|
272 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 |
|
273 have ?lhs proof(cases "a\<in>s") |
|
274 case True thus ?thesis |
|
275 apply(rule_tac x="\<lambda>x. (if x=a then v else 0) + u x" in exI) |
|
276 unfolding setsum_clauses(2)[OF `?as`] apply simp |
|
277 unfolding scaleR_left_distrib and setsum_addf |
|
278 unfolding vu and * and scaleR_zero_left |
|
279 by (auto simp add: setsum_delta[OF `?as`]) |
|
280 next |
|
281 case False |
|
282 hence **:"\<And>x. x \<in> s \<Longrightarrow> u x = (if x = a then v else u x)" |
|
283 "\<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 |
|
284 from False show ?thesis |
|
285 apply(rule_tac x="\<lambda>x. if x=a then v else u x" in exI) |
|
286 unfolding setsum_clauses(2)[OF `?as`] and * using vu |
|
287 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)] |
|
288 using setsum_cong2[of s u "\<lambda>x. if x = a then v else u x", OF **(1)] by auto |
|
289 qed } |
|
290 ultimately show "?lhs = ?rhs" by blast |
|
291 qed |
|
292 |
|
293 lemma affine_hull_2: |
|
294 fixes a b :: "'a::real_vector" |
|
295 shows "affine hull {a,b} = {u *\<^sub>R a + v *\<^sub>R b| u v. (u + v = 1)}" (is "?lhs = ?rhs") |
|
296 proof- |
|
297 have *:"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)" |
|
298 "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto |
|
299 have "?lhs = {y. \<exists>u. setsum u {a, b} = 1 \<and> (\<Sum>v\<in>{a, b}. u v *\<^sub>R v) = y}" |
|
300 using affine_hull_finite[of "{a,b}"] by auto |
|
301 also have "\<dots> = {y. \<exists>v u. u b = 1 - v \<and> u b *\<^sub>R b = y - v *\<^sub>R a}" |
|
302 by(simp add: affine_hull_finite_step(2)[of "{b}" a]) |
|
303 also have "\<dots> = ?rhs" unfolding * by auto |
|
304 finally show ?thesis by auto |
|
305 qed |
|
306 |
|
307 lemma affine_hull_3: |
|
308 fixes a b c :: "'a::real_vector" |
|
309 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") |
|
310 proof- |
|
311 have *:"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)" |
|
312 "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto |
|
313 show ?thesis apply(simp add: affine_hull_finite affine_hull_finite_step) |
|
314 unfolding * apply auto |
|
315 apply(rule_tac x=v in exI) apply(rule_tac x=va in exI) apply auto |
|
316 apply(rule_tac x=u in exI) by(auto intro!: exI) |
|
317 qed |
|
318 |
|
319 subsection {* Some relations between affine hull and subspaces. *} |
|
320 |
|
321 lemma affine_hull_insert_subset_span: |
|
322 fixes a :: "real ^ _" |
|
323 shows "affine hull (insert a s) \<subseteq> {a + v| v . v \<in> span {x - a | x . x \<in> s}}" |
|
324 unfolding subset_eq Ball_def unfolding affine_hull_explicit span_explicit mem_Collect_eq smult_conv_scaleR |
|
325 apply(rule,rule) apply(erule exE)+ apply(erule conjE)+ proof- |
|
326 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" |
|
327 have "(\<lambda>x. x - a) ` (t - {a}) \<subseteq> {x - a |x. x \<in> s}" using as(3) by auto |
|
328 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)" |
|
329 apply(rule_tac x="x - a" in exI) |
|
330 apply (rule conjI, simp) |
|
331 apply(rule_tac x="(\<lambda>x. x - a) ` (t - {a})" in exI) |
|
332 apply(rule_tac x="\<lambda>x. u (x + a)" in exI) |
|
333 apply (rule conjI) using as(1) apply simp |
|
334 apply (erule conjI) |
|
335 using as(1) |
|
336 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) |
|
337 unfolding as by simp qed |
|
338 |
|
339 lemma affine_hull_insert_span: |
|
340 fixes a :: "real ^ _" |
|
341 assumes "a \<notin> s" |
|
342 shows "affine hull (insert a s) = |
|
343 {a + v | v . v \<in> span {x - a | x. x \<in> s}}" |
|
344 apply(rule, rule affine_hull_insert_subset_span) unfolding subset_eq Ball_def |
|
345 unfolding affine_hull_explicit and mem_Collect_eq proof(rule,rule,erule exE,erule conjE) |
|
346 fix y v assume "y = a + v" "v \<in> span {x - a |x. x \<in> s}" |
|
347 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 smult_conv_scaleR by auto |
|
348 def f \<equiv> "(\<lambda>x. x + a) ` t" |
|
349 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 |
|
350 by(auto simp add: setsum_reindex[unfolded inj_on_def]) |
|
351 have *:"f \<inter> {a} = {}" "f \<inter> - {a} = f" using f(2) assms by auto |
|
352 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" |
|
353 apply(rule_tac x="insert a f" in exI) |
|
354 apply(rule_tac x="\<lambda>x. if x=a then 1 - setsum (\<lambda>x. u (x - a)) f else u (x - a)" in exI) |
|
355 using assms and f unfolding setsum_clauses(2)[OF f(1)] and if_smult |
|
356 unfolding setsum_cases[OF f(1), of "{a}", unfolded singleton_iff] and * |
|
357 by (auto simp add: setsum_subtractf scaleR_left.setsum algebra_simps) qed |
|
358 |
|
359 lemma affine_hull_span: |
|
360 fixes a :: "real ^ _" |
|
361 assumes "a \<in> s" |
|
362 shows "affine hull s = {a + v | v. v \<in> span {x - a | x. x \<in> s - {a}}}" |
|
363 using affine_hull_insert_span[of a "s - {a}", unfolded insert_Diff[OF assms]] by auto |
|
364 |
|
365 subsection {* Convexity. *} |
|
366 |
|
367 definition |
|
368 convex :: "'a::real_vector set \<Rightarrow> bool" where |
|
369 "convex s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u\<ge>0. \<forall>v\<ge>0. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s)" |
|
370 |
|
371 lemma convex_alt: "convex s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u. 0 \<le> u \<and> u \<le> 1 \<longrightarrow> ((1 - u) *\<^sub>R x + u *\<^sub>R y) \<in> s)" |
|
372 proof- have *:"\<And>u v::real. u + v = 1 \<longleftrightarrow> u = 1 - v" by auto |
|
373 show ?thesis unfolding convex_def apply auto |
|
374 apply(erule_tac x=x in ballE) apply(erule_tac x=y in ballE) apply(erule_tac x="1 - u" in allE) |
|
375 by (auto simp add: *) qed |
|
376 |
|
377 lemma mem_convex: |
|
378 assumes "convex s" "a \<in> s" "b \<in> s" "0 \<le> u" "u \<le> 1" |
|
379 shows "((1 - u) *\<^sub>R a + u *\<^sub>R b) \<in> s" |
|
380 using assms unfolding convex_alt by auto |
|
381 |
|
382 lemma convex_empty[intro]: "convex {}" |
|
383 unfolding convex_def by simp |
|
384 |
|
385 lemma convex_singleton[intro]: "convex {a}" |
|
386 unfolding convex_def by (auto simp add:scaleR_left_distrib[THEN sym]) |
|
387 |
|
388 lemma convex_UNIV[intro]: "convex UNIV" |
|
389 unfolding convex_def by auto |
|
390 |
|
391 lemma convex_Inter: "(\<forall>s\<in>f. convex s) ==> convex(\<Inter> f)" |
|
392 unfolding convex_def by auto |
|
393 |
|
394 lemma convex_Int: "convex s \<Longrightarrow> convex t \<Longrightarrow> convex (s \<inter> t)" |
|
395 unfolding convex_def by auto |
|
396 |
|
397 lemma convex_halfspace_le: "convex {x. inner a x \<le> b}" |
|
398 unfolding convex_def apply auto |
|
399 unfolding inner_add inner_scaleR |
|
400 by (metis real_convex_bound_le) |
|
401 |
|
402 lemma convex_halfspace_ge: "convex {x. inner a x \<ge> b}" |
|
403 proof- have *:"{x. inner a x \<ge> b} = {x. inner (-a) x \<le> -b}" by auto |
|
404 show ?thesis apply(unfold *) using convex_halfspace_le[of "-a" "-b"] by auto qed |
|
405 |
|
406 lemma convex_hyperplane: "convex {x. inner a x = b}" |
|
407 proof- |
|
408 have *:"{x. inner a x = b} = {x. inner a x \<le> b} \<inter> {x. inner a x \<ge> b}" by auto |
|
409 show ?thesis unfolding * apply(rule convex_Int) |
|
410 using convex_halfspace_le convex_halfspace_ge by auto |
|
411 qed |
|
412 |
|
413 lemma convex_halfspace_lt: "convex {x. inner a x < b}" |
|
414 unfolding convex_def |
|
415 by(auto simp add: real_convex_bound_lt inner_add) |
|
416 |
|
417 lemma convex_halfspace_gt: "convex {x. inner a x > b}" |
|
418 using convex_halfspace_lt[of "-a" "-b"] by auto |
|
419 |
|
420 lemma convex_positive_orthant: "convex {x::real^'n::finite. (\<forall>i. 0 \<le> x$i)}" |
|
421 unfolding convex_def apply auto apply(erule_tac x=i in allE)+ |
|
422 apply(rule add_nonneg_nonneg) by(auto simp add: mult_nonneg_nonneg) |
|
423 |
|
424 subsection {* Explicit expressions for convexity in terms of arbitrary sums. *} |
|
425 |
|
426 lemma convex: "convex s \<longleftrightarrow> |
|
427 (\<forall>(k::nat) u x. (\<forall>i. 1\<le>i \<and> i\<le>k \<longrightarrow> 0 \<le> u i \<and> x i \<in>s) \<and> (setsum u {1..k} = 1) |
|
428 \<longrightarrow> setsum (\<lambda>i. u i *\<^sub>R x i) {1..k} \<in> s)" |
|
429 unfolding convex_def apply rule apply(rule allI)+ defer apply(rule ballI)+ apply(rule allI)+ proof(rule,rule,rule,rule) |
|
430 fix x y u v assume as:"\<forall>(k::nat) u x. (\<forall>i. 1 \<le> i \<and> i \<le> k \<longrightarrow> 0 \<le> u i \<and> x i \<in> s) \<and> setsum u {1..k} = 1 \<longrightarrow> (\<Sum>i = 1..k. u i *\<^sub>R x i) \<in> s" |
|
431 "x \<in> s" "y \<in> s" "0 \<le> u" "0 \<le> v" "u + v = (1::real)" |
|
432 show "u *\<^sub>R x + v *\<^sub>R y \<in> s" using as(1)[THEN spec[where x=2], THEN spec[where x="\<lambda>n. if n=1 then u else v"], THEN spec[where x="\<lambda>n. if n=1 then x else y"]] and as(2-) |
|
433 by (auto simp add: setsum_head_Suc) |
|
434 next |
|
435 fix k u x assume as:"\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u\<ge>0. \<forall>v\<ge>0. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s" |
|
436 show "(\<forall>i::nat. 1 \<le> i \<and> i \<le> k \<longrightarrow> 0 \<le> u i \<and> x i \<in> s) \<and> setsum u {1..k} = 1 \<longrightarrow> (\<Sum>i = 1..k. u i *\<^sub>R x i) \<in> s" apply(rule,erule conjE) proof(induct k arbitrary: u) |
|
437 case (Suc k) show ?case proof(cases "u (Suc k) = 1") |
|
438 case True hence "(\<Sum>i = Suc 0..k. u i *\<^sub>R x i) = 0" apply(rule_tac setsum_0') apply(rule ccontr) unfolding ball_simps apply(erule bexE) proof- |
|
439 fix i assume i:"i \<in> {Suc 0..k}" "u i *\<^sub>R x i \<noteq> 0" |
|
440 hence ui:"u i \<noteq> 0" by auto |
|
441 hence "setsum (\<lambda>k. if k=i then u i else 0) {1 .. k} \<le> setsum u {1 .. k}" apply(rule_tac setsum_mono) using Suc(2) by auto |
|
442 hence "setsum u {1 .. k} \<ge> u i" using i(1) by(auto simp add: setsum_delta) |
|
443 hence "setsum u {1 .. k} > 0" using ui apply(rule_tac less_le_trans[of _ "u i"]) using Suc(2)[THEN spec[where x=i]] and i(1) by auto |
|
444 thus False using Suc(3) unfolding setsum_cl_ivl_Suc and True by simp qed |
|
445 thus ?thesis unfolding setsum_cl_ivl_Suc using True and Suc(2) by auto |
|
446 next |
|
447 have *:"setsum u {1..k} = 1 - u (Suc k)" using Suc(3)[unfolded setsum_cl_ivl_Suc] by auto |
|
448 have **:"u (Suc k) \<le> 1" apply(rule ccontr) unfolding not_le using Suc(3) using setsum_nonneg[of "{1..k}" u] using Suc(2) by auto |
|
449 have ***:"\<And>i k. (u i / (1 - u (Suc k))) *\<^sub>R x i = (inverse (1 - u (Suc k))) *\<^sub>R (u i *\<^sub>R x i)" unfolding real_divide_def by (auto simp add: algebra_simps) |
|
450 case False hence nn:"1 - u (Suc k) \<noteq> 0" by auto |
|
451 have "(\<Sum>i = 1..k. (u i / (1 - u (Suc k))) *\<^sub>R x i) \<in> s" apply(rule Suc(1)) unfolding setsum_divide_distrib[THEN sym] and * |
|
452 apply(rule_tac allI) apply(rule,rule) apply(rule divide_nonneg_pos) using nn Suc(2) ** by auto |
|
453 hence "(1 - u (Suc k)) *\<^sub>R (\<Sum>i = 1..k. (u i / (1 - u (Suc k))) *\<^sub>R x i) + u (Suc k) *\<^sub>R x (Suc k) \<in> s" |
|
454 apply(rule as[THEN bspec, THEN bspec, THEN spec, THEN mp, THEN spec, THEN mp, THEN mp]) using Suc(2)[THEN spec[where x="Suc k"]] and ** by auto |
|
455 thus ?thesis unfolding setsum_cl_ivl_Suc and *** and scaleR_right.setsum [symmetric] using nn by auto qed qed auto qed |
|
456 |
|
457 |
|
458 lemma convex_explicit: |
|
459 fixes s :: "'a::real_vector set" |
|
460 shows "convex s \<longleftrightarrow> |
|
461 (\<forall>t u. finite t \<and> t \<subseteq> s \<and> (\<forall>x\<in>t. 0 \<le> u x) \<and> setsum u t = 1 \<longrightarrow> setsum (\<lambda>x. u x *\<^sub>R x) t \<in> s)" |
|
462 unfolding convex_def apply(rule,rule,rule) apply(subst imp_conjL,rule) defer apply(rule,rule,rule,rule,rule,rule,rule) proof- |
|
463 fix x y u v assume as:"\<forall>t u. finite t \<and> t \<subseteq> s \<and> (\<forall>x\<in>t. 0 \<le> u x) \<and> setsum u t = 1 \<longrightarrow> (\<Sum>x\<in>t. u x *\<^sub>R x) \<in> s" "x \<in> s" "y \<in> s" "0 \<le> u" "0 \<le> v" "u + v = (1::real)" |
|
464 show "u *\<^sub>R x + v *\<^sub>R y \<in> s" proof(cases "x=y") |
|
465 case True show ?thesis unfolding True and scaleR_left_distrib[THEN sym] using as(3,6) by auto next |
|
466 case False thus ?thesis using as(1)[THEN spec[where x="{x,y}"], THEN spec[where x="\<lambda>z. if z=x then u else v"]] and as(2-) by auto qed |
|
467 next |
|
468 fix t u assume asm:"\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u\<ge>0. \<forall>v\<ge>0. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s" "finite (t::'a set)" |
|
469 (*"finite t" "t \<subseteq> s" "\<forall>x\<in>t. (0::real) \<le> u x" "setsum u t = 1"*) |
|
470 from this(2) have "\<forall>u. t \<subseteq> s \<and> (\<forall>x\<in>t. 0 \<le> u x) \<and> setsum u t = 1 \<longrightarrow> (\<Sum>x\<in>t. u x *\<^sub>R x) \<in> s" apply(induct_tac t rule:finite_induct) |
|
471 prefer 3 apply (rule,rule) apply(erule conjE)+ proof- |
|
472 fix x f u assume ind:"\<forall>u. f \<subseteq> s \<and> (\<forall>x\<in>f. 0 \<le> u x) \<and> setsum u f = 1 \<longrightarrow> (\<Sum>x\<in>f. u x *\<^sub>R x) \<in> s" |
|
473 assume as:"finite f" "x \<notin> f" "insert x f \<subseteq> s" "\<forall>x\<in>insert x f. 0 \<le> u x" "setsum u (insert x f) = (1::real)" |
|
474 show "(\<Sum>x\<in>insert x f. u x *\<^sub>R x) \<in> s" proof(cases "u x = 1") |
|
475 case True hence "setsum (\<lambda>x. u x *\<^sub>R x) f = 0" apply(rule_tac setsum_0') apply(rule ccontr) unfolding ball_simps apply(erule bexE) proof- |
|
476 fix y assume y:"y \<in> f" "u y *\<^sub>R y \<noteq> 0" |
|
477 hence uy:"u y \<noteq> 0" by auto |
|
478 hence "setsum (\<lambda>k. if k=y then u y else 0) f \<le> setsum u f" apply(rule_tac setsum_mono) using as(4) by auto |
|
479 hence "setsum u f \<ge> u y" using y(1) and as(1) by(auto simp add: setsum_delta) |
|
480 hence "setsum u f > 0" using uy apply(rule_tac less_le_trans[of _ "u y"]) using as(4) and y(1) by auto |
|
481 thus False using as(2,5) unfolding setsum_clauses(2)[OF as(1)] and True by auto qed |
|
482 thus ?thesis unfolding setsum_clauses(2)[OF as(1)] using as(2,3) unfolding True by auto |
|
483 next |
|
484 have *:"setsum u f = setsum u (insert x f) - u x" using as(2) unfolding setsum_clauses(2)[OF as(1)] by auto |
|
485 have **:"u x \<le> 1" apply(rule ccontr) unfolding not_le using as(5)[unfolded setsum_clauses(2)[OF as(1)]] and as(2) |
|
486 using setsum_nonneg[of f u] and as(4) by auto |
|
487 case False hence "inverse (1 - u x) *\<^sub>R (\<Sum>x\<in>f. u x *\<^sub>R x) \<in> s" unfolding scaleR_right.setsum and scaleR_scaleR |
|
488 apply(rule_tac ind[THEN spec, THEN mp]) apply rule defer apply rule apply rule apply(rule mult_nonneg_nonneg) |
|
489 unfolding setsum_right_distrib[THEN sym] and * using as and ** by auto |
|
490 hence "u x *\<^sub>R x + (1 - u x) *\<^sub>R ((inverse (1 - u x)) *\<^sub>R setsum (\<lambda>x. u x *\<^sub>R x) f) \<in>s" |
|
491 apply(rule_tac asm(1)[THEN bspec, THEN bspec, THEN spec, THEN mp, THEN spec, THEN mp, THEN mp]) using as and ** False by auto |
|
492 thus ?thesis unfolding setsum_clauses(2)[OF as(1)] using as(2) and False by auto qed |
|
493 qed auto thus "t \<subseteq> s \<and> (\<forall>x\<in>t. 0 \<le> u x) \<and> setsum u t = 1 \<longrightarrow> (\<Sum>x\<in>t. u x *\<^sub>R x) \<in> s" by auto |
|
494 qed |
|
495 |
|
496 lemma convex_finite: assumes "finite s" |
|
497 shows "convex s \<longleftrightarrow> (\<forall>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 |
|
498 \<longrightarrow> setsum (\<lambda>x. u x *\<^sub>R x) s \<in> s)" |
|
499 unfolding convex_explicit apply(rule, rule, rule) defer apply(rule,rule,rule)apply(erule conjE)+ proof- |
|
500 fix t u assume as:"\<forall>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<longrightarrow> (\<Sum>x\<in>s. u x *\<^sub>R x) \<in> s" " finite t" "t \<subseteq> s" "\<forall>x\<in>t. 0 \<le> u x" "setsum u t = (1::real)" |
|
501 have *:"s \<inter> t = t" using as(3) by auto |
|
502 show "(\<Sum>x\<in>t. u x *\<^sub>R x) \<in> s" using as(1)[THEN spec[where x="\<lambda>x. if x\<in>t then u x else 0"]] |
|
503 unfolding if_smult and setsum_cases[OF assms] and * using as(2-) by auto |
|
504 qed (erule_tac x=s in allE, erule_tac x=u in allE, auto) |
|
505 |
|
506 subsection {* Cones. *} |
|
507 |
|
508 definition |
|
509 cone :: "'a::real_vector set \<Rightarrow> bool" where |
|
510 "cone s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>c\<ge>0. (c *\<^sub>R x) \<in> s)" |
|
511 |
|
512 lemma cone_empty[intro, simp]: "cone {}" |
|
513 unfolding cone_def by auto |
|
514 |
|
515 lemma cone_univ[intro, simp]: "cone UNIV" |
|
516 unfolding cone_def by auto |
|
517 |
|
518 lemma cone_Inter[intro]: "(\<forall>s\<in>f. cone s) \<Longrightarrow> cone(\<Inter> f)" |
|
519 unfolding cone_def by auto |
|
520 |
|
521 subsection {* Conic hull. *} |
|
522 |
|
523 lemma cone_cone_hull: "cone (cone hull s)" |
|
524 unfolding hull_def using cone_Inter[of "{t \<in> conic. s \<subseteq> t}"] |
|
525 by (auto simp add: mem_def) |
|
526 |
|
527 lemma cone_hull_eq: "(cone hull s = s) \<longleftrightarrow> cone s" |
|
528 apply(rule hull_eq[unfolded mem_def]) |
|
529 using cone_Inter unfolding subset_eq by (auto simp add: mem_def) |
|
530 |
|
531 subsection {* Affine dependence and consequential theorems (from Lars Schewe). *} |
|
532 |
|
533 definition |
|
534 affine_dependent :: "'a::real_vector set \<Rightarrow> bool" where |
|
535 "affine_dependent s \<longleftrightarrow> (\<exists>x\<in>s. x \<in> (affine hull (s - {x})))" |
|
536 |
|
537 lemma affine_dependent_explicit: |
|
538 "affine_dependent p \<longleftrightarrow> |
|
539 (\<exists>s u. finite s \<and> s \<subseteq> p \<and> setsum u s = 0 \<and> |
|
540 (\<exists>v\<in>s. u v \<noteq> 0) \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = 0)" |
|
541 unfolding affine_dependent_def affine_hull_explicit mem_Collect_eq apply(rule) |
|
542 apply(erule bexE,erule exE,erule exE) apply(erule conjE)+ defer apply(erule exE,erule exE) apply(erule conjE)+ apply(erule bexE) |
|
543 proof- |
|
544 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" |
|
545 have "x\<notin>s" using as(1,4) by auto |
|
546 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" |
|
547 apply(rule_tac x="insert x s" in exI, rule_tac x="\<lambda>v. if v = x then - 1 else u v" in exI) |
|
548 unfolding if_smult and setsum_clauses(2)[OF as(2)] and setsum_delta_notmem[OF `x\<notin>s`] and as using as by auto |
|
549 next |
|
550 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" |
|
551 have "s \<noteq> {v}" using as(3,6) by auto |
|
552 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" |
|
553 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) |
|
554 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 |
|
555 qed |
|
556 |
|
557 lemma affine_dependent_explicit_finite: |
|
558 fixes s :: "'a::real_vector set" assumes "finite s" |
|
559 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)" |
|
560 (is "?lhs = ?rhs") |
|
561 proof |
|
562 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 |
|
563 assume ?lhs |
|
564 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" |
|
565 unfolding affine_dependent_explicit by auto |
|
566 thus ?rhs apply(rule_tac x="\<lambda>x. if x\<in>t then u x else 0" in exI) |
|
567 apply auto unfolding * and setsum_restrict_set[OF assms, THEN sym] |
|
568 unfolding Int_absorb1[OF `t\<subseteq>s`] by auto |
|
569 next |
|
570 assume ?rhs |
|
571 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 |
|
572 thus ?lhs unfolding affine_dependent_explicit using assms by auto |
|
573 qed |
|
574 |
|
575 subsection {* A general lemma. *} |
|
576 |
|
577 lemma convex_connected: |
|
578 fixes s :: "'a::real_normed_vector set" |
|
579 assumes "convex s" shows "connected s" |
|
580 proof- |
|
581 { fix e1 e2 assume as:"open e1" "open e2" "e1 \<inter> e2 \<inter> s = {}" "s \<subseteq> e1 \<union> e2" |
|
582 assume "e1 \<inter> s \<noteq> {}" "e2 \<inter> s \<noteq> {}" |
|
583 then obtain x1 x2 where x1:"x1\<in>e1" "x1\<in>s" and x2:"x2\<in>e2" "x2\<in>s" by auto |
|
584 hence n:"norm (x1 - x2) > 0" unfolding zero_less_norm_iff using as(3) by auto |
|
585 |
|
586 { fix x e::real assume as:"0 \<le> x" "x \<le> 1" "0 < e" |
|
587 { 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" |
|
588 by (simp add: algebra_simps) |
|
589 assume "\<bar>y - x\<bar> < e / norm (x1 - x2)" |
|
590 hence "norm ((1 - x) *\<^sub>R x1 + x *\<^sub>R x2 - ((1 - y) *\<^sub>R x1 + y *\<^sub>R x2)) < e" |
|
591 unfolding * and scaleR_right_diff_distrib[THEN sym] |
|
592 unfolding less_divide_eq using n by auto } |
|
593 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" |
|
594 apply(rule_tac x="e / norm (x1 - x2)" in exI) using as |
|
595 apply auto unfolding zero_less_divide_iff using n by simp } note * = this |
|
596 |
|
597 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" |
|
598 apply(rule connected_real_lemma) apply (simp add: `x1\<in>e1` `x2\<in>e2` dist_commute)+ |
|
599 using * apply(simp add: dist_norm) |
|
600 using as(1,2)[unfolded open_dist] apply simp |
|
601 using as(1,2)[unfolded open_dist] apply simp |
|
602 using assms[unfolded convex_alt, THEN bspec[where x=x1], THEN bspec[where x=x2]] using x1 x2 |
|
603 using as(3) by auto |
|
604 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 |
|
605 hence False using as(4) |
|
606 using assms[unfolded convex_alt, THEN bspec[where x=x1], THEN bspec[where x=x2]] |
|
607 using x1(2) x2(2) by auto } |
|
608 thus ?thesis unfolding connected_def by auto |
|
609 qed |
|
610 |
|
611 subsection {* One rather trivial consequence. *} |
|
612 |
|
613 lemma connected_UNIV: "connected (UNIV :: 'a::real_normed_vector set)" |
|
614 by(simp add: convex_connected convex_UNIV) |
|
615 |
|
616 subsection {* Convex functions into the reals. *} |
|
617 |
|
618 definition |
|
619 convex_on :: "'a::real_vector set \<Rightarrow> ('a \<Rightarrow> real) \<Rightarrow> bool" where |
|
620 "convex_on s f \<longleftrightarrow> |
|
621 (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u\<ge>0. \<forall>v\<ge>0. u + v = 1 \<longrightarrow> f (u *\<^sub>R x + v *\<^sub>R y) \<le> u * f x + v * f y)" |
|
622 |
|
623 lemma convex_on_subset: "convex_on t f \<Longrightarrow> s \<subseteq> t \<Longrightarrow> convex_on s f" |
|
624 unfolding convex_on_def by auto |
|
625 |
|
626 lemma convex_add: |
|
627 assumes "convex_on s f" "convex_on s g" |
|
628 shows "convex_on s (\<lambda>x. f x + g x)" |
|
629 proof- |
|
630 { fix x y assume "x\<in>s" "y\<in>s" moreover |
|
631 fix u v ::real assume "0 \<le> u" "0 \<le> v" "u + v = 1" |
|
632 ultimately have "f (u *\<^sub>R x + v *\<^sub>R y) + g (u *\<^sub>R x + v *\<^sub>R y) \<le> (u * f x + v * f y) + (u * g x + v * g y)" |
|
633 using assms(1)[unfolded convex_on_def, THEN bspec[where x=x], THEN bspec[where x=y], THEN spec[where x=u]] |
|
634 using assms(2)[unfolded convex_on_def, THEN bspec[where x=x], THEN bspec[where x=y], THEN spec[where x=u]] |
|
635 apply - apply(rule add_mono) by auto |
|
636 hence "f (u *\<^sub>R x + v *\<^sub>R y) + g (u *\<^sub>R x + v *\<^sub>R y) \<le> u * (f x + g x) + v * (f y + g y)" by (simp add: ring_simps) } |
|
637 thus ?thesis unfolding convex_on_def by auto |
|
638 qed |
|
639 |
|
640 lemma convex_cmul: |
|
641 assumes "0 \<le> (c::real)" "convex_on s f" |
|
642 shows "convex_on s (\<lambda>x. c * f x)" |
|
643 proof- |
|
644 have *:"\<And>u c fx v fy ::real. u * (c * fx) + v * (c * fy) = c * (u * fx + v * fy)" by (simp add: ring_simps) |
|
645 show ?thesis using assms(2) and mult_mono1[OF _ assms(1)] unfolding convex_on_def and * by auto |
|
646 qed |
|
647 |
|
648 lemma convex_lower: |
|
649 assumes "convex_on s f" "x\<in>s" "y \<in> s" "0 \<le> u" "0 \<le> v" "u + v = 1" |
|
650 shows "f (u *\<^sub>R x + v *\<^sub>R y) \<le> max (f x) (f y)" |
|
651 proof- |
|
652 let ?m = "max (f x) (f y)" |
|
653 have "u * f x + v * f y \<le> u * max (f x) (f y) + v * max (f x) (f y)" apply(rule add_mono) |
|
654 using assms(4,5) by(auto simp add: mult_mono1) |
|
655 also have "\<dots> = max (f x) (f y)" using assms(6) unfolding distrib[THEN sym] by auto |
|
656 finally show ?thesis using assms(1)[unfolded convex_on_def, THEN bspec[where x=x], THEN bspec[where x=y], THEN spec[where x=u]] |
|
657 using assms(2-6) by auto |
|
658 qed |
|
659 |
|
660 lemma convex_local_global_minimum: |
|
661 fixes s :: "'a::real_normed_vector set" |
|
662 assumes "0<e" "convex_on s f" "ball x e \<subseteq> s" "\<forall>y\<in>ball x e. f x \<le> f y" |
|
663 shows "\<forall>y\<in>s. f x \<le> f y" |
|
664 proof(rule ccontr) |
|
665 have "x\<in>s" using assms(1,3) by auto |
|
666 assume "\<not> (\<forall>y\<in>s. f x \<le> f y)" |
|
667 then obtain y where "y\<in>s" and y:"f x > f y" by auto |
|
668 hence xy:"0 < dist x y" by (auto simp add: dist_nz[THEN sym]) |
|
669 |
|
670 then obtain u where "0 < u" "u \<le> 1" and u:"u < e / dist x y" |
|
671 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 |
|
672 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` |
|
673 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 |
|
674 moreover |
|
675 have *:"x - ((1 - u) *\<^sub>R x + u *\<^sub>R y) = u *\<^sub>R (x - y)" by (simp add: algebra_simps) |
|
676 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] |
|
677 using u unfolding pos_less_divide_eq[OF xy] by auto |
|
678 hence "f x \<le> f ((1 - u) *\<^sub>R x + u *\<^sub>R y)" using assms(4) by auto |
|
679 ultimately show False using mult_strict_left_mono[OF y `u>0`] unfolding left_diff_distrib by auto |
|
680 qed |
|
681 |
|
682 lemma convex_distance: |
|
683 fixes s :: "'a::real_normed_vector set" |
|
684 shows "convex_on s (\<lambda>x. dist a x)" |
|
685 proof(auto simp add: convex_on_def dist_norm) |
|
686 fix x y assume "x\<in>s" "y\<in>s" |
|
687 fix u v ::real assume "0 \<le> u" "0 \<le> v" "u + v = 1" |
|
688 have "a = u *\<^sub>R a + v *\<^sub>R a" unfolding scaleR_left_distrib[THEN sym] and `u+v=1` by simp |
|
689 hence *:"a - (u *\<^sub>R x + v *\<^sub>R y) = (u *\<^sub>R (a - x)) + (v *\<^sub>R (a - y))" |
|
690 by (auto simp add: algebra_simps) |
|
691 show "norm (a - (u *\<^sub>R x + v *\<^sub>R y)) \<le> u * norm (a - x) + v * norm (a - y)" |
|
692 unfolding * using norm_triangle_ineq[of "u *\<^sub>R (a - x)" "v *\<^sub>R (a - y)"] |
|
693 using `0 \<le> u` `0 \<le> v` by auto |
|
694 qed |
|
695 |
|
696 subsection {* Arithmetic operations on sets preserve convexity. *} |
|
697 |
|
698 lemma convex_scaling: "convex s \<Longrightarrow> convex ((\<lambda>x. c *\<^sub>R x) ` s)" |
|
699 unfolding convex_def and image_iff apply auto |
|
700 apply (rule_tac x="u *\<^sub>R x+v *\<^sub>R y" in bexI) by (auto simp add: algebra_simps) |
|
701 |
|
702 lemma convex_negations: "convex s \<Longrightarrow> convex ((\<lambda>x. -x)` s)" |
|
703 unfolding convex_def and image_iff apply auto |
|
704 apply (rule_tac x="u *\<^sub>R x+v *\<^sub>R y" in bexI) by auto |
|
705 |
|
706 lemma convex_sums: |
|
707 assumes "convex s" "convex t" |
|
708 shows "convex {x + y| x y. x \<in> s \<and> y \<in> t}" |
|
709 proof(auto simp add: convex_def image_iff scaleR_right_distrib) |
|
710 fix xa xb ya yb assume xy:"xa\<in>s" "xb\<in>s" "ya\<in>t" "yb\<in>t" |
|
711 fix u v ::real assume uv:"0 \<le> u" "0 \<le> v" "u + v = 1" |
|
712 show "\<exists>x y. u *\<^sub>R xa + u *\<^sub>R ya + (v *\<^sub>R xb + v *\<^sub>R yb) = x + y \<and> x \<in> s \<and> y \<in> t" |
|
713 apply(rule_tac x="u *\<^sub>R xa + v *\<^sub>R xb" in exI) apply(rule_tac x="u *\<^sub>R ya + v *\<^sub>R yb" in exI) |
|
714 using assms(1)[unfolded convex_def, THEN bspec[where x=xa], THEN bspec[where x=xb]] |
|
715 using assms(2)[unfolded convex_def, THEN bspec[where x=ya], THEN bspec[where x=yb]] |
|
716 using uv xy by auto |
|
717 qed |
|
718 |
|
719 lemma convex_differences: |
|
720 assumes "convex s" "convex t" |
|
721 shows "convex {x - y| x y. x \<in> s \<and> y \<in> t}" |
|
722 proof- |
|
723 have "{x - y| x y. x \<in> s \<and> y \<in> t} = {x + y |x y. x \<in> s \<and> y \<in> uminus ` t}" unfolding image_iff apply auto |
|
724 apply(rule_tac x=xa in exI) apply(rule_tac x="-y" in exI) apply simp |
|
725 apply(rule_tac x=xa in exI) apply(rule_tac x=xb in exI) by simp |
|
726 thus ?thesis using convex_sums[OF assms(1) convex_negations[OF assms(2)]] by auto |
|
727 qed |
|
728 |
|
729 lemma convex_translation: assumes "convex s" shows "convex ((\<lambda>x. a + x) ` s)" |
|
730 proof- have "{a + y |y. y \<in> s} = (\<lambda>x. a + x) ` s" by auto |
|
731 thus ?thesis using convex_sums[OF convex_singleton[of a] assms] by auto qed |
|
732 |
|
733 lemma convex_affinity: assumes "convex s" shows "convex ((\<lambda>x. a + c *\<^sub>R x) ` s)" |
|
734 proof- have "(\<lambda>x. a + c *\<^sub>R x) ` s = op + a ` op *\<^sub>R c ` s" by auto |
|
735 thus ?thesis using convex_translation[OF convex_scaling[OF assms], of a c] by auto qed |
|
736 |
|
737 lemma convex_linear_image: |
|
738 assumes c:"convex s" and l:"bounded_linear f" |
|
739 shows "convex(f ` s)" |
|
740 proof(auto simp add: convex_def) |
|
741 interpret f: bounded_linear f by fact |
|
742 fix x y assume xy:"x \<in> s" "y \<in> s" |
|
743 fix u v ::real assume uv:"0 \<le> u" "0 \<le> v" "u + v = 1" |
|
744 show "u *\<^sub>R f x + v *\<^sub>R f y \<in> f ` s" unfolding image_iff |
|
745 apply(rule_tac x="u *\<^sub>R x + v *\<^sub>R y" in bexI) |
|
746 unfolding f.add f.scaleR |
|
747 using c[unfolded convex_def] xy uv by auto |
|
748 qed |
|
749 |
|
750 subsection {* Balls, being convex, are connected. *} |
|
751 |
|
752 lemma convex_ball: |
|
753 fixes x :: "'a::real_normed_vector" |
|
754 shows "convex (ball x e)" |
|
755 proof(auto simp add: convex_def) |
|
756 fix y z assume yz:"dist x y < e" "dist x z < e" |
|
757 fix u v ::real assume uv:"0 \<le> u" "0 \<le> v" "u + v = 1" |
|
758 have "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> u * dist x y + v * dist x z" using uv yz |
|
759 using convex_distance[of "ball x e" x, unfolded convex_on_def, THEN bspec[where x=y], THEN bspec[where x=z]] by auto |
|
760 thus "dist x (u *\<^sub>R y + v *\<^sub>R z) < e" using real_convex_bound_lt[OF yz uv] by auto |
|
761 qed |
|
762 |
|
763 lemma convex_cball: |
|
764 fixes x :: "'a::real_normed_vector" |
|
765 shows "convex(cball x e)" |
|
766 proof(auto simp add: convex_def Ball_def mem_cball) |
|
767 fix y z assume yz:"dist x y \<le> e" "dist x z \<le> e" |
|
768 fix u v ::real assume uv:" 0 \<le> u" "0 \<le> v" "u + v = 1" |
|
769 have "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> u * dist x y + v * dist x z" using uv yz |
|
770 using convex_distance[of "cball x e" x, unfolded convex_on_def, THEN bspec[where x=y], THEN bspec[where x=z]] by auto |
|
771 thus "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> e" using real_convex_bound_le[OF yz uv] by auto |
|
772 qed |
|
773 |
|
774 lemma connected_ball: |
|
775 fixes x :: "'a::real_normed_vector" |
|
776 shows "connected (ball x e)" |
|
777 using convex_connected convex_ball by auto |
|
778 |
|
779 lemma connected_cball: |
|
780 fixes x :: "'a::real_normed_vector" |
|
781 shows "connected(cball x e)" |
|
782 using convex_connected convex_cball by auto |
|
783 |
|
784 subsection {* Convex hull. *} |
|
785 |
|
786 lemma convex_convex_hull: "convex(convex hull s)" |
|
787 unfolding hull_def using convex_Inter[of "{t\<in>convex. s\<subseteq>t}"] |
|
788 unfolding mem_def by auto |
|
789 |
|
790 lemma convex_hull_eq: "(convex hull s = s) \<longleftrightarrow> convex s" apply(rule hull_eq[unfolded mem_def]) |
|
791 using convex_Inter[unfolded Ball_def mem_def] by auto |
|
792 |
|
793 lemma bounded_convex_hull: |
|
794 fixes s :: "'a::real_normed_vector set" |
|
795 assumes "bounded s" shows "bounded(convex hull s)" |
|
796 proof- from assms obtain B where B:"\<forall>x\<in>s. norm x \<le> B" unfolding bounded_iff by auto |
|
797 show ?thesis apply(rule bounded_subset[OF bounded_cball, of _ 0 B]) |
|
798 unfolding subset_hull[unfolded mem_def, of convex, OF convex_cball] |
|
799 unfolding subset_eq mem_cball dist_norm using B by auto qed |
|
800 |
|
801 lemma finite_imp_bounded_convex_hull: |
|
802 fixes s :: "'a::real_normed_vector set" |
|
803 shows "finite s \<Longrightarrow> bounded(convex hull s)" |
|
804 using bounded_convex_hull finite_imp_bounded by auto |
|
805 |
|
806 subsection {* Stepping theorems for convex hulls of finite sets. *} |
|
807 |
|
808 lemma convex_hull_empty[simp]: "convex hull {} = {}" |
|
809 apply(rule hull_unique) unfolding mem_def by auto |
|
810 |
|
811 lemma convex_hull_singleton[simp]: "convex hull {a} = {a}" |
|
812 apply(rule hull_unique) unfolding mem_def by auto |
|
813 |
|
814 lemma convex_hull_insert: |
|
815 fixes s :: "'a::real_vector set" |
|
816 assumes "s \<noteq> {}" |
|
817 shows "convex hull (insert a s) = {x. \<exists>u\<ge>0. \<exists>v\<ge>0. \<exists>b. (u + v = 1) \<and> |
|
818 b \<in> (convex hull s) \<and> (x = u *\<^sub>R a + v *\<^sub>R b)}" (is "?xyz = ?hull") |
|
819 apply(rule,rule hull_minimal,rule) unfolding mem_def[of _ convex] and insert_iff prefer 3 apply rule proof- |
|
820 fix x assume x:"x = a \<or> x \<in> s" |
|
821 thus "x\<in>?hull" apply rule unfolding mem_Collect_eq apply(rule_tac x=1 in exI) defer |
|
822 apply(rule_tac x=0 in exI) using assms hull_subset[of s convex] by auto |
|
823 next |
|
824 fix x assume "x\<in>?hull" |
|
825 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 |
|
826 have "a\<in>convex hull insert a s" "b\<in>convex hull insert a s" |
|
827 using hull_mono[of s "insert a s" convex] hull_mono[of "{a}" "insert a s" convex] and obt(4) by auto |
|
828 thus "x\<in> convex hull insert a s" unfolding obt(5) using convex_convex_hull[of "insert a s", unfolded convex_def] |
|
829 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 |
|
830 next |
|
831 show "convex ?hull" unfolding convex_def apply(rule,rule,rule,rule,rule,rule,rule) proof- |
|
832 fix x y u v assume as:"(0::real) \<le> u" "0 \<le> v" "u + v = 1" "x\<in>?hull" "y\<in>?hull" |
|
833 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 |
|
834 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 |
|
835 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) |
|
836 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)" |
|
837 proof(cases "u * v1 + v * v2 = 0") |
|
838 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) |
|
839 case True hence **:"u * v1 = 0" "v * v2 = 0" apply- apply(rule_tac [!] ccontr) |
|
840 using mult_nonneg_nonneg[OF `u\<ge>0` `v1\<ge>0`] mult_nonneg_nonneg[OF `v\<ge>0` `v2\<ge>0`] by auto |
|
841 hence "u * u1 + v * u2 = 1" using as(3) obt1(3) obt2(3) by auto |
|
842 thus ?thesis unfolding obt1(5) obt2(5) * using assms hull_subset[of s convex] by(auto simp add: ** scaleR_right_distrib) |
|
843 next |
|
844 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) |
|
845 also have "\<dots> = u * (v1 + u1 - u1) + v * (v2 + u2 - u2)" using as(3) obt1(3) obt2(3) by (auto simp add: field_simps) |
|
846 also have "\<dots> = u * v1 + v * v2" by simp finally have **:"1 - (u * u1 + v * u2) = u * v1 + v * v2" by auto |
|
847 case False have "0 \<le> u * v1 + v * v2" "0 \<le> u * v1" "0 \<le> u * v1 + v * v2" "0 \<le> v * v2" apply - |
|
848 apply(rule add_nonneg_nonneg) prefer 4 apply(rule add_nonneg_nonneg) apply(rule_tac [!] mult_nonneg_nonneg) |
|
849 using as(1,2) obt1(1,2) obt2(1,2) by auto |
|
850 thus ?thesis unfolding obt1(5) obt2(5) unfolding * and ** using False |
|
851 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 |
|
852 apply(rule convex_convex_hull[of s, unfolded convex_def, rule_format]) using obt1(4) obt2(4) |
|
853 unfolding add_divide_distrib[THEN sym] and real_0_le_divide_iff |
|
854 by (auto simp add: scaleR_left_distrib scaleR_right_distrib) |
|
855 qed note * = this |
|
856 have u1:"u1 \<le> 1" apply(rule ccontr) unfolding obt1(3)[THEN sym] and not_le using obt1(2) by auto |
|
857 have u2:"u2 \<le> 1" apply(rule ccontr) unfolding obt2(3)[THEN sym] and not_le using obt2(2) by auto |
|
858 have "u1 * u + u2 * v \<le> (max u1 u2) * u + (max u1 u2) * v" apply(rule add_mono) |
|
859 apply(rule_tac [!] mult_right_mono) using as(1,2) obt1(1,2) obt2(1,2) by auto |
|
860 also have "\<dots> \<le> 1" unfolding mult.add_right[THEN sym] and as(3) using u1 u2 by auto |
|
861 finally |
|
862 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) |
|
863 apply(rule conjI) defer apply(rule_tac x="1 - u * u1 - v * u2" in exI) unfolding Bex_def |
|
864 using as(1,2) obt1(1,2) obt2(1,2) * by(auto intro!: mult_nonneg_nonneg add_nonneg_nonneg simp add: algebra_simps) |
|
865 qed |
|
866 qed |
|
867 |
|
868 |
|
869 subsection {* Explicit expression for convex hull. *} |
|
870 |
|
871 lemma convex_hull_indexed: |
|
872 fixes s :: "'a::real_vector set" |
|
873 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> |
|
874 (setsum u {1..k} = 1) \<and> |
|
875 (setsum (\<lambda>i. u i *\<^sub>R x i) {1..k} = y)}" (is "?xyz = ?hull") |
|
876 apply(rule hull_unique) unfolding mem_def[of _ convex] apply(rule) defer |
|
877 apply(subst convex_def) apply(rule,rule,rule,rule,rule,rule,rule) |
|
878 proof- |
|
879 fix x assume "x\<in>s" |
|
880 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 |
|
881 next |
|
882 fix t assume as:"s \<subseteq> t" "convex t" |
|
883 show "?hull \<subseteq> t" apply(rule) unfolding mem_Collect_eq apply(erule exE | erule conjE)+ proof- |
|
884 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" |
|
885 show "x\<in>t" unfolding assm(3)[THEN sym] apply(rule as(2)[unfolded convex, rule_format]) |
|
886 using assm(1,2) as(1) by auto qed |
|
887 next |
|
888 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" |
|
889 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 |
|
890 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 |
|
891 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)" |
|
892 "{1..k1 + k2} \<inter> {1..k1} = {1..k1}" "{1..k1 + k2} \<inter> - {1..k1} = (\<lambda>i. i + k1) ` {1..k2}" |
|
893 prefer 3 apply(rule,rule) unfolding image_iff apply(rule_tac x="x - k1" in bexI) by(auto simp add: not_le) |
|
894 have inj:"inj_on (\<lambda>i. i + k1) {1..k2}" unfolding inj_on_def by auto |
|
895 show "u *\<^sub>R x + v *\<^sub>R y \<in> ?hull" apply(rule) |
|
896 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) |
|
897 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) |
|
898 unfolding * and setsum_cases[OF finite_atLeastAtMost[of 1 "k1 + k2"]] and setsum_reindex[OF inj] and o_def |
|
899 unfolding scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] setsum_right_distrib[THEN sym] proof- |
|
900 fix i assume i:"i \<in> {1..k1+k2}" |
|
901 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" |
|
902 proof(cases "i\<in>{1..k1}") |
|
903 case True thus ?thesis using mult_nonneg_nonneg[of u "u1 i"] and uv(1) x(1)[THEN bspec[where x=i]] by auto |
|
904 next def j \<equiv> "i - k1" |
|
905 case False with i have "j \<in> {1..k2}" unfolding j_def by auto |
|
906 thus ?thesis unfolding j_def[symmetric] using False |
|
907 using mult_nonneg_nonneg[of v "u2 j"] and uv(2) y(1)[THEN bspec[where x=j]] by auto qed |
|
908 qed(auto simp add: not_le x(2,3) y(2,3) uv(3)) |
|
909 qed |
|
910 |
|
911 lemma convex_hull_finite: |
|
912 fixes s :: "'a::real_vector set" |
|
913 assumes "finite s" |
|
914 shows "convex hull s = {y. \<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> |
|
915 setsum u s = 1 \<and> setsum (\<lambda>x. u x *\<^sub>R x) s = y}" (is "?HULL = ?set") |
|
916 proof(rule hull_unique, auto simp add: mem_def[of _ convex] convex_def[of ?set]) |
|
917 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" |
|
918 apply(rule_tac x="\<lambda>y. if x=y then 1 else 0" in exI) apply auto |
|
919 unfolding setsum_delta'[OF assms] and setsum_delta''[OF assms] by auto |
|
920 next |
|
921 fix u v ::real assume uv:"0 \<le> u" "0 \<le> v" "u + v = 1" |
|
922 fix ux assume ux:"\<forall>x\<in>s. 0 \<le> ux x" "setsum ux s = (1::real)" |
|
923 fix uy assume uy:"\<forall>x\<in>s. 0 \<le> uy x" "setsum uy s = (1::real)" |
|
924 { fix x assume "x\<in>s" |
|
925 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) |
|
926 by (auto, metis add_nonneg_nonneg mult_nonneg_nonneg uv(1) uv(2)) } |
|
927 moreover have "(\<Sum>x\<in>s. u * ux x + v * uy x) = 1" |
|
928 unfolding setsum_addf and setsum_right_distrib[THEN sym] and ux(2) uy(2) using uv(3) by auto |
|
929 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)" |
|
930 unfolding scaleR_left_distrib and setsum_addf and scaleR_scaleR[THEN sym] and scaleR_right.setsum [symmetric] by auto |
|
931 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)" |
|
932 apply(rule_tac x="\<lambda>x. u * ux x + v * uy x" in exI) by auto |
|
933 next |
|
934 fix t assume t:"s \<subseteq> t" "convex t" |
|
935 fix u assume u:"\<forall>x\<in>s. 0 \<le> u x" "setsum u s = (1::real)" |
|
936 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]] |
|
937 using assms and t(1) by auto |
|
938 qed |
|
939 |
|
940 subsection {* Another formulation from Lars Schewe. *} |
|
941 |
|
942 lemma setsum_constant_scaleR: |
|
943 fixes y :: "'a::real_vector" |
|
944 shows "(\<Sum>x\<in>A. y) = of_nat (card A) *\<^sub>R y" |
|
945 apply (cases "finite A") |
|
946 apply (induct set: finite) |
|
947 apply (simp_all add: algebra_simps) |
|
948 done |
|
949 |
|
950 lemma convex_hull_explicit: |
|
951 fixes p :: "'a::real_vector set" |
|
952 shows "convex hull p = {y. \<exists>s u. finite s \<and> s \<subseteq> p \<and> |
|
953 (\<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") |
|
954 proof- |
|
955 { fix x assume "x\<in>?lhs" |
|
956 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" |
|
957 unfolding convex_hull_indexed by auto |
|
958 |
|
959 have fin:"finite {1..k}" by auto |
|
960 have fin':"\<And>v. finite {i \<in> {1..k}. y i = v}" by auto |
|
961 { fix j assume "j\<in>{1..k}" |
|
962 hence "y j \<in> p" "0 \<le> setsum u {i. Suc 0 \<le> i \<and> i \<le> k \<and> y i = y j}" |
|
963 using obt(1)[THEN bspec[where x=j]] and obt(2) apply simp |
|
964 apply(rule setsum_nonneg) using obt(1) by auto } |
|
965 moreover |
|
966 have "(\<Sum>v\<in>y ` {1..k}. setsum u {i \<in> {1..k}. y i = v}) = 1" |
|
967 unfolding setsum_image_gen[OF fin, THEN sym] using obt(2) by auto |
|
968 moreover have "(\<Sum>v\<in>y ` {1..k}. setsum u {i \<in> {1..k}. y i = v} *\<^sub>R v) = x" |
|
969 using setsum_image_gen[OF fin, of "\<lambda>i. u i *\<^sub>R y i" y, THEN sym] |
|
970 unfolding scaleR_left.setsum using obt(3) by auto |
|
971 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" |
|
972 apply(rule_tac x="y ` {1..k}" in exI) |
|
973 apply(rule_tac x="\<lambda>v. setsum u {i\<in>{1..k}. y i = v}" in exI) by auto |
|
974 hence "x\<in>?rhs" by auto } |
|
975 moreover |
|
976 { fix y assume "y\<in>?rhs" |
|
977 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 |
|
978 |
|
979 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 |
|
980 |
|
981 { fix i::nat assume "i\<in>{1..card s}" |
|
982 hence "f i \<in> s" apply(subst f(2)[THEN sym]) by auto |
|
983 hence "0 \<le> u (f i)" "f i \<in> p" using obt(2,3) by auto } |
|
984 moreover have *:"finite {1..card s}" by auto |
|
985 { fix y assume "y\<in>s" |
|
986 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 |
|
987 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 |
|
988 hence "card {x. Suc 0 \<le> x \<and> x \<le> card s \<and> f x = y} = 1" by auto |
|
989 hence "(\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x)) = u y" |
|
990 "(\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x) *\<^sub>R f x) = u y *\<^sub>R y" |
|
991 by (auto simp add: setsum_constant_scaleR) } |
|
992 |
|
993 hence "(\<Sum>x = 1..card s. u (f x)) = 1" "(\<Sum>i = 1..card s. u (f i) *\<^sub>R f i) = y" |
|
994 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] |
|
995 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"] |
|
996 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 |
|
997 |
|
998 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" |
|
999 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 |
|
1000 hence "y \<in> ?lhs" unfolding convex_hull_indexed by auto } |
|
1001 ultimately show ?thesis unfolding expand_set_eq by blast |
|
1002 qed |
|
1003 |
|
1004 subsection {* A stepping theorem for that expansion. *} |
|
1005 |
|
1006 lemma convex_hull_finite_step: |
|
1007 fixes s :: "'a::real_vector set" assumes "finite s" |
|
1008 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) |
|
1009 \<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") |
|
1010 proof(rule, case_tac[!] "a\<in>s") |
|
1011 assume "a\<in>s" hence *:"insert a s = s" by auto |
|
1012 assume ?lhs thus ?rhs unfolding * apply(rule_tac x=0 in exI) by auto |
|
1013 next |
|
1014 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 |
|
1015 assume "a\<notin>s" thus ?rhs apply(rule_tac x="u a" in exI) using u(1)[THEN bspec[where x=a]] apply simp |
|
1016 apply(rule_tac x=u in exI) using u[unfolded setsum_clauses(2)[OF assms]] and `a\<notin>s` by auto |
|
1017 next |
|
1018 assume "a\<in>s" hence *:"insert a s = s" by auto |
|
1019 have fin:"finite (insert a s)" using assms by auto |
|
1020 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 |
|
1021 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] |
|
1022 unfolding setsum_clauses(2)[OF assms] using uv and uv(2)[THEN bspec[where x=a]] and `a\<in>s` by auto |
|
1023 next |
|
1024 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 |
|
1025 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)" |
|
1026 apply(rule_tac setsum_cong2) defer apply(rule_tac setsum_cong2) using `a\<notin>s` by auto |
|
1027 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 |
|
1028 qed |
|
1029 |
|
1030 subsection {* Hence some special cases. *} |
|
1031 |
|
1032 lemma convex_hull_2: |
|
1033 "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}" |
|
1034 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 |
|
1035 show ?thesis apply(simp add: convex_hull_finite) unfolding convex_hull_finite_step[OF **, of a 1, unfolded * conj_assoc] |
|
1036 apply auto apply(rule_tac x=v in exI) apply(rule_tac x="1 - v" in exI) apply simp |
|
1037 apply(rule_tac x=u in exI) apply simp apply(rule_tac x="\<lambda>x. v" in exI) by simp qed |
|
1038 |
|
1039 lemma convex_hull_2_alt: "convex hull {a,b} = {a + u *\<^sub>R (b - a) | u. 0 \<le> u \<and> u \<le> 1}" |
|
1040 unfolding convex_hull_2 unfolding Collect_def |
|
1041 proof(rule ext) have *:"\<And>x y ::real. x + y = 1 \<longleftrightarrow> x = 1 - y" by auto |
|
1042 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)" |
|
1043 unfolding * apply auto apply(rule_tac[!] x=u in exI) by (auto simp add: algebra_simps) qed |
|
1044 |
|
1045 lemma convex_hull_3: |
|
1046 "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}" |
|
1047 proof- |
|
1048 have fin:"finite {a,b,c}" "finite {b,c}" "finite {c}" by auto |
|
1049 have *:"\<And>x y z ::real. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z" |
|
1050 "\<And>x y z ::real^'n. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z" by (auto simp add: ring_simps) |
|
1051 show ?thesis unfolding convex_hull_finite[OF fin(1)] and Collect_def and convex_hull_finite_step[OF fin(2)] and * |
|
1052 unfolding convex_hull_finite_step[OF fin(3)] apply(rule ext) apply simp apply auto |
|
1053 apply(rule_tac x=va in exI) apply (rule_tac x="u c" in exI) apply simp |
|
1054 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 |
|
1055 |
|
1056 lemma convex_hull_3_alt: |
|
1057 "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}" |
|
1058 proof- have *:"\<And>x y z ::real. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z" by auto |
|
1059 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) |
|
1060 apply(rule_tac x=u in exI) apply(rule_tac x=v in exI) by (simp add: algebra_simps) qed |
|
1061 |
|
1062 subsection {* Relations among closure notions and corresponding hulls. *} |
|
1063 |
|
1064 text {* TODO: Generalize linear algebra concepts defined in @{text |
|
1065 Euclidean_Space.thy} so that we can generalize these lemmas. *} |
|
1066 |
|
1067 lemma subspace_imp_affine: |
|
1068 fixes s :: "(real ^ _) set" shows "subspace s \<Longrightarrow> affine s" |
|
1069 unfolding subspace_def affine_def smult_conv_scaleR by auto |
|
1070 |
|
1071 lemma affine_imp_convex: "affine s \<Longrightarrow> convex s" |
|
1072 unfolding affine_def convex_def by auto |
|
1073 |
|
1074 lemma subspace_imp_convex: |
|
1075 fixes s :: "(real ^ _) set" shows "subspace s \<Longrightarrow> convex s" |
|
1076 using subspace_imp_affine affine_imp_convex by auto |
|
1077 |
|
1078 lemma affine_hull_subset_span: |
|
1079 fixes s :: "(real ^ _) set" shows "(affine hull s) \<subseteq> (span s)" |
|
1080 unfolding span_def apply(rule hull_antimono) unfolding subset_eq Ball_def mem_def |
|
1081 using subspace_imp_affine by auto |
|
1082 |
|
1083 lemma convex_hull_subset_span: |
|
1084 fixes s :: "(real ^ _) set" shows "(convex hull s) \<subseteq> (span s)" |
|
1085 unfolding span_def apply(rule hull_antimono) unfolding subset_eq Ball_def mem_def |
|
1086 using subspace_imp_convex by auto |
|
1087 |
|
1088 lemma convex_hull_subset_affine_hull: "(convex hull s) \<subseteq> (affine hull s)" |
|
1089 unfolding span_def apply(rule hull_antimono) unfolding subset_eq Ball_def mem_def |
|
1090 using affine_imp_convex by auto |
|
1091 |
|
1092 lemma affine_dependent_imp_dependent: |
|
1093 fixes s :: "(real ^ _) set" shows "affine_dependent s \<Longrightarrow> dependent s" |
|
1094 unfolding affine_dependent_def dependent_def |
|
1095 using affine_hull_subset_span by auto |
|
1096 |
|
1097 lemma dependent_imp_affine_dependent: |
|
1098 fixes s :: "(real ^ _) set" |
|
1099 assumes "dependent {x - a| x . x \<in> s}" "a \<notin> s" |
|
1100 shows "affine_dependent (insert a s)" |
|
1101 proof- |
|
1102 from assms(1)[unfolded dependent_explicit smult_conv_scaleR] obtain S u v |
|
1103 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 |
|
1104 def t \<equiv> "(\<lambda>x. x + a) ` S" |
|
1105 |
|
1106 have inj:"inj_on (\<lambda>x. x + a) S" unfolding inj_on_def by auto |
|
1107 have "0\<notin>S" using obt(2) assms(2) unfolding subset_eq by auto |
|
1108 have fin:"finite t" and "t\<subseteq>s" unfolding t_def using obt(1,2) by auto |
|
1109 |
|
1110 hence "finite (insert a t)" and "insert a t \<subseteq> insert a s" by auto |
|
1111 moreover have *:"\<And>P Q. (\<Sum>x\<in>t. (if x = a then P x else Q x)) = (\<Sum>x\<in>t. Q x)" |
|
1112 apply(rule setsum_cong2) using `a\<notin>s` `t\<subseteq>s` by auto |
|
1113 have "(\<Sum>x\<in>insert a t. if x = a then - (\<Sum>x\<in>t. u (x - a)) else u (x - a)) = 0" |
|
1114 unfolding setsum_clauses(2)[OF fin] using `a\<notin>s` `t\<subseteq>s` apply auto unfolding * by auto |
|
1115 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" |
|
1116 apply(rule_tac x="v + a" in bexI) using obt(3,4) and `0\<notin>S` unfolding t_def by auto |
|
1117 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)" |
|
1118 apply(rule setsum_cong2) using `a\<notin>s` `t\<subseteq>s` by auto |
|
1119 have "(\<Sum>x\<in>t. u (x - a)) *\<^sub>R a = (\<Sum>v\<in>t. u (v - a) *\<^sub>R v)" |
|
1120 unfolding scaleR_left.setsum unfolding t_def and setsum_reindex[OF inj] and o_def |
|
1121 using obt(5) by (auto simp add: setsum_addf scaleR_right_distrib) |
|
1122 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" |
|
1123 unfolding setsum_clauses(2)[OF fin] using `a\<notin>s` `t\<subseteq>s` by (auto simp add: * vector_smult_lneg) |
|
1124 ultimately show ?thesis unfolding affine_dependent_explicit |
|
1125 apply(rule_tac x="insert a t" in exI) by auto |
|
1126 qed |
|
1127 |
|
1128 lemma convex_cone: |
|
1129 "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") |
|
1130 proof- |
|
1131 { fix x y assume "x\<in>s" "y\<in>s" and ?lhs |
|
1132 hence "2 *\<^sub>R x \<in>s" "2 *\<^sub>R y \<in> s" unfolding cone_def by auto |
|
1133 hence "x + y \<in> s" using `?lhs`[unfolded convex_def, THEN conjunct1] |
|
1134 apply(erule_tac x="2*\<^sub>R x" in ballE) apply(erule_tac x="2*\<^sub>R y" in ballE) |
|
1135 apply(erule_tac x="1/2" in allE) apply simp apply(erule_tac x="1/2" in allE) by auto } |
|
1136 thus ?thesis unfolding convex_def cone_def by blast |
|
1137 qed |
|
1138 |
|
1139 lemma affine_dependent_biggerset: fixes s::"(real^'n::finite) set" |
|
1140 assumes "finite s" "card s \<ge> CARD('n) + 2" |
|
1141 shows "affine_dependent s" |
|
1142 proof- |
|
1143 have "s\<noteq>{}" using assms by auto then obtain a where "a\<in>s" by auto |
|
1144 have *:"{x - a |x. x \<in> s - {a}} = (\<lambda>x. x - a) ` (s - {a})" by auto |
|
1145 have "card {x - a |x. x \<in> s - {a}} = card (s - {a})" unfolding * |
|
1146 apply(rule card_image) unfolding inj_on_def by auto |
|
1147 also have "\<dots> > CARD('n)" using assms(2) |
|
1148 unfolding card_Diff_singleton[OF assms(1) `a\<in>s`] by auto |
|
1149 finally show ?thesis apply(subst insert_Diff[OF `a\<in>s`, THEN sym]) |
|
1150 apply(rule dependent_imp_affine_dependent) |
|
1151 apply(rule dependent_biggerset) by auto qed |
|
1152 |
|
1153 lemma affine_dependent_biggerset_general: |
|
1154 assumes "finite (s::(real^'n::finite) set)" "card s \<ge> dim s + 2" |
|
1155 shows "affine_dependent s" |
|
1156 proof- |
|
1157 from assms(2) have "s \<noteq> {}" by auto |
|
1158 then obtain a where "a\<in>s" by auto |
|
1159 have *:"{x - a |x. x \<in> s - {a}} = (\<lambda>x. x - a) ` (s - {a})" by auto |
|
1160 have **:"card {x - a |x. x \<in> s - {a}} = card (s - {a})" unfolding * |
|
1161 apply(rule card_image) unfolding inj_on_def by auto |
|
1162 have "dim {x - a |x. x \<in> s - {a}} \<le> dim s" |
|
1163 apply(rule subset_le_dim) unfolding subset_eq |
|
1164 using `a\<in>s` by (auto simp add:span_superset span_sub) |
|
1165 also have "\<dots> < dim s + 1" by auto |
|
1166 also have "\<dots> \<le> card (s - {a})" using assms |
|
1167 using card_Diff_singleton[OF assms(1) `a\<in>s`] by auto |
|
1168 finally show ?thesis apply(subst insert_Diff[OF `a\<in>s`, THEN sym]) |
|
1169 apply(rule dependent_imp_affine_dependent) apply(rule dependent_biggerset_general) unfolding ** by auto qed |
|
1170 |
|
1171 subsection {* Caratheodory's theorem. *} |
|
1172 |
|
1173 lemma convex_hull_caratheodory: fixes p::"(real^'n::finite) set" |
|
1174 shows "convex hull p = {y. \<exists>s u. finite s \<and> s \<subseteq> p \<and> card s \<le> CARD('n) + 1 \<and> |
|
1175 (\<forall>x\<in>s. 0 \<le> u x) \<and> setsum u s = 1 \<and> setsum (\<lambda>v. u v *\<^sub>R v) s = y}" |
|
1176 unfolding convex_hull_explicit expand_set_eq mem_Collect_eq |
|
1177 proof(rule,rule) |
|
1178 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" |
|
1179 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" |
|
1180 then obtain N where "?P N" by auto |
|
1181 hence "\<exists>n\<le>N. (\<forall>k<n. \<not> ?P k) \<and> ?P n" apply(rule_tac ex_least_nat_le) by auto |
|
1182 then obtain n where "?P n" and smallest:"\<forall>k<n. \<not> ?P k" by blast |
|
1183 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 |
|
1184 |
|
1185 have "card s \<le> CARD('n) + 1" proof(rule ccontr, simp only: not_le) |
|
1186 assume "CARD('n) + 1 < card s" |
|
1187 hence "affine_dependent s" using affine_dependent_biggerset[OF obt(1)] by auto |
|
1188 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" |
|
1189 using affine_dependent_explicit_finite[OF obt(1)] by auto |
|
1190 def i \<equiv> "(\<lambda>v. (u v) / (- w v)) ` {v\<in>s. w v < 0}" def t \<equiv> "Min i" |
|
1191 have "\<exists>x\<in>s. w x < 0" proof(rule ccontr, simp add: not_less) |
|
1192 assume as:"\<forall>x\<in>s. 0 \<le> w x" |
|
1193 hence "setsum w (s - {v}) \<ge> 0" apply(rule_tac setsum_nonneg) by auto |
|
1194 hence "setsum w s > 0" unfolding setsum_diff1'[OF obt(1) `v\<in>s`] |
|
1195 using as[THEN bspec[where x=v]] and `v\<in>s` using `w v \<noteq> 0` by auto |
|
1196 thus False using wv(1) by auto |
|
1197 qed hence "i\<noteq>{}" unfolding i_def by auto |
|
1198 |
|
1199 hence "t \<ge> 0" using Min_ge_iff[of i 0 ] and obt(1) unfolding t_def i_def |
|
1200 using obt(4)[unfolded le_less] apply auto unfolding divide_le_0_iff by auto |
|
1201 have t:"\<forall>v\<in>s. u v + t * w v \<ge> 0" proof |
|
1202 fix v assume "v\<in>s" hence v:"0\<le>u v" using obt(4)[THEN bspec[where x=v]] by auto |
|
1203 show"0 \<le> u v + t * w v" proof(cases "w v < 0") |
|
1204 case False thus ?thesis apply(rule_tac add_nonneg_nonneg) |
|
1205 using v apply simp apply(rule mult_nonneg_nonneg) using `t\<ge>0` by auto next |
|
1206 case True hence "t \<le> u v / (- w v)" using `v\<in>s` |
|
1207 unfolding t_def i_def apply(rule_tac Min_le) using obt(1) by auto |
|
1208 thus ?thesis unfolding real_0_le_add_iff |
|
1209 using pos_le_divide_eq[OF True[unfolded neg_0_less_iff_less[THEN sym]]] by auto |
|
1210 qed qed |
|
1211 |
|
1212 obtain a where "a\<in>s" and "t = (\<lambda>v. (u v) / (- w v)) a" and "w a < 0" |
|
1213 using Min_in[OF _ `i\<noteq>{}`] and obt(1) unfolding i_def t_def by auto |
|
1214 hence a:"a\<in>s" "u a + t * w a = 0" by auto |
|
1215 have *:"\<And>f. setsum f (s - {a}) = setsum f s - ((f a)::'a::ring)" unfolding setsum_diff1'[OF obt(1) `a\<in>s`] by auto |
|
1216 have "(\<Sum>v\<in>s. u v + t * w v) = 1" |
|
1217 unfolding setsum_addf wv(1) setsum_right_distrib[THEN sym] obt(5) by auto |
|
1218 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" |
|
1219 unfolding setsum_addf obt(6) scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] wv(4) |
|
1220 using a(2) [THEN eq_neg_iff_add_eq_0 [THEN iffD2]] |
|
1221 by (simp add: vector_smult_lneg) |
|
1222 ultimately have "?P (n - 1)" apply(rule_tac x="(s - {a})" in exI) |
|
1223 apply(rule_tac x="\<lambda>v. u v + t * w v" in exI) using obt(1-3) and t and a by (auto simp add: * scaleR_left_distrib) |
|
1224 thus False using smallest[THEN spec[where x="n - 1"]] by auto qed |
|
1225 thus "\<exists>s u. finite s \<and> s \<subseteq> p \<and> card s \<le> CARD('n) + 1 |
|
1226 \<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 |
|
1227 qed auto |
|
1228 |
|
1229 lemma caratheodory: |
|
1230 "convex hull p = {x::real^'n::finite. \<exists>s. finite s \<and> s \<subseteq> p \<and> |
|
1231 card s \<le> CARD('n) + 1 \<and> x \<in> convex hull s}" |
|
1232 unfolding expand_set_eq apply(rule, rule) unfolding mem_Collect_eq proof- |
|
1233 fix x assume "x \<in> convex hull p" |
|
1234 then obtain s u where "finite s" "s \<subseteq> p" "card s \<le> CARD('n) + 1" |
|
1235 "\<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 |
|
1236 thus "\<exists>s. finite s \<and> s \<subseteq> p \<and> card s \<le> CARD('n) + 1 \<and> x \<in> convex hull s" |
|
1237 apply(rule_tac x=s in exI) using hull_subset[of s convex] |
|
1238 using convex_convex_hull[unfolded convex_explicit, of s, THEN spec[where x=s], THEN spec[where x=u]] by auto |
|
1239 next |
|
1240 fix x assume "\<exists>s. finite s \<and> s \<subseteq> p \<and> card s \<le> CARD('n) + 1 \<and> x \<in> convex hull s" |
|
1241 then obtain s where "finite s" "s \<subseteq> p" "card s \<le> CARD('n) + 1" "x \<in> convex hull s" by auto |
|
1242 thus "x \<in> convex hull p" using hull_mono[OF `s\<subseteq>p`] by auto |
|
1243 qed |
|
1244 |
|
1245 subsection {* Openness and compactness are preserved by convex hull operation. *} |
|
1246 |
|
1247 lemma open_convex_hull: |
|
1248 fixes s :: "'a::real_normed_vector set" |
|
1249 assumes "open s" |
|
1250 shows "open(convex hull s)" |
|
1251 unfolding open_contains_cball convex_hull_explicit unfolding mem_Collect_eq ball_simps(10) |
|
1252 proof(rule, rule) fix a |
|
1253 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" |
|
1254 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 |
|
1255 |
|
1256 from assms[unfolded open_contains_cball] obtain b where b:"\<forall>x\<in>s. 0 < b x \<and> cball x (b x) \<subseteq> s" |
|
1257 using bchoice[of s "\<lambda>x e. e>0 \<and> cball x e \<subseteq> s"] by auto |
|
1258 have "b ` t\<noteq>{}" unfolding i_def using obt by auto def i \<equiv> "b ` t" |
|
1259 |
|
1260 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}" |
|
1261 apply(rule_tac x="Min i" in exI) unfolding subset_eq apply rule defer apply rule unfolding mem_Collect_eq |
|
1262 proof- |
|
1263 show "0 < Min i" unfolding i_def and Min_gr_iff[OF finite_imageI[OF obt(1)] `b \` t\<noteq>{}`] |
|
1264 using b apply simp apply rule apply(erule_tac x=x in ballE) using `t\<subseteq>s` by auto |
|
1265 next fix y assume "y \<in> cball a (Min i)" |
|
1266 hence y:"norm (a - y) \<le> Min i" unfolding dist_norm[THEN sym] by auto |
|
1267 { fix x assume "x\<in>t" |
|
1268 hence "Min i \<le> b x" unfolding i_def apply(rule_tac Min_le) using obt(1) by auto |
|
1269 hence "x + (y - a) \<in> cball x (b x)" using y unfolding mem_cball dist_norm by auto |
|
1270 moreover from `x\<in>t` have "x\<in>s" using obt(2) by auto |
|
1271 ultimately have "x + (y - a) \<in> s" using y and b[THEN bspec[where x=x]] unfolding subset_eq by auto } |
|
1272 moreover |
|
1273 have *:"inj_on (\<lambda>v. v + (y - a)) t" unfolding inj_on_def by auto |
|
1274 have "(\<Sum>v\<in>(\<lambda>v. v + (y - a)) ` t. u (v - (y - a))) = 1" |
|
1275 unfolding setsum_reindex[OF *] o_def using obt(4) by auto |
|
1276 moreover have "(\<Sum>v\<in>(\<lambda>v. v + (y - a)) ` t. u (v - (y - a)) *\<^sub>R v) = y" |
|
1277 unfolding setsum_reindex[OF *] o_def using obt(4,5) |
|
1278 by (simp add: setsum_addf setsum_subtractf scaleR_left.setsum[THEN sym] scaleR_right_distrib) |
|
1279 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" |
|
1280 apply(rule_tac x="(\<lambda>v. v + (y - a)) ` t" in exI) apply(rule_tac x="\<lambda>v. u (v - (y - a))" in exI) |
|
1281 using obt(1, 3) by auto |
|
1282 qed |
|
1283 qed |
|
1284 |
|
1285 lemma open_dest_vec1_vimage: "open S \<Longrightarrow> open (dest_vec1 -` S)" |
|
1286 unfolding open_vector_def all_1 |
|
1287 by (auto simp add: dest_vec1_def) |
|
1288 |
|
1289 lemma tendsto_dest_vec1 [tendsto_intros]: |
|
1290 "(f ---> l) net \<Longrightarrow> ((\<lambda>x. dest_vec1 (f x)) ---> dest_vec1 l) net" |
|
1291 unfolding tendsto_def |
|
1292 apply clarify |
|
1293 apply (drule_tac x="dest_vec1 -` S" in spec) |
|
1294 apply (simp add: open_dest_vec1_vimage) |
|
1295 done |
|
1296 |
|
1297 lemma continuous_dest_vec1: "continuous net f \<Longrightarrow> continuous net (\<lambda>x. dest_vec1 (f x))" |
|
1298 unfolding continuous_def by (rule tendsto_dest_vec1) |
|
1299 |
|
1300 (* TODO: move *) |
|
1301 lemma compact_real_interval: |
|
1302 fixes a b :: real shows "compact {a..b}" |
|
1303 proof - |
|
1304 have "continuous_on {vec1 a .. vec1 b} dest_vec1" |
|
1305 unfolding continuous_on |
|
1306 by (simp add: tendsto_dest_vec1 Lim_at_within Lim_ident_at) |
|
1307 moreover have "compact {vec1 a .. vec1 b}" by (rule compact_interval) |
|
1308 ultimately have "compact (dest_vec1 ` {vec1 a .. vec1 b})" |
|
1309 by (rule compact_continuous_image) |
|
1310 also have "dest_vec1 ` {vec1 a .. vec1 b} = {a..b}" |
|
1311 by (auto simp add: image_def Bex_def exists_vec1) |
|
1312 finally show ?thesis . |
|
1313 qed |
|
1314 |
|
1315 lemma compact_convex_combinations: |
|
1316 fixes s t :: "'a::real_normed_vector set" |
|
1317 assumes "compact s" "compact t" |
|
1318 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}" |
|
1319 proof- |
|
1320 let ?X = "{0..1} \<times> s \<times> t" |
|
1321 let ?h = "(\<lambda>z. (1 - fst z) *\<^sub>R fst (snd z) + fst z *\<^sub>R snd (snd z))" |
|
1322 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" |
|
1323 apply(rule set_ext) unfolding image_iff mem_Collect_eq |
|
1324 apply rule apply auto |
|
1325 apply (rule_tac x=u in rev_bexI, simp) |
|
1326 apply (erule rev_bexI, erule rev_bexI, simp) |
|
1327 by auto |
|
1328 have "continuous_on ({0..1} \<times> s \<times> t) |
|
1329 (\<lambda>z. (1 - fst z) *\<^sub>R fst (snd z) + fst z *\<^sub>R snd (snd z))" |
|
1330 unfolding continuous_on by (rule ballI) (intro tendsto_intros) |
|
1331 thus ?thesis unfolding * |
|
1332 apply (rule compact_continuous_image) |
|
1333 apply (intro compact_Times compact_real_interval assms) |
|
1334 done |
|
1335 qed |
|
1336 |
|
1337 lemma compact_convex_hull: fixes s::"(real^'n::finite) set" |
|
1338 assumes "compact s" shows "compact(convex hull s)" |
|
1339 proof(cases "s={}") |
|
1340 case True thus ?thesis using compact_empty by simp |
|
1341 next |
|
1342 case False then obtain w where "w\<in>s" by auto |
|
1343 show ?thesis unfolding caratheodory[of s] |
|
1344 proof(induct "CARD('n) + 1") |
|
1345 have *:"{x.\<exists>sa. finite sa \<and> sa \<subseteq> s \<and> card sa \<le> 0 \<and> x \<in> convex hull sa} = {}" |
|
1346 using compact_empty by (auto simp add: convex_hull_empty) |
|
1347 case 0 thus ?case unfolding * by simp |
|
1348 next |
|
1349 case (Suc n) |
|
1350 show ?case proof(cases "n=0") |
|
1351 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" |
|
1352 unfolding expand_set_eq and mem_Collect_eq proof(rule, rule) |
|
1353 fix x assume "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t" |
|
1354 then obtain t where t:"finite t" "t \<subseteq> s" "card t \<le> Suc n" "x \<in> convex hull t" by auto |
|
1355 show "x\<in>s" proof(cases "card t = 0") |
|
1356 case True thus ?thesis using t(4) unfolding card_0_eq[OF t(1)] by(simp add: convex_hull_empty) |
|
1357 next |
|
1358 case False hence "card t = Suc 0" using t(3) `n=0` by auto |
|
1359 then obtain a where "t = {a}" unfolding card_Suc_eq by auto |
|
1360 thus ?thesis using t(2,4) by (simp add: convex_hull_singleton) |
|
1361 qed |
|
1362 next |
|
1363 fix x assume "x\<in>s" |
|
1364 thus "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t" |
|
1365 apply(rule_tac x="{x}" in exI) unfolding convex_hull_singleton by auto |
|
1366 qed thus ?thesis using assms by simp |
|
1367 next |
|
1368 case False have "{x. \<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t} = |
|
1369 { (1 - u) *\<^sub>R x + u *\<^sub>R y | x y u. |
|
1370 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}}" |
|
1371 unfolding expand_set_eq and mem_Collect_eq proof(rule,rule) |
|
1372 fix x assume "\<exists>u v c. x = (1 - c) *\<^sub>R u + c *\<^sub>R v \<and> |
|
1373 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)" |
|
1374 then obtain u v c t where obt:"x = (1 - c) *\<^sub>R u + c *\<^sub>R v" |
|
1375 "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 |
|
1376 moreover have "(1 - c) *\<^sub>R u + c *\<^sub>R v \<in> convex hull insert u t" |
|
1377 apply(rule mem_convex) using obt(2) and convex_convex_hull and hull_subset[of "insert u t" convex] |
|
1378 using obt(7) and hull_mono[of t "insert u t"] by auto |
|
1379 ultimately show "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t" |
|
1380 apply(rule_tac x="insert u t" in exI) by (auto simp add: card_insert_if) |
|
1381 next |
|
1382 fix x assume "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t" |
|
1383 then obtain t where t:"finite t" "t \<subseteq> s" "card t \<le> Suc n" "x \<in> convex hull t" by auto |
|
1384 let ?P = "\<exists>u v c. x = (1 - c) *\<^sub>R u + c *\<^sub>R v \<and> |
|
1385 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)" |
|
1386 show ?P proof(cases "card t = Suc n") |
|
1387 case False hence "card t \<le> n" using t(3) by auto |
|
1388 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 |
|
1389 by(auto intro!: exI[where x=t]) |
|
1390 next |
|
1391 case True then obtain a u where au:"t = insert a u" "a\<notin>u" apply(drule_tac card_eq_SucD) by auto |
|
1392 show ?P proof(cases "u={}") |
|
1393 case True hence "x=a" using t(4)[unfolded au] by auto |
|
1394 show ?P unfolding `x=a` apply(rule_tac x=a in exI, rule_tac x=a in exI, rule_tac x=1 in exI) |
|
1395 using t and `n\<noteq>0` unfolding au by(auto intro!: exI[where x="{a}"] simp add: convex_hull_singleton) |
|
1396 next |
|
1397 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" |
|
1398 using t(4)[unfolded au convex_hull_insert[OF False]] by auto |
|
1399 have *:"1 - vx = ux" using obt(3) by auto |
|
1400 show ?P apply(rule_tac x=a in exI, rule_tac x=b in exI, rule_tac x=vx in exI) |
|
1401 using obt and t(1-3) unfolding au and * using card_insert_disjoint[OF _ au(2)] |
|
1402 by(auto intro!: exI[where x=u]) |
|
1403 qed |
|
1404 qed |
|
1405 qed |
|
1406 thus ?thesis using compact_convex_combinations[OF assms Suc] by simp |
|
1407 qed |
|
1408 qed |
|
1409 qed |
|
1410 |
|
1411 lemma finite_imp_compact_convex_hull: |
|
1412 fixes s :: "(real ^ _) set" |
|
1413 shows "finite s \<Longrightarrow> compact(convex hull s)" |
|
1414 apply(drule finite_imp_compact, drule compact_convex_hull) by assumption |
|
1415 |
|
1416 subsection {* Extremal points of a simplex are some vertices. *} |
|
1417 |
|
1418 lemma dist_increases_online: |
|
1419 fixes a b d :: "'a::real_inner" |
|
1420 assumes "d \<noteq> 0" |
|
1421 shows "dist a (b + d) > dist a b \<or> dist a (b - d) > dist a b" |
|
1422 proof(cases "inner a d - inner b d > 0") |
|
1423 case True hence "0 < inner d d + (inner a d * 2 - inner b d * 2)" |
|
1424 apply(rule_tac add_pos_pos) using assms by auto |
|
1425 thus ?thesis apply(rule_tac disjI2) unfolding dist_norm and norm_eq_sqrt_inner and real_sqrt_less_iff |
|
1426 by (simp add: algebra_simps inner_commute) |
|
1427 next |
|
1428 case False hence "0 < inner d d + (inner b d * 2 - inner a d * 2)" |
|
1429 apply(rule_tac add_pos_nonneg) using assms by auto |
|
1430 thus ?thesis apply(rule_tac disjI1) unfolding dist_norm and norm_eq_sqrt_inner and real_sqrt_less_iff |
|
1431 by (simp add: algebra_simps inner_commute) |
|
1432 qed |
|
1433 |
|
1434 lemma norm_increases_online: |
|
1435 fixes d :: "'a::real_inner" |
|
1436 shows "d \<noteq> 0 \<Longrightarrow> norm(a + d) > norm a \<or> norm(a - d) > norm a" |
|
1437 using dist_increases_online[of d a 0] unfolding dist_norm by auto |
|
1438 |
|
1439 lemma simplex_furthest_lt: |
|
1440 fixes s::"'a::real_inner set" assumes "finite s" |
|
1441 shows "\<forall>x \<in> (convex hull s). x \<notin> s \<longrightarrow> (\<exists>y\<in>(convex hull s). norm(x - a) < norm(y - a))" |
|
1442 proof(induct_tac rule: finite_induct[of s]) |
|
1443 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))" |
|
1444 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))" |
|
1445 proof(rule,rule,cases "s = {}") |
|
1446 case False fix y assume y:"y \<in> convex hull insert x s" "y \<notin> insert x s" |
|
1447 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" |
|
1448 using y(1)[unfolded convex_hull_insert[OF False]] by auto |
|
1449 show "\<exists>z\<in>convex hull insert x s. norm (y - a) < norm (z - a)" |
|
1450 proof(cases "y\<in>convex hull s") |
|
1451 case True then obtain z where "z\<in>convex hull s" "norm (y - a) < norm (z - a)" |
|
1452 using as(3)[THEN bspec[where x=y]] and y(2) by auto |
|
1453 thus ?thesis apply(rule_tac x=z in bexI) unfolding convex_hull_insert[OF False] by auto |
|
1454 next |
|
1455 case False show ?thesis using obt(3) proof(cases "u=0", case_tac[!] "v=0") |
|
1456 assume "u=0" "v\<noteq>0" hence "y = b" using obt by auto |
|
1457 thus ?thesis using False and obt(4) by auto |
|
1458 next |
|
1459 assume "u\<noteq>0" "v=0" hence "y = x" using obt by auto |
|
1460 thus ?thesis using y(2) by auto |
|
1461 next |
|
1462 assume "u\<noteq>0" "v\<noteq>0" |
|
1463 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 |
|
1464 have "x\<noteq>b" proof(rule ccontr) |
|
1465 assume "\<not> x\<noteq>b" hence "y=b" unfolding obt(5) |
|
1466 using obt(3) by(auto simp add: scaleR_left_distrib[THEN sym]) |
|
1467 thus False using obt(4) and False by simp qed |
|
1468 hence *:"w *\<^sub>R (x - b) \<noteq> 0" using w(1) by auto |
|
1469 show ?thesis using dist_increases_online[OF *, of a y] |
|
1470 proof(erule_tac disjE) |
|
1471 assume "dist a y < dist a (y + w *\<^sub>R (x - b))" |
|
1472 hence "norm (y - a) < norm ((u + w) *\<^sub>R x + (v - w) *\<^sub>R b - a)" |
|
1473 unfolding dist_commute[of a] unfolding dist_norm obt(5) by (simp add: algebra_simps) |
|
1474 moreover have "(u + w) *\<^sub>R x + (v - w) *\<^sub>R b \<in> convex hull insert x s" |
|
1475 unfolding convex_hull_insert[OF `s\<noteq>{}`] and mem_Collect_eq |
|
1476 apply(rule_tac x="u + w" in exI) apply rule defer |
|
1477 apply(rule_tac x="v - w" in exI) using `u\<ge>0` and w and obt(3,4) by auto |
|
1478 ultimately show ?thesis by auto |
|
1479 next |
|
1480 assume "dist a y < dist a (y - w *\<^sub>R (x - b))" |
|
1481 hence "norm (y - a) < norm ((u - w) *\<^sub>R x + (v + w) *\<^sub>R b - a)" |
|
1482 unfolding dist_commute[of a] unfolding dist_norm obt(5) by (simp add: algebra_simps) |
|
1483 moreover have "(u - w) *\<^sub>R x + (v + w) *\<^sub>R b \<in> convex hull insert x s" |
|
1484 unfolding convex_hull_insert[OF `s\<noteq>{}`] and mem_Collect_eq |
|
1485 apply(rule_tac x="u - w" in exI) apply rule defer |
|
1486 apply(rule_tac x="v + w" in exI) using `u\<ge>0` and w and obt(3,4) by auto |
|
1487 ultimately show ?thesis by auto |
|
1488 qed |
|
1489 qed auto |
|
1490 qed |
|
1491 qed auto |
|
1492 qed (auto simp add: assms) |
|
1493 |
|
1494 lemma simplex_furthest_le: |
|
1495 fixes s :: "(real ^ _) set" |
|
1496 assumes "finite s" "s \<noteq> {}" |
|
1497 shows "\<exists>y\<in>s. \<forall>x\<in>(convex hull s). norm(x - a) \<le> norm(y - a)" |
|
1498 proof- |
|
1499 have "convex hull s \<noteq> {}" using hull_subset[of s convex] and assms(2) by auto |
|
1500 then obtain x where x:"x\<in>convex hull s" "\<forall>y\<in>convex hull s. norm (y - a) \<le> norm (x - a)" |
|
1501 using distance_attains_sup[OF finite_imp_compact_convex_hull[OF assms(1)], of a] |
|
1502 unfolding dist_commute[of a] unfolding dist_norm by auto |
|
1503 thus ?thesis proof(cases "x\<in>s") |
|
1504 case False then obtain y where "y\<in>convex hull s" "norm (x - a) < norm (y - a)" |
|
1505 using simplex_furthest_lt[OF assms(1), THEN bspec[where x=x]] and x(1) by auto |
|
1506 thus ?thesis using x(2)[THEN bspec[where x=y]] by auto |
|
1507 qed auto |
|
1508 qed |
|
1509 |
|
1510 lemma simplex_furthest_le_exists: |
|
1511 fixes s :: "(real ^ _) set" |
|
1512 shows "finite s \<Longrightarrow> (\<forall>x\<in>(convex hull s). \<exists>y\<in>s. norm(x - a) \<le> norm(y - a))" |
|
1513 using simplex_furthest_le[of s] by (cases "s={}")auto |
|
1514 |
|
1515 lemma simplex_extremal_le: |
|
1516 fixes s :: "(real ^ _) set" |
|
1517 assumes "finite s" "s \<noteq> {}" |
|
1518 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)" |
|
1519 proof- |
|
1520 have "convex hull s \<noteq> {}" using hull_subset[of s convex] and assms(2) by auto |
|
1521 then obtain u v where obt:"u\<in>convex hull s" "v\<in>convex hull s" |
|
1522 "\<forall>x\<in>convex hull s. \<forall>y\<in>convex hull s. norm (x - y) \<le> norm (u - v)" |
|
1523 using compact_sup_maxdistance[OF finite_imp_compact_convex_hull[OF assms(1)]] by auto |
|
1524 thus ?thesis proof(cases "u\<notin>s \<or> v\<notin>s", erule_tac disjE) |
|
1525 assume "u\<notin>s" then obtain y where "y\<in>convex hull s" "norm (u - v) < norm (y - v)" |
|
1526 using simplex_furthest_lt[OF assms(1), THEN bspec[where x=u]] and obt(1) by auto |
|
1527 thus ?thesis using obt(3)[THEN bspec[where x=y], THEN bspec[where x=v]] and obt(2) by auto |
|
1528 next |
|
1529 assume "v\<notin>s" then obtain y where "y\<in>convex hull s" "norm (v - u) < norm (y - u)" |
|
1530 using simplex_furthest_lt[OF assms(1), THEN bspec[where x=v]] and obt(2) by auto |
|
1531 thus ?thesis using obt(3)[THEN bspec[where x=u], THEN bspec[where x=y]] and obt(1) |
|
1532 by (auto simp add: norm_minus_commute) |
|
1533 qed auto |
|
1534 qed |
|
1535 |
|
1536 lemma simplex_extremal_le_exists: |
|
1537 fixes s :: "(real ^ _) set" |
|
1538 shows "finite s \<Longrightarrow> x \<in> convex hull s \<Longrightarrow> y \<in> convex hull s |
|
1539 \<Longrightarrow> (\<exists>u\<in>s. \<exists>v\<in>s. norm(x - y) \<le> norm(u - v))" |
|
1540 using convex_hull_empty simplex_extremal_le[of s] by(cases "s={}")auto |
|
1541 |
|
1542 subsection {* Closest point of a convex set is unique, with a continuous projection. *} |
|
1543 |
|
1544 definition |
|
1545 closest_point :: "(real ^ 'n::finite) set \<Rightarrow> real ^ 'n \<Rightarrow> real ^ 'n" where |
|
1546 "closest_point s a = (SOME x. x \<in> s \<and> (\<forall>y\<in>s. dist a x \<le> dist a y))" |
|
1547 |
|
1548 lemma closest_point_exists: |
|
1549 assumes "closed s" "s \<noteq> {}" |
|
1550 shows "closest_point s a \<in> s" "\<forall>y\<in>s. dist a (closest_point s a) \<le> dist a y" |
|
1551 unfolding closest_point_def apply(rule_tac[!] someI2_ex) |
|
1552 using distance_attains_inf[OF assms(1,2), of a] by auto |
|
1553 |
|
1554 lemma closest_point_in_set: |
|
1555 "closed s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> (closest_point s a) \<in> s" |
|
1556 by(meson closest_point_exists) |
|
1557 |
|
1558 lemma closest_point_le: |
|
1559 "closed s \<Longrightarrow> x \<in> s \<Longrightarrow> dist a (closest_point s a) \<le> dist a x" |
|
1560 using closest_point_exists[of s] by auto |
|
1561 |
|
1562 lemma closest_point_self: |
|
1563 assumes "x \<in> s" shows "closest_point s x = x" |
|
1564 unfolding closest_point_def apply(rule some1_equality, rule ex1I[of _ x]) |
|
1565 using assms by auto |
|
1566 |
|
1567 lemma closest_point_refl: |
|
1568 "closed s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> (closest_point s x = x \<longleftrightarrow> x \<in> s)" |
|
1569 using closest_point_in_set[of s x] closest_point_self[of x s] by auto |
|
1570 |
|
1571 (* TODO: move *) |
|
1572 lemma norm_lt: "norm x < norm y \<longleftrightarrow> inner x x < inner y y" |
|
1573 unfolding norm_eq_sqrt_inner by simp |
|
1574 |
|
1575 (* TODO: move *) |
|
1576 lemma norm_le: "norm x \<le> norm y \<longleftrightarrow> inner x x \<le> inner y y" |
|
1577 unfolding norm_eq_sqrt_inner by simp |
|
1578 |
|
1579 lemma closer_points_lemma: fixes y::"real^'n::finite" |
|
1580 assumes "inner y z > 0" |
|
1581 shows "\<exists>u>0. \<forall>v>0. v \<le> u \<longrightarrow> norm(v *\<^sub>R z - y) < norm y" |
|
1582 proof- have z:"inner z z > 0" unfolding inner_gt_zero_iff using assms by auto |
|
1583 thus ?thesis using assms apply(rule_tac x="inner y z / inner z z" in exI) apply(rule) defer proof(rule+) |
|
1584 fix v assume "0<v" "v \<le> inner y z / inner z z" |
|
1585 thus "norm (v *\<^sub>R z - y) < norm y" unfolding norm_lt using z and assms |
|
1586 by (simp add: field_simps inner_diff inner_commute mult_strict_left_mono[OF _ `0<v`]) |
|
1587 qed(rule divide_pos_pos, auto) qed |
|
1588 |
|
1589 lemma closer_point_lemma: |
|
1590 fixes x y z :: "real ^ 'n::finite" |
|
1591 assumes "inner (y - x) (z - x) > 0" |
|
1592 shows "\<exists>u>0. u \<le> 1 \<and> dist (x + u *\<^sub>R (z - x)) y < dist x y" |
|
1593 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)" |
|
1594 using closer_points_lemma[OF assms] by auto |
|
1595 show ?thesis apply(rule_tac x="min u 1" in exI) using u[THEN spec[where x="min u 1"]] and `u>0` |
|
1596 unfolding dist_norm by(auto simp add: norm_minus_commute field_simps) qed |
|
1597 |
|
1598 lemma any_closest_point_dot: |
|
1599 fixes s :: "(real ^ _) set" |
|
1600 assumes "convex s" "closed s" "x \<in> s" "y \<in> s" "\<forall>z\<in>s. dist a x \<le> dist a z" |
|
1601 shows "inner (a - x) (y - x) \<le> 0" |
|
1602 proof(rule ccontr) assume "\<not> inner (a - x) (y - x) \<le> 0" |
|
1603 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 |
|
1604 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 |
|
1605 thus False using assms(5)[THEN bspec[where x="?z"]] and u(3) by (auto simp add: dist_commute algebra_simps) qed |
|
1606 |
|
1607 (* TODO: move *) |
|
1608 lemma norm_le_square: "norm x \<le> a \<longleftrightarrow> 0 \<le> a \<and> inner x x \<le> a\<twosuperior>" |
|
1609 proof - |
|
1610 have "norm x \<le> a \<longleftrightarrow> 0 \<le> a \<and> norm x \<le> a" |
|
1611 using norm_ge_zero [of x] by arith |
|
1612 also have "\<dots> \<longleftrightarrow> 0 \<le> a \<and> (norm x)\<twosuperior> \<le> a\<twosuperior>" |
|
1613 by (auto intro: power_mono dest: power2_le_imp_le) |
|
1614 also have "\<dots> \<longleftrightarrow> 0 \<le> a \<and> inner x x \<le> a\<twosuperior>" |
|
1615 unfolding power2_norm_eq_inner .. |
|
1616 finally show ?thesis . |
|
1617 qed |
|
1618 |
|
1619 lemma any_closest_point_unique: |
|
1620 fixes s :: "(real ^ _) set" |
|
1621 assumes "convex s" "closed s" "x \<in> s" "y \<in> s" |
|
1622 "\<forall>z\<in>s. dist a x \<le> dist a z" "\<forall>z\<in>s. dist a y \<le> dist a z" |
|
1623 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)] |
|
1624 unfolding norm_pths(1) and norm_le_square |
|
1625 by (auto simp add: algebra_simps) |
|
1626 |
|
1627 lemma closest_point_unique: |
|
1628 assumes "convex s" "closed s" "x \<in> s" "\<forall>z\<in>s. dist a x \<le> dist a z" |
|
1629 shows "x = closest_point s a" |
|
1630 using any_closest_point_unique[OF assms(1-3) _ assms(4), of "closest_point s a"] |
|
1631 using closest_point_exists[OF assms(2)] and assms(3) by auto |
|
1632 |
|
1633 lemma closest_point_dot: |
|
1634 assumes "convex s" "closed s" "x \<in> s" |
|
1635 shows "inner (a - closest_point s a) (x - closest_point s a) \<le> 0" |
|
1636 apply(rule any_closest_point_dot[OF assms(1,2) _ assms(3)]) |
|
1637 using closest_point_exists[OF assms(2)] and assms(3) by auto |
|
1638 |
|
1639 lemma closest_point_lt: |
|
1640 assumes "convex s" "closed s" "x \<in> s" "x \<noteq> closest_point s a" |
|
1641 shows "dist a (closest_point s a) < dist a x" |
|
1642 apply(rule ccontr) apply(rule_tac notE[OF assms(4)]) |
|
1643 apply(rule closest_point_unique[OF assms(1-3), of a]) |
|
1644 using closest_point_le[OF assms(2), of _ a] by fastsimp |
|
1645 |
|
1646 lemma closest_point_lipschitz: |
|
1647 assumes "convex s" "closed s" "s \<noteq> {}" |
|
1648 shows "dist (closest_point s x) (closest_point s y) \<le> dist x y" |
|
1649 proof- |
|
1650 have "inner (x - closest_point s x) (closest_point s y - closest_point s x) \<le> 0" |
|
1651 "inner (y - closest_point s y) (closest_point s x - closest_point s y) \<le> 0" |
|
1652 apply(rule_tac[!] any_closest_point_dot[OF assms(1-2)]) |
|
1653 using closest_point_exists[OF assms(2-3)] by auto |
|
1654 thus ?thesis unfolding dist_norm and norm_le |
|
1655 using inner_ge_zero[of "(x - closest_point s x) - (y - closest_point s y)"] |
|
1656 by (simp add: inner_add inner_diff inner_commute) qed |
|
1657 |
|
1658 lemma continuous_at_closest_point: |
|
1659 assumes "convex s" "closed s" "s \<noteq> {}" |
|
1660 shows "continuous (at x) (closest_point s)" |
|
1661 unfolding continuous_at_eps_delta |
|
1662 using le_less_trans[OF closest_point_lipschitz[OF assms]] by auto |
|
1663 |
|
1664 lemma continuous_on_closest_point: |
|
1665 assumes "convex s" "closed s" "s \<noteq> {}" |
|
1666 shows "continuous_on t (closest_point s)" |
|
1667 apply(rule continuous_at_imp_continuous_on) using continuous_at_closest_point[OF assms] by auto |
|
1668 |
|
1669 subsection {* Various point-to-set separating/supporting hyperplane theorems. *} |
|
1670 |
|
1671 lemma supporting_hyperplane_closed_point: |
|
1672 fixes s :: "(real ^ _) set" |
|
1673 assumes "convex s" "closed s" "s \<noteq> {}" "z \<notin> s" |
|
1674 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)" |
|
1675 proof- |
|
1676 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 |
|
1677 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) |
|
1678 apply rule defer apply rule defer apply(rule, rule ccontr) using `y\<in>s` proof- |
|
1679 show "inner (y - z) z < inner (y - z) y" apply(subst diff_less_iff(1)[THEN sym]) |
|
1680 unfolding inner_diff_right[THEN sym] and inner_gt_zero_iff using `y\<in>s` `z\<notin>s` by auto |
|
1681 next |
|
1682 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)" |
|
1683 using assms(1)[unfolded convex_alt] and y and `x\<in>s` and `y\<in>s` by auto |
|
1684 assume "\<not> inner (y - z) y \<le> inner (y - z) x" then obtain v where |
|
1685 "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) |
|
1686 thus False using *[THEN spec[where x=v]] by(auto simp add: dist_commute algebra_simps) |
|
1687 qed auto |
|
1688 qed |
|
1689 |
|
1690 lemma separating_hyperplane_closed_point: |
|
1691 fixes s :: "(real ^ _) set" |
|
1692 assumes "convex s" "closed s" "z \<notin> s" |
|
1693 shows "\<exists>a b. inner a z < b \<and> (\<forall>x\<in>s. inner a x > b)" |
|
1694 proof(cases "s={}") |
|
1695 case True thus ?thesis apply(rule_tac x="-z" in exI, rule_tac x=1 in exI) |
|
1696 using less_le_trans[OF _ inner_ge_zero[of z]] by auto |
|
1697 next |
|
1698 case False obtain y where "y\<in>s" and y:"\<forall>x\<in>s. dist z y \<le> dist z x" |
|
1699 using distance_attains_inf[OF assms(2) False] by auto |
|
1700 show ?thesis apply(rule_tac x="y - z" in exI, rule_tac x="inner (y - z) z + (norm(y - z))\<twosuperior> / 2" in exI) |
|
1701 apply rule defer apply rule proof- |
|
1702 fix x assume "x\<in>s" |
|
1703 have "\<not> 0 < inner (z - y) (x - y)" apply(rule_tac notI) proof(drule closer_point_lemma) |
|
1704 assume "\<exists>u>0. u \<le> 1 \<and> dist (y + u *\<^sub>R (x - y)) z < dist y z" |
|
1705 then obtain u where "u>0" "u\<le>1" "dist (y + u *\<^sub>R (x - y)) z < dist y z" by auto |
|
1706 thus False using y[THEN bspec[where x="y + u *\<^sub>R (x - y)"]] |
|
1707 using assms(1)[unfolded convex_alt, THEN bspec[where x=y]] |
|
1708 using `x\<in>s` `y\<in>s` by (auto simp add: dist_commute algebra_simps) qed |
|
1709 moreover have "0 < norm (y - z) ^ 2" using `y\<in>s` `z\<notin>s` by auto |
|
1710 hence "0 < inner (y - z) (y - z)" unfolding power2_norm_eq_inner by simp |
|
1711 ultimately show "inner (y - z) z + (norm (y - z))\<twosuperior> / 2 < inner (y - z) x" |
|
1712 unfolding power2_norm_eq_inner and not_less by (auto simp add: field_simps inner_commute inner_diff) |
|
1713 qed(insert `y\<in>s` `z\<notin>s`, auto) |
|
1714 qed |
|
1715 |
|
1716 lemma separating_hyperplane_closed_0: |
|
1717 assumes "convex (s::(real^'n::finite) set)" "closed s" "0 \<notin> s" |
|
1718 shows "\<exists>a b. a \<noteq> 0 \<and> 0 < b \<and> (\<forall>x\<in>s. inner a x > b)" |
|
1719 proof(cases "s={}") guess a using UNIV_witness[where 'a='n] .. |
|
1720 case True have "norm ((basis a)::real^'n::finite) = 1" |
|
1721 using norm_basis and dimindex_ge_1 by auto |
|
1722 thus ?thesis apply(rule_tac x="basis a" in exI, rule_tac x=1 in exI) using True by auto |
|
1723 next case False thus ?thesis using False using separating_hyperplane_closed_point[OF assms] |
|
1724 apply - apply(erule exE)+ unfolding dot_rzero apply(rule_tac x=a in exI, rule_tac x=b in exI) by auto qed |
|
1725 |
|
1726 subsection {* Now set-to-set for closed/compact sets. *} |
|
1727 |
|
1728 lemma separating_hyperplane_closed_compact: |
|
1729 assumes "convex (s::(real^'n::finite) set)" "closed s" "convex t" "compact t" "t \<noteq> {}" "s \<inter> t = {}" |
|
1730 shows "\<exists>a b. (\<forall>x\<in>s. inner a x < b) \<and> (\<forall>x\<in>t. inner a x > b)" |
|
1731 proof(cases "s={}") |
|
1732 case True |
|
1733 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 |
|
1734 obtain z::"real^'n" where z:"norm z = b + 1" using vector_choose_size[of "b + 1"] and b(1) by auto |
|
1735 hence "z\<notin>t" using b(2)[THEN bspec[where x=z]] by auto |
|
1736 then obtain a b where ab:"inner a z < b" "\<forall>x\<in>t. b < inner a x" |
|
1737 using separating_hyperplane_closed_point[OF assms(3) compact_imp_closed[OF assms(4)], of z] by auto |
|
1738 thus ?thesis using True by auto |
|
1739 next |
|
1740 case False then obtain y where "y\<in>s" by auto |
|
1741 obtain a b where "0 < b" "\<forall>x\<in>{x - y |x y. x \<in> s \<and> y \<in> t}. b < inner a x" |
|
1742 using separating_hyperplane_closed_point[OF convex_differences[OF assms(1,3)], of 0] |
|
1743 using closed_compact_differences[OF assms(2,4)] using assms(6) by(auto, blast) |
|
1744 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) |
|
1745 def k \<equiv> "rsup ((\<lambda>x. inner a x) ` t)" |
|
1746 show ?thesis apply(rule_tac x="-a" in exI, rule_tac x="-(k + b / 2)" in exI) |
|
1747 apply(rule,rule) defer apply(rule) unfolding inner_minus_left and neg_less_iff_less proof- |
|
1748 from ab have "((\<lambda>x. inner a x) ` t) *<= (inner a y - b)" |
|
1749 apply(erule_tac x=y in ballE) apply(rule setleI) using `y\<in>s` by auto |
|
1750 hence k:"isLub UNIV ((\<lambda>x. inner a x) ` t) k" unfolding k_def apply(rule_tac rsup) using assms(5) by auto |
|
1751 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 |
|
1752 next |
|
1753 fix x assume "x\<in>s" |
|
1754 hence "k \<le> inner a x - b" unfolding k_def apply(rule_tac rsup_le) using assms(5) |
|
1755 unfolding setle_def |
|
1756 using ab[THEN bspec[where x=x]] by auto |
|
1757 thus "k + b / 2 < inner a x" using `0 < b` by auto |
|
1758 qed |
|
1759 qed |
|
1760 |
|
1761 lemma separating_hyperplane_compact_closed: |
|
1762 fixes s :: "(real ^ _) set" |
|
1763 assumes "convex s" "compact s" "s \<noteq> {}" "convex t" "closed t" "s \<inter> t = {}" |
|
1764 shows "\<exists>a b. (\<forall>x\<in>s. inner a x < b) \<and> (\<forall>x\<in>t. inner a x > b)" |
|
1765 proof- obtain a b where "(\<forall>x\<in>t. inner a x < b) \<and> (\<forall>x\<in>s. b < inner a x)" |
|
1766 using separating_hyperplane_closed_compact[OF assms(4-5,1-2,3)] and assms(6) by auto |
|
1767 thus ?thesis apply(rule_tac x="-a" in exI, rule_tac x="-b" in exI) by auto qed |
|
1768 |
|
1769 subsection {* General case without assuming closure and getting non-strict separation. *} |
|
1770 |
|
1771 lemma separating_hyperplane_set_0: |
|
1772 assumes "convex s" "(0::real^'n::finite) \<notin> s" |
|
1773 shows "\<exists>a. a \<noteq> 0 \<and> (\<forall>x\<in>s. 0 \<le> inner a x)" |
|
1774 proof- let ?k = "\<lambda>c. {x::real^'n. 0 \<le> inner c x}" |
|
1775 have "frontier (cball 0 1) \<inter> (\<Inter> (?k ` s)) \<noteq> {}" |
|
1776 apply(rule compact_imp_fip) apply(rule compact_frontier[OF compact_cball]) |
|
1777 defer apply(rule,rule,erule conjE) proof- |
|
1778 fix f assume as:"f \<subseteq> ?k ` s" "finite f" |
|
1779 obtain c where c:"f = ?k ` c" "c\<subseteq>s" "finite c" using finite_subset_image[OF as(2,1)] by auto |
|
1780 then obtain a b where ab:"a \<noteq> 0" "0 < b" "\<forall>x\<in>convex hull c. b < inner a x" |
|
1781 using separating_hyperplane_closed_0[OF convex_convex_hull, of c] |
|
1782 using finite_imp_compact_convex_hull[OF c(3), THEN compact_imp_closed] and assms(2) |
|
1783 using subset_hull[unfolded mem_def, of convex, OF assms(1), THEN sym, of c] by auto |
|
1784 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) |
|
1785 using hull_subset[of c convex] unfolding subset_eq and inner_scaleR |
|
1786 apply- apply rule defer apply rule apply(rule mult_nonneg_nonneg) |
|
1787 by(auto simp add: inner_commute elim!: ballE) |
|
1788 thus "frontier (cball 0 1) \<inter> \<Inter>f \<noteq> {}" unfolding c(1) frontier_cball dist_norm by auto |
|
1789 qed(insert closed_halfspace_ge, auto) |
|
1790 then obtain x where "norm x = 1" "\<forall>y\<in>s. x\<in>?k y" unfolding frontier_cball dist_norm by auto |
|
1791 thus ?thesis apply(rule_tac x=x in exI) by(auto simp add: inner_commute) qed |
|
1792 |
|
1793 lemma separating_hyperplane_sets: |
|
1794 assumes "convex s" "convex (t::(real^'n::finite) set)" "s \<noteq> {}" "t \<noteq> {}" "s \<inter> t = {}" |
|
1795 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)" |
|
1796 proof- from separating_hyperplane_set_0[OF convex_differences[OF assms(2,1)]] |
|
1797 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" using assms(3-5) by auto |
|
1798 hence "\<forall>x\<in>t. \<forall>y\<in>s. inner a y \<le> inner a x" apply- apply(rule, rule) apply(erule_tac x="x - y" in ballE) by (auto simp add: inner_diff) |
|
1799 thus ?thesis apply(rule_tac x=a in exI, rule_tac x="rsup ((\<lambda>x. inner a x) ` s)" in exI) using `a\<noteq>0` |
|
1800 apply(rule) apply(rule,rule) apply(rule rsup[THEN isLubD2]) prefer 4 apply(rule,rule rsup_le) unfolding setle_def |
|
1801 prefer 4 using assms(3-5) by blast+ qed |
|
1802 |
|
1803 subsection {* More convexity generalities. *} |
|
1804 |
|
1805 lemma convex_closure: |
|
1806 fixes s :: "'a::real_normed_vector set" |
|
1807 assumes "convex s" shows "convex(closure s)" |
|
1808 unfolding convex_def Ball_def closure_sequential |
|
1809 apply(rule,rule,rule,rule,rule,rule,rule,rule,rule) apply(erule_tac exE)+ |
|
1810 apply(rule_tac x="\<lambda>n. u *\<^sub>R xb n + v *\<^sub>R xc n" in exI) apply(rule,rule) |
|
1811 apply(rule assms[unfolded convex_def, rule_format]) prefer 6 |
|
1812 apply(rule Lim_add) apply(rule_tac [1-2] Lim_cmul) by auto |
|
1813 |
|
1814 lemma convex_interior: |
|
1815 fixes s :: "'a::real_normed_vector set" |
|
1816 assumes "convex s" shows "convex(interior s)" |
|
1817 unfolding convex_alt Ball_def mem_interior apply(rule,rule,rule,rule,rule,rule) apply(erule exE | erule conjE)+ proof- |
|
1818 fix x y u assume u:"0 \<le> u" "u \<le> (1::real)" |
|
1819 fix e d assume ed:"ball x e \<subseteq> s" "ball y d \<subseteq> s" "0<d" "0<e" |
|
1820 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) |
|
1821 apply rule unfolding subset_eq defer apply rule proof- |
|
1822 fix z assume "z \<in> ball ((1 - u) *\<^sub>R x + u *\<^sub>R y) (min d e)" |
|
1823 hence "(1- u) *\<^sub>R (z - u *\<^sub>R (y - x)) + u *\<^sub>R (z + (1 - u) *\<^sub>R (y - x)) \<in> s" |
|
1824 apply(rule_tac assms[unfolded convex_alt, rule_format]) |
|
1825 using ed(1,2) and u unfolding subset_eq mem_ball Ball_def dist_norm by(auto simp add: algebra_simps) |
|
1826 thus "z \<in> s" using u by (auto simp add: algebra_simps) qed(insert u ed(3-4), auto) qed |
|
1827 |
|
1828 lemma convex_hull_eq_empty: "convex hull s = {} \<longleftrightarrow> s = {}" |
|
1829 using hull_subset[of s convex] convex_hull_empty by auto |
|
1830 |
|
1831 subsection {* Moving and scaling convex hulls. *} |
|
1832 |
|
1833 lemma convex_hull_translation_lemma: |
|
1834 "convex hull ((\<lambda>x. a + x) ` s) \<subseteq> (\<lambda>x. a + x) ` (convex hull s)" |
|
1835 apply(rule hull_minimal, rule image_mono, rule hull_subset) unfolding mem_def |
|
1836 using convex_translation[OF convex_convex_hull, of a s] by assumption |
|
1837 |
|
1838 lemma convex_hull_bilemma: fixes neg |
|
1839 assumes "(\<forall>s a. (convex hull (up a s)) \<subseteq> up a (convex hull s))" |
|
1840 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) |
|
1841 \<Longrightarrow> \<forall>s. (convex hull (up a s)) = up a (convex hull s)" |
|
1842 using assms by(metis subset_antisym) |
|
1843 |
|
1844 lemma convex_hull_translation: |
|
1845 "convex hull ((\<lambda>x. a + x) ` s) = (\<lambda>x. a + x) ` (convex hull s)" |
|
1846 apply(rule convex_hull_bilemma[rule_format, of _ _ "\<lambda>a. -a"], rule convex_hull_translation_lemma) unfolding image_image by auto |
|
1847 |
|
1848 lemma convex_hull_scaling_lemma: |
|
1849 "(convex hull ((\<lambda>x. c *\<^sub>R x) ` s)) \<subseteq> (\<lambda>x. c *\<^sub>R x) ` (convex hull s)" |
|
1850 apply(rule hull_minimal, rule image_mono, rule hull_subset) |
|
1851 unfolding mem_def by(rule convex_scaling, rule convex_convex_hull) |
|
1852 |
|
1853 lemma convex_hull_scaling: |
|
1854 "convex hull ((\<lambda>x. c *\<^sub>R x) ` s) = (\<lambda>x. c *\<^sub>R x) ` (convex hull s)" |
|
1855 apply(cases "c=0") defer apply(rule convex_hull_bilemma[rule_format, of _ _ inverse]) apply(rule convex_hull_scaling_lemma) |
|
1856 unfolding image_image scaleR_scaleR by(auto simp add:image_constant_conv convex_hull_eq_empty) |
|
1857 |
|
1858 lemma convex_hull_affinity: |
|
1859 "convex hull ((\<lambda>x. a + c *\<^sub>R x) ` s) = (\<lambda>x. a + c *\<^sub>R x) ` (convex hull s)" |
|
1860 unfolding image_image[THEN sym] convex_hull_scaling convex_hull_translation .. |
|
1861 |
|
1862 subsection {* Convex set as intersection of halfspaces. *} |
|
1863 |
|
1864 lemma convex_halfspace_intersection: |
|
1865 fixes s :: "(real ^ _) set" |
|
1866 assumes "closed s" "convex s" |
|
1867 shows "s = \<Inter> {h. s \<subseteq> h \<and> (\<exists>a b. h = {x. inner a x \<le> b})}" |
|
1868 apply(rule set_ext, rule) unfolding Inter_iff Ball_def mem_Collect_eq apply(rule,rule,erule conjE) proof- |
|
1869 fix x assume "\<forall>xa. s \<subseteq> xa \<and> (\<exists>a b. xa = {x. inner a x \<le> b}) \<longrightarrow> x \<in> xa" |
|
1870 hence "\<forall>a b. s \<subseteq> {x. inner a x \<le> b} \<longrightarrow> x \<in> {x. inner a x \<le> b}" by blast |
|
1871 thus "x\<in>s" apply(rule_tac ccontr) apply(drule separating_hyperplane_closed_point[OF assms(2,1)]) |
|
1872 apply(erule exE)+ apply(erule_tac x="-a" in allE, erule_tac x="-b" in allE) by auto |
|
1873 qed auto |
|
1874 |
|
1875 subsection {* Radon's theorem (from Lars Schewe). *} |
|
1876 |
|
1877 lemma radon_ex_lemma: |
|
1878 assumes "finite c" "affine_dependent c" |
|
1879 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" |
|
1880 proof- from assms(2)[unfolded affine_dependent_explicit] guess s .. then guess u .. |
|
1881 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 |
|
1882 and setsum_restrict_set[OF assms(1), THEN sym] by(auto simp add: Int_absorb1) qed |
|
1883 |
|
1884 lemma radon_s_lemma: |
|
1885 assumes "finite s" "setsum f s = (0::real)" |
|
1886 shows "setsum f {x\<in>s. 0 < f x} = - setsum f {x\<in>s. f x < 0}" |
|
1887 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 |
|
1888 show ?thesis unfolding real_add_eq_0_iff[THEN sym] and setsum_restrict_set''[OF assms(1)] and setsum_addf[THEN sym] and * |
|
1889 using assms(2) by assumption qed |
|
1890 |
|
1891 lemma radon_v_lemma: |
|
1892 assumes "finite s" "setsum f s = 0" "\<forall>x. g x = (0::real) \<longrightarrow> f x = (0::real^'n)" |
|
1893 shows "(setsum f {x\<in>s. 0 < g x}) = - setsum f {x\<in>s. g x < 0}" |
|
1894 proof- |
|
1895 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 |
|
1896 show ?thesis unfolding eq_neg_iff_add_eq_0 and setsum_restrict_set''[OF assms(1)] and setsum_addf[THEN sym] and * |
|
1897 using assms(2) by assumption qed |
|
1898 |
|
1899 lemma radon_partition: |
|
1900 assumes "finite c" "affine_dependent c" |
|
1901 shows "\<exists>m p. m \<inter> p = {} \<and> m \<union> p = c \<and> (convex hull m) \<inter> (convex hull p) \<noteq> {}" proof- |
|
1902 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 |
|
1903 have fin:"finite {x \<in> c. 0 < u x}" "finite {x \<in> c. 0 > u x}" using assms(1) by auto |
|
1904 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}" |
|
1905 have "setsum u {x \<in> c. 0 < u x} \<noteq> 0" proof(cases "u v \<ge> 0") |
|
1906 case False hence "u v < 0" by auto |
|
1907 thus ?thesis proof(cases "\<exists>w\<in>{x \<in> c. 0 < u x}. u w > 0") |
|
1908 case True thus ?thesis using setsum_nonneg_eq_0_iff[of _ u, OF fin(1)] by auto |
|
1909 next |
|
1910 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 |
|
1911 thus ?thesis unfolding setsum_delta[OF assms(1)] using uv(2) and `u v < 0` and uv(1) by auto qed |
|
1912 qed (insert setsum_nonneg_eq_0_iff[of _ u, OF fin(1)] uv(2-3), auto) |
|
1913 |
|
1914 hence *:"setsum u {x\<in>c. u x > 0} > 0" unfolding real_less_def apply(rule_tac conjI, rule_tac setsum_nonneg) by auto |
|
1915 moreover have "setsum u ({x \<in> c. 0 < u x} \<union> {x \<in> c. u x < 0}) = setsum u c" |
|
1916 "(\<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)" |
|
1917 using assms(1) apply(rule_tac[!] setsum_mono_zero_left) by auto |
|
1918 hence "setsum u {x \<in> c. 0 < u x} = - setsum u {x \<in> c. 0 > u x}" |
|
1919 "(\<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)" |
|
1920 unfolding eq_neg_iff_add_eq_0 using uv(1,4) by (auto simp add: setsum_Un_zero[OF fin, THEN sym]) |
|
1921 moreover have "\<forall>x\<in>{v \<in> c. u v < 0}. 0 \<le> inverse (setsum u {x \<in> c. 0 < u x}) * - u x" |
|
1922 apply (rule) apply (rule mult_nonneg_nonneg) using * by auto |
|
1923 |
|
1924 ultimately have "z \<in> convex hull {v \<in> c. u v \<le> 0}" unfolding convex_hull_explicit mem_Collect_eq |
|
1925 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) |
|
1926 using assms(1) unfolding scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] and z_def |
|
1927 by(auto simp add: setsum_negf vector_smult_lneg mult_right.setsum[THEN sym]) |
|
1928 moreover have "\<forall>x\<in>{v \<in> c. 0 < u v}. 0 \<le> inverse (setsum u {x \<in> c. 0 < u x}) * u x" |
|
1929 apply (rule) apply (rule mult_nonneg_nonneg) using * by auto |
|
1930 hence "z \<in> convex hull {v \<in> c. u v > 0}" unfolding convex_hull_explicit mem_Collect_eq |
|
1931 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) |
|
1932 using assms(1) unfolding scaleR_scaleR[THEN sym] scaleR_right.setsum [symmetric] and z_def using * |
|
1933 by(auto simp add: setsum_negf vector_smult_lneg mult_right.setsum[THEN sym]) |
|
1934 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 |
|
1935 qed |
|
1936 |
|
1937 lemma radon: assumes "affine_dependent c" |
|
1938 obtains m p where "m\<subseteq>c" "p\<subseteq>c" "m \<inter> p = {}" "(convex hull m) \<inter> (convex hull p) \<noteq> {}" |
|
1939 proof- from assms[unfolded affine_dependent_explicit] guess s .. then guess u .. |
|
1940 hence *:"finite s" "affine_dependent s" and s:"s \<subseteq> c" unfolding affine_dependent_explicit by auto |
|
1941 from radon_partition[OF *] guess m .. then guess p .. |
|
1942 thus ?thesis apply(rule_tac that[of p m]) using s by auto qed |
|
1943 |
|
1944 subsection {* Helly's theorem. *} |
|
1945 |
|
1946 lemma helly_induct: fixes f::"(real^'n::finite) set set" |
|
1947 assumes "f hassize n" "n \<ge> CARD('n) + 1" |
|
1948 "\<forall>s\<in>f. convex s" "\<forall>t\<subseteq>f. card t = CARD('n) + 1 \<longrightarrow> \<Inter> t \<noteq> {}" |
|
1949 shows "\<Inter> f \<noteq> {}" |
|
1950 using assms unfolding hassize_def apply(erule_tac conjE) proof(induct n arbitrary: f) |
|
1951 case (Suc n) |
|
1952 show "\<Inter> f \<noteq> {}" apply(cases "n = CARD('n)") apply(rule Suc(4)[rule_format]) |
|
1953 unfolding card_Diff_singleton_if[OF Suc(5)] and Suc(6) proof- |
|
1954 assume ng:"n \<noteq> CARD('n)" hence "\<exists>X. \<forall>s\<in>f. X s \<in> \<Inter>(f - {s})" apply(rule_tac bchoice) unfolding ex_in_conv |
|
1955 apply(rule, rule Suc(1)[rule_format]) unfolding card_Diff_singleton_if[OF Suc(5)] and Suc(6) |
|
1956 defer apply(rule Suc(3)[rule_format]) defer apply(rule Suc(4)[rule_format]) using Suc(2,5) by auto |
|
1957 then obtain X where X:"\<forall>s\<in>f. X s \<in> \<Inter>(f - {s})" by auto |
|
1958 show ?thesis proof(cases "inj_on X f") |
|
1959 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 |
|
1960 hence *:"\<Inter> f = \<Inter> (f - {s}) \<inter> \<Inter> (f - {t})" by auto |
|
1961 show ?thesis unfolding * unfolding ex_in_conv[THEN sym] apply(rule_tac x="X s" in exI) |
|
1962 apply(rule, rule X[rule_format]) using X st by auto |
|
1963 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> {}" |
|
1964 using radon_partition[of "X ` f"] and affine_dependent_biggerset[of "X ` f"] |
|
1965 unfolding card_image[OF True] and Suc(6) using Suc(2,5) and ng by auto |
|
1966 have "m \<subseteq> X ` f" "p \<subseteq> X ` f" using mp(2) by auto |
|
1967 then obtain g h where gh:"m = X ` g" "p = X ` h" "g \<subseteq> f" "h \<subseteq> f" unfolding subset_image_iff by auto |
|
1968 hence "f \<union> (g \<union> h) = f" by auto |
|
1969 hence f:"f = g \<union> h" using inj_on_Un_image_eq_iff[of X f "g \<union> h"] and True |
|
1970 unfolding mp(2)[unfolded image_Un[THEN sym] gh] by auto |
|
1971 have *:"g \<inter> h = {}" using mp(1) unfolding gh using inj_on_image_Int[OF True gh(3,4)] by auto |
|
1972 have "convex hull (X ` h) \<subseteq> \<Inter> g" "convex hull (X ` g) \<subseteq> \<Inter> h" |
|
1973 apply(rule_tac [!] hull_minimal) using Suc(3) gh(3-4) unfolding mem_def unfolding subset_eq |
|
1974 apply(rule_tac [2] convex_Inter, rule_tac [4] convex_Inter) apply rule prefer 3 apply rule proof- |
|
1975 fix x assume "x\<in>X ` g" then guess y unfolding image_iff .. |
|
1976 thus "x\<in>\<Inter>h" using X[THEN bspec[where x=y]] using * f by auto next |
|
1977 fix x assume "x\<in>X ` h" then guess y unfolding image_iff .. |
|
1978 thus "x\<in>\<Inter>g" using X[THEN bspec[where x=y]] using * f by auto |
|
1979 qed(auto) |
|
1980 thus ?thesis unfolding f using mp(3)[unfolded gh] by blast qed |
|
1981 qed(insert dimindex_ge_1, auto) qed(auto) |
|
1982 |
|
1983 lemma helly: fixes f::"(real^'n::finite) set set" |
|
1984 assumes "finite f" "card f \<ge> CARD('n) + 1" "\<forall>s\<in>f. convex s" |
|
1985 "\<forall>t\<subseteq>f. card t = CARD('n) + 1 \<longrightarrow> \<Inter> t \<noteq> {}" |
|
1986 shows "\<Inter> f \<noteq>{}" |
|
1987 apply(rule helly_induct) unfolding hassize_def using assms by auto |
|
1988 |
|
1989 subsection {* Convex hull is "preserved" by a linear function. *} |
|
1990 |
|
1991 lemma convex_hull_linear_image: |
|
1992 assumes "bounded_linear f" |
|
1993 shows "f ` (convex hull s) = convex hull (f ` s)" |
|
1994 apply rule unfolding subset_eq ball_simps apply(rule_tac[!] hull_induct, rule hull_inc) prefer 3 |
|
1995 apply(erule imageE)apply(rule_tac x=xa in image_eqI) apply assumption |
|
1996 apply(rule hull_subset[unfolded subset_eq, rule_format]) apply assumption |
|
1997 proof- |
|
1998 interpret f: bounded_linear f by fact |
|
1999 show "convex {x. f x \<in> convex hull f ` s}" |
|
2000 unfolding convex_def by(auto simp add: f.scaleR f.add convex_convex_hull[unfolded convex_def, rule_format]) next |
|
2001 interpret f: bounded_linear f by fact |
|
2002 show "convex {x. x \<in> f ` (convex hull s)}" using convex_convex_hull[unfolded convex_def, of s] |
|
2003 unfolding convex_def by (auto simp add: f.scaleR [symmetric] f.add [symmetric]) |
|
2004 qed auto |
|
2005 |
|
2006 lemma in_convex_hull_linear_image: |
|
2007 assumes "bounded_linear f" "x \<in> convex hull s" |
|
2008 shows "(f x) \<in> convex hull (f ` s)" |
|
2009 using convex_hull_linear_image[OF assms(1)] assms(2) by auto |
|
2010 |
|
2011 subsection {* Homeomorphism of all convex compact sets with nonempty interior. *} |
|
2012 |
|
2013 lemma compact_frontier_line_lemma: |
|
2014 fixes s :: "(real ^ _) set" |
|
2015 assumes "compact s" "0 \<in> s" "x \<noteq> 0" |
|
2016 obtains u where "0 \<le> u" "(u *\<^sub>R x) \<in> frontier s" "\<forall>v>u. (v *\<^sub>R x) \<notin> s" |
|
2017 proof- |
|
2018 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 |
|
2019 let ?A = "{y. \<exists>u. 0 \<le> u \<and> u \<le> b / norm(x) \<and> (y = u *\<^sub>R x)}" |
|
2020 have A:"?A = (\<lambda>u. dest_vec1 u *\<^sub>R x) ` {0 .. vec1 (b / norm x)}" |
|
2021 unfolding image_image[of "\<lambda>u. u *\<^sub>R x" "\<lambda>x. dest_vec1 x", THEN sym] |
|
2022 unfolding dest_vec1_inverval vec1_dest_vec1 by auto |
|
2023 have "compact ?A" unfolding A apply(rule compact_continuous_image, rule continuous_at_imp_continuous_on) |
|
2024 apply(rule, rule continuous_vmul) |
|
2025 apply (rule continuous_dest_vec1) |
|
2026 apply(rule continuous_at_id) by(rule compact_interval) |
|
2027 moreover have "{y. \<exists>u\<ge>0. u \<le> b / norm x \<and> y = u *\<^sub>R x} \<inter> s \<noteq> {}" apply(rule not_disjointI[OF _ assms(2)]) |
|
2028 unfolding mem_Collect_eq using `b>0` assms(3) by(auto intro!: divide_nonneg_pos) |
|
2029 ultimately obtain u y where obt: "u\<ge>0" "u \<le> b / norm x" "y = u *\<^sub>R x" |
|
2030 "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 |
|
2031 |
|
2032 have "norm x > 0" using assms(3)[unfolded zero_less_norm_iff[THEN sym]] by auto |
|
2033 { fix v assume as:"v > u" "v *\<^sub>R x \<in> s" |
|
2034 hence "v \<le> b / norm x" using b(2)[rule_format, OF as(2)] |
|
2035 using `u\<ge>0` unfolding pos_le_divide_eq[OF `norm x > 0`] by auto |
|
2036 hence "norm (v *\<^sub>R x) \<le> norm y" apply(rule_tac obt(6)[rule_format, unfolded dist_0_norm]) apply(rule IntI) defer |
|
2037 apply(rule as(2)) unfolding mem_Collect_eq apply(rule_tac x=v in exI) |
|
2038 using as(1) `u\<ge>0` by(auto simp add:field_simps) |
|
2039 hence False unfolding obt(3) using `u\<ge>0` `norm x > 0` `v>u` by(auto simp add:field_simps) |
|
2040 } note u_max = this |
|
2041 |
|
2042 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] |
|
2043 prefer 3 apply(rule_tac x="(u + (e / 2) / norm x) *\<^sub>R x" in exI) apply(rule, rule) proof- |
|
2044 fix e assume "0 < e" and as:"(u + e / 2 / norm x) *\<^sub>R x \<in> s" |
|
2045 hence "u + e / 2 / norm x > u" using`norm x > 0` by(auto simp del:zero_less_norm_iff intro!: divide_pos_pos) |
|
2046 thus False using u_max[OF _ as] by auto |
|
2047 qed(insert `y\<in>s`, auto simp add: dist_norm scaleR_left_distrib obt(3)) |
|
2048 thus ?thesis apply(rule_tac that[of u]) apply(rule obt(1), assumption) |
|
2049 apply(rule,rule,rule ccontr) apply(rule u_max) by auto qed |
|
2050 |
|
2051 lemma starlike_compact_projective: |
|
2052 assumes "compact s" "cball (0::real^'n::finite) 1 \<subseteq> s " |
|
2053 "\<forall>x\<in>s. \<forall>u. 0 \<le> u \<and> u < 1 \<longrightarrow> (u *\<^sub>R x) \<in> (s - frontier s )" |
|
2054 shows "s homeomorphic (cball (0::real^'n::finite) 1)" |
|
2055 proof- |
|
2056 have fs:"frontier s \<subseteq> s" apply(rule frontier_subset_closed) using compact_imp_closed[OF assms(1)] by simp |
|
2057 def pi \<equiv> "\<lambda>x::real^'n. inverse (norm x) *\<^sub>R x" |
|
2058 have "0 \<notin> frontier s" unfolding frontier_straddle apply(rule ccontr) unfolding not_not apply(erule_tac x=1 in allE) |
|
2059 using assms(2)[unfolded subset_eq Ball_def mem_cball] by auto |
|
2060 have injpi:"\<And>x y. pi x = pi y \<and> norm x = norm y \<longleftrightarrow> x = y" unfolding pi_def by auto |
|
2061 |
|
2062 have contpi:"continuous_on (UNIV - {0}) pi" apply(rule continuous_at_imp_continuous_on) |
|
2063 apply rule unfolding pi_def |
|
2064 apply (rule continuous_mul) |
|
2065 apply (rule continuous_at_inv[unfolded o_def]) |
|
2066 apply (rule continuous_at_norm) |
|
2067 apply simp |
|
2068 apply (rule continuous_at_id) |
|
2069 done |
|
2070 def sphere \<equiv> "{x::real^'n. norm x = 1}" |
|
2071 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 |
|
2072 |
|
2073 have "0\<in>s" using assms(2) and centre_in_cball[of 0 1] by auto |
|
2074 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) |
|
2075 fix x u assume x:"x\<in>frontier s" and "(0::real)\<le>u" |
|
2076 hence "x\<noteq>0" using `0\<notin>frontier s` by auto |
|
2077 obtain v where v:"0 \<le> v" "v *\<^sub>R x \<in> frontier s" "\<forall>w>v. w *\<^sub>R x \<notin> s" |
|
2078 using compact_frontier_line_lemma[OF assms(1) `0\<in>s` `x\<noteq>0`] by auto |
|
2079 have "v=1" apply(rule ccontr) unfolding neq_iff apply(erule disjE) proof- |
|
2080 assume "v<1" thus False using v(3)[THEN spec[where x=1]] using x and fs by auto next |
|
2081 assume "v>1" thus False using assms(3)[THEN bspec[where x="v *\<^sub>R x"], THEN spec[where x="inverse v"]] |
|
2082 using v and x and fs unfolding inverse_less_1_iff by auto qed |
|
2083 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- |
|
2084 assume "u\<le>1" thus "u *\<^sub>R x \<in> s" apply(cases "u=1") |
|
2085 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 |
|
2086 |
|
2087 have "\<exists>surf. homeomorphism (frontier s) sphere pi surf" |
|
2088 apply(rule homeomorphism_compact) apply(rule compact_frontier[OF assms(1)]) |
|
2089 apply(rule continuous_on_subset[OF contpi]) defer apply(rule set_ext,rule) |
|
2090 unfolding inj_on_def prefer 3 apply(rule,rule,rule) |
|
2091 proof- fix x assume "x\<in>pi ` frontier s" then obtain y where "y\<in>frontier s" "x = pi y" by auto |
|
2092 thus "x \<in> sphere" using pi(1)[of y] and `0 \<notin> frontier s` by auto |
|
2093 next fix x assume "x\<in>sphere" hence "norm x = 1" "x\<noteq>0" unfolding sphere_def by auto |
|
2094 then obtain u where "0 \<le> u" "u *\<^sub>R x \<in> frontier s" "\<forall>v>u. v *\<^sub>R x \<notin> s" |
|
2095 using compact_frontier_line_lemma[OF assms(1) `0\<in>s`, of x] by auto |
|
2096 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 |
|
2097 next fix x y assume as:"x \<in> frontier s" "y \<in> frontier s" "pi x = pi y" |
|
2098 hence xys:"x\<in>s" "y\<in>s" using fs by auto |
|
2099 from as(1,2) have nor:"norm x \<noteq> 0" "norm y \<noteq> 0" using `0\<notin>frontier s` by auto |
|
2100 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 |
|
2101 from nor have y:"y = norm y *\<^sub>R ((inverse (norm x)) *\<^sub>R x)" unfolding as(3)[unfolded pi_def] by auto |
|
2102 have "0 \<le> norm y * inverse (norm x)" "0 \<le> norm x * inverse (norm y)" |
|
2103 unfolding divide_inverse[THEN sym] apply(rule_tac[!] divide_nonneg_pos) using nor by auto |
|
2104 hence "norm x = norm y" apply(rule_tac ccontr) unfolding neq_iff |
|
2105 using x y and front_smul[THEN bspec, OF as(1), THEN spec[where x="norm y * (inverse (norm x))"]] |
|
2106 using front_smul[THEN bspec, OF as(2), THEN spec[where x="norm x * (inverse (norm y))"]] |
|
2107 using xys nor by(auto simp add:field_simps divide_le_eq_1 divide_inverse[THEN sym]) |
|
2108 thus "x = y" apply(subst injpi[THEN sym]) using as(3) by auto |
|
2109 qed(insert `0 \<notin> frontier s`, auto) |
|
2110 then obtain surf where surf:"\<forall>x\<in>frontier s. surf (pi x) = x" "pi ` frontier s = sphere" "continuous_on (frontier s) pi" |
|
2111 "\<forall>y\<in>sphere. pi (surf y) = y" "surf ` sphere = frontier s" "continuous_on sphere surf" unfolding homeomorphism_def by auto |
|
2112 |
|
2113 have cont_surfpi:"continuous_on (UNIV - {0}) (surf \<circ> pi)" apply(rule continuous_on_compose, rule contpi) |
|
2114 apply(rule continuous_on_subset[of sphere], rule surf(6)) using pi(1) by auto |
|
2115 |
|
2116 { fix x assume as:"x \<in> cball (0::real^'n) 1" |
|
2117 have "norm x *\<^sub>R surf (pi x) \<in> s" proof(cases "x=0 \<or> norm x = 1") |
|
2118 case False hence "pi x \<in> sphere" "norm x < 1" using pi(1)[of x] as by(auto simp add: dist_norm) |
|
2119 thus ?thesis apply(rule_tac assms(3)[rule_format, THEN DiffD1]) |
|
2120 apply(rule_tac fs[unfolded subset_eq, rule_format]) |
|
2121 unfolding surf(5)[THEN sym] by auto |
|
2122 next case True thus ?thesis apply rule defer unfolding pi_def apply(rule fs[unfolded subset_eq, rule_format]) |
|
2123 unfolding surf(5)[unfolded sphere_def, THEN sym] using `0\<in>s` by auto qed } note hom = this |
|
2124 |
|
2125 { fix x assume "x\<in>s" |
|
2126 hence "x \<in> (\<lambda>x. norm x *\<^sub>R surf (pi x)) ` cball 0 1" proof(cases "x=0") |
|
2127 case True show ?thesis unfolding image_iff True apply(rule_tac x=0 in bexI) by auto |
|
2128 next let ?a = "inverse (norm (surf (pi x)))" |
|
2129 case False hence invn:"inverse (norm x) \<noteq> 0" by auto |
|
2130 from False have pix:"pi x\<in>sphere" using pi(1) by auto |
|
2131 hence "pi (surf (pi x)) = pi x" apply(rule_tac surf(4)[rule_format]) by assumption |
|
2132 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 |
|
2133 hence *:"?a * norm x > 0" and"?a > 0" "?a \<noteq> 0" using surf(5) `0\<notin>frontier s` apply - |
|
2134 apply(rule_tac mult_pos_pos) using False[unfolded zero_less_norm_iff[THEN sym]] by auto |
|
2135 have "norm (surf (pi x)) \<noteq> 0" using ** False by auto |
|
2136 hence "norm x = norm ((?a * norm x) *\<^sub>R surf (pi x))" |
|
2137 unfolding norm_scaleR abs_mult abs_norm_cancel abs_of_pos[OF `?a > 0`] by auto |
|
2138 moreover have "pi x = pi ((inverse (norm (surf (pi x))) * norm x) *\<^sub>R surf (pi x))" |
|
2139 unfolding pi(2)[OF *] surf(4)[rule_format, OF pix] .. |
|
2140 moreover have "surf (pi x) \<in> frontier s" using surf(5) pix by auto |
|
2141 hence "dist 0 (inverse (norm (surf (pi x))) *\<^sub>R x) \<le> 1" unfolding dist_norm |
|
2142 using ** and * using front_smul[THEN bspec[where x="surf (pi x)"], THEN spec[where x="norm x * ?a"]] |
|
2143 using False `x\<in>s` by(auto simp add:field_simps) |
|
2144 ultimately show ?thesis unfolding image_iff apply(rule_tac x="inverse (norm (surf(pi x))) *\<^sub>R x" in bexI) |
|
2145 apply(subst injpi[THEN sym]) unfolding abs_mult abs_norm_cancel abs_of_pos[OF `?a > 0`] |
|
2146 unfolding pi(2)[OF `?a > 0`] by auto |
|
2147 qed } note hom2 = this |
|
2148 |
|
2149 show ?thesis apply(subst homeomorphic_sym) apply(rule homeomorphic_compact[where f="\<lambda>x. norm x *\<^sub>R surf (pi x)"]) |
|
2150 apply(rule compact_cball) defer apply(rule set_ext, rule, erule imageE, drule hom) |
|
2151 prefer 4 apply(rule continuous_at_imp_continuous_on, rule) apply(rule_tac [3] hom2) proof- |
|
2152 fix x::"real^'n" assume as:"x \<in> cball 0 1" |
|
2153 thus "continuous (at x) (\<lambda>x. norm x *\<^sub>R surf (pi x))" proof(cases "x=0") |
|
2154 case False thus ?thesis apply(rule_tac continuous_mul, rule_tac continuous_at_norm) |
|
2155 using cont_surfpi unfolding continuous_on_eq_continuous_at[OF open_delete[OF open_UNIV]] o_def by auto |
|
2156 next guess a using UNIV_witness[where 'a = 'n] .. |
|
2157 obtain B where B:"\<forall>x\<in>s. norm x \<le> B" using compact_imp_bounded[OF assms(1)] unfolding bounded_iff by auto |
|
2158 hence "B > 0" using assms(2) unfolding subset_eq apply(erule_tac x="basis a" in ballE) defer apply(erule_tac x="basis a" in ballE) |
|
2159 unfolding Ball_def mem_cball dist_norm by (auto simp add: norm_basis[unfolded One_nat_def]) |
|
2160 case True show ?thesis unfolding True continuous_at Lim_at apply(rule,rule) apply(rule_tac x="e / B" in exI) |
|
2161 apply(rule) apply(rule divide_pos_pos) prefer 3 apply(rule,rule,erule conjE) |
|
2162 unfolding norm_0 scaleR_zero_left dist_norm diff_0_right norm_scaleR abs_norm_cancel proof- |
|
2163 fix e and x::"real^'n" assume as:"norm x < e / B" "0 < norm x" "0<e" |
|
2164 hence "surf (pi x) \<in> frontier s" using pi(1)[of x] unfolding surf(5)[THEN sym] by auto |
|
2165 hence "norm (surf (pi x)) \<le> B" using B fs by auto |
|
2166 hence "norm x * norm (surf (pi x)) \<le> norm x * B" using as(2) by auto |
|
2167 also have "\<dots> < e / B * B" apply(rule mult_strict_right_mono) using as(1) `B>0` by auto |
|
2168 also have "\<dots> = e" using `B>0` by auto |
|
2169 finally show "norm x * norm (surf (pi x)) < e" by assumption |
|
2170 qed(insert `B>0`, auto) qed |
|
2171 next { fix x assume as:"surf (pi x) = 0" |
|
2172 have "x = 0" proof(rule ccontr) |
|
2173 assume "x\<noteq>0" hence "pi x \<in> sphere" using pi(1) by auto |
|
2174 hence "surf (pi x) \<in> frontier s" using surf(5) by auto |
|
2175 thus False using `0\<notin>frontier s` unfolding as by simp qed |
|
2176 } note surf_0 = this |
|
2177 show "inj_on (\<lambda>x. norm x *\<^sub>R surf (pi x)) (cball 0 1)" unfolding inj_on_def proof(rule,rule,rule) |
|
2178 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)" |
|
2179 thus "x=y" proof(cases "x=0 \<or> y=0") |
|
2180 case True thus ?thesis using as by(auto elim: surf_0) next |
|
2181 case False |
|
2182 hence "pi (surf (pi x)) = pi (surf (pi y))" using as(3) |
|
2183 using pi(2)[of "norm x" "surf (pi x)"] pi(2)[of "norm y" "surf (pi y)"] by auto |
|
2184 moreover have "pi x \<in> sphere" "pi y \<in> sphere" using pi(1) False by auto |
|
2185 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 |
|
2186 moreover have "norm x = norm y" using as(3)[unfolded *] using False by(auto dest:surf_0) |
|
2187 ultimately show ?thesis using injpi by auto qed qed |
|
2188 qed auto qed |
|
2189 |
|
2190 lemma homeomorphic_convex_compact_lemma: fixes s::"(real^'n::finite) set" |
|
2191 assumes "convex s" "compact s" "cball 0 1 \<subseteq> s" |
|
2192 shows "s homeomorphic (cball (0::real^'n) 1)" |
|
2193 apply(rule starlike_compact_projective[OF assms(2-3)]) proof(rule,rule,rule,erule conjE) |
|
2194 fix x u assume as:"x \<in> s" "0 \<le> u" "u < (1::real)" |
|
2195 hence "u *\<^sub>R x \<in> interior s" unfolding interior_def mem_Collect_eq |
|
2196 apply(rule_tac x="ball (u *\<^sub>R x) (1 - u)" in exI) apply(rule, rule open_ball) |
|
2197 unfolding centre_in_ball apply rule defer apply(rule) unfolding mem_ball proof- |
|
2198 fix y assume "dist (u *\<^sub>R x) y < 1 - u" |
|
2199 hence "inverse (1 - u) *\<^sub>R (y - u *\<^sub>R x) \<in> s" |
|
2200 using assms(3) apply(erule_tac subsetD) unfolding mem_cball dist_commute dist_norm |
|
2201 unfolding group_add_class.diff_0 group_add_class.diff_0_right norm_minus_cancel norm_scaleR |
|
2202 apply (rule mult_left_le_imp_le[of "1 - u"]) |
|
2203 unfolding class_semiring.mul_a using `u<1` by auto |
|
2204 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] |
|
2205 using as unfolding scaleR_scaleR by auto qed auto |
|
2206 thus "u *\<^sub>R x \<in> s - frontier s" using frontier_def and interior_subset by auto qed |
|
2207 |
|
2208 lemma homeomorphic_convex_compact_cball: fixes e::real and s::"(real^'n::finite) set" |
|
2209 assumes "convex s" "compact s" "interior s \<noteq> {}" "0 < e" |
|
2210 shows "s homeomorphic (cball (b::real^'n::finite) e)" |
|
2211 proof- obtain a where "a\<in>interior s" using assms(3) by auto |
|
2212 then obtain d where "d>0" and d:"cball a d \<subseteq> s" unfolding mem_interior_cball by auto |
|
2213 let ?d = "inverse d" and ?n = "0::real^'n" |
|
2214 have "cball ?n 1 \<subseteq> (\<lambda>x. inverse d *\<^sub>R (x - a)) ` s" |
|
2215 apply(rule, rule_tac x="d *\<^sub>R x + a" in image_eqI) defer |
|
2216 apply(rule d[unfolded subset_eq, rule_format]) using `d>0` unfolding mem_cball dist_norm |
|
2217 by(auto simp add: mult_right_le_one_le) |
|
2218 hence "(\<lambda>x. inverse d *\<^sub>R (x - a)) ` s homeomorphic cball ?n 1" |
|
2219 using homeomorphic_convex_compact_lemma[of "(\<lambda>x. ?d *\<^sub>R -a + ?d *\<^sub>R x) ` s", OF convex_affinity compact_affinity] |
|
2220 using assms(1,2) by(auto simp add: uminus_add_conv_diff scaleR_right_diff_distrib) |
|
2221 thus ?thesis apply(rule_tac homeomorphic_trans[OF _ homeomorphic_balls(2)[of 1 _ ?n]]) |
|
2222 apply(rule homeomorphic_trans[OF homeomorphic_affinity[of "?d" s "?d *\<^sub>R -a"]]) |
|
2223 using `d>0` `e>0` by(auto simp add: uminus_add_conv_diff scaleR_right_diff_distrib) qed |
|
2224 |
|
2225 lemma homeomorphic_convex_compact: fixes s::"(real^'n::finite) set" and t::"(real^'n) set" |
|
2226 assumes "convex s" "compact s" "interior s \<noteq> {}" |
|
2227 "convex t" "compact t" "interior t \<noteq> {}" |
|
2228 shows "s homeomorphic t" |
|
2229 using assms by(meson zero_less_one homeomorphic_trans homeomorphic_convex_compact_cball homeomorphic_sym) |
|
2230 |
|
2231 subsection {* Epigraphs of convex functions. *} |
|
2232 |
|
2233 definition "epigraph s (f::real^'n \<Rightarrow> real) = {xy. fstcart xy \<in> s \<and> f(fstcart xy) \<le> dest_vec1 (sndcart xy)}" |
|
2234 |
|
2235 lemma mem_epigraph: "(pastecart x (vec1 y)) \<in> epigraph s f \<longleftrightarrow> x \<in> s \<and> f x \<le> y" unfolding epigraph_def by auto |
|
2236 |
|
2237 lemma convex_epigraph: |
|
2238 "convex(epigraph s f) \<longleftrightarrow> convex_on s f \<and> convex s" |
|
2239 unfolding convex_def convex_on_def unfolding Ball_def forall_pastecart epigraph_def |
|
2240 unfolding mem_Collect_eq fstcart_pastecart sndcart_pastecart sndcart_add sndcart_cmul [where 'a=real, unfolded smult_conv_scaleR] fstcart_add fstcart_cmul [where 'a=real, unfolded smult_conv_scaleR] |
|
2241 unfolding Ball_def[symmetric] unfolding dest_vec1_add dest_vec1_cmul [where 'a=real, unfolded smult_conv_scaleR] |
|
2242 apply(subst forall_dest_vec1[THEN sym])+ by(meson real_le_refl real_le_trans add_mono mult_left_mono) |
|
2243 |
|
2244 lemma convex_epigraphI: assumes "convex_on s f" "convex s" |
|
2245 shows "convex(epigraph s f)" using assms unfolding convex_epigraph by auto |
|
2246 |
|
2247 lemma convex_epigraph_convex: "convex s \<Longrightarrow> (convex_on s f \<longleftrightarrow> convex(epigraph s f))" |
|
2248 using convex_epigraph by auto |
|
2249 |
|
2250 subsection {* Use this to derive general bound property of convex function. *} |
|
2251 |
|
2252 lemma forall_of_pastecart: |
|
2253 "(\<forall>p. P (\<lambda>x. fstcart (p x)) (\<lambda>x. sndcart (p x))) \<longleftrightarrow> (\<forall>x y. P x y)" apply meson |
|
2254 apply(erule_tac x="\<lambda>a. pastecart (x a) (y a)" in allE) unfolding o_def by auto |
|
2255 |
|
2256 lemma forall_of_pastecart': |
|
2257 "(\<forall>p. P (fstcart p) (sndcart p)) \<longleftrightarrow> (\<forall>x y. P x y)" apply meson |
|
2258 apply(erule_tac x="pastecart x y" in allE) unfolding o_def by auto |
|
2259 |
|
2260 lemma forall_of_dest_vec1: "(\<forall>v. P (\<lambda>x. dest_vec1 (v x))) \<longleftrightarrow> (\<forall>x. P x)" |
|
2261 apply rule apply rule apply(erule_tac x="(vec1 \<circ> x)" in allE) unfolding o_def vec1_dest_vec1 by auto |
|
2262 |
|
2263 lemma forall_of_dest_vec1': "(\<forall>v. P (dest_vec1 v)) \<longleftrightarrow> (\<forall>x. P x)" |
|
2264 apply rule apply rule apply(erule_tac x="(vec1 x)" in allE) defer apply rule |
|
2265 apply(erule_tac x="dest_vec1 v" in allE) unfolding o_def vec1_dest_vec1 by auto |
|
2266 |
|
2267 lemma convex_on: |
|
2268 fixes s :: "(real ^ _) set" |
|
2269 assumes "convex s" |
|
2270 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> |
|
2271 f (setsum (\<lambda>i. u i *\<^sub>R x i) {1..k} ) \<le> setsum (\<lambda>i. u i * f(x i)) {1..k} ) " |
|
2272 unfolding convex_epigraph_convex[OF assms] convex epigraph_def Ball_def mem_Collect_eq |
|
2273 unfolding sndcart_setsum[OF finite_atLeastAtMost] fstcart_setsum[OF finite_atLeastAtMost] dest_vec1_setsum[OF finite_atLeastAtMost] |
|
2274 unfolding fstcart_pastecart sndcart_pastecart sndcart_add sndcart_cmul [where 'a=real, unfolded smult_conv_scaleR] fstcart_add fstcart_cmul [where 'a=real, unfolded smult_conv_scaleR] |
|
2275 unfolding dest_vec1_add dest_vec1_cmul [where 'a=real, unfolded smult_conv_scaleR] apply(subst forall_of_pastecart)+ apply(subst forall_of_dest_vec1)+ apply rule |
|
2276 using assms[unfolded convex] apply simp apply(rule,rule,rule) |
|
2277 apply(erule_tac x=k in allE, erule_tac x=u in allE, erule_tac x=x in allE) apply rule apply rule apply rule defer |
|
2278 apply(rule_tac j="\<Sum>i = 1..k. u i * f (x i)" in real_le_trans) |
|
2279 defer apply(rule setsum_mono) apply(erule conjE)+ apply(erule_tac x=i in allE)apply(rule mult_left_mono) |
|
2280 using assms[unfolded convex] by auto |
|
2281 |
|
2282 subsection {* Convexity of general and special intervals. *} |
|
2283 |
|
2284 lemma is_interval_convex: |
|
2285 fixes s :: "(real ^ _) set" |
|
2286 assumes "is_interval s" shows "convex s" |
|
2287 unfolding convex_def apply(rule,rule,rule,rule,rule,rule,rule) proof- |
|
2288 fix x y u v assume as:"x \<in> s" "y \<in> s" "0 \<le> u" "0 \<le> v" "u + v = (1::real)" |
|
2289 hence *:"u = 1 - v" "1 - v \<ge> 0" and **:"v = 1 - u" "1 - u \<ge> 0" by auto |
|
2290 { fix a b assume "\<not> b \<le> u * a + v * b" |
|
2291 hence "u * a < (1 - v) * b" unfolding not_le using as(4) by(auto simp add: field_simps) |
|
2292 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) |
|
2293 hence "a \<le> u * a + v * b" unfolding * using as(4) by (auto simp add: field_simps intro!:mult_right_mono) |
|
2294 } moreover |
|
2295 { fix a b assume "\<not> u * a + v * b \<le> a" |
|
2296 hence "v * b > (1 - u) * a" unfolding not_le using as(4) by(auto simp add: field_simps) |
|
2297 hence "a < b" unfolding * using as(4) apply(rule_tac mult_left_less_imp_less) by(auto simp add: ring_simps) |
|
2298 hence "u * a + v * b \<le> b" unfolding ** using **(2) as(3) by(auto simp add: field_simps intro!:mult_right_mono) } |
|
2299 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)]) |
|
2300 using as(3-) dimindex_ge_1 apply- by(auto simp add: vector_component) qed |
|
2301 |
|
2302 lemma is_interval_connected: |
|
2303 fixes s :: "(real ^ _) set" |
|
2304 shows "is_interval s \<Longrightarrow> connected s" |
|
2305 using is_interval_convex convex_connected by auto |
|
2306 |
|
2307 lemma convex_interval: "convex {a .. b}" "convex {a<..<b::real^'n::finite}" |
|
2308 apply(rule_tac[!] is_interval_convex) using is_interval_interval by auto |
|
2309 |
|
2310 subsection {* On @{text "real^1"}, @{text "is_interval"}, @{text "convex"} and @{text "connected"} are all equivalent. *} |
|
2311 |
|
2312 lemma is_interval_1: |
|
2313 "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)" |
|
2314 unfolding is_interval_def dest_vec1_def forall_1 by auto |
|
2315 |
|
2316 lemma is_interval_connected_1: "is_interval s \<longleftrightarrow> connected (s::(real^1) set)" |
|
2317 apply(rule, rule is_interval_connected, assumption) unfolding is_interval_1 |
|
2318 apply(rule,rule,rule,rule,erule conjE,rule ccontr) proof- |
|
2319 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" |
|
2320 hence *:"dest_vec1 a < dest_vec1 x" "dest_vec1 x < dest_vec1 b" apply(rule_tac [!] ccontr) unfolding not_less by auto |
|
2321 let ?halfl = "{z. inner (basis 1) z < dest_vec1 x} " and ?halfr = "{z. inner (basis 1) z > dest_vec1 x} " |
|
2322 { fix y assume "y \<in> s" have "y \<in> ?halfr \<union> ?halfl" apply(rule ccontr) |
|
2323 using as(6) `y\<in>s` by (auto simp add: inner_vector_def dest_vec1_eq [unfolded dest_vec1_def] dest_vec1_def) } |
|
2324 moreover have "a\<in>?halfl" "b\<in>?halfr" using * by (auto simp add: inner_vector_def dest_vec1_def) |
|
2325 hence "?halfl \<inter> s \<noteq> {}" "?halfr \<inter> s \<noteq> {}" using as(2-3) by auto |
|
2326 ultimately show False apply(rule_tac notE[OF as(1)[unfolded connected_def]]) |
|
2327 apply(rule_tac x="?halfl" in exI, rule_tac x="?halfr" in exI) |
|
2328 apply(rule, rule open_halfspace_lt, rule, rule open_halfspace_gt) apply(rule, rule, rule ccontr) |
|
2329 by(auto simp add: basis_component field_simps) qed |
|
2330 |
|
2331 lemma is_interval_convex_1: |
|
2332 "is_interval s \<longleftrightarrow> convex (s::(real^1) set)" |
|
2333 using is_interval_convex convex_connected is_interval_connected_1 by auto |
|
2334 |
|
2335 lemma convex_connected_1: |
|
2336 "connected s \<longleftrightarrow> convex (s::(real^1) set)" |
|
2337 using is_interval_convex convex_connected is_interval_connected_1 by auto |
|
2338 |
|
2339 subsection {* Another intermediate value theorem formulation. *} |
|
2340 |
|
2341 lemma ivt_increasing_component_on_1: fixes f::"real^1 \<Rightarrow> real^'n::finite" |
|
2342 assumes "dest_vec1 a \<le> dest_vec1 b" "continuous_on {a .. b} f" "(f a)$k \<le> y" "y \<le> (f b)$k" |
|
2343 shows "\<exists>x\<in>{a..b}. (f x)$k = y" |
|
2344 proof- have "f a \<in> f ` {a..b}" "f b \<in> f ` {a..b}" apply(rule_tac[!] imageI) |
|
2345 using assms(1) by(auto simp add: vector_less_eq_def dest_vec1_def) |
|
2346 thus ?thesis using connected_ivt_component[of "f ` {a..b}" "f a" "f b" k y] |
|
2347 using connected_continuous_image[OF assms(2) convex_connected[OF convex_interval(1)]] |
|
2348 using assms by(auto intro!: imageI) qed |
|
2349 |
|
2350 lemma ivt_increasing_component_1: fixes f::"real^1 \<Rightarrow> real^'n::finite" |
|
2351 assumes "dest_vec1 a \<le> dest_vec1 b" |
|
2352 "\<forall>x\<in>{a .. b}. continuous (at x) f" "f a$k \<le> y" "y \<le> f b$k" |
|
2353 shows "\<exists>x\<in>{a..b}. (f x)$k = y" |
|
2354 apply(rule ivt_increasing_component_on_1) using assms using continuous_at_imp_continuous_on by auto |
|
2355 |
|
2356 lemma ivt_decreasing_component_on_1: fixes f::"real^1 \<Rightarrow> real^'n::finite" |
|
2357 assumes "dest_vec1 a \<le> dest_vec1 b" "continuous_on {a .. b} f" "(f b)$k \<le> y" "y \<le> (f a)$k" |
|
2358 shows "\<exists>x\<in>{a..b}. (f x)$k = y" |
|
2359 apply(subst neg_equal_iff_equal[THEN sym]) unfolding vector_uminus_component[THEN sym] |
|
2360 apply(rule ivt_increasing_component_on_1) using assms using continuous_on_neg |
|
2361 by(auto simp add:vector_uminus_component) |
|
2362 |
|
2363 lemma ivt_decreasing_component_1: fixes f::"real^1 \<Rightarrow> real^'n::finite" |
|
2364 assumes "dest_vec1 a \<le> dest_vec1 b" "\<forall>x\<in>{a .. b}. continuous (at x) f" "f b$k \<le> y" "y \<le> f a$k" |
|
2365 shows "\<exists>x\<in>{a..b}. (f x)$k = y" |
|
2366 apply(rule ivt_decreasing_component_on_1) using assms using continuous_at_imp_continuous_on by auto |
|
2367 |
|
2368 subsection {* A bound within a convex hull, and so an interval. *} |
|
2369 |
|
2370 lemma convex_on_convex_hull_bound: |
|
2371 fixes s :: "(real ^ _) set" |
|
2372 assumes "convex_on (convex hull s) f" "\<forall>x\<in>s. f x \<le> b" |
|
2373 shows "\<forall>x\<in> convex hull s. f x \<le> b" proof |
|
2374 fix x assume "x\<in>convex hull s" |
|
2375 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" |
|
2376 unfolding convex_hull_indexed mem_Collect_eq by auto |
|
2377 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"] |
|
2378 unfolding setsum_left_distrib[THEN sym] obt(2) mult_1 apply(drule_tac meta_mp) apply(rule mult_left_mono) |
|
2379 using assms(2) obt(1) by auto |
|
2380 thus "f x \<le> b" using assms(1)[unfolded convex_on[OF convex_convex_hull], rule_format, of k u v] |
|
2381 unfolding obt(2-3) using obt(1) and hull_subset[unfolded subset_eq, rule_format, of _ s] by auto qed |
|
2382 |
|
2383 lemma unit_interval_convex_hull: |
|
2384 "{0::real^'n::finite .. 1} = convex hull {x. \<forall>i. (x$i = 0) \<or> (x$i = 1)}" (is "?int = convex hull ?points") |
|
2385 proof- have 01:"{0,1} \<subseteq> convex hull ?points" apply rule apply(rule_tac hull_subset[unfolded subset_eq, rule_format]) by auto |
|
2386 { fix n x assume "x\<in>{0::real^'n .. 1}" "n \<le> CARD('n)" "card {i. x$i \<noteq> 0} \<le> n" |
|
2387 hence "x\<in>convex hull ?points" proof(induct n arbitrary: x) |
|
2388 case 0 hence "x = 0" apply(subst Cart_eq) apply rule by auto |
|
2389 thus "x\<in>convex hull ?points" using 01 by auto |
|
2390 next |
|
2391 case (Suc n) show "x\<in>convex hull ?points" proof(cases "{i. x$i \<noteq> 0} = {}") |
|
2392 case True hence "x = 0" unfolding Cart_eq by auto |
|
2393 thus "x\<in>convex hull ?points" using 01 by auto |
|
2394 next |
|
2395 case False def xi \<equiv> "Min ((\<lambda>i. x$i) ` {i. x$i \<noteq> 0})" |
|
2396 have "xi \<in> (\<lambda>i. x$i) ` {i. x$i \<noteq> 0}" unfolding xi_def apply(rule Min_in) using False by auto |
|
2397 then obtain i where i':"x$i = xi" "x$i \<noteq> 0" by auto |
|
2398 have i:"\<And>j. x$j > 0 \<Longrightarrow> x$i \<le> x$j" |
|
2399 unfolding i'(1) xi_def apply(rule_tac Min_le) unfolding image_iff |
|
2400 defer apply(rule_tac x=j in bexI) using i' by auto |
|
2401 have i01:"x$i \<le> 1" "x$i > 0" using Suc(2)[unfolded mem_interval,rule_format,of i] using i'(2) `x$i \<noteq> 0` |
|
2402 by(auto simp add: Cart_lambda_beta) |
|
2403 show ?thesis proof(cases "x$i=1") |
|
2404 case True have "\<forall>j\<in>{i. x$i \<noteq> 0}. x$j = 1" apply(rule, rule ccontr) unfolding mem_Collect_eq proof- |
|
2405 fix j assume "x $ j \<noteq> 0" "x $ j \<noteq> 1" |
|
2406 hence j:"x$j \<in> {0<..<1}" using Suc(2) by(auto simp add: vector_less_eq_def elim!:allE[where x=j]) |
|
2407 hence "x$j \<in> op $ x ` {i. x $ i \<noteq> 0}" by auto |
|
2408 hence "x$j \<ge> x$i" unfolding i'(1) xi_def apply(rule_tac Min_le) by auto |
|
2409 thus False using True Suc(2) j by(auto simp add: vector_less_eq_def elim!:ballE[where x=j]) qed |
|
2410 thus "x\<in>convex hull ?points" apply(rule_tac hull_subset[unfolded subset_eq, rule_format]) |
|
2411 by(auto simp add: Cart_lambda_beta) |
|
2412 next let ?y = "\<lambda>j. if x$j = 0 then 0 else (x$j - x$i) / (1 - x$i)" |
|
2413 case False hence *:"x = x$i *\<^sub>R (\<chi> j. if x$j = 0 then 0 else 1) + (1 - x$i) *\<^sub>R (\<chi> j. ?y j)" unfolding Cart_eq |
|
2414 by(auto simp add: Cart_lambda_beta vector_add_component vector_smult_component vector_minus_component field_simps) |
|
2415 { fix j have "x$j \<noteq> 0 \<Longrightarrow> 0 \<le> (x $ j - x $ i) / (1 - x $ i)" "(x $ j - x $ i) / (1 - x $ i) \<le> 1" |
|
2416 apply(rule_tac divide_nonneg_pos) using i(1)[of j] using False i01 |
|
2417 using Suc(2)[unfolded mem_interval, rule_format, of j] by(auto simp add:field_simps Cart_lambda_beta) |
|
2418 hence "0 \<le> ?y j \<and> ?y j \<le> 1" by auto } |
|
2419 moreover have "i\<in>{j. x$j \<noteq> 0} - {j. ((\<chi> j. ?y j)::real^'n) $ j \<noteq> 0}" using i01 by(auto simp add: Cart_lambda_beta) |
|
2420 hence "{j. x$j \<noteq> 0} \<noteq> {j. ((\<chi> j. ?y j)::real^'n::finite) $ j \<noteq> 0}" by auto |
|
2421 hence **:"{j. ((\<chi> j. ?y j)::real^'n::finite) $ j \<noteq> 0} \<subset> {j. x$j \<noteq> 0}" apply - apply rule by(auto simp add: Cart_lambda_beta) |
|
2422 have "card {j. ((\<chi> j. ?y j)::real^'n) $ j \<noteq> 0} \<le> n" using less_le_trans[OF psubset_card_mono[OF _ **] Suc(4)] by auto |
|
2423 ultimately show ?thesis apply(subst *) apply(rule convex_convex_hull[unfolded convex_def, rule_format]) |
|
2424 apply(rule_tac hull_subset[unfolded subset_eq, rule_format]) defer apply(rule Suc(1)) |
|
2425 unfolding mem_interval using i01 Suc(3) by (auto simp add: Cart_lambda_beta) |
|
2426 qed qed qed } note * = this |
|
2427 show ?thesis apply rule defer apply(rule hull_minimal) unfolding subset_eq prefer 3 apply rule |
|
2428 apply(rule_tac n2="CARD('n)" in *) prefer 3 apply(rule card_mono) using 01 and convex_interval(1) prefer 5 apply - apply rule |
|
2429 unfolding mem_interval apply rule unfolding mem_Collect_eq apply(erule_tac x=i in allE) |
|
2430 by(auto simp add: vector_less_eq_def mem_def[of _ convex]) qed |
|
2431 |
|
2432 subsection {* And this is a finite set of vertices. *} |
|
2433 |
|
2434 lemma unit_cube_convex_hull: obtains s where "finite s" "{0 .. 1::real^'n::finite} = convex hull s" |
|
2435 apply(rule that[of "{x::real^'n::finite. \<forall>i. x$i=0 \<or> x$i=1}"]) |
|
2436 apply(rule finite_subset[of _ "(\<lambda>s. (\<chi> i. if i\<in>s then 1::real else 0)::real^'n::finite) ` UNIV"]) |
|
2437 prefer 3 apply(rule unit_interval_convex_hull) apply rule unfolding mem_Collect_eq proof- |
|
2438 fix x::"real^'n" assume as:"\<forall>i. x $ i = 0 \<or> x $ i = 1" |
|
2439 show "x \<in> (\<lambda>s. \<chi> i. if i \<in> s then 1 else 0) ` UNIV" apply(rule image_eqI[where x="{i. x$i = 1}"]) |
|
2440 unfolding Cart_eq using as by(auto simp add:Cart_lambda_beta) qed auto |
|
2441 |
|
2442 subsection {* Hence any cube (could do any nonempty interval). *} |
|
2443 |
|
2444 lemma cube_convex_hull: |
|
2445 assumes "0 < d" obtains s::"(real^'n::finite) set" where "finite s" "{x - (\<chi> i. d) .. x + (\<chi> i. d)} = convex hull s" proof- |
|
2446 let ?d = "(\<chi> i. d)::real^'n" |
|
2447 have *:"{x - ?d .. x + ?d} = (\<lambda>y. x - ?d + (2 * d) *\<^sub>R y) ` {0 .. 1}" apply(rule set_ext, rule) |
|
2448 unfolding image_iff defer apply(erule bexE) proof- |
|
2449 fix y assume as:"y\<in>{x - ?d .. x + ?d}" |
|
2450 { fix i::'n have "x $ i \<le> d + y $ i" "y $ i \<le> d + x $ i" using as[unfolded mem_interval, THEN spec[where x=i]] |
|
2451 by(auto simp add: vector_component) |
|
2452 hence "1 \<ge> inverse d * (x $ i - y $ i)" "1 \<ge> inverse d * (y $ i - x $ i)" |
|
2453 apply(rule_tac[!] mult_left_le_imp_le[OF _ assms]) unfolding mult_assoc[THEN sym] |
|
2454 using assms by(auto simp add: field_simps right_inverse) |
|
2455 hence "inverse d * (x $ i * 2) \<le> 2 + inverse d * (y $ i * 2)" |
|
2456 "inverse d * (y $ i * 2) \<le> 2 + inverse d * (x $ i * 2)" by(auto simp add:field_simps) } |
|
2457 hence "inverse (2 * d) *\<^sub>R (y - (x - ?d)) \<in> {0..1}" unfolding mem_interval using assms |
|
2458 by(auto simp add: Cart_eq vector_component_simps field_simps) |
|
2459 thus "\<exists>z\<in>{0..1}. y = x - ?d + (2 * d) *\<^sub>R z" apply- apply(rule_tac x="inverse (2 * d) *\<^sub>R (y - (x - ?d))" in bexI) |
|
2460 using assms by(auto simp add: Cart_eq vector_less_eq_def Cart_lambda_beta) |
|
2461 next |
|
2462 fix y z assume as:"z\<in>{0..1}" "y = x - ?d + (2*d) *\<^sub>R z" |
|
2463 have "\<And>i. 0 \<le> d * z $ i \<and> d * z $ i \<le> d" using assms as(1)[unfolded mem_interval] apply(erule_tac x=i in allE) |
|
2464 apply rule apply(rule mult_nonneg_nonneg) prefer 3 apply(rule mult_right_le_one_le) |
|
2465 using assms by(auto simp add: vector_component_simps Cart_eq) |
|
2466 thus "y \<in> {x - ?d..x + ?d}" unfolding as(2) mem_interval apply- apply rule using as(1)[unfolded mem_interval] |
|
2467 apply(erule_tac x=i in allE) using assms by(auto simp add: vector_component_simps Cart_eq) qed |
|
2468 obtain s where "finite s" "{0..1::real^'n} = convex hull s" using unit_cube_convex_hull by auto |
|
2469 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 |
|
2470 |
|
2471 subsection {* Bounded convex function on open set is continuous. *} |
|
2472 |
|
2473 lemma convex_on_bounded_continuous: |
|
2474 fixes s :: "(real ^ _) set" |
|
2475 assumes "open s" "convex_on s f" "\<forall>x\<in>s. abs(f x) \<le> b" |
|
2476 shows "continuous_on s f" |
|
2477 apply(rule continuous_at_imp_continuous_on) unfolding continuous_at_real_range proof(rule,rule,rule) |
|
2478 fix x e assume "x\<in>s" "(0::real) < e" |
|
2479 def B \<equiv> "abs b + 1" |
|
2480 have B:"0 < B" "\<And>x. x\<in>s \<Longrightarrow> abs (f x) \<le> B" |
|
2481 unfolding B_def defer apply(drule assms(3)[rule_format]) by auto |
|
2482 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 |
|
2483 show "\<exists>d>0. \<forall>x'. norm (x' - x) < d \<longrightarrow> \<bar>f x' - f x\<bar> < e" |
|
2484 apply(rule_tac x="min (k / 2) (e / (2 * B) * k)" in exI) apply rule defer proof(rule,rule) |
|
2485 fix y assume as:"norm (y - x) < min (k / 2) (e / (2 * B) * k)" |
|
2486 show "\<bar>f y - f x\<bar> < e" proof(cases "y=x") |
|
2487 case False def t \<equiv> "k / norm (y - x)" |
|
2488 have "2 < t" "0<t" unfolding t_def using as False and `k>0` by(auto simp add:field_simps) |
|
2489 have "y\<in>s" apply(rule k[unfolded subset_eq,rule_format]) unfolding mem_cball dist_norm |
|
2490 apply(rule order_trans[of _ "2 * norm (x - y)"]) using as by(auto simp add: field_simps norm_minus_commute) |
|
2491 { def w \<equiv> "x + t *\<^sub>R (y - x)" |
|
2492 have "w\<in>s" unfolding w_def apply(rule k[unfolded subset_eq,rule_format]) unfolding mem_cball dist_norm |
|
2493 unfolding t_def using `k>0` by auto |
|
2494 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) |
|
2495 also have "\<dots> = 0" using `t>0` by(auto simp add:field_simps) |
|
2496 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) |
|
2497 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) |
|
2498 hence "(f w - f x) / t < e" |
|
2499 using B(2)[OF `w\<in>s`] and B(2)[OF `x\<in>s`] using `t>0` by(auto simp add:field_simps) |
|
2500 hence th1:"f y - f x < e" apply- apply(rule le_less_trans) defer apply assumption |
|
2501 using assms(2)[unfolded convex_on_def,rule_format,of w x "1/t" "(t - 1)/t", unfolded w] |
|
2502 using `0<t` `2<t` and `x\<in>s` `w\<in>s` by(auto simp add:field_simps) } |
|
2503 moreover |
|
2504 { def w \<equiv> "x - t *\<^sub>R (y - x)" |
|
2505 have "w\<in>s" unfolding w_def apply(rule k[unfolded subset_eq,rule_format]) unfolding mem_cball dist_norm |
|
2506 unfolding t_def using `k>0` by auto |
|
2507 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) |
|
2508 also have "\<dots>=x" using `t>0` by (auto simp add:field_simps) |
|
2509 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) |
|
2510 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) |
|
2511 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) |
|
2512 have "f x \<le> 1 / (1 + t) * f w + (t / (1 + t)) * f y" |
|
2513 using assms(2)[unfolded convex_on_def,rule_format,of w y "1/(1+t)" "t / (1+t)",unfolded w] |
|
2514 using `0<t` `2<t` and `y\<in>s` `w\<in>s` by (auto simp add:field_simps) |
|
2515 also have "\<dots> = (f w + t * f y) / (1 + t)" using `t>0` unfolding real_divide_def by (auto simp add:field_simps) |
|
2516 also have "\<dots> < e + f y" using `t>0` * `e>0` by(auto simp add:field_simps) |
|
2517 finally have "f x - f y < e" by auto } |
|
2518 ultimately show ?thesis by auto |
|
2519 qed(insert `0<e`, auto) |
|
2520 qed(insert `0<e` `0<k` `0<B`, auto simp add:field_simps intro!:mult_pos_pos) qed |
|
2521 |
|
2522 subsection {* Upper bound on a ball implies upper and lower bounds. *} |
|
2523 |
|
2524 lemma convex_bounds_lemma: |
|
2525 fixes x :: "real ^ _" |
|
2526 assumes "convex_on (cball x e) f" "\<forall>y \<in> cball x e. f y \<le> b" |
|
2527 shows "\<forall>y \<in> cball x e. abs(f y) \<le> b + 2 * abs(f x)" |
|
2528 apply(rule) proof(cases "0 \<le> e") case True |
|
2529 fix y assume y:"y\<in>cball x e" def z \<equiv> "2 *\<^sub>R x - y" |
|
2530 have *:"x - (2 *\<^sub>R x - y) = y - x" by vector |
|
2531 have z:"z\<in>cball x e" using y unfolding z_def mem_cball dist_norm * by(auto simp add: norm_minus_commute) |
|
2532 have "(1 / 2) *\<^sub>R y + (1 / 2) *\<^sub>R z = x" unfolding z_def by (auto simp add: algebra_simps) |
|
2533 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"] |
|
2534 using assms(2)[rule_format,OF y] assms(2)[rule_format,OF z] by(auto simp add:field_simps) |
|
2535 next case False fix y assume "y\<in>cball x e" |
|
2536 hence "dist x y < 0" using False unfolding mem_cball not_le by (auto simp del: dist_not_less_zero) |
|
2537 thus "\<bar>f y\<bar> \<le> b + 2 * \<bar>f x\<bar>" using zero_le_dist[of x y] by auto qed |
|
2538 |
|
2539 subsection {* Hence a convex function on an open set is continuous. *} |
|
2540 |
|
2541 lemma convex_on_continuous: |
|
2542 assumes "open (s::(real^'n::finite) set)" "convex_on s f" |
|
2543 shows "continuous_on s f" |
|
2544 unfolding continuous_on_eq_continuous_at[OF assms(1)] proof |
|
2545 note dimge1 = dimindex_ge_1[where 'a='n] |
|
2546 fix x assume "x\<in>s" |
|
2547 then obtain e where e:"cball x e \<subseteq> s" "e>0" using assms(1) unfolding open_contains_cball by auto |
|
2548 def d \<equiv> "e / real CARD('n)" |
|
2549 have "0 < d" unfolding d_def using `e>0` dimge1 by(rule_tac divide_pos_pos, auto) |
|
2550 let ?d = "(\<chi> i. d)::real^'n" |
|
2551 obtain c where c:"finite c" "{x - ?d..x + ?d} = convex hull c" using cube_convex_hull[OF `d>0`, of x] by auto |
|
2552 have "x\<in>{x - ?d..x + ?d}" using `d>0` unfolding mem_interval by(auto simp add:vector_component_simps) |
|
2553 hence "c\<noteq>{}" apply(rule_tac ccontr) using c by(auto simp add:convex_hull_empty) |
|
2554 def k \<equiv> "Max (f ` c)" |
|
2555 have "convex_on {x - ?d..x + ?d} f" apply(rule convex_on_subset[OF assms(2)]) |
|
2556 apply(rule subset_trans[OF _ e(1)]) unfolding subset_eq mem_cball proof |
|
2557 fix z assume z:"z\<in>{x - ?d..x + ?d}" |
|
2558 have e:"e = setsum (\<lambda>i. d) (UNIV::'n set)" unfolding setsum_constant d_def using dimge1 |
|
2559 by (metis card_enum field_simps d_def not_one_le_zero of_nat_le_iff real_eq_of_nat real_of_nat_1) |
|
2560 show "dist x z \<le> e" unfolding dist_norm e apply(rule_tac order_trans[OF norm_le_l1], rule setsum_mono) |
|
2561 using z[unfolded mem_interval] apply(erule_tac x=i in allE) by(auto simp add:field_simps vector_component_simps) qed |
|
2562 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 |
|
2563 unfolding k_def apply(rule, rule Max_ge) using c(1) by auto |
|
2564 have "d \<le> e" unfolding d_def apply(rule mult_imp_div_pos_le) using `e>0` dimge1 unfolding mult_le_cancel_left1 using real_dimindex_ge_1 by auto |
|
2565 hence dsube:"cball x d \<subseteq> cball x e" unfolding subset_eq Ball_def mem_cball by auto |
|
2566 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 |
|
2567 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 |
|
2568 fix y assume y:"y\<in>cball x d" |
|
2569 { fix i::'n have "x $ i - d \<le> y $ i" "y $ i \<le> x $ i + d" |
|
2570 using order_trans[OF component_le_norm y[unfolded mem_cball dist_norm], of i] by(auto simp add: vector_component) } |
|
2571 thus "f y \<le> k" apply(rule_tac k[rule_format]) unfolding mem_cball mem_interval dist_norm |
|
2572 by(auto simp add: vector_component_simps) qed |
|
2573 hence "continuous_on (ball x d) f" apply(rule_tac convex_on_bounded_continuous) |
|
2574 apply(rule open_ball, rule convex_on_subset[OF conv], rule ball_subset_cball) by auto |
|
2575 thus "continuous (at x) f" unfolding continuous_on_eq_continuous_at[OF open_ball] using `d>0` by auto qed |
|
2576 |
|
2577 subsection {* Line segments, starlike sets etc. *) |
|
2578 (* Use the same overloading tricks as for intervals, so that *) |
|
2579 (* segment[a,b] is closed and segment(a,b) is open relative to affine hull. *} |
|
2580 |
|
2581 definition |
|
2582 midpoint :: "real ^ 'n::finite \<Rightarrow> real ^ 'n \<Rightarrow> real ^ 'n" where |
|
2583 "midpoint a b = (inverse (2::real)) *\<^sub>R (a + b)" |
|
2584 |
|
2585 definition |
|
2586 open_segment :: "real ^ 'n::finite \<Rightarrow> real ^ 'n \<Rightarrow> (real ^ 'n) set" where |
|
2587 "open_segment a b = {(1 - u) *\<^sub>R a + u *\<^sub>R b | u::real. 0 < u \<and> u < 1}" |
|
2588 |
|
2589 definition |
|
2590 closed_segment :: "real ^ 'n::finite \<Rightarrow> real ^ 'n \<Rightarrow> (real ^ 'n) set" where |
|
2591 "closed_segment a b = {(1 - u) *\<^sub>R a + u *\<^sub>R b | u::real. 0 \<le> u \<and> u \<le> 1}" |
|
2592 |
|
2593 definition "between = (\<lambda> (a,b). closed_segment a b)" |
|
2594 |
|
2595 lemmas segment = open_segment_def closed_segment_def |
|
2596 |
|
2597 definition "starlike s \<longleftrightarrow> (\<exists>a\<in>s. \<forall>x\<in>s. closed_segment a x \<subseteq> s)" |
|
2598 |
|
2599 lemma midpoint_refl: "midpoint x x = x" |
|
2600 unfolding midpoint_def unfolding scaleR_right_distrib unfolding scaleR_left_distrib[THEN sym] by auto |
|
2601 |
|
2602 lemma midpoint_sym: "midpoint a b = midpoint b a" unfolding midpoint_def by (auto simp add: scaleR_right_distrib) |
|
2603 |
|
2604 lemma dist_midpoint: |
|
2605 "dist a (midpoint a b) = (dist a b) / 2" (is ?t1) |
|
2606 "dist b (midpoint a b) = (dist a b) / 2" (is ?t2) |
|
2607 "dist (midpoint a b) a = (dist a b) / 2" (is ?t3) |
|
2608 "dist (midpoint a b) b = (dist a b) / 2" (is ?t4) |
|
2609 proof- |
|
2610 have *: "\<And>x y::real^'n::finite. 2 *\<^sub>R x = - y \<Longrightarrow> norm x = (norm y) / 2" unfolding equation_minus_iff by auto |
|
2611 have **:"\<And>x y::real^'n::finite. 2 *\<^sub>R x = y \<Longrightarrow> norm x = (norm y) / 2" by auto |
|
2612 note scaleR_right_distrib [simp] |
|
2613 show ?t1 unfolding midpoint_def dist_norm apply (rule **) by(auto,vector) |
|
2614 show ?t2 unfolding midpoint_def dist_norm apply (rule *) by(auto,vector) |
|
2615 show ?t3 unfolding midpoint_def dist_norm apply (rule *) by(auto,vector) |
|
2616 show ?t4 unfolding midpoint_def dist_norm apply (rule **) by(auto,vector) qed |
|
2617 |
|
2618 lemma midpoint_eq_endpoint: |
|
2619 "midpoint a b = a \<longleftrightarrow> a = (b::real^'n::finite)" |
|
2620 "midpoint a b = b \<longleftrightarrow> a = b" |
|
2621 unfolding dist_eq_0_iff[where 'a="real^'n", THEN sym] dist_midpoint by auto |
|
2622 |
|
2623 lemma convex_contains_segment: |
|
2624 "convex s \<longleftrightarrow> (\<forall>a\<in>s. \<forall>b\<in>s. closed_segment a b \<subseteq> s)" |
|
2625 unfolding convex_alt closed_segment_def by auto |
|
2626 |
|
2627 lemma convex_imp_starlike: |
|
2628 "convex s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> starlike s" |
|
2629 unfolding convex_contains_segment starlike_def by auto |
|
2630 |
|
2631 lemma segment_convex_hull: |
|
2632 "closed_segment a b = convex hull {a,b}" proof- |
|
2633 have *:"\<And>x. {x} \<noteq> {}" by auto |
|
2634 have **:"\<And>u v. u + v = 1 \<longleftrightarrow> u = 1 - (v::real)" by auto |
|
2635 show ?thesis unfolding segment convex_hull_insert[OF *] convex_hull_singleton apply(rule set_ext) |
|
2636 unfolding mem_Collect_eq apply(rule,erule exE) |
|
2637 apply(rule_tac x="1 - u" in exI) apply rule defer apply(rule_tac x=u in exI) defer |
|
2638 apply(erule exE, (erule conjE)?)+ apply(rule_tac x="1 - u" in exI) unfolding ** by auto qed |
|
2639 |
|
2640 lemma convex_segment: "convex (closed_segment a b)" |
|
2641 unfolding segment_convex_hull by(rule convex_convex_hull) |
|
2642 |
|
2643 lemma ends_in_segment: "a \<in> closed_segment a b" "b \<in> closed_segment a b" |
|
2644 unfolding segment_convex_hull apply(rule_tac[!] hull_subset[unfolded subset_eq, rule_format]) by auto |
|
2645 |
|
2646 lemma segment_furthest_le: |
|
2647 assumes "x \<in> closed_segment a b" shows "norm(y - x) \<le> norm(y - a) \<or> norm(y - x) \<le> norm(y - b)" proof- |
|
2648 obtain z where "z\<in>{a, b}" "norm (x - y) \<le> norm (z - y)" using simplex_furthest_le[of "{a, b}" y] |
|
2649 using assms[unfolded segment_convex_hull] by auto |
|
2650 thus ?thesis by(auto simp add:norm_minus_commute) qed |
|
2651 |
|
2652 lemma segment_bound: |
|
2653 assumes "x \<in> closed_segment a b" |
|
2654 shows "norm(x - a) \<le> norm(b - a)" "norm(x - b) \<le> norm(b - a)" |
|
2655 using segment_furthest_le[OF assms, of a] |
|
2656 using segment_furthest_le[OF assms, of b] |
|
2657 by (auto simp add:norm_minus_commute) |
|
2658 |
|
2659 lemma segment_refl:"closed_segment a a = {a}" unfolding segment by (auto simp add: algebra_simps) |
|
2660 |
|
2661 lemma between_mem_segment: "between (a,b) x \<longleftrightarrow> x \<in> closed_segment a b" |
|
2662 unfolding between_def mem_def by auto |
|
2663 |
|
2664 lemma between:"between (a,b) (x::real^'n::finite) \<longleftrightarrow> dist a b = (dist a x) + (dist x b)" |
|
2665 proof(cases "a = b") |
|
2666 case True thus ?thesis unfolding between_def split_conv mem_def[of x, symmetric] |
|
2667 by(auto simp add:segment_refl dist_commute) next |
|
2668 case False hence Fal:"norm (a - b) \<noteq> 0" and Fal2: "norm (a - b) > 0" by auto |
|
2669 have *:"\<And>u. a - ((1 - u) *\<^sub>R a + u *\<^sub>R b) = u *\<^sub>R (a - b)" by (auto simp add: algebra_simps) |
|
2670 show ?thesis unfolding between_def split_conv mem_def[of x, symmetric] closed_segment_def mem_Collect_eq |
|
2671 apply rule apply(erule exE, (erule conjE)+) apply(subst dist_triangle_eq) proof- |
|
2672 fix u assume as:"x = (1 - u) *\<^sub>R a + u *\<^sub>R b" "0 \<le> u" "u \<le> 1" |
|
2673 hence *:"a - x = u *\<^sub>R (a - b)" "x - b = (1 - u) *\<^sub>R (a - b)" |
|
2674 unfolding as(1) by(auto simp add:algebra_simps) |
|
2675 show "norm (a - x) *\<^sub>R (x - b) = norm (x - b) *\<^sub>R (a - x)" |
|
2676 unfolding norm_minus_commute[of x a] * Cart_eq using as(2,3) |
|
2677 by(auto simp add: vector_component_simps field_simps) |
|
2678 next assume as:"dist a b = dist a x + dist x b" |
|
2679 have "norm (a - x) / norm (a - b) \<le> 1" unfolding divide_le_eq_1_pos[OF Fal2] unfolding as[unfolded dist_norm] norm_ge_zero by auto |
|
2680 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) |
|
2681 unfolding dist_norm Cart_eq apply- apply rule defer apply(rule, rule divide_nonneg_pos) prefer 4 proof rule |
|
2682 fix i::'n have "((1 - norm (a - x) / norm (a - b)) *\<^sub>R a + (norm (a - x) / norm (a - b)) *\<^sub>R b) $ i = |
|
2683 ((norm (a - b) - norm (a - x)) * (a $ i) + norm (a - x) * (b $ i)) / norm (a - b)" |
|
2684 using Fal by(auto simp add:vector_component_simps field_simps) |
|
2685 also have "\<dots> = x$i" apply(rule divide_eq_imp[OF Fal]) |
|
2686 unfolding as[unfolded dist_norm] using as[unfolded dist_triangle_eq Cart_eq,rule_format, of i] |
|
2687 by(auto simp add:field_simps vector_component_simps) |
|
2688 finally show "x $ i = ((1 - norm (a - x) / norm (a - b)) *\<^sub>R a + (norm (a - x) / norm (a - b)) *\<^sub>R b) $ i" by auto |
|
2689 qed(insert Fal2, auto) qed qed |
|
2690 |
|
2691 lemma between_midpoint: fixes a::"real^'n::finite" shows |
|
2692 "between (a,b) (midpoint a b)" (is ?t1) |
|
2693 "between (b,a) (midpoint a b)" (is ?t2) |
|
2694 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 |
|
2695 show ?t1 ?t2 unfolding between midpoint_def dist_norm apply(rule_tac[!] *) |
|
2696 by(auto simp add:field_simps Cart_eq vector_component_simps) qed |
|
2697 |
|
2698 lemma between_mem_convex_hull: |
|
2699 "between (a,b) x \<longleftrightarrow> x \<in> convex hull {a,b}" |
|
2700 unfolding between_mem_segment segment_convex_hull .. |
|
2701 |
|
2702 subsection {* Shrinking towards the interior of a convex set. *} |
|
2703 |
|
2704 lemma mem_interior_convex_shrink: |
|
2705 fixes s :: "(real ^ _) set" |
|
2706 assumes "convex s" "c \<in> interior s" "x \<in> s" "0 < e" "e \<le> 1" |
|
2707 shows "x - e *\<^sub>R (x - c) \<in> interior s" |
|
2708 proof- obtain d where "d>0" and d:"ball c d \<subseteq> s" using assms(2) unfolding mem_interior by auto |
|
2709 show ?thesis unfolding mem_interior apply(rule_tac x="e*d" in exI) |
|
2710 apply(rule) defer unfolding subset_eq Ball_def mem_ball proof(rule,rule) |
|
2711 fix y assume as:"dist (x - e *\<^sub>R (x - c)) y < e * d" |
|
2712 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) |
|
2713 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)" |
|
2714 unfolding dist_norm unfolding norm_scaleR[THEN sym] apply(rule norm_eqI) using `e>0` |
|
2715 by(auto simp add:vector_component_simps Cart_eq field_simps) |
|
2716 also have "\<dots> = abs(1/e) * norm (x - e *\<^sub>R (x - c) - y)" by(auto intro!:norm_eqI simp add: algebra_simps) |
|
2717 also have "\<dots> < d" using as[unfolded dist_norm] and `e>0` |
|
2718 by(auto simp add:pos_divide_less_eq[OF `e>0`] real_mult_commute) |
|
2719 finally show "y \<in> s" apply(subst *) apply(rule assms(1)[unfolded convex_alt,rule_format]) |
|
2720 apply(rule d[unfolded subset_eq,rule_format]) unfolding mem_ball using assms(3-5) by auto |
|
2721 qed(rule mult_pos_pos, insert `e>0` `d>0`, auto) qed |
|
2722 |
|
2723 lemma mem_interior_closure_convex_shrink: |
|
2724 fixes s :: "(real ^ _) set" |
|
2725 assumes "convex s" "c \<in> interior s" "x \<in> closure s" "0 < e" "e \<le> 1" |
|
2726 shows "x - e *\<^sub>R (x - c) \<in> interior s" |
|
2727 proof- obtain d where "d>0" and d:"ball c d \<subseteq> s" using assms(2) unfolding mem_interior by auto |
|
2728 have "\<exists>y\<in>s. norm (y - x) * (1 - e) < e * d" proof(cases "x\<in>s") |
|
2729 case True thus ?thesis using `e>0` `d>0` by(rule_tac bexI[where x=x], auto intro!: mult_pos_pos) next |
|
2730 case False hence x:"x islimpt s" using assms(3)[unfolded closure_def] by auto |
|
2731 show ?thesis proof(cases "e=1") |
|
2732 case True obtain y where "y\<in>s" "y \<noteq> x" "dist y x < 1" |
|
2733 using x[unfolded islimpt_approachable,THEN spec[where x=1]] by auto |
|
2734 thus ?thesis apply(rule_tac x=y in bexI) unfolding True using `d>0` by auto next |
|
2735 case False hence "0 < e * d / (1 - e)" and *:"1 - e > 0" |
|
2736 using `e\<le>1` `e>0` `d>0` by(auto intro!:mult_pos_pos divide_pos_pos) |
|
2737 then obtain y where "y\<in>s" "y \<noteq> x" "dist y x < e * d / (1 - e)" |
|
2738 using x[unfolded islimpt_approachable,THEN spec[where x="e*d / (1 - e)"]] by auto |
|
2739 thus ?thesis apply(rule_tac x=y in bexI) unfolding dist_norm using pos_less_divide_eq[OF *] by auto qed qed |
|
2740 then obtain y where "y\<in>s" and y:"norm (y - x) * (1 - e) < e * d" by auto |
|
2741 def z \<equiv> "c + ((1 - e) / e) *\<^sub>R (x - y)" |
|
2742 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) |
|
2743 have "z\<in>interior s" apply(rule subset_interior[OF d,unfolded subset_eq,rule_format]) |
|
2744 unfolding interior_open[OF open_ball] mem_ball z_def dist_norm using y and assms(4,5) |
|
2745 by(auto simp add:field_simps norm_minus_commute) |
|
2746 thus ?thesis unfolding * apply - apply(rule mem_interior_convex_shrink) |
|
2747 using assms(1,4-5) `y\<in>s` by auto qed |
|
2748 |
|
2749 subsection {* Some obvious but surprisingly hard simplex lemmas. *} |
|
2750 |
|
2751 lemma simplex: |
|
2752 assumes "finite s" "0 \<notin> s" |
|
2753 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)}" |
|
2754 unfolding convex_hull_finite[OF finite.insertI[OF assms(1)]] apply(rule set_ext, rule) unfolding mem_Collect_eq |
|
2755 apply(erule_tac[!] exE) apply(erule_tac[!] conjE)+ unfolding setsum_clauses(2)[OF assms(1)] |
|
2756 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) |
|
2757 unfolding if_smult and setsum_delta_notmem[OF assms(2)] by auto |
|
2758 |
|
2759 lemma std_simplex: |
|
2760 "convex hull (insert 0 { basis i | i. i\<in>UNIV}) = |
|
2761 {x::real^'n::finite . (\<forall>i. 0 \<le> x$i) \<and> setsum (\<lambda>i. x$i) UNIV \<le> 1 }" (is "convex hull (insert 0 ?p) = ?s") |
|
2762 proof- let ?D = "UNIV::'n set" |
|
2763 have "0\<notin>?p" by(auto simp add: basis_nonzero) |
|
2764 have "{(basis i)::real^'n |i. i \<in> ?D} = basis ` ?D" by auto |
|
2765 note sumbas = this setsum_reindex[OF basis_inj, unfolded o_def] |
|
2766 show ?thesis unfolding simplex[OF finite_stdbasis `0\<notin>?p`] apply(rule set_ext) unfolding mem_Collect_eq apply rule |
|
2767 apply(erule exE, (erule conjE)+) apply(erule_tac[2] conjE)+ proof- |
|
2768 fix x::"real^'n" and u assume as: "\<forall>x\<in>{basis i |i. i \<in>?D}. 0 \<le> u x" "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" |
|
2769 have *:"\<forall>i. u (basis i) = x$i" using as(3) unfolding sumbas and basis_expansion_unique [where 'a=real, unfolded smult_conv_scaleR] by auto |
|
2770 hence **:"setsum u {basis i |i. i \<in> ?D} = setsum (op $ x) ?D" unfolding sumbas by(rule_tac setsum_cong, auto) |
|
2771 show " (\<forall>i. 0 \<le> x $ i) \<and> setsum (op $ x) ?D \<le> 1" apply - proof(rule,rule) |
|
2772 fix i::'n show "0 \<le> x$i" unfolding *[rule_format,of i,THEN sym] apply(rule_tac as(1)[rule_format]) by auto |
|
2773 qed(insert as(2)[unfolded **], auto) |
|
2774 next fix x::"real^'n" assume as:"\<forall>i. 0 \<le> x $ i" "setsum (op $ x) ?D \<le> 1" |
|
2775 show "\<exists>u. (\<forall>x\<in>{basis i |i. i \<in> ?D}. 0 \<le> u x) \<and> 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" |
|
2776 apply(rule_tac x="\<lambda>y. inner y x" in exI) apply(rule,rule) unfolding mem_Collect_eq apply(erule exE) using as(1) apply(erule_tac x=i in allE) |
|
2777 unfolding sumbas using as(2) and basis_expansion_unique [where 'a=real, unfolded smult_conv_scaleR] by(auto simp add:inner_basis) qed qed |
|
2778 |
|
2779 lemma interior_std_simplex: |
|
2780 "interior (convex hull (insert 0 { basis i| i. i\<in>UNIV})) = |
|
2781 {x::real^'n::finite. (\<forall>i. 0 < x$i) \<and> setsum (\<lambda>i. x$i) UNIV < 1 }" |
|
2782 apply(rule set_ext) unfolding mem_interior std_simplex unfolding subset_eq mem_Collect_eq Ball_def mem_ball |
|
2783 unfolding Ball_def[symmetric] apply rule apply(erule exE, (erule conjE)+) defer apply(erule conjE) proof- |
|
2784 fix x::"real^'n" and e assume "0<e" and as:"\<forall>xa. dist x xa < e \<longrightarrow> (\<forall>x. 0 \<le> xa $ x) \<and> setsum (op $ xa) UNIV \<le> 1" |
|
2785 show "(\<forall>xa. 0 < x $ xa) \<and> setsum (op $ x) UNIV < 1" apply(rule,rule) proof- |
|
2786 fix i::'n show "0 < x $ i" using as[THEN spec[where x="x - (e / 2) *\<^sub>R basis i"]] and `e>0` |
|
2787 unfolding dist_norm by(auto simp add: norm_basis vector_component_simps basis_component elim:allE[where x=i]) |
|
2788 next guess a using UNIV_witness[where 'a='n] .. |
|
2789 have **:"dist x (x + (e / 2) *\<^sub>R basis a) < e" using `e>0` and norm_basis[of a] |
|
2790 unfolding dist_norm by(auto simp add: vector_component_simps basis_component intro!: mult_strict_left_mono_comm) |
|
2791 have "\<And>i. (x + (e / 2) *\<^sub>R basis a) $ i = x$i + (if i = a then e/2 else 0)" by(auto simp add:vector_component_simps) |
|
2792 hence *:"setsum (op $ (x + (e / 2) *\<^sub>R basis a)) UNIV = setsum (\<lambda>i. x$i + (if a = i then e/2 else 0)) UNIV" by(rule_tac setsum_cong, auto) |
|
2793 have "setsum (op $ x) UNIV < setsum (op $ (x + (e / 2) *\<^sub>R basis a)) UNIV" unfolding * setsum_addf |
|
2794 using `0<e` dimindex_ge_1 by(auto simp add: setsum_delta') |
|
2795 also have "\<dots> \<le> 1" using ** apply(drule_tac as[rule_format]) by auto |
|
2796 finally show "setsum (op $ x) UNIV < 1" by auto qed |
|
2797 next |
|
2798 fix x::"real^'n::finite" assume as:"\<forall>i. 0 < x $ i" "setsum (op $ x) UNIV < 1" |
|
2799 guess a using UNIV_witness[where 'a='b] .. |
|
2800 let ?d = "(1 - setsum (op $ x) UNIV) / real (CARD('n))" |
|
2801 have "Min ((op $ x) ` UNIV) > 0" apply(rule Min_grI) using as(1) dimindex_ge_1 by auto |
|
2802 moreover have"?d > 0" apply(rule divide_pos_pos) using as(2) using dimindex_ge_1 by(auto simp add: Suc_le_eq) |
|
2803 ultimately show "\<exists>e>0. \<forall>y. dist x y < e \<longrightarrow> (\<forall>i. 0 \<le> y $ i) \<and> setsum (op $ y) UNIV \<le> 1" |
|
2804 apply(rule_tac x="min (Min ((op $ x) ` UNIV)) ?D" in exI) apply rule defer apply(rule,rule) proof- |
|
2805 fix y assume y:"dist x y < min (Min (op $ x ` UNIV)) ?d" |
|
2806 have "setsum (op $ y) UNIV \<le> setsum (\<lambda>i. x$i + ?d) UNIV" proof(rule setsum_mono) |
|
2807 fix i::'n have "abs (y$i - x$i) < ?d" apply(rule le_less_trans) using component_le_norm[of "y - x" i] |
|
2808 using y[unfolded min_less_iff_conj dist_norm, THEN conjunct2] by(auto simp add:vector_component_simps norm_minus_commute) |
|
2809 thus "y $ i \<le> x $ i + ?d" by auto qed |
|
2810 also have "\<dots> \<le> 1" unfolding setsum_addf setsum_constant card_enum real_eq_of_nat using dimindex_ge_1 by(auto simp add: Suc_le_eq) |
|
2811 finally show "(\<forall>i. 0 \<le> y $ i) \<and> setsum (op $ y) UNIV \<le> 1" apply- proof(rule,rule) |
|
2812 fix i::'n have "norm (x - y) < x$i" using y[unfolded min_less_iff_conj dist_norm, THEN conjunct1] |
|
2813 using Min_gr_iff[of "op $ x ` dimset x"] dimindex_ge_1 by auto |
|
2814 thus "0 \<le> y$i" using component_le_norm[of "x - y" i] and as(1)[rule_format, of i] by(auto simp add: vector_component_simps) |
|
2815 qed auto qed auto qed |
|
2816 |
|
2817 lemma interior_std_simplex_nonempty: obtains a::"real^'n::finite" where |
|
2818 "a \<in> interior(convex hull (insert 0 {basis i | i . i \<in> UNIV}))" proof- |
|
2819 let ?D = "UNIV::'n set" let ?a = "setsum (\<lambda>b::real^'n. inverse (2 * real CARD('n)) *\<^sub>R b) {(basis i) | i. i \<in> ?D}" |
|
2820 have *:"{basis i :: real ^ 'n | i. i \<in> ?D} = basis ` ?D" by auto |
|
2821 { fix i have "?a $ i = inverse (2 * real CARD('n))" |
|
2822 unfolding setsum_component vector_smult_component and * and setsum_reindex[OF basis_inj] and o_def |
|
2823 apply(rule trans[of _ "setsum (\<lambda>j. if i = j then inverse (2 * real CARD('n)) else 0) ?D"]) apply(rule setsum_cong2) |
|
2824 unfolding setsum_delta'[OF finite_UNIV[where 'a='n]] and real_dimindex_ge_1[where 'n='n] by(auto simp add: basis_component[of i]) } |
|
2825 note ** = this |
|
2826 show ?thesis apply(rule that[of ?a]) unfolding interior_std_simplex mem_Collect_eq proof(rule,rule) |
|
2827 fix i::'n show "0 < ?a $ i" unfolding ** using dimindex_ge_1 by(auto simp add: Suc_le_eq) next |
|
2828 have "setsum (op $ ?a) ?D = setsum (\<lambda>i. inverse (2 * real CARD('n))) ?D" by(rule setsum_cong2, rule **) |
|
2829 also have "\<dots> < 1" unfolding setsum_constant card_enum real_eq_of_nat real_divide_def[THEN sym] by (auto simp add:field_simps) |
|
2830 finally show "setsum (op $ ?a) ?D < 1" by auto qed qed |
|
2831 |
|
2832 subsection {* Paths. *} |
|
2833 |
|
2834 definition "path (g::real^1 \<Rightarrow> real^'n::finite) \<longleftrightarrow> continuous_on {0 .. 1} g" |
|
2835 |
|
2836 definition "pathstart (g::real^1 \<Rightarrow> real^'n) = g 0" |
|
2837 |
|
2838 definition "pathfinish (g::real^1 \<Rightarrow> real^'n) = g 1" |
|
2839 |
|
2840 definition "path_image (g::real^1 \<Rightarrow> real^'n) = g ` {0 .. 1}" |
|
2841 |
|
2842 definition "reversepath (g::real^1 \<Rightarrow> real^'n) = (\<lambda>x. g(1 - x))" |
|
2843 |
|
2844 definition joinpaths:: "(real^1 \<Rightarrow> real^'n) \<Rightarrow> (real^1 \<Rightarrow> real^'n) \<Rightarrow> (real^1 \<Rightarrow> real^'n)" (infixr "+++" 75) |
|
2845 where "joinpaths g1 g2 = (\<lambda>x. if dest_vec1 x \<le> ((1 / 2)::real) then g1 (2 *\<^sub>R x) else g2(2 *\<^sub>R x - 1))" |
|
2846 definition "simple_path (g::real^1 \<Rightarrow> real^'n) \<longleftrightarrow> |
|
2847 (\<forall>x\<in>{0..1}. \<forall>y\<in>{0..1}. g x = g y \<longrightarrow> x = y \<or> x = 0 \<and> y = 1 \<or> x = 1 \<and> y = 0)" |
|
2848 |
|
2849 definition "injective_path (g::real^1 \<Rightarrow> real^'n) \<longleftrightarrow> |
|
2850 (\<forall>x\<in>{0..1}. \<forall>y\<in>{0..1}. g x = g y \<longrightarrow> x = y)" |
|
2851 |
|
2852 subsection {* Some lemmas about these concepts. *} |
|
2853 |
|
2854 lemma injective_imp_simple_path: |
|
2855 "injective_path g \<Longrightarrow> simple_path g" |
|
2856 unfolding injective_path_def simple_path_def by auto |
|
2857 |
|
2858 lemma path_image_nonempty: "path_image g \<noteq> {}" |
|
2859 unfolding path_image_def image_is_empty interval_eq_empty by auto |
|
2860 |
|
2861 lemma pathstart_in_path_image[intro]: "(pathstart g) \<in> path_image g" |
|
2862 unfolding pathstart_def path_image_def apply(rule imageI) |
|
2863 unfolding mem_interval_1 vec_1[THEN sym] dest_vec1_vec by auto |
|
2864 |
|
2865 lemma pathfinish_in_path_image[intro]: "(pathfinish g) \<in> path_image g" |
|
2866 unfolding pathfinish_def path_image_def apply(rule imageI) |
|
2867 unfolding mem_interval_1 vec_1[THEN sym] dest_vec1_vec by auto |
|
2868 |
|
2869 lemma connected_path_image[intro]: "path g \<Longrightarrow> connected(path_image g)" |
|
2870 unfolding path_def path_image_def apply(rule connected_continuous_image, assumption) |
|
2871 by(rule convex_connected, rule convex_interval) |
|
2872 |
|
2873 lemma compact_path_image[intro]: "path g \<Longrightarrow> compact(path_image g)" |
|
2874 unfolding path_def path_image_def apply(rule compact_continuous_image, assumption) |
|
2875 by(rule compact_interval) |
|
2876 |
|
2877 lemma reversepath_reversepath[simp]: "reversepath(reversepath g) = g" |
|
2878 unfolding reversepath_def by auto |
|
2879 |
|
2880 lemma pathstart_reversepath[simp]: "pathstart(reversepath g) = pathfinish g" |
|
2881 unfolding pathstart_def reversepath_def pathfinish_def by auto |
|
2882 |
|
2883 lemma pathfinish_reversepath[simp]: "pathfinish(reversepath g) = pathstart g" |
|
2884 unfolding pathstart_def reversepath_def pathfinish_def by auto |
|
2885 |
|
2886 lemma pathstart_join[simp]: "pathstart(g1 +++ g2) = pathstart g1" |
|
2887 unfolding pathstart_def joinpaths_def pathfinish_def by auto |
|
2888 |
|
2889 lemma pathfinish_join[simp]:"pathfinish(g1 +++ g2) = pathfinish g2" proof- |
|
2890 have "2 *\<^sub>R 1 - 1 = (1::real^1)" unfolding Cart_eq by(auto simp add:vector_component_simps) |
|
2891 thus ?thesis unfolding pathstart_def joinpaths_def pathfinish_def |
|
2892 unfolding vec_1[THEN sym] dest_vec1_vec by auto qed |
|
2893 |
|
2894 lemma path_image_reversepath[simp]: "path_image(reversepath g) = path_image g" proof- |
|
2895 have *:"\<And>g. path_image(reversepath g) \<subseteq> path_image g" |
|
2896 unfolding path_image_def subset_eq reversepath_def Ball_def image_iff apply(rule,rule,erule bexE) |
|
2897 apply(rule_tac x="1 - xa" in bexI) by(auto simp add:vector_less_eq_def vector_component_simps elim!:ballE) |
|
2898 show ?thesis using *[of g] *[of "reversepath g"] unfolding reversepath_reversepath by auto qed |
|
2899 |
|
2900 lemma path_reversepath[simp]: "path(reversepath g) \<longleftrightarrow> path g" proof- |
|
2901 have *:"\<And>g. path g \<Longrightarrow> path(reversepath g)" unfolding path_def reversepath_def |
|
2902 apply(rule continuous_on_compose[unfolded o_def, of _ "\<lambda>x. 1 - x"]) |
|
2903 apply(rule continuous_on_sub, rule continuous_on_const, rule continuous_on_id) |
|
2904 apply(rule continuous_on_subset[of "{0..1}"], assumption) |
|
2905 by (auto, auto simp add:vector_less_eq_def vector_component_simps elim!:ballE) |
|
2906 show ?thesis using *[of g] *[of "reversepath g"] unfolding reversepath_reversepath by auto qed |
|
2907 |
|
2908 lemmas reversepath_simps = path_reversepath path_image_reversepath pathstart_reversepath pathfinish_reversepath |
|
2909 |
|
2910 lemma path_join[simp]: assumes "pathfinish g1 = pathstart g2" shows "path (g1 +++ g2) \<longleftrightarrow> path g1 \<and> path g2" |
|
2911 unfolding path_def pathfinish_def pathstart_def apply rule defer apply(erule conjE) proof- |
|
2912 assume as:"continuous_on {0..1} (g1 +++ g2)" |
|
2913 have *:"g1 = (\<lambda>x. g1 (2 *\<^sub>R x)) \<circ> (\<lambda>x. (1/2) *\<^sub>R x)" |
|
2914 "g2 = (\<lambda>x. g2 (2 *\<^sub>R x - 1)) \<circ> (\<lambda>x. (1/2) *\<^sub>R (x + 1))" unfolding o_def by auto |
|
2915 have "op *\<^sub>R (1 / 2) ` {0::real^1..1} \<subseteq> {0..1}" "(\<lambda>x. (1 / 2) *\<^sub>R (x + 1)) ` {(0::real^1)..1} \<subseteq> {0..1}" |
|
2916 unfolding image_smult_interval by (auto, auto simp add:vector_less_eq_def vector_component_simps elim!:ballE) |
|
2917 thus "continuous_on {0..1} g1 \<and> continuous_on {0..1} g2" apply -apply rule |
|
2918 apply(subst *) defer apply(subst *) apply (rule_tac[!] continuous_on_compose) |
|
2919 apply (rule continuous_on_cmul, rule continuous_on_add, rule continuous_on_id, rule continuous_on_const) defer |
|
2920 apply (rule continuous_on_cmul, rule continuous_on_id) apply(rule_tac[!] continuous_on_eq[of _ "g1 +++ g2"]) defer prefer 3 |
|
2921 apply(rule_tac[1-2] continuous_on_subset[of "{0 .. 1}"]) apply(rule as, assumption, rule as, assumption) |
|
2922 apply(rule) defer apply rule proof- |
|
2923 fix x assume "x \<in> op *\<^sub>R (1 / 2) ` {0::real^1..1}" |
|
2924 hence "dest_vec1 x \<le> 1 / 2" unfolding image_iff by(auto simp add: vector_component_simps) |
|
2925 thus "(g1 +++ g2) x = g1 (2 *\<^sub>R x)" unfolding joinpaths_def by auto next |
|
2926 fix x assume "x \<in> (\<lambda>x. (1 / 2) *\<^sub>R (x + 1)) ` {0::real^1..1}" |
|
2927 hence "dest_vec1 x \<ge> 1 / 2" unfolding image_iff by(auto simp add: vector_component_simps) |
|
2928 thus "(g1 +++ g2) x = g2 (2 *\<^sub>R x - 1)" proof(cases "dest_vec1 x = 1 / 2") |
|
2929 case True hence "x = (1/2) *\<^sub>R 1" unfolding Cart_eq by(auto simp add: forall_1 vector_component_simps) |
|
2930 thus ?thesis unfolding joinpaths_def using assms[unfolded pathstart_def pathfinish_def] by auto |
|
2931 qed (auto simp add:le_less joinpaths_def) qed |
|
2932 next assume as:"continuous_on {0..1} g1" "continuous_on {0..1} g2" |
|
2933 have *:"{0 .. 1::real^1} = {0.. (1/2)*\<^sub>R 1} \<union> {(1/2) *\<^sub>R 1 .. 1}" by(auto simp add: vector_component_simps) |
|
2934 have **:"op *\<^sub>R 2 ` {0..(1 / 2) *\<^sub>R 1} = {0..1::real^1}" apply(rule set_ext, rule) unfolding image_iff |
|
2935 defer apply(rule_tac x="(1/2)*\<^sub>R x" in bexI) by(auto simp add: vector_component_simps) |
|
2936 have ***:"(\<lambda>x. 2 *\<^sub>R x - 1) ` {(1 / 2) *\<^sub>R 1..1} = {0..1::real^1}" |
|
2937 unfolding image_affinity_interval[of _ "- 1", unfolded diff_def[symmetric]] and interval_eq_empty_1 |
|
2938 by(auto simp add: vector_component_simps) |
|
2939 have ****:"\<And>x::real^1. x $ 1 * 2 = 1 \<longleftrightarrow> x = (1/2) *\<^sub>R 1" unfolding Cart_eq by(auto simp add: forall_1 vector_component_simps) |
|
2940 show "continuous_on {0..1} (g1 +++ g2)" unfolding * apply(rule continuous_on_union) apply(rule closed_interval)+ proof- |
|
2941 show "continuous_on {0..(1 / 2) *\<^sub>R 1} (g1 +++ g2)" apply(rule continuous_on_eq[of _ "\<lambda>x. g1 (2 *\<^sub>R x)"]) defer |
|
2942 unfolding o_def[THEN sym] apply(rule continuous_on_compose) apply(rule continuous_on_cmul, rule continuous_on_id) |
|
2943 unfolding ** apply(rule as(1)) unfolding joinpaths_def by(auto simp add: vector_component_simps) next |
|
2944 show "continuous_on {(1/2)*\<^sub>R1..1} (g1 +++ g2)" apply(rule continuous_on_eq[of _ "g2 \<circ> (\<lambda>x. 2 *\<^sub>R x - 1)"]) defer |
|
2945 apply(rule continuous_on_compose) apply(rule continuous_on_sub, rule continuous_on_cmul, rule continuous_on_id, rule continuous_on_const) |
|
2946 unfolding *** o_def joinpaths_def apply(rule as(2)) using assms[unfolded pathstart_def pathfinish_def] |
|
2947 by(auto simp add: vector_component_simps ****) qed qed |
|
2948 |
|
2949 lemma path_image_join_subset: "path_image(g1 +++ g2) \<subseteq> (path_image g1 \<union> path_image g2)" proof |
|
2950 fix x assume "x \<in> path_image (g1 +++ g2)" |
|
2951 then obtain y where y:"y\<in>{0..1}" "x = (if dest_vec1 y \<le> 1 / 2 then g1 (2 *\<^sub>R y) else g2 (2 *\<^sub>R y - 1))" |
|
2952 unfolding path_image_def image_iff joinpaths_def by auto |
|
2953 thus "x \<in> path_image g1 \<union> path_image g2" apply(cases "dest_vec1 y \<le> 1/2") |
|
2954 apply(rule_tac UnI1) defer apply(rule_tac UnI2) unfolding y(2) path_image_def using y(1) |
|
2955 by(auto intro!: imageI simp add: vector_component_simps) qed |
|
2956 |
|
2957 lemma subset_path_image_join: |
|
2958 assumes "path_image g1 \<subseteq> s" "path_image g2 \<subseteq> s" shows "path_image(g1 +++ g2) \<subseteq> s" |
|
2959 using path_image_join_subset[of g1 g2] and assms by auto |
|
2960 |
|
2961 lemma path_image_join: |
|
2962 assumes "path g1" "path g2" "pathfinish g1 = pathstart g2" |
|
2963 shows "path_image(g1 +++ g2) = (path_image g1) \<union> (path_image g2)" |
|
2964 apply(rule, rule path_image_join_subset, rule) unfolding Un_iff proof(erule disjE) |
|
2965 fix x assume "x \<in> path_image g1" |
|
2966 then obtain y where y:"y\<in>{0..1}" "x = g1 y" unfolding path_image_def image_iff by auto |
|
2967 thus "x \<in> path_image (g1 +++ g2)" unfolding joinpaths_def path_image_def image_iff |
|
2968 apply(rule_tac x="(1/2) *\<^sub>R y" in bexI) by(auto simp add: vector_component_simps) next |
|
2969 fix x assume "x \<in> path_image g2" |
|
2970 then obtain y where y:"y\<in>{0..1}" "x = g2 y" unfolding path_image_def image_iff by auto |
|
2971 moreover have *:"y $ 1 = 0 \<Longrightarrow> y = 0" unfolding Cart_eq by auto |
|
2972 ultimately show "x \<in> path_image (g1 +++ g2)" unfolding joinpaths_def path_image_def image_iff |
|
2973 apply(rule_tac x="(1/2) *\<^sub>R (y + 1)" in bexI) using assms(3)[unfolded pathfinish_def pathstart_def] |
|
2974 by(auto simp add: vector_component_simps) qed |
|
2975 |
|
2976 lemma not_in_path_image_join: |
|
2977 assumes "x \<notin> path_image g1" "x \<notin> path_image g2" shows "x \<notin> path_image(g1 +++ g2)" |
|
2978 using assms and path_image_join_subset[of g1 g2] by auto |
|
2979 |
|
2980 lemma simple_path_reversepath: assumes "simple_path g" shows "simple_path (reversepath g)" |
|
2981 using assms unfolding simple_path_def reversepath_def apply- apply(rule ballI)+ |
|
2982 apply(erule_tac x="1-x" in ballE, erule_tac x="1-y" in ballE) |
|
2983 unfolding mem_interval_1 by(auto simp add:vector_component_simps) |
|
2984 |
|
2985 lemma dest_vec1_scaleR [simp]: |
|
2986 "dest_vec1 (scaleR a x) = scaleR a (dest_vec1 x)" |
|
2987 unfolding dest_vec1_def by simp |
|
2988 |
|
2989 lemma simple_path_join_loop: |
|
2990 assumes "injective_path g1" "injective_path g2" "pathfinish g2 = pathstart g1" |
|
2991 "(path_image g1 \<inter> path_image g2) \<subseteq> {pathstart g1,pathstart g2}" |
|
2992 shows "simple_path(g1 +++ g2)" |
|
2993 unfolding simple_path_def proof((rule ballI)+, rule impI) let ?g = "g1 +++ g2" |
|
2994 note inj = assms(1,2)[unfolded injective_path_def, rule_format] |
|
2995 fix x y::"real^1" assume xy:"x \<in> {0..1}" "y \<in> {0..1}" "?g x = ?g y" |
|
2996 show "x = y \<or> x = 0 \<and> y = 1 \<or> x = 1 \<and> y = 0" proof(case_tac "x$1 \<le> 1/2",case_tac[!] "y$1 \<le> 1/2", unfold not_le) |
|
2997 assume as:"x $ 1 \<le> 1 / 2" "y $ 1 \<le> 1 / 2" |
|
2998 hence "g1 (2 *\<^sub>R x) = g1 (2 *\<^sub>R y)" using xy(3) unfolding joinpaths_def dest_vec1_def by auto |
|
2999 moreover have "2 *\<^sub>R x \<in> {0..1}" "2 *\<^sub>R y \<in> {0..1}" using xy(1,2) as |
|
3000 unfolding mem_interval_1 dest_vec1_def by(auto simp add:vector_component_simps) |
|
3001 ultimately show ?thesis using inj(1)[of "2*\<^sub>R x" "2*\<^sub>R y"] by auto |
|
3002 next assume as:"x $ 1 > 1 / 2" "y $ 1 > 1 / 2" |
|
3003 hence "g2 (2 *\<^sub>R x - 1) = g2 (2 *\<^sub>R y - 1)" using xy(3) unfolding joinpaths_def dest_vec1_def by auto |
|
3004 moreover have "2 *\<^sub>R x - 1 \<in> {0..1}" "2 *\<^sub>R y - 1 \<in> {0..1}" using xy(1,2) as |
|
3005 unfolding mem_interval_1 dest_vec1_def by(auto simp add:vector_component_simps) |
|
3006 ultimately show ?thesis using inj(2)[of "2*\<^sub>R x - 1" "2*\<^sub>R y - 1"] by auto |
|
3007 next assume as:"x $ 1 \<le> 1 / 2" "y $ 1 > 1 / 2" |
|
3008 hence "?g x \<in> path_image g1" "?g y \<in> path_image g2" unfolding path_image_def joinpaths_def |
|
3009 using xy(1,2)[unfolded mem_interval_1] by(auto simp add:vector_component_simps intro!: imageI) |
|
3010 moreover have "?g y \<noteq> pathstart g2" using as(2) unfolding pathstart_def joinpaths_def |
|
3011 using inj(2)[of "2 *\<^sub>R y - 1" 0] and xy(2)[unfolded mem_interval_1] |
|
3012 apply(rule_tac ccontr) by(auto simp add:vector_component_simps field_simps Cart_eq) |
|
3013 ultimately have *:"?g x = pathstart g1" using assms(4) unfolding xy(3) by auto |
|
3014 hence "x = 0" unfolding pathstart_def joinpaths_def using as(1) and xy(1)[unfolded mem_interval_1] |
|
3015 using inj(1)[of "2 *\<^sub>R x" 0] by(auto simp add:vector_component_simps) |
|
3016 moreover have "y = 1" using * unfolding xy(3) assms(3)[THEN sym] |
|
3017 unfolding joinpaths_def pathfinish_def using as(2) and xy(2)[unfolded mem_interval_1] |
|
3018 using inj(2)[of "2 *\<^sub>R y - 1" 1] by (auto simp add:vector_component_simps Cart_eq) |
|
3019 ultimately show ?thesis by auto |
|
3020 next assume as:"x $ 1 > 1 / 2" "y $ 1 \<le> 1 / 2" |
|
3021 hence "?g x \<in> path_image g2" "?g y \<in> path_image g1" unfolding path_image_def joinpaths_def |
|
3022 using xy(1,2)[unfolded mem_interval_1] by(auto simp add:vector_component_simps intro!: imageI) |
|
3023 moreover have "?g x \<noteq> pathstart g2" using as(1) unfolding pathstart_def joinpaths_def |
|
3024 using inj(2)[of "2 *\<^sub>R x - 1" 0] and xy(1)[unfolded mem_interval_1] |
|
3025 apply(rule_tac ccontr) by(auto simp add:vector_component_simps field_simps Cart_eq) |
|
3026 ultimately have *:"?g y = pathstart g1" using assms(4) unfolding xy(3) by auto |
|
3027 hence "y = 0" unfolding pathstart_def joinpaths_def using as(2) and xy(2)[unfolded mem_interval_1] |
|
3028 using inj(1)[of "2 *\<^sub>R y" 0] by(auto simp add:vector_component_simps) |
|
3029 moreover have "x = 1" using * unfolding xy(3)[THEN sym] assms(3)[THEN sym] |
|
3030 unfolding joinpaths_def pathfinish_def using as(1) and xy(1)[unfolded mem_interval_1] |
|
3031 using inj(2)[of "2 *\<^sub>R x - 1" 1] by(auto simp add:vector_component_simps Cart_eq) |
|
3032 ultimately show ?thesis by auto qed qed |
|
3033 |
|
3034 lemma injective_path_join: |
|
3035 assumes "injective_path g1" "injective_path g2" "pathfinish g1 = pathstart g2" |
|
3036 "(path_image g1 \<inter> path_image g2) \<subseteq> {pathstart g2}" |
|
3037 shows "injective_path(g1 +++ g2)" |
|
3038 unfolding injective_path_def proof(rule,rule,rule) let ?g = "g1 +++ g2" |
|
3039 note inj = assms(1,2)[unfolded injective_path_def, rule_format] |
|
3040 fix x y assume xy:"x \<in> {0..1}" "y \<in> {0..1}" "(g1 +++ g2) x = (g1 +++ g2) y" |
|
3041 show "x = y" proof(cases "x$1 \<le> 1/2", case_tac[!] "y$1 \<le> 1/2", unfold not_le) |
|
3042 assume "x $ 1 \<le> 1 / 2" "y $ 1 \<le> 1 / 2" thus ?thesis using inj(1)[of "2*\<^sub>R x" "2*\<^sub>R y"] and xy |
|
3043 unfolding mem_interval_1 joinpaths_def by(auto simp add:vector_component_simps) |
|
3044 next assume "x $ 1 > 1 / 2" "y $ 1 > 1 / 2" thus ?thesis using inj(2)[of "2*\<^sub>R x - 1" "2*\<^sub>R y - 1"] and xy |
|
3045 unfolding mem_interval_1 joinpaths_def by(auto simp add:vector_component_simps) |
|
3046 next assume as:"x $ 1 \<le> 1 / 2" "y $ 1 > 1 / 2" |
|
3047 hence "?g x \<in> path_image g1" "?g y \<in> path_image g2" unfolding path_image_def joinpaths_def |
|
3048 using xy(1,2)[unfolded mem_interval_1] by(auto simp add:vector_component_simps intro!: imageI) |
|
3049 hence "?g x = pathfinish g1" "?g y = pathstart g2" using assms(4) unfolding assms(3) xy(3) by auto |
|
3050 thus ?thesis using as and inj(1)[of "2 *\<^sub>R x" 1] inj(2)[of "2 *\<^sub>R y - 1" 0] and xy(1,2) |
|
3051 unfolding pathstart_def pathfinish_def joinpaths_def mem_interval_1 |
|
3052 by(auto simp add:vector_component_simps Cart_eq forall_1) |
|
3053 next assume as:"x $ 1 > 1 / 2" "y $ 1 \<le> 1 / 2" |
|
3054 hence "?g x \<in> path_image g2" "?g y \<in> path_image g1" unfolding path_image_def joinpaths_def |
|
3055 using xy(1,2)[unfolded mem_interval_1] by(auto simp add:vector_component_simps intro!: imageI) |
|
3056 hence "?g x = pathstart g2" "?g y = pathfinish g1" using assms(4) unfolding assms(3) xy(3) by auto |
|
3057 thus ?thesis using as and inj(2)[of "2 *\<^sub>R x - 1" 0] inj(1)[of "2 *\<^sub>R y" 1] and xy(1,2) |
|
3058 unfolding pathstart_def pathfinish_def joinpaths_def mem_interval_1 |
|
3059 by(auto simp add:vector_component_simps forall_1 Cart_eq) qed qed |
|
3060 |
|
3061 lemmas join_paths_simps = path_join path_image_join pathstart_join pathfinish_join |
|
3062 |
|
3063 subsection {* Reparametrizing a closed curve to start at some chosen point. *} |
|
3064 |
|
3065 definition "shiftpath a (f::real^1 \<Rightarrow> real^'n) = |
|
3066 (\<lambda>x. if dest_vec1 (a + x) \<le> 1 then f(a + x) else f(a + x - 1))" |
|
3067 |
|
3068 lemma pathstart_shiftpath: "a \<le> 1 \<Longrightarrow> pathstart(shiftpath a g) = g a" |
|
3069 unfolding pathstart_def shiftpath_def by auto |
|
3070 |
|
3071 (** move this **) |
|
3072 declare forall_1[simp] ex_1[simp] |
|
3073 |
|
3074 lemma pathfinish_shiftpath: assumes "0 \<le> a" "pathfinish g = pathstart g" |
|
3075 shows "pathfinish(shiftpath a g) = g a" |
|
3076 using assms unfolding pathstart_def pathfinish_def shiftpath_def |
|
3077 by(auto simp add: vector_component_simps) |
|
3078 |
|
3079 lemma endpoints_shiftpath: |
|
3080 assumes "pathfinish g = pathstart g" "a \<in> {0 .. 1}" |
|
3081 shows "pathfinish(shiftpath a g) = g a" "pathstart(shiftpath a g) = g a" |
|
3082 using assms by(auto intro!:pathfinish_shiftpath pathstart_shiftpath) |
|
3083 |
|
3084 lemma closed_shiftpath: |
|
3085 assumes "pathfinish g = pathstart g" "a \<in> {0..1}" |
|
3086 shows "pathfinish(shiftpath a g) = pathstart(shiftpath a g)" |
|
3087 using endpoints_shiftpath[OF assms] by auto |
|
3088 |
|
3089 lemma path_shiftpath: |
|
3090 assumes "path g" "pathfinish g = pathstart g" "a \<in> {0..1}" |
|
3091 shows "path(shiftpath a g)" proof- |
|
3092 have *:"{0 .. 1} = {0 .. 1-a} \<union> {1-a .. 1}" using assms(3) by(auto simp add: vector_component_simps) |
|
3093 have **:"\<And>x. x + a = 1 \<Longrightarrow> g (x + a - 1) = g (x + a)" |
|
3094 using assms(2)[unfolded pathfinish_def pathstart_def] by auto |
|
3095 show ?thesis unfolding path_def shiftpath_def * apply(rule continuous_on_union) |
|
3096 apply(rule closed_interval)+ apply(rule continuous_on_eq[of _ "g \<circ> (\<lambda>x. a + x)"]) prefer 3 |
|
3097 apply(rule continuous_on_eq[of _ "g \<circ> (\<lambda>x. a - 1 + x)"]) defer prefer 3 |
|
3098 apply(rule continuous_on_intros)+ prefer 2 apply(rule continuous_on_intros)+ |
|
3099 apply(rule_tac[1-2] continuous_on_subset[OF assms(1)[unfolded path_def]]) |
|
3100 using assms(3) and ** by(auto simp add:vector_component_simps field_simps Cart_eq) qed |
|
3101 |
|
3102 lemma shiftpath_shiftpath: assumes "pathfinish g = pathstart g" "a \<in> {0..1}" "x \<in> {0..1}" |
|
3103 shows "shiftpath (1 - a) (shiftpath a g) x = g x" |
|
3104 using assms unfolding pathfinish_def pathstart_def shiftpath_def |
|
3105 by(auto simp add: vector_component_simps) |
|
3106 |
|
3107 lemma path_image_shiftpath: |
|
3108 assumes "a \<in> {0..1}" "pathfinish g = pathstart g" |
|
3109 shows "path_image(shiftpath a g) = path_image g" proof- |
|
3110 { fix x assume as:"g 1 = g 0" "x \<in> {0..1::real^1}" " \<forall>y\<in>{0..1} \<inter> {x. \<not> a $ 1 + x $ 1 \<le> 1}. g x \<noteq> g (a + y - 1)" |
|
3111 hence "\<exists>y\<in>{0..1} \<inter> {x. a $ 1 + x $ 1 \<le> 1}. g x = g (a + y)" proof(cases "a \<le> x") |
|
3112 case False thus ?thesis apply(rule_tac x="1 + x - a" in bexI) |
|
3113 using as(1,2) and as(3)[THEN bspec[where x="1 + x - a"]] and assms(1) |
|
3114 by(auto simp add:vector_component_simps field_simps atomize_not) next |
|
3115 case True thus ?thesis using as(1-2) and assms(1) apply(rule_tac x="x - a" in bexI) |
|
3116 by(auto simp add:vector_component_simps field_simps) qed } |
|
3117 thus ?thesis using assms unfolding shiftpath_def path_image_def pathfinish_def pathstart_def |
|
3118 by(auto simp add:vector_component_simps image_iff) qed |
|
3119 |
|
3120 subsection {* Special case of straight-line paths. *} |
|
3121 |
|
3122 definition |
|
3123 linepath :: "real ^ 'n::finite \<Rightarrow> real ^ 'n \<Rightarrow> real ^ 1 \<Rightarrow> real ^ 'n" where |
|
3124 "linepath a b = (\<lambda>x. (1 - dest_vec1 x) *\<^sub>R a + dest_vec1 x *\<^sub>R b)" |
|
3125 |
|
3126 lemma pathstart_linepath[simp]: "pathstart(linepath a b) = a" |
|
3127 unfolding pathstart_def linepath_def by auto |
|
3128 |
|
3129 lemma pathfinish_linepath[simp]: "pathfinish(linepath a b) = b" |
|
3130 unfolding pathfinish_def linepath_def by auto |
|
3131 |
|
3132 lemma continuous_linepath_at[intro]: "continuous (at x) (linepath a b)" |
|
3133 unfolding linepath_def |
|
3134 by (intro continuous_intros continuous_dest_vec1) |
|
3135 |
|
3136 lemma continuous_on_linepath[intro]: "continuous_on s (linepath a b)" |
|
3137 using continuous_linepath_at by(auto intro!: continuous_at_imp_continuous_on) |
|
3138 |
|
3139 lemma path_linepath[intro]: "path(linepath a b)" |
|
3140 unfolding path_def by(rule continuous_on_linepath) |
|
3141 |
|
3142 lemma path_image_linepath[simp]: "path_image(linepath a b) = (closed_segment a b)" |
|
3143 unfolding path_image_def segment linepath_def apply (rule set_ext, rule) defer |
|
3144 unfolding mem_Collect_eq image_iff apply(erule exE) apply(rule_tac x="u *\<^sub>R 1" in bexI) |
|
3145 by(auto simp add:vector_component_simps) |
|
3146 |
|
3147 lemma reversepath_linepath[simp]: "reversepath(linepath a b) = linepath b a" |
|
3148 unfolding reversepath_def linepath_def by(rule ext, auto simp add:vector_component_simps) |
|
3149 |
|
3150 lemma injective_path_linepath: assumes "a \<noteq> b" shows "injective_path(linepath a b)" proof- |
|
3151 { obtain i where i:"a$i \<noteq> b$i" using assms[unfolded Cart_eq] by auto |
|
3152 fix x y::"real^1" assume "x $ 1 *\<^sub>R b + y $ 1 *\<^sub>R a = x $ 1 *\<^sub>R a + y $ 1 *\<^sub>R b" |
|
3153 hence "x$1 * (b$i - a$i) = y$1 * (b$i - a$i)" unfolding Cart_eq by(auto simp add:field_simps vector_component_simps) |
|
3154 hence "x = y" unfolding mult_cancel_right Cart_eq using i(1) by(auto simp add:field_simps) } |
|
3155 thus ?thesis unfolding injective_path_def linepath_def by(auto simp add:vector_component_simps algebra_simps) qed |
|
3156 |
|
3157 lemma simple_path_linepath[intro]: "a \<noteq> b \<Longrightarrow> simple_path(linepath a b)" by(auto intro!: injective_imp_simple_path injective_path_linepath) |
|
3158 |
|
3159 subsection {* Bounding a point away from a path. *} |
|
3160 |
|
3161 lemma not_on_path_ball: assumes "path g" "z \<notin> path_image g" |
|
3162 shows "\<exists>e>0. ball z e \<inter> (path_image g) = {}" proof- |
|
3163 obtain a where "a\<in>path_image g" "\<forall>y\<in>path_image g. dist z a \<le> dist z y" |
|
3164 using distance_attains_inf[OF _ path_image_nonempty, of g z] |
|
3165 using compact_path_image[THEN compact_imp_closed, OF assms(1)] by auto |
|
3166 thus ?thesis apply(rule_tac x="dist z a" in exI) using assms(2) by(auto intro!: dist_pos_lt) qed |
|
3167 |
|
3168 lemma not_on_path_cball: assumes "path g" "z \<notin> path_image g" |
|
3169 shows "\<exists>e>0. cball z e \<inter> (path_image g) = {}" proof- |
|
3170 obtain e where "ball z e \<inter> path_image g = {}" "e>0" using not_on_path_ball[OF assms] by auto |
|
3171 moreover have "cball z (e/2) \<subseteq> ball z e" using `e>0` by auto |
|
3172 ultimately show ?thesis apply(rule_tac x="e/2" in exI) by auto qed |
|
3173 |
|
3174 subsection {* Path component, considered as a "joinability" relation (from Tom Hales). *} |
|
3175 |
|
3176 definition "path_component s x y \<longleftrightarrow> (\<exists>g. path g \<and> path_image g \<subseteq> s \<and> pathstart g = x \<and> pathfinish g = y)" |
|
3177 |
|
3178 lemmas path_defs = path_def pathstart_def pathfinish_def path_image_def path_component_def |
|
3179 |
|
3180 lemma path_component_mem: assumes "path_component s x y" shows "x \<in> s" "y \<in> s" |
|
3181 using assms unfolding path_defs by auto |
|
3182 |
|
3183 lemma path_component_refl: assumes "x \<in> s" shows "path_component s x x" |
|
3184 unfolding path_defs apply(rule_tac x="\<lambda>u. x" in exI) using assms |
|
3185 by(auto intro!:continuous_on_intros) |
|
3186 |
|
3187 lemma path_component_refl_eq: "path_component s x x \<longleftrightarrow> x \<in> s" |
|
3188 by(auto intro!: path_component_mem path_component_refl) |
|
3189 |
|
3190 lemma path_component_sym: "path_component s x y \<Longrightarrow> path_component s y x" |
|
3191 using assms unfolding path_component_def apply(erule exE) apply(rule_tac x="reversepath g" in exI) |
|
3192 by(auto simp add: reversepath_simps) |
|
3193 |
|
3194 lemma path_component_trans: assumes "path_component s x y" "path_component s y z" shows "path_component s x z" |
|
3195 using assms unfolding path_component_def apply- apply(erule exE)+ apply(rule_tac x="g +++ ga" in exI) by(auto simp add: path_image_join) |
|
3196 |
|
3197 lemma path_component_of_subset: "s \<subseteq> t \<Longrightarrow> path_component s x y \<Longrightarrow> path_component t x y" |
|
3198 unfolding path_component_def by auto |
|
3199 |
|
3200 subsection {* Can also consider it as a set, as the name suggests. *} |
|
3201 |
|
3202 lemma path_component_set: "path_component s x = { y. (\<exists>g. path g \<and> path_image g \<subseteq> s \<and> pathstart g = x \<and> pathfinish g = y )}" |
|
3203 apply(rule set_ext) unfolding mem_Collect_eq unfolding mem_def path_component_def by auto |
|
3204 |
|
3205 lemma mem_path_component_set:"x \<in> path_component s y \<longleftrightarrow> path_component s y x" unfolding mem_def by auto |
|
3206 |
|
3207 lemma path_component_subset: "(path_component s x) \<subseteq> s" |
|
3208 apply(rule, rule path_component_mem(2)) by(auto simp add:mem_def) |
|
3209 |
|
3210 lemma path_component_eq_empty: "path_component s x = {} \<longleftrightarrow> x \<notin> s" |
|
3211 apply rule apply(drule equals0D[of _ x]) defer apply(rule equals0I) unfolding mem_path_component_set |
|
3212 apply(drule path_component_mem(1)) using path_component_refl by auto |
|
3213 |
|
3214 subsection {* Path connectedness of a space. *} |
|
3215 |
|
3216 definition "path_connected s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<exists>g. path g \<and> (path_image g) \<subseteq> s \<and> pathstart g = x \<and> pathfinish g = y)" |
|
3217 |
|
3218 lemma path_connected_component: "path_connected s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. path_component s x y)" |
|
3219 unfolding path_connected_def path_component_def by auto |
|
3220 |
|
3221 lemma path_connected_component_set: "path_connected s \<longleftrightarrow> (\<forall>x\<in>s. path_component s x = s)" |
|
3222 unfolding path_connected_component apply(rule, rule, rule, rule path_component_subset) |
|
3223 unfolding subset_eq mem_path_component_set Ball_def mem_def by auto |
|
3224 |
|
3225 subsection {* Some useful lemmas about path-connectedness. *} |
|
3226 |
|
3227 lemma convex_imp_path_connected: assumes "convex s" shows "path_connected s" |
|
3228 unfolding path_connected_def apply(rule,rule,rule_tac x="linepath x y" in exI) |
|
3229 unfolding path_image_linepath using assms[unfolded convex_contains_segment] by auto |
|
3230 |
|
3231 lemma path_connected_imp_connected: assumes "path_connected s" shows "connected s" |
|
3232 unfolding connected_def not_ex apply(rule,rule,rule ccontr) unfolding not_not apply(erule conjE)+ proof- |
|
3233 fix e1 e2 assume as:"open e1" "open e2" "s \<subseteq> e1 \<union> e2" "e1 \<inter> e2 \<inter> s = {}" "e1 \<inter> s \<noteq> {}" "e2 \<inter> s \<noteq> {}" |
|
3234 then obtain x1 x2 where obt:"x1\<in>e1\<inter>s" "x2\<in>e2\<inter>s" by auto |
|
3235 then obtain g where g:"path g" "path_image g \<subseteq> s" "pathstart g = x1" "pathfinish g = x2" |
|
3236 using assms[unfolded path_connected_def,rule_format,of x1 x2] by auto |
|
3237 have *:"connected {0..1::real^1}" by(auto intro!: convex_connected convex_interval) |
|
3238 have "{0..1} \<subseteq> {x \<in> {0..1}. g x \<in> e1} \<union> {x \<in> {0..1}. g x \<in> e2}" using as(3) g(2)[unfolded path_defs] by blast |
|
3239 moreover have "{x \<in> {0..1}. g x \<in> e1} \<inter> {x \<in> {0..1}. g x \<in> e2} = {}" using as(4) g(2)[unfolded path_defs] unfolding subset_eq by auto |
|
3240 moreover have "{x \<in> {0..1}. g x \<in> e1} \<noteq> {} \<and> {x \<in> {0..1}. g x \<in> e2} \<noteq> {}" using g(3,4)[unfolded path_defs] using obt by(auto intro!: exI) |
|
3241 ultimately show False using *[unfolded connected_local not_ex,rule_format, of "{x\<in>{0..1}. g x \<in> e1}" "{x\<in>{0..1}. g x \<in> e2}"] |
|
3242 using continuous_open_in_preimage[OF g(1)[unfolded path_def] as(1)] |
|
3243 using continuous_open_in_preimage[OF g(1)[unfolded path_def] as(2)] by auto qed |
|
3244 |
|
3245 lemma open_path_component: assumes "open s" shows "open(path_component s x)" |
|
3246 unfolding open_contains_ball proof |
|
3247 fix y assume as:"y \<in> path_component s x" |
|
3248 hence "y\<in>s" apply- apply(rule path_component_mem(2)) unfolding mem_def by auto |
|
3249 then obtain e where e:"e>0" "ball y e \<subseteq> s" using assms[unfolded open_contains_ball] by auto |
|
3250 show "\<exists>e>0. ball y e \<subseteq> path_component s x" apply(rule_tac x=e in exI) apply(rule,rule `e>0`,rule) unfolding mem_ball mem_path_component_set proof- |
|
3251 fix z assume "dist y z < e" thus "path_component s x z" apply(rule_tac path_component_trans[of _ _ y]) defer |
|
3252 apply(rule path_component_of_subset[OF e(2)]) apply(rule convex_imp_path_connected[OF convex_ball, unfolded path_connected_component, rule_format]) using `e>0` |
|
3253 using as[unfolded mem_def] by auto qed qed |
|
3254 |
|
3255 lemma open_non_path_component: assumes "open s" shows "open(s - path_component s x)" unfolding open_contains_ball proof |
|
3256 fix y assume as:"y\<in>s - path_component s x" |
|
3257 then obtain e where e:"e>0" "ball y e \<subseteq> s" using assms[unfolded open_contains_ball] by auto |
|
3258 show "\<exists>e>0. ball y e \<subseteq> s - path_component s x" apply(rule_tac x=e in exI) apply(rule,rule `e>0`,rule,rule) defer proof(rule ccontr) |
|
3259 fix z assume "z\<in>ball y e" "\<not> z \<notin> path_component s x" |
|
3260 hence "y \<in> path_component s x" unfolding not_not mem_path_component_set using `e>0` |
|
3261 apply- apply(rule path_component_trans,assumption) apply(rule path_component_of_subset[OF e(2)]) |
|
3262 apply(rule convex_imp_path_connected[OF convex_ball, unfolded path_connected_component, rule_format]) by auto |
|
3263 thus False using as by auto qed(insert e(2), auto) qed |
|
3264 |
|
3265 lemma connected_open_path_connected: assumes "open s" "connected s" shows "path_connected s" |
|
3266 unfolding path_connected_component_set proof(rule,rule,rule path_component_subset, rule) |
|
3267 fix x y assume "x \<in> s" "y \<in> s" show "y \<in> path_component s x" proof(rule ccontr) |
|
3268 assume "y \<notin> path_component s x" moreover |
|
3269 have "path_component s x \<inter> s \<noteq> {}" using `x\<in>s` path_component_eq_empty path_component_subset[of s x] by auto |
|
3270 ultimately show False using `y\<in>s` open_non_path_component[OF assms(1)] open_path_component[OF assms(1)] |
|
3271 using assms(2)[unfolded connected_def not_ex, rule_format, of"path_component s x" "s - path_component s x"] by auto |
|
3272 qed qed |
|
3273 |
|
3274 lemma path_connected_continuous_image: |
|
3275 assumes "continuous_on s f" "path_connected s" shows "path_connected (f ` s)" |
|
3276 unfolding path_connected_def proof(rule,rule) |
|
3277 fix x' y' assume "x' \<in> f ` s" "y' \<in> f ` s" |
|
3278 then obtain x y where xy:"x\<in>s" "y\<in>s" "x' = f x" "y' = f y" by auto |
|
3279 guess g using assms(2)[unfolded path_connected_def,rule_format,OF xy(1,2)] .. |
|
3280 thus "\<exists>g. path g \<and> path_image g \<subseteq> f ` s \<and> pathstart g = x' \<and> pathfinish g = y'" |
|
3281 unfolding xy apply(rule_tac x="f \<circ> g" in exI) unfolding path_defs |
|
3282 using assms(1) by(auto intro!: continuous_on_compose continuous_on_subset[of _ _ "g ` {0..1}"]) qed |
|
3283 |
|
3284 lemma homeomorphic_path_connectedness: |
|
3285 "s homeomorphic t \<Longrightarrow> (path_connected s \<longleftrightarrow> path_connected t)" |
|
3286 unfolding homeomorphic_def homeomorphism_def apply(erule exE|erule conjE)+ apply rule |
|
3287 apply(drule_tac f=f in path_connected_continuous_image) prefer 3 |
|
3288 apply(drule_tac f=g in path_connected_continuous_image) by auto |
|
3289 |
|
3290 lemma path_connected_empty: "path_connected {}" |
|
3291 unfolding path_connected_def by auto |
|
3292 |
|
3293 lemma path_connected_singleton: "path_connected {a}" |
|
3294 unfolding path_connected_def apply(rule,rule) |
|
3295 apply(rule_tac x="linepath a a" in exI) by(auto simp add:segment scaleR_left_diff_distrib) |
|
3296 |
|
3297 lemma path_connected_Un: assumes "path_connected s" "path_connected t" "s \<inter> t \<noteq> {}" |
|
3298 shows "path_connected (s \<union> t)" unfolding path_connected_component proof(rule,rule) |
|
3299 fix x y assume as:"x \<in> s \<union> t" "y \<in> s \<union> t" |
|
3300 from assms(3) obtain z where "z \<in> s \<inter> t" by auto |
|
3301 thus "path_component (s \<union> t) x y" using as using assms(1-2)[unfolded path_connected_component] apply- |
|
3302 apply(erule_tac[!] UnE)+ apply(rule_tac[2-3] path_component_trans[of _ _ z]) |
|
3303 by(auto simp add:path_component_of_subset [OF Un_upper1] path_component_of_subset[OF Un_upper2]) qed |
|
3304 |
|
3305 subsection {* sphere is path-connected. *} |
|
3306 |
|
3307 lemma path_connected_punctured_universe: |
|
3308 assumes "2 \<le> CARD('n::finite)" shows "path_connected((UNIV::(real^'n::finite) set) - {a})" proof- |
|
3309 obtain \<psi> where \<psi>:"bij_betw \<psi> {1..CARD('n)} (UNIV::'n set)" using ex_bij_betw_nat_finite_1[OF finite_UNIV] by auto |
|
3310 let ?U = "UNIV::(real^'n) set" let ?u = "?U - {0}" |
|
3311 let ?basis = "\<lambda>k. basis (\<psi> k)" |
|
3312 let ?A = "\<lambda>k. {x::real^'n. \<exists>i\<in>{1..k}. inner (basis (\<psi> i)) x \<noteq> 0}" |
|
3313 have "\<forall>k\<in>{2..CARD('n)}. path_connected (?A k)" proof |
|
3314 have *:"\<And>k. ?A (Suc k) = {x. inner (?basis (Suc k)) x < 0} \<union> {x. inner (?basis (Suc k)) x > 0} \<union> ?A k" apply(rule set_ext,rule) defer |
|
3315 apply(erule UnE)+ unfolding mem_Collect_eq apply(rule_tac[1-2] x="Suc k" in bexI) |
|
3316 by(auto elim!: ballE simp add: not_less le_Suc_eq) |
|
3317 fix k assume "k \<in> {2..CARD('n)}" thus "path_connected (?A k)" proof(induct k) |
|
3318 case (Suc k) show ?case proof(cases "k = 1") |
|
3319 case False from Suc have d:"k \<in> {1..CARD('n)}" "Suc k \<in> {1..CARD('n)}" by auto |
|
3320 hence "\<psi> k \<noteq> \<psi> (Suc k)" using \<psi>[unfolded bij_betw_def inj_on_def, THEN conjunct1, THEN bspec[where x=k]] by auto |
|
3321 hence **:"?basis k + ?basis (Suc k) \<in> {x. 0 < inner (?basis (Suc k)) x} \<inter> (?A k)" |
|
3322 "?basis k - ?basis (Suc k) \<in> {x. 0 > inner (?basis (Suc k)) x} \<inter> ({x. 0 < inner (?basis (Suc k)) x} \<union> (?A k))" using d |
|
3323 by(auto simp add: inner_basis vector_component_simps intro!:bexI[where x=k]) |
|
3324 show ?thesis unfolding * Un_assoc apply(rule path_connected_Un) defer apply(rule path_connected_Un) |
|
3325 prefer 5 apply(rule_tac[1-2] convex_imp_path_connected, rule convex_halfspace_lt, rule convex_halfspace_gt) |
|
3326 apply(rule Suc(1)) apply(rule_tac[2-3] ccontr) using d ** False by auto |
|
3327 next case True hence d:"1\<in>{1..CARD('n)}" "2\<in>{1..CARD('n)}" using Suc(2) by auto |
|
3328 have ***:"Suc 1 = 2" by auto |
|
3329 have **:"\<And>s t P Q. s \<union> t \<union> {x. P x \<or> Q x} = (s \<union> {x. P x}) \<union> (t \<union> {x. Q x})" by auto |
|
3330 have "\<psi> 2 \<noteq> \<psi> (Suc 0)" apply(rule ccontr) using \<psi>[unfolded bij_betw_def inj_on_def, THEN conjunct1, THEN bspec[where x=2]] using assms by auto |
|
3331 thus ?thesis unfolding * True unfolding ** neq_iff bex_disj_distrib apply - |
|
3332 apply(rule path_connected_Un, rule_tac[1-2] path_connected_Un) defer 3 apply(rule_tac[1-4] convex_imp_path_connected) |
|
3333 apply(rule_tac[5] x=" ?basis 1 + ?basis 2" in nequals0I) |
|
3334 apply(rule_tac[6] x="-?basis 1 + ?basis 2" in nequals0I) |
|
3335 apply(rule_tac[7] x="-?basis 1 - ?basis 2" in nequals0I) |
|
3336 using d unfolding *** by(auto intro!: convex_halfspace_gt convex_halfspace_lt, auto simp add:vector_component_simps inner_basis) |
|
3337 qed qed auto qed note lem = this |
|
3338 |
|
3339 have ***:"\<And>x::real^'n. (\<exists>i\<in>{1..CARD('n)}. inner (basis (\<psi> i)) x \<noteq> 0) \<longleftrightarrow> (\<exists>i. inner (basis i) x \<noteq> 0)" |
|
3340 apply rule apply(erule bexE) apply(rule_tac x="\<psi> i" in exI) defer apply(erule exE) proof- |
|
3341 fix x::"real^'n" and i assume as:"inner (basis i) x \<noteq> 0" |
|
3342 have "i\<in>\<psi> ` {1..CARD('n)}" using \<psi>[unfolded bij_betw_def, THEN conjunct2] by auto |
|
3343 then obtain j where "j\<in>{1..CARD('n)}" "\<psi> j = i" by auto |
|
3344 thus "\<exists>i\<in>{1..CARD('n)}. inner (basis (\<psi> i)) x \<noteq> 0" apply(rule_tac x=j in bexI) using as by auto qed auto |
|
3345 have *:"?U - {a} = (\<lambda>x. x + a) ` {x. x \<noteq> 0}" apply(rule set_ext) unfolding image_iff |
|
3346 apply rule apply(rule_tac x="x - a" in bexI) by auto |
|
3347 have **:"\<And>x::real^'n. x\<noteq>0 \<longleftrightarrow> (\<exists>i. inner (basis i) x \<noteq> 0)" unfolding Cart_eq by(auto simp add: inner_basis) |
|
3348 show ?thesis unfolding * apply(rule path_connected_continuous_image) apply(rule continuous_on_intros)+ |
|
3349 unfolding ** apply(rule lem[THEN bspec[where x="CARD('n)"], unfolded ***]) using assms by auto qed |
|
3350 |
|
3351 lemma path_connected_sphere: assumes "2 \<le> CARD('n::finite)" shows "path_connected {x::real^'n::finite. norm(x - a) = r}" proof(cases "r\<le>0") |
|
3352 case True thus ?thesis proof(cases "r=0") |
|
3353 case False hence "{x::real^'n. norm(x - a) = r} = {}" using True by auto |
|
3354 thus ?thesis using path_connected_empty by auto |
|
3355 qed(auto intro!:path_connected_singleton) next |
|
3356 case False hence *:"{x::real^'n. norm(x - a) = r} = (\<lambda>x. a + r *\<^sub>R x) ` {x. norm x = 1}" unfolding not_le apply -apply(rule set_ext,rule) |
|
3357 unfolding image_iff apply(rule_tac x="(1/r) *\<^sub>R (x - a)" in bexI) unfolding mem_Collect_eq norm_scaleR by (auto simp add: scaleR_right_diff_distrib) |
|
3358 have **:"{x::real^'n. norm x = 1} = (\<lambda>x. (1/norm x) *\<^sub>R x) ` (UNIV - {0})" apply(rule set_ext,rule) |
|
3359 unfolding image_iff apply(rule_tac x=x in bexI) unfolding mem_Collect_eq by(auto split:split_if_asm) |
|
3360 have "continuous_on (UNIV - {0}) (\<lambda>x::real^'n. 1 / norm x)" unfolding o_def continuous_on_eq_continuous_within |
|
3361 apply(rule, rule continuous_at_within_inv[unfolded o_def inverse_eq_divide]) apply(rule continuous_at_within) |
|
3362 apply(rule continuous_at_norm[unfolded o_def]) by auto |
|
3363 thus ?thesis unfolding * ** using path_connected_punctured_universe[OF assms] |
|
3364 by(auto intro!: path_connected_continuous_image continuous_on_intros continuous_on_mul) qed |
|
3365 |
|
3366 lemma connected_sphere: "2 \<le> CARD('n) \<Longrightarrow> connected {x::real^'n::finite. norm(x - a) = r}" |
|
3367 using path_connected_sphere path_connected_imp_connected by auto |
|
3368 |
|
3369 (** In continuous_at_vec1_norm : Use \<And> instead of \<forall>. **) |
|
3370 |
|
3371 end |