author | huffman |
Thu, 17 May 2007 21:51:32 +0200 | |
changeset 22998 | 97e1f9c2cc46 |
parent 22984 | 67d434ad9ef8 |
child 23041 | a0f26d47369b |
permissions | -rw-r--r-- |
21164 | 1 |
(* Title : Deriv.thy |
2 |
ID : $Id$ |
|
3 |
Author : Jacques D. Fleuriot |
|
4 |
Copyright : 1998 University of Cambridge |
|
5 |
Conversion to Isar and new proofs by Lawrence C Paulson, 2004 |
|
6 |
GMVT by Benjamin Porter, 2005 |
|
7 |
*) |
|
8 |
||
9 |
header{* Differentiation *} |
|
10 |
||
11 |
theory Deriv |
|
22653
8e016bfdbf2f
moved nonstandard derivative stuff from Deriv.thy into new file HDeriv.thy
huffman
parents:
22641
diff
changeset
|
12 |
imports Lim |
21164 | 13 |
begin |
14 |
||
22984 | 15 |
text{*Standard Definitions*} |
21164 | 16 |
|
17 |
definition |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
18 |
deriv :: "['a::real_normed_field \<Rightarrow> 'a, 'a, 'a] \<Rightarrow> bool" |
21164 | 19 |
--{*Differentiation: D is derivative of function f at x*} |
21404
eb85850d3eb7
more robust syntax for definition/abbreviation/notation;
wenzelm
parents:
21239
diff
changeset
|
20 |
("(DERIV (_)/ (_)/ :> (_))" [1000, 1000, 60] 60) where |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
21 |
"DERIV f x :> D = ((%h. (f(x + h) - f x) / h) -- 0 --> D)" |
21164 | 22 |
|
21404
eb85850d3eb7
more robust syntax for definition/abbreviation/notation;
wenzelm
parents:
21239
diff
changeset
|
23 |
definition |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
24 |
differentiable :: "['a::real_normed_field \<Rightarrow> 'a, 'a] \<Rightarrow> bool" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
25 |
(infixl "differentiable" 60) where |
21164 | 26 |
"f differentiable x = (\<exists>D. DERIV f x :> D)" |
27 |
||
28 |
||
29 |
consts |
|
30 |
Bolzano_bisect :: "[real*real=>bool, real, real, nat] => (real*real)" |
|
31 |
primrec |
|
32 |
"Bolzano_bisect P a b 0 = (a,b)" |
|
33 |
"Bolzano_bisect P a b (Suc n) = |
|
34 |
(let (x,y) = Bolzano_bisect P a b n |
|
35 |
in if P(x, (x+y)/2) then ((x+y)/2, y) |
|
36 |
else (x, (x+y)/2))" |
|
37 |
||
38 |
||
39 |
subsection {* Derivatives *} |
|
40 |
||
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
41 |
lemma DERIV_iff: "(DERIV f x :> D) = ((%h. (f(x + h) - f(x))/h) -- 0 --> D)" |
21164 | 42 |
by (simp add: deriv_def) |
43 |
||
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
44 |
lemma DERIV_D: "DERIV f x :> D ==> (%h. (f(x + h) - f(x))/h) -- 0 --> D" |
21164 | 45 |
by (simp add: deriv_def) |
46 |
||
47 |
lemma DERIV_const [simp]: "DERIV (\<lambda>x. k) x :> 0" |
|
48 |
by (simp add: deriv_def) |
|
49 |
||
50 |
lemma DERIV_Id [simp]: "DERIV (\<lambda>x. x) x :> 1" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
51 |
by (simp add: deriv_def divide_self cong: LIM_cong) |
21164 | 52 |
|
53 |
lemma add_diff_add: |
|
54 |
fixes a b c d :: "'a::ab_group_add" |
|
55 |
shows "(a + c) - (b + d) = (a - b) + (c - d)" |
|
56 |
by simp |
|
57 |
||
58 |
lemma DERIV_add: |
|
59 |
"\<lbrakk>DERIV f x :> D; DERIV g x :> E\<rbrakk> \<Longrightarrow> DERIV (\<lambda>x. f x + g x) x :> D + E" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
60 |
by (simp only: deriv_def add_diff_add add_divide_distrib LIM_add) |
21164 | 61 |
|
62 |
lemma DERIV_minus: |
|
63 |
"DERIV f x :> D \<Longrightarrow> DERIV (\<lambda>x. - f x) x :> - D" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
64 |
by (simp only: deriv_def minus_diff_minus divide_minus_left LIM_minus) |
21164 | 65 |
|
66 |
lemma DERIV_diff: |
|
67 |
"\<lbrakk>DERIV f x :> D; DERIV g x :> E\<rbrakk> \<Longrightarrow> DERIV (\<lambda>x. f x - g x) x :> D - E" |
|
68 |
by (simp only: diff_def DERIV_add DERIV_minus) |
|
69 |
||
70 |
lemma DERIV_add_minus: |
|
71 |
"\<lbrakk>DERIV f x :> D; DERIV g x :> E\<rbrakk> \<Longrightarrow> DERIV (\<lambda>x. f x + - g x) x :> D + - E" |
|
72 |
by (simp only: DERIV_add DERIV_minus) |
|
73 |
||
74 |
lemma DERIV_isCont: "DERIV f x :> D \<Longrightarrow> isCont f x" |
|
75 |
proof (unfold isCont_iff) |
|
76 |
assume "DERIV f x :> D" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
77 |
hence "(\<lambda>h. (f(x+h) - f(x)) / h) -- 0 --> D" |
21164 | 78 |
by (rule DERIV_D) |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
79 |
hence "(\<lambda>h. (f(x+h) - f(x)) / h * h) -- 0 --> D * 0" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
80 |
by (intro LIM_mult LIM_self) |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
81 |
hence "(\<lambda>h. (f(x+h) - f(x)) * (h / h)) -- 0 --> 0" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
82 |
by simp |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
83 |
hence "(\<lambda>h. f(x+h) - f(x)) -- 0 --> 0" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
84 |
by (simp cong: LIM_cong add: divide_self) |
21164 | 85 |
thus "(\<lambda>h. f(x+h)) -- 0 --> f(x)" |
86 |
by (simp add: LIM_def) |
|
87 |
qed |
|
88 |
||
89 |
lemma DERIV_mult_lemma: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
90 |
fixes a b c d :: "'a::real_field" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
91 |
shows "(a * b - c * d) / h = a * ((b - d) / h) + ((a - c) / h) * d" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
92 |
by (simp add: diff_minus add_divide_distrib [symmetric] ring_distrib) |
21164 | 93 |
|
94 |
lemma DERIV_mult': |
|
95 |
assumes f: "DERIV f x :> D" |
|
96 |
assumes g: "DERIV g x :> E" |
|
97 |
shows "DERIV (\<lambda>x. f x * g x) x :> f x * E + D * g x" |
|
98 |
proof (unfold deriv_def) |
|
99 |
from f have "isCont f x" |
|
100 |
by (rule DERIV_isCont) |
|
101 |
hence "(\<lambda>h. f(x+h)) -- 0 --> f x" |
|
102 |
by (simp only: isCont_iff) |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
103 |
hence "(\<lambda>h. f(x+h) * ((g(x+h) - g x) / h) + |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
104 |
((f(x+h) - f x) / h) * g x) |
21164 | 105 |
-- 0 --> f x * E + D * g x" |
22613 | 106 |
by (intro LIM_add LIM_mult LIM_const DERIV_D f g) |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
107 |
thus "(\<lambda>h. (f(x+h) * g(x+h) - f x * g x) / h) |
21164 | 108 |
-- 0 --> f x * E + D * g x" |
109 |
by (simp only: DERIV_mult_lemma) |
|
110 |
qed |
|
111 |
||
112 |
lemma DERIV_mult: |
|
113 |
"[| DERIV f x :> Da; DERIV g x :> Db |] |
|
114 |
==> DERIV (%x. f x * g x) x :> (Da * g(x)) + (Db * f(x))" |
|
115 |
by (drule (1) DERIV_mult', simp only: mult_commute add_commute) |
|
116 |
||
117 |
lemma DERIV_unique: |
|
118 |
"[| DERIV f x :> D; DERIV f x :> E |] ==> D = E" |
|
119 |
apply (simp add: deriv_def) |
|
120 |
apply (blast intro: LIM_unique) |
|
121 |
done |
|
122 |
||
123 |
text{*Differentiation of finite sum*} |
|
124 |
||
125 |
lemma DERIV_sumr [rule_format (no_asm)]: |
|
126 |
"(\<forall>r. m \<le> r & r < (m + n) --> DERIV (%x. f r x) x :> (f' r x)) |
|
127 |
--> DERIV (%x. \<Sum>n=m..<n::nat. f n x :: real) x :> (\<Sum>r=m..<n. f' r x)" |
|
128 |
apply (induct "n") |
|
129 |
apply (auto intro: DERIV_add) |
|
130 |
done |
|
131 |
||
132 |
text{*Alternative definition for differentiability*} |
|
133 |
||
134 |
lemma DERIV_LIM_iff: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
135 |
"((%h. (f(a + h) - f(a)) / h) -- 0 --> D) = |
21164 | 136 |
((%x. (f(x)-f(a)) / (x-a)) -- a --> D)" |
137 |
apply (rule iffI) |
|
138 |
apply (drule_tac k="- a" in LIM_offset) |
|
139 |
apply (simp add: diff_minus) |
|
140 |
apply (drule_tac k="a" in LIM_offset) |
|
141 |
apply (simp add: add_commute) |
|
142 |
done |
|
143 |
||
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
144 |
lemma DERIV_iff2: "(DERIV f x :> D) = ((%z. (f(z) - f(x)) / (z-x)) -- x --> D)" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
145 |
by (simp add: deriv_def diff_minus [symmetric] DERIV_LIM_iff) |
21164 | 146 |
|
147 |
lemma inverse_diff_inverse: |
|
148 |
"\<lbrakk>(a::'a::division_ring) \<noteq> 0; b \<noteq> 0\<rbrakk> |
|
149 |
\<Longrightarrow> inverse a - inverse b = - (inverse a * (a - b) * inverse b)" |
|
150 |
by (simp add: right_diff_distrib left_diff_distrib mult_assoc) |
|
151 |
||
152 |
lemma DERIV_inverse_lemma: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
153 |
"\<lbrakk>a \<noteq> 0; b \<noteq> (0::'a::real_normed_field)\<rbrakk> |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
154 |
\<Longrightarrow> (inverse a - inverse b) / h |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
155 |
= - (inverse a * ((a - b) / h) * inverse b)" |
21164 | 156 |
by (simp add: inverse_diff_inverse) |
157 |
||
158 |
lemma DERIV_inverse': |
|
159 |
assumes der: "DERIV f x :> D" |
|
160 |
assumes neq: "f x \<noteq> 0" |
|
161 |
shows "DERIV (\<lambda>x. inverse (f x)) x :> - (inverse (f x) * D * inverse (f x))" |
|
162 |
(is "DERIV _ _ :> ?E") |
|
163 |
proof (unfold DERIV_iff2) |
|
164 |
from der have lim_f: "f -- x --> f x" |
|
165 |
by (rule DERIV_isCont [unfolded isCont_def]) |
|
166 |
||
167 |
from neq have "0 < norm (f x)" by simp |
|
168 |
with LIM_D [OF lim_f] obtain s |
|
169 |
where s: "0 < s" |
|
170 |
and less_fx: "\<And>z. \<lbrakk>z \<noteq> x; norm (z - x) < s\<rbrakk> |
|
171 |
\<Longrightarrow> norm (f z - f x) < norm (f x)" |
|
172 |
by fast |
|
173 |
||
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
174 |
show "(\<lambda>z. (inverse (f z) - inverse (f x)) / (z - x)) -- x --> ?E" |
21164 | 175 |
proof (rule LIM_equal2 [OF s]) |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
176 |
fix z |
21164 | 177 |
assume "z \<noteq> x" "norm (z - x) < s" |
178 |
hence "norm (f z - f x) < norm (f x)" by (rule less_fx) |
|
179 |
hence "f z \<noteq> 0" by auto |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
180 |
thus "(inverse (f z) - inverse (f x)) / (z - x) = |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
181 |
- (inverse (f z) * ((f z - f x) / (z - x)) * inverse (f x))" |
21164 | 182 |
using neq by (rule DERIV_inverse_lemma) |
183 |
next |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
184 |
from der have "(\<lambda>z. (f z - f x) / (z - x)) -- x --> D" |
21164 | 185 |
by (unfold DERIV_iff2) |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
186 |
thus "(\<lambda>z. - (inverse (f z) * ((f z - f x) / (z - x)) * inverse (f x))) |
21164 | 187 |
-- x --> ?E" |
22613 | 188 |
by (intro LIM_mult LIM_inverse LIM_minus LIM_const lim_f neq) |
21164 | 189 |
qed |
190 |
qed |
|
191 |
||
192 |
lemma DERIV_divide: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
193 |
"\<lbrakk>DERIV f x :> D; DERIV g x :> E; g x \<noteq> 0\<rbrakk> |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
194 |
\<Longrightarrow> DERIV (\<lambda>x. f x / g x) x :> (D * g x - f x * E) / (g x * g x)" |
21164 | 195 |
apply (subgoal_tac "f x * - (inverse (g x) * E * inverse (g x)) + |
196 |
D * inverse (g x) = (D * g x - f x * E) / (g x * g x)") |
|
197 |
apply (erule subst) |
|
198 |
apply (unfold divide_inverse) |
|
199 |
apply (erule DERIV_mult') |
|
200 |
apply (erule (1) DERIV_inverse') |
|
201 |
apply (simp add: left_diff_distrib nonzero_inverse_mult_distrib) |
|
202 |
apply (simp add: mult_ac) |
|
203 |
done |
|
204 |
||
205 |
lemma DERIV_power_Suc: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
206 |
fixes f :: "'a \<Rightarrow> 'a::{real_normed_field,recpower}" |
21164 | 207 |
assumes f: "DERIV f x :> D" |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
208 |
shows "DERIV (\<lambda>x. f x ^ Suc n) x :> (of_nat n + 1) * (D * f x ^ n)" |
21164 | 209 |
proof (induct n) |
210 |
case 0 |
|
211 |
show ?case by (simp add: power_Suc f) |
|
212 |
case (Suc k) |
|
213 |
from DERIV_mult' [OF f Suc] show ?case |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
214 |
apply (simp only: of_nat_Suc left_distrib mult_1_left) |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
215 |
apply (simp only: power_Suc right_distrib mult_ac) |
21164 | 216 |
done |
217 |
qed |
|
218 |
||
219 |
lemma DERIV_power: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
220 |
fixes f :: "'a \<Rightarrow> 'a::{real_normed_field,recpower}" |
21164 | 221 |
assumes f: "DERIV f x :> D" |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
222 |
shows "DERIV (\<lambda>x. f x ^ n) x :> of_nat n * (D * f x ^ (n - Suc 0))" |
21164 | 223 |
by (cases "n", simp, simp add: DERIV_power_Suc f) |
224 |
||
225 |
||
226 |
(* ------------------------------------------------------------------------ *) |
|
227 |
(* Caratheodory formulation of derivative at a point: standard proof *) |
|
228 |
(* ------------------------------------------------------------------------ *) |
|
229 |
||
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
230 |
lemma nonzero_mult_divide_cancel_right: |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
231 |
"b \<noteq> 0 \<Longrightarrow> a * b / b = (a::'a::field)" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
232 |
proof - |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
233 |
assume b: "b \<noteq> 0" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
234 |
have "a * b / b = a * (b / b)" by simp |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
235 |
also have "\<dots> = a" by (simp add: divide_self b) |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
236 |
finally show "a * b / b = a" . |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
237 |
qed |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
238 |
|
21164 | 239 |
lemma CARAT_DERIV: |
240 |
"(DERIV f x :> l) = |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
241 |
(\<exists>g. (\<forall>z. f z - f x = g z * (z-x)) & isCont g x & g x = l)" |
21164 | 242 |
(is "?lhs = ?rhs") |
243 |
proof |
|
244 |
assume der: "DERIV f x :> l" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
245 |
show "\<exists>g. (\<forall>z. f z - f x = g z * (z-x)) \<and> isCont g x \<and> g x = l" |
21164 | 246 |
proof (intro exI conjI) |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
247 |
let ?g = "(%z. if z = x then l else (f z - f x) / (z-x))" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
248 |
show "\<forall>z. f z - f x = ?g z * (z-x)" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
249 |
by (simp add: nonzero_mult_divide_cancel_right) |
21164 | 250 |
show "isCont ?g x" using der |
251 |
by (simp add: isCont_iff DERIV_iff diff_minus |
|
252 |
cong: LIM_equal [rule_format]) |
|
253 |
show "?g x = l" by simp |
|
254 |
qed |
|
255 |
next |
|
256 |
assume "?rhs" |
|
257 |
then obtain g where |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
258 |
"(\<forall>z. f z - f x = g z * (z-x))" and "isCont g x" and "g x = l" by blast |
21164 | 259 |
thus "(DERIV f x :> l)" |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
260 |
by (auto simp add: isCont_iff DERIV_iff nonzero_mult_divide_cancel_right |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
261 |
cong: LIM_cong) |
21164 | 262 |
qed |
263 |
||
264 |
lemma DERIV_chain': |
|
265 |
assumes f: "DERIV f x :> D" |
|
266 |
assumes g: "DERIV g (f x) :> E" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
267 |
shows "DERIV (\<lambda>x. g (f x)) x :> E * D" |
21164 | 268 |
proof (unfold DERIV_iff2) |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
269 |
obtain d where d: "\<forall>y. g y - g (f x) = d y * (y - f x)" |
21164 | 270 |
and cont_d: "isCont d (f x)" and dfx: "d (f x) = E" |
271 |
using CARAT_DERIV [THEN iffD1, OF g] by fast |
|
272 |
from f have "f -- x --> f x" |
|
273 |
by (rule DERIV_isCont [unfolded isCont_def]) |
|
274 |
with cont_d have "(\<lambda>z. d (f z)) -- x --> d (f x)" |
|
21239 | 275 |
by (rule isCont_LIM_compose) |
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
276 |
hence "(\<lambda>z. d (f z) * ((f z - f x) / (z - x))) |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
277 |
-- x --> d (f x) * D" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
278 |
by (rule LIM_mult [OF _ f [unfolded DERIV_iff2]]) |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
279 |
thus "(\<lambda>z. (g (f z) - g (f x)) / (z - x)) -- x --> E * D" |
21164 | 280 |
by (simp add: d dfx real_scaleR_def) |
281 |
qed |
|
282 |
||
283 |
(* let's do the standard proof though theorem *) |
|
284 |
(* LIM_mult2 follows from a NS proof *) |
|
285 |
||
286 |
lemma DERIV_cmult: |
|
287 |
"DERIV f x :> D ==> DERIV (%x. c * f x) x :> c*D" |
|
288 |
by (drule DERIV_mult' [OF DERIV_const], simp) |
|
289 |
||
290 |
(* standard version *) |
|
291 |
lemma DERIV_chain: "[| DERIV f (g x) :> Da; DERIV g x :> Db |] ==> DERIV (f o g) x :> Da * Db" |
|
292 |
by (drule (1) DERIV_chain', simp add: o_def real_scaleR_def mult_commute) |
|
293 |
||
294 |
lemma DERIV_chain2: "[| DERIV f (g x) :> Da; DERIV g x :> Db |] ==> DERIV (%x. f (g x)) x :> Da * Db" |
|
295 |
by (auto dest: DERIV_chain simp add: o_def) |
|
296 |
||
297 |
(*derivative of linear multiplication*) |
|
298 |
lemma DERIV_cmult_Id [simp]: "DERIV (op * c) x :> c" |
|
299 |
by (cut_tac c = c and x = x in DERIV_Id [THEN DERIV_cmult], simp) |
|
300 |
||
301 |
lemma DERIV_pow: "DERIV (%x. x ^ n) x :> real n * (x ^ (n - Suc 0))" |
|
302 |
apply (cut_tac DERIV_power [OF DERIV_Id]) |
|
303 |
apply (simp add: real_scaleR_def real_of_nat_def) |
|
304 |
done |
|
305 |
||
306 |
text{*Power of -1*} |
|
307 |
||
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
308 |
lemma DERIV_inverse: |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
309 |
fixes x :: "'a::{real_normed_field,recpower}" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
310 |
shows "x \<noteq> 0 ==> DERIV (%x. inverse(x)) x :> (-(inverse x ^ Suc (Suc 0)))" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
311 |
by (drule DERIV_inverse' [OF DERIV_Id]) (simp add: power_Suc) |
21164 | 312 |
|
313 |
text{*Derivative of inverse*} |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
314 |
lemma DERIV_inverse_fun: |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
315 |
fixes x :: "'a::{real_normed_field,recpower}" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
316 |
shows "[| DERIV f x :> d; f(x) \<noteq> 0 |] |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
317 |
==> DERIV (%x. inverse(f x)) x :> (- (d * inverse(f(x) ^ Suc (Suc 0))))" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
318 |
by (drule (1) DERIV_inverse') (simp add: mult_ac power_Suc nonzero_inverse_mult_distrib) |
21164 | 319 |
|
320 |
text{*Derivative of quotient*} |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
321 |
lemma DERIV_quotient: |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
322 |
fixes x :: "'a::{real_normed_field,recpower}" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
323 |
shows "[| DERIV f x :> d; DERIV g x :> e; g(x) \<noteq> 0 |] |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
324 |
==> DERIV (%y. f(y) / (g y)) x :> (d*g(x) - (e*f(x))) / (g(x) ^ Suc (Suc 0))" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
325 |
by (drule (2) DERIV_divide) (simp add: mult_commute power_Suc) |
21164 | 326 |
|
22984 | 327 |
|
328 |
subsection {* Differentiability predicate *} |
|
21164 | 329 |
|
330 |
lemma differentiableD: "f differentiable x ==> \<exists>D. DERIV f x :> D" |
|
331 |
by (simp add: differentiable_def) |
|
332 |
||
333 |
lemma differentiableI: "DERIV f x :> D ==> f differentiable x" |
|
334 |
by (force simp add: differentiable_def) |
|
335 |
||
336 |
lemma differentiable_const: "(\<lambda>z. a) differentiable x" |
|
337 |
apply (unfold differentiable_def) |
|
338 |
apply (rule_tac x=0 in exI) |
|
339 |
apply simp |
|
340 |
done |
|
341 |
||
342 |
lemma differentiable_sum: |
|
343 |
assumes "f differentiable x" |
|
344 |
and "g differentiable x" |
|
345 |
shows "(\<lambda>x. f x + g x) differentiable x" |
|
346 |
proof - |
|
347 |
from prems have "\<exists>D. DERIV f x :> D" by (unfold differentiable_def) |
|
348 |
then obtain df where "DERIV f x :> df" .. |
|
349 |
moreover from prems have "\<exists>D. DERIV g x :> D" by (unfold differentiable_def) |
|
350 |
then obtain dg where "DERIV g x :> dg" .. |
|
351 |
ultimately have "DERIV (\<lambda>x. f x + g x) x :> df + dg" by (rule DERIV_add) |
|
352 |
hence "\<exists>D. DERIV (\<lambda>x. f x + g x) x :> D" by auto |
|
353 |
thus ?thesis by (fold differentiable_def) |
|
354 |
qed |
|
355 |
||
356 |
lemma differentiable_diff: |
|
357 |
assumes "f differentiable x" |
|
358 |
and "g differentiable x" |
|
359 |
shows "(\<lambda>x. f x - g x) differentiable x" |
|
360 |
proof - |
|
361 |
from prems have "f differentiable x" by simp |
|
362 |
moreover |
|
363 |
from prems have "\<exists>D. DERIV g x :> D" by (unfold differentiable_def) |
|
364 |
then obtain dg where "DERIV g x :> dg" .. |
|
365 |
then have "DERIV (\<lambda>x. - g x) x :> -dg" by (rule DERIV_minus) |
|
366 |
hence "\<exists>D. DERIV (\<lambda>x. - g x) x :> D" by auto |
|
367 |
hence "(\<lambda>x. - g x) differentiable x" by (fold differentiable_def) |
|
368 |
ultimately |
|
369 |
show ?thesis |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
370 |
by (auto simp: diff_def dest: differentiable_sum) |
21164 | 371 |
qed |
372 |
||
373 |
lemma differentiable_mult: |
|
374 |
assumes "f differentiable x" |
|
375 |
and "g differentiable x" |
|
376 |
shows "(\<lambda>x. f x * g x) differentiable x" |
|
377 |
proof - |
|
378 |
from prems have "\<exists>D. DERIV f x :> D" by (unfold differentiable_def) |
|
379 |
then obtain df where "DERIV f x :> df" .. |
|
380 |
moreover from prems have "\<exists>D. DERIV g x :> D" by (unfold differentiable_def) |
|
381 |
then obtain dg where "DERIV g x :> dg" .. |
|
382 |
ultimately have "DERIV (\<lambda>x. f x * g x) x :> df * g x + dg * f x" by (simp add: DERIV_mult) |
|
383 |
hence "\<exists>D. DERIV (\<lambda>x. f x * g x) x :> D" by auto |
|
384 |
thus ?thesis by (fold differentiable_def) |
|
385 |
qed |
|
386 |
||
22984 | 387 |
|
21164 | 388 |
subsection {* Nested Intervals and Bisection *} |
389 |
||
390 |
text{*Lemmas about nested intervals and proof by bisection (cf.Harrison). |
|
391 |
All considerably tidied by lcp.*} |
|
392 |
||
393 |
lemma lemma_f_mono_add [rule_format (no_asm)]: "(\<forall>n. (f::nat=>real) n \<le> f (Suc n)) --> f m \<le> f(m + no)" |
|
394 |
apply (induct "no") |
|
395 |
apply (auto intro: order_trans) |
|
396 |
done |
|
397 |
||
398 |
lemma f_inc_g_dec_Beq_f: "[| \<forall>n. f(n) \<le> f(Suc n); |
|
399 |
\<forall>n. g(Suc n) \<le> g(n); |
|
400 |
\<forall>n. f(n) \<le> g(n) |] |
|
401 |
==> Bseq (f :: nat \<Rightarrow> real)" |
|
402 |
apply (rule_tac k = "f 0" and K = "g 0" in BseqI2, rule allI) |
|
403 |
apply (induct_tac "n") |
|
404 |
apply (auto intro: order_trans) |
|
405 |
apply (rule_tac y = "g (Suc na)" in order_trans) |
|
406 |
apply (induct_tac [2] "na") |
|
407 |
apply (auto intro: order_trans) |
|
408 |
done |
|
409 |
||
410 |
lemma f_inc_g_dec_Beq_g: "[| \<forall>n. f(n) \<le> f(Suc n); |
|
411 |
\<forall>n. g(Suc n) \<le> g(n); |
|
412 |
\<forall>n. f(n) \<le> g(n) |] |
|
413 |
==> Bseq (g :: nat \<Rightarrow> real)" |
|
414 |
apply (subst Bseq_minus_iff [symmetric]) |
|
415 |
apply (rule_tac g = "%x. - (f x)" in f_inc_g_dec_Beq_f) |
|
416 |
apply auto |
|
417 |
done |
|
418 |
||
419 |
lemma f_inc_imp_le_lim: |
|
420 |
fixes f :: "nat \<Rightarrow> real" |
|
421 |
shows "\<lbrakk>\<forall>n. f n \<le> f (Suc n); convergent f\<rbrakk> \<Longrightarrow> f n \<le> lim f" |
|
422 |
apply (rule linorder_not_less [THEN iffD1]) |
|
423 |
apply (auto simp add: convergent_LIMSEQ_iff LIMSEQ_iff monoseq_Suc) |
|
424 |
apply (drule real_less_sum_gt_zero) |
|
425 |
apply (drule_tac x = "f n + - lim f" in spec, safe) |
|
426 |
apply (drule_tac P = "%na. no\<le>na --> ?Q na" and x = "no + n" in spec, auto) |
|
427 |
apply (subgoal_tac "lim f \<le> f (no + n) ") |
|
428 |
apply (drule_tac no=no and m=n in lemma_f_mono_add) |
|
429 |
apply (auto simp add: add_commute) |
|
430 |
apply (induct_tac "no") |
|
431 |
apply simp |
|
432 |
apply (auto intro: order_trans simp add: diff_minus abs_if) |
|
433 |
done |
|
434 |
||
435 |
lemma lim_uminus: "convergent g ==> lim (%x. - g x) = - (lim g)" |
|
436 |
apply (rule LIMSEQ_minus [THEN limI]) |
|
437 |
apply (simp add: convergent_LIMSEQ_iff) |
|
438 |
done |
|
439 |
||
440 |
lemma g_dec_imp_lim_le: |
|
441 |
fixes g :: "nat \<Rightarrow> real" |
|
442 |
shows "\<lbrakk>\<forall>n. g (Suc n) \<le> g(n); convergent g\<rbrakk> \<Longrightarrow> lim g \<le> g n" |
|
443 |
apply (subgoal_tac "- (g n) \<le> - (lim g) ") |
|
444 |
apply (cut_tac [2] f = "%x. - (g x)" in f_inc_imp_le_lim) |
|
445 |
apply (auto simp add: lim_uminus convergent_minus_iff [symmetric]) |
|
446 |
done |
|
447 |
||
448 |
lemma lemma_nest: "[| \<forall>n. f(n) \<le> f(Suc n); |
|
449 |
\<forall>n. g(Suc n) \<le> g(n); |
|
450 |
\<forall>n. f(n) \<le> g(n) |] |
|
451 |
==> \<exists>l m :: real. l \<le> m & ((\<forall>n. f(n) \<le> l) & f ----> l) & |
|
452 |
((\<forall>n. m \<le> g(n)) & g ----> m)" |
|
453 |
apply (subgoal_tac "monoseq f & monoseq g") |
|
454 |
prefer 2 apply (force simp add: LIMSEQ_iff monoseq_Suc) |
|
455 |
apply (subgoal_tac "Bseq f & Bseq g") |
|
456 |
prefer 2 apply (blast intro: f_inc_g_dec_Beq_f f_inc_g_dec_Beq_g) |
|
457 |
apply (auto dest!: Bseq_monoseq_convergent simp add: convergent_LIMSEQ_iff) |
|
458 |
apply (rule_tac x = "lim f" in exI) |
|
459 |
apply (rule_tac x = "lim g" in exI) |
|
460 |
apply (auto intro: LIMSEQ_le) |
|
461 |
apply (auto simp add: f_inc_imp_le_lim g_dec_imp_lim_le convergent_LIMSEQ_iff) |
|
462 |
done |
|
463 |
||
464 |
lemma lemma_nest_unique: "[| \<forall>n. f(n) \<le> f(Suc n); |
|
465 |
\<forall>n. g(Suc n) \<le> g(n); |
|
466 |
\<forall>n. f(n) \<le> g(n); |
|
467 |
(%n. f(n) - g(n)) ----> 0 |] |
|
468 |
==> \<exists>l::real. ((\<forall>n. f(n) \<le> l) & f ----> l) & |
|
469 |
((\<forall>n. l \<le> g(n)) & g ----> l)" |
|
470 |
apply (drule lemma_nest, auto) |
|
471 |
apply (subgoal_tac "l = m") |
|
472 |
apply (drule_tac [2] X = f in LIMSEQ_diff) |
|
473 |
apply (auto intro: LIMSEQ_unique) |
|
474 |
done |
|
475 |
||
476 |
text{*The universal quantifiers below are required for the declaration |
|
477 |
of @{text Bolzano_nest_unique} below.*} |
|
478 |
||
479 |
lemma Bolzano_bisect_le: |
|
480 |
"a \<le> b ==> \<forall>n. fst (Bolzano_bisect P a b n) \<le> snd (Bolzano_bisect P a b n)" |
|
481 |
apply (rule allI) |
|
482 |
apply (induct_tac "n") |
|
483 |
apply (auto simp add: Let_def split_def) |
|
484 |
done |
|
485 |
||
486 |
lemma Bolzano_bisect_fst_le_Suc: "a \<le> b ==> |
|
487 |
\<forall>n. fst(Bolzano_bisect P a b n) \<le> fst (Bolzano_bisect P a b (Suc n))" |
|
488 |
apply (rule allI) |
|
489 |
apply (induct_tac "n") |
|
490 |
apply (auto simp add: Bolzano_bisect_le Let_def split_def) |
|
491 |
done |
|
492 |
||
493 |
lemma Bolzano_bisect_Suc_le_snd: "a \<le> b ==> |
|
494 |
\<forall>n. snd(Bolzano_bisect P a b (Suc n)) \<le> snd (Bolzano_bisect P a b n)" |
|
495 |
apply (rule allI) |
|
496 |
apply (induct_tac "n") |
|
497 |
apply (auto simp add: Bolzano_bisect_le Let_def split_def) |
|
498 |
done |
|
499 |
||
500 |
lemma eq_divide_2_times_iff: "((x::real) = y / (2 * z)) = (2 * x = y/z)" |
|
501 |
apply (auto) |
|
502 |
apply (drule_tac f = "%u. (1/2) *u" in arg_cong) |
|
503 |
apply (simp) |
|
504 |
done |
|
505 |
||
506 |
lemma Bolzano_bisect_diff: |
|
507 |
"a \<le> b ==> |
|
508 |
snd(Bolzano_bisect P a b n) - fst(Bolzano_bisect P a b n) = |
|
509 |
(b-a) / (2 ^ n)" |
|
510 |
apply (induct "n") |
|
511 |
apply (auto simp add: eq_divide_2_times_iff add_divide_distrib Let_def split_def) |
|
512 |
done |
|
513 |
||
514 |
lemmas Bolzano_nest_unique = |
|
515 |
lemma_nest_unique |
|
516 |
[OF Bolzano_bisect_fst_le_Suc Bolzano_bisect_Suc_le_snd Bolzano_bisect_le] |
|
517 |
||
518 |
||
519 |
lemma not_P_Bolzano_bisect: |
|
520 |
assumes P: "!!a b c. [| P(a,b); P(b,c); a \<le> b; b \<le> c|] ==> P(a,c)" |
|
521 |
and notP: "~ P(a,b)" |
|
522 |
and le: "a \<le> b" |
|
523 |
shows "~ P(fst(Bolzano_bisect P a b n), snd(Bolzano_bisect P a b n))" |
|
524 |
proof (induct n) |
|
525 |
case 0 thus ?case by simp |
|
526 |
next |
|
527 |
case (Suc n) |
|
528 |
thus ?case |
|
529 |
by (auto simp del: surjective_pairing [symmetric] |
|
530 |
simp add: Let_def split_def Bolzano_bisect_le [OF le] |
|
531 |
P [of "fst (Bolzano_bisect P a b n)" _ "snd (Bolzano_bisect P a b n)"]) |
|
532 |
qed |
|
533 |
||
534 |
(*Now we re-package P_prem as a formula*) |
|
535 |
lemma not_P_Bolzano_bisect': |
|
536 |
"[| \<forall>a b c. P(a,b) & P(b,c) & a \<le> b & b \<le> c --> P(a,c); |
|
537 |
~ P(a,b); a \<le> b |] ==> |
|
538 |
\<forall>n. ~ P(fst(Bolzano_bisect P a b n), snd(Bolzano_bisect P a b n))" |
|
539 |
by (blast elim!: not_P_Bolzano_bisect [THEN [2] rev_notE]) |
|
540 |
||
541 |
||
542 |
||
543 |
lemma lemma_BOLZANO: |
|
544 |
"[| \<forall>a b c. P(a,b) & P(b,c) & a \<le> b & b \<le> c --> P(a,c); |
|
545 |
\<forall>x. \<exists>d::real. 0 < d & |
|
546 |
(\<forall>a b. a \<le> x & x \<le> b & (b-a) < d --> P(a,b)); |
|
547 |
a \<le> b |] |
|
548 |
==> P(a,b)" |
|
549 |
apply (rule Bolzano_nest_unique [where P1=P, THEN exE], assumption+) |
|
550 |
apply (rule LIMSEQ_minus_cancel) |
|
551 |
apply (simp (no_asm_simp) add: Bolzano_bisect_diff LIMSEQ_divide_realpow_zero) |
|
552 |
apply (rule ccontr) |
|
553 |
apply (drule not_P_Bolzano_bisect', assumption+) |
|
554 |
apply (rename_tac "l") |
|
555 |
apply (drule_tac x = l in spec, clarify) |
|
556 |
apply (simp add: LIMSEQ_def) |
|
557 |
apply (drule_tac P = "%r. 0<r --> ?Q r" and x = "d/2" in spec) |
|
558 |
apply (drule_tac P = "%r. 0<r --> ?Q r" and x = "d/2" in spec) |
|
559 |
apply (drule real_less_half_sum, auto) |
|
560 |
apply (drule_tac x = "fst (Bolzano_bisect P a b (no + noa))" in spec) |
|
561 |
apply (drule_tac x = "snd (Bolzano_bisect P a b (no + noa))" in spec) |
|
562 |
apply safe |
|
563 |
apply (simp_all (no_asm_simp)) |
|
564 |
apply (rule_tac y = "abs (fst (Bolzano_bisect P a b (no + noa)) - l) + abs (snd (Bolzano_bisect P a b (no + noa)) - l)" in order_le_less_trans) |
|
565 |
apply (simp (no_asm_simp) add: abs_if) |
|
566 |
apply (rule real_sum_of_halves [THEN subst]) |
|
567 |
apply (rule add_strict_mono) |
|
568 |
apply (simp_all add: diff_minus [symmetric]) |
|
569 |
done |
|
570 |
||
571 |
||
572 |
lemma lemma_BOLZANO2: "((\<forall>a b c. (a \<le> b & b \<le> c & P(a,b) & P(b,c)) --> P(a,c)) & |
|
573 |
(\<forall>x. \<exists>d::real. 0 < d & |
|
574 |
(\<forall>a b. a \<le> x & x \<le> b & (b-a) < d --> P(a,b)))) |
|
575 |
--> (\<forall>a b. a \<le> b --> P(a,b))" |
|
576 |
apply clarify |
|
577 |
apply (blast intro: lemma_BOLZANO) |
|
578 |
done |
|
579 |
||
580 |
||
581 |
subsection {* Intermediate Value Theorem *} |
|
582 |
||
583 |
text {*Prove Contrapositive by Bisection*} |
|
584 |
||
585 |
lemma IVT: "[| f(a::real) \<le> (y::real); y \<le> f(b); |
|
586 |
a \<le> b; |
|
587 |
(\<forall>x. a \<le> x & x \<le> b --> isCont f x) |] |
|
588 |
==> \<exists>x. a \<le> x & x \<le> b & f(x) = y" |
|
589 |
apply (rule contrapos_pp, assumption) |
|
590 |
apply (cut_tac P = "% (u,v) . a \<le> u & u \<le> v & v \<le> b --> ~ (f (u) \<le> y & y \<le> f (v))" in lemma_BOLZANO2) |
|
591 |
apply safe |
|
592 |
apply simp_all |
|
593 |
apply (simp add: isCont_iff LIM_def) |
|
594 |
apply (rule ccontr) |
|
595 |
apply (subgoal_tac "a \<le> x & x \<le> b") |
|
596 |
prefer 2 |
|
597 |
apply simp |
|
598 |
apply (drule_tac P = "%d. 0<d --> ?P d" and x = 1 in spec, arith) |
|
599 |
apply (drule_tac x = x in spec)+ |
|
600 |
apply simp |
|
601 |
apply (drule_tac P = "%r. ?P r --> (\<exists>s>0. ?Q r s) " and x = "\<bar>y - f x\<bar>" in spec) |
|
602 |
apply safe |
|
603 |
apply simp |
|
604 |
apply (drule_tac x = s in spec, clarify) |
|
605 |
apply (cut_tac x = "f x" and y = y in linorder_less_linear, safe) |
|
606 |
apply (drule_tac x = "ba-x" in spec) |
|
607 |
apply (simp_all add: abs_if) |
|
608 |
apply (drule_tac x = "aa-x" in spec) |
|
609 |
apply (case_tac "x \<le> aa", simp_all) |
|
610 |
done |
|
611 |
||
612 |
lemma IVT2: "[| f(b::real) \<le> (y::real); y \<le> f(a); |
|
613 |
a \<le> b; |
|
614 |
(\<forall>x. a \<le> x & x \<le> b --> isCont f x) |
|
615 |
|] ==> \<exists>x. a \<le> x & x \<le> b & f(x) = y" |
|
616 |
apply (subgoal_tac "- f a \<le> -y & -y \<le> - f b", clarify) |
|
617 |
apply (drule IVT [where f = "%x. - f x"], assumption) |
|
618 |
apply (auto intro: isCont_minus) |
|
619 |
done |
|
620 |
||
621 |
(*HOL style here: object-level formulations*) |
|
622 |
lemma IVT_objl: "(f(a::real) \<le> (y::real) & y \<le> f(b) & a \<le> b & |
|
623 |
(\<forall>x. a \<le> x & x \<le> b --> isCont f x)) |
|
624 |
--> (\<exists>x. a \<le> x & x \<le> b & f(x) = y)" |
|
625 |
apply (blast intro: IVT) |
|
626 |
done |
|
627 |
||
628 |
lemma IVT2_objl: "(f(b::real) \<le> (y::real) & y \<le> f(a) & a \<le> b & |
|
629 |
(\<forall>x. a \<le> x & x \<le> b --> isCont f x)) |
|
630 |
--> (\<exists>x. a \<le> x & x \<le> b & f(x) = y)" |
|
631 |
apply (blast intro: IVT2) |
|
632 |
done |
|
633 |
||
634 |
text{*By bisection, function continuous on closed interval is bounded above*} |
|
635 |
||
636 |
lemma isCont_bounded: |
|
637 |
"[| a \<le> b; \<forall>x. a \<le> x & x \<le> b --> isCont f x |] |
|
638 |
==> \<exists>M::real. \<forall>x::real. a \<le> x & x \<le> b --> f(x) \<le> M" |
|
639 |
apply (cut_tac P = "% (u,v) . a \<le> u & u \<le> v & v \<le> b --> (\<exists>M. \<forall>x. u \<le> x & x \<le> v --> f x \<le> M)" in lemma_BOLZANO2) |
|
640 |
apply safe |
|
641 |
apply simp_all |
|
642 |
apply (rename_tac x xa ya M Ma) |
|
643 |
apply (cut_tac x = M and y = Ma in linorder_linear, safe) |
|
644 |
apply (rule_tac x = Ma in exI, clarify) |
|
645 |
apply (cut_tac x = xb and y = xa in linorder_linear, force) |
|
646 |
apply (rule_tac x = M in exI, clarify) |
|
647 |
apply (cut_tac x = xb and y = xa in linorder_linear, force) |
|
648 |
apply (case_tac "a \<le> x & x \<le> b") |
|
649 |
apply (rule_tac [2] x = 1 in exI) |
|
650 |
prefer 2 apply force |
|
651 |
apply (simp add: LIM_def isCont_iff) |
|
652 |
apply (drule_tac x = x in spec, auto) |
|
653 |
apply (erule_tac V = "\<forall>M. \<exists>x. a \<le> x & x \<le> b & ~ f x \<le> M" in thin_rl) |
|
654 |
apply (drule_tac x = 1 in spec, auto) |
|
655 |
apply (rule_tac x = s in exI, clarify) |
|
656 |
apply (rule_tac x = "\<bar>f x\<bar> + 1" in exI, clarify) |
|
657 |
apply (drule_tac x = "xa-x" in spec) |
|
658 |
apply (auto simp add: abs_ge_self) |
|
659 |
done |
|
660 |
||
661 |
text{*Refine the above to existence of least upper bound*} |
|
662 |
||
663 |
lemma lemma_reals_complete: "((\<exists>x. x \<in> S) & (\<exists>y. isUb UNIV S (y::real))) --> |
|
664 |
(\<exists>t. isLub UNIV S t)" |
|
665 |
by (blast intro: reals_complete) |
|
666 |
||
667 |
lemma isCont_has_Ub: "[| a \<le> b; \<forall>x. a \<le> x & x \<le> b --> isCont f x |] |
|
668 |
==> \<exists>M::real. (\<forall>x::real. a \<le> x & x \<le> b --> f(x) \<le> M) & |
|
669 |
(\<forall>N. N < M --> (\<exists>x. a \<le> x & x \<le> b & N < f(x)))" |
|
670 |
apply (cut_tac S = "Collect (%y. \<exists>x. a \<le> x & x \<le> b & y = f x)" |
|
671 |
in lemma_reals_complete) |
|
672 |
apply auto |
|
673 |
apply (drule isCont_bounded, assumption) |
|
674 |
apply (auto simp add: isUb_def leastP_def isLub_def setge_def setle_def) |
|
675 |
apply (rule exI, auto) |
|
676 |
apply (auto dest!: spec simp add: linorder_not_less) |
|
677 |
done |
|
678 |
||
679 |
text{*Now show that it attains its upper bound*} |
|
680 |
||
681 |
lemma isCont_eq_Ub: |
|
682 |
assumes le: "a \<le> b" |
|
683 |
and con: "\<forall>x::real. a \<le> x & x \<le> b --> isCont f x" |
|
684 |
shows "\<exists>M::real. (\<forall>x. a \<le> x & x \<le> b --> f(x) \<le> M) & |
|
685 |
(\<exists>x. a \<le> x & x \<le> b & f(x) = M)" |
|
686 |
proof - |
|
687 |
from isCont_has_Ub [OF le con] |
|
688 |
obtain M where M1: "\<forall>x. a \<le> x \<and> x \<le> b \<longrightarrow> f x \<le> M" |
|
689 |
and M2: "!!N. N<M ==> \<exists>x. a \<le> x \<and> x \<le> b \<and> N < f x" by blast |
|
690 |
show ?thesis |
|
691 |
proof (intro exI, intro conjI) |
|
692 |
show " \<forall>x. a \<le> x \<and> x \<le> b \<longrightarrow> f x \<le> M" by (rule M1) |
|
693 |
show "\<exists>x. a \<le> x \<and> x \<le> b \<and> f x = M" |
|
694 |
proof (rule ccontr) |
|
695 |
assume "\<not> (\<exists>x. a \<le> x \<and> x \<le> b \<and> f x = M)" |
|
696 |
with M1 have M3: "\<forall>x. a \<le> x & x \<le> b --> f x < M" |
|
697 |
by (fastsimp simp add: linorder_not_le [symmetric]) |
|
698 |
hence "\<forall>x. a \<le> x & x \<le> b --> isCont (%x. inverse (M - f x)) x" |
|
699 |
by (auto simp add: isCont_inverse isCont_diff con) |
|
700 |
from isCont_bounded [OF le this] |
|
701 |
obtain k where k: "!!x. a \<le> x & x \<le> b --> inverse (M - f x) \<le> k" by auto |
|
702 |
have Minv: "!!x. a \<le> x & x \<le> b --> 0 < inverse (M - f (x))" |
|
703 |
by (simp add: M3 compare_rls) |
|
704 |
have "!!x. a \<le> x & x \<le> b --> inverse (M - f x) < k+1" using k |
|
705 |
by (auto intro: order_le_less_trans [of _ k]) |
|
706 |
with Minv |
|
707 |
have "!!x. a \<le> x & x \<le> b --> inverse(k+1) < inverse(inverse(M - f x))" |
|
708 |
by (intro strip less_imp_inverse_less, simp_all) |
|
709 |
hence invlt: "!!x. a \<le> x & x \<le> b --> inverse(k+1) < M - f x" |
|
710 |
by simp |
|
711 |
have "M - inverse (k+1) < M" using k [of a] Minv [of a] le |
|
712 |
by (simp, arith) |
|
713 |
from M2 [OF this] |
|
714 |
obtain x where ax: "a \<le> x & x \<le> b & M - inverse(k+1) < f x" .. |
|
715 |
thus False using invlt [of x] by force |
|
716 |
qed |
|
717 |
qed |
|
718 |
qed |
|
719 |
||
720 |
||
721 |
text{*Same theorem for lower bound*} |
|
722 |
||
723 |
lemma isCont_eq_Lb: "[| a \<le> b; \<forall>x. a \<le> x & x \<le> b --> isCont f x |] |
|
724 |
==> \<exists>M::real. (\<forall>x::real. a \<le> x & x \<le> b --> M \<le> f(x)) & |
|
725 |
(\<exists>x. a \<le> x & x \<le> b & f(x) = M)" |
|
726 |
apply (subgoal_tac "\<forall>x. a \<le> x & x \<le> b --> isCont (%x. - (f x)) x") |
|
727 |
prefer 2 apply (blast intro: isCont_minus) |
|
728 |
apply (drule_tac f = "(%x. - (f x))" in isCont_eq_Ub) |
|
729 |
apply safe |
|
730 |
apply auto |
|
731 |
done |
|
732 |
||
733 |
||
734 |
text{*Another version.*} |
|
735 |
||
736 |
lemma isCont_Lb_Ub: "[|a \<le> b; \<forall>x. a \<le> x & x \<le> b --> isCont f x |] |
|
737 |
==> \<exists>L M::real. (\<forall>x::real. a \<le> x & x \<le> b --> L \<le> f(x) & f(x) \<le> M) & |
|
738 |
(\<forall>y. L \<le> y & y \<le> M --> (\<exists>x. a \<le> x & x \<le> b & (f(x) = y)))" |
|
739 |
apply (frule isCont_eq_Lb) |
|
740 |
apply (frule_tac [2] isCont_eq_Ub) |
|
741 |
apply (assumption+, safe) |
|
742 |
apply (rule_tac x = "f x" in exI) |
|
743 |
apply (rule_tac x = "f xa" in exI, simp, safe) |
|
744 |
apply (cut_tac x = x and y = xa in linorder_linear, safe) |
|
745 |
apply (cut_tac f = f and a = x and b = xa and y = y in IVT_objl) |
|
746 |
apply (cut_tac [2] f = f and a = xa and b = x and y = y in IVT2_objl, safe) |
|
747 |
apply (rule_tac [2] x = xb in exI) |
|
748 |
apply (rule_tac [4] x = xb in exI, simp_all) |
|
749 |
done |
|
750 |
||
751 |
||
752 |
text{*If @{term "0 < f'(x)"} then @{term x} is Locally Strictly Increasing At The Right*} |
|
753 |
||
754 |
lemma DERIV_left_inc: |
|
755 |
fixes f :: "real => real" |
|
756 |
assumes der: "DERIV f x :> l" |
|
757 |
and l: "0 < l" |
|
758 |
shows "\<exists>d > 0. \<forall>h > 0. h < d --> f(x) < f(x + h)" |
|
759 |
proof - |
|
760 |
from l der [THEN DERIV_D, THEN LIM_D [where r = "l"]] |
|
761 |
have "\<exists>s > 0. (\<forall>z. z \<noteq> 0 \<and> \<bar>z\<bar> < s \<longrightarrow> \<bar>(f(x+z) - f x) / z - l\<bar> < l)" |
|
762 |
by (simp add: diff_minus) |
|
763 |
then obtain s |
|
764 |
where s: "0 < s" |
|
765 |
and all: "!!z. z \<noteq> 0 \<and> \<bar>z\<bar> < s \<longrightarrow> \<bar>(f(x+z) - f x) / z - l\<bar> < l" |
|
766 |
by auto |
|
767 |
thus ?thesis |
|
768 |
proof (intro exI conjI strip) |
|
769 |
show "0<s" . |
|
770 |
fix h::real |
|
771 |
assume "0 < h" "h < s" |
|
772 |
with all [of h] show "f x < f (x+h)" |
|
773 |
proof (simp add: abs_if pos_less_divide_eq diff_minus [symmetric] |
|
774 |
split add: split_if_asm) |
|
775 |
assume "~ (f (x+h) - f x) / h < l" and h: "0 < h" |
|
776 |
with l |
|
777 |
have "0 < (f (x+h) - f x) / h" by arith |
|
778 |
thus "f x < f (x+h)" |
|
779 |
by (simp add: pos_less_divide_eq h) |
|
780 |
qed |
|
781 |
qed |
|
782 |
qed |
|
783 |
||
784 |
lemma DERIV_left_dec: |
|
785 |
fixes f :: "real => real" |
|
786 |
assumes der: "DERIV f x :> l" |
|
787 |
and l: "l < 0" |
|
788 |
shows "\<exists>d > 0. \<forall>h > 0. h < d --> f(x) < f(x-h)" |
|
789 |
proof - |
|
790 |
from l der [THEN DERIV_D, THEN LIM_D [where r = "-l"]] |
|
791 |
have "\<exists>s > 0. (\<forall>z. z \<noteq> 0 \<and> \<bar>z\<bar> < s \<longrightarrow> \<bar>(f(x+z) - f x) / z - l\<bar> < -l)" |
|
792 |
by (simp add: diff_minus) |
|
793 |
then obtain s |
|
794 |
where s: "0 < s" |
|
795 |
and all: "!!z. z \<noteq> 0 \<and> \<bar>z\<bar> < s \<longrightarrow> \<bar>(f(x+z) - f x) / z - l\<bar> < -l" |
|
796 |
by auto |
|
797 |
thus ?thesis |
|
798 |
proof (intro exI conjI strip) |
|
799 |
show "0<s" . |
|
800 |
fix h::real |
|
801 |
assume "0 < h" "h < s" |
|
802 |
with all [of "-h"] show "f x < f (x-h)" |
|
803 |
proof (simp add: abs_if pos_less_divide_eq diff_minus [symmetric] |
|
804 |
split add: split_if_asm) |
|
805 |
assume " - ((f (x-h) - f x) / h) < l" and h: "0 < h" |
|
806 |
with l |
|
807 |
have "0 < (f (x-h) - f x) / h" by arith |
|
808 |
thus "f x < f (x-h)" |
|
809 |
by (simp add: pos_less_divide_eq h) |
|
810 |
qed |
|
811 |
qed |
|
812 |
qed |
|
813 |
||
814 |
lemma DERIV_local_max: |
|
815 |
fixes f :: "real => real" |
|
816 |
assumes der: "DERIV f x :> l" |
|
817 |
and d: "0 < d" |
|
818 |
and le: "\<forall>y. \<bar>x-y\<bar> < d --> f(y) \<le> f(x)" |
|
819 |
shows "l = 0" |
|
820 |
proof (cases rule: linorder_cases [of l 0]) |
|
821 |
case equal show ?thesis . |
|
822 |
next |
|
823 |
case less |
|
824 |
from DERIV_left_dec [OF der less] |
|
825 |
obtain d' where d': "0 < d'" |
|
826 |
and lt: "\<forall>h > 0. h < d' \<longrightarrow> f x < f (x-h)" by blast |
|
827 |
from real_lbound_gt_zero [OF d d'] |
|
828 |
obtain e where "0 < e \<and> e < d \<and> e < d'" .. |
|
829 |
with lt le [THEN spec [where x="x-e"]] |
|
830 |
show ?thesis by (auto simp add: abs_if) |
|
831 |
next |
|
832 |
case greater |
|
833 |
from DERIV_left_inc [OF der greater] |
|
834 |
obtain d' where d': "0 < d'" |
|
835 |
and lt: "\<forall>h > 0. h < d' \<longrightarrow> f x < f (x + h)" by blast |
|
836 |
from real_lbound_gt_zero [OF d d'] |
|
837 |
obtain e where "0 < e \<and> e < d \<and> e < d'" .. |
|
838 |
with lt le [THEN spec [where x="x+e"]] |
|
839 |
show ?thesis by (auto simp add: abs_if) |
|
840 |
qed |
|
841 |
||
842 |
||
843 |
text{*Similar theorem for a local minimum*} |
|
844 |
lemma DERIV_local_min: |
|
845 |
fixes f :: "real => real" |
|
846 |
shows "[| DERIV f x :> l; 0 < d; \<forall>y. \<bar>x-y\<bar> < d --> f(x) \<le> f(y) |] ==> l = 0" |
|
847 |
by (drule DERIV_minus [THEN DERIV_local_max], auto) |
|
848 |
||
849 |
||
850 |
text{*In particular, if a function is locally flat*} |
|
851 |
lemma DERIV_local_const: |
|
852 |
fixes f :: "real => real" |
|
853 |
shows "[| DERIV f x :> l; 0 < d; \<forall>y. \<bar>x-y\<bar> < d --> f(x) = f(y) |] ==> l = 0" |
|
854 |
by (auto dest!: DERIV_local_max) |
|
855 |
||
856 |
text{*Lemma about introducing open ball in open interval*} |
|
857 |
lemma lemma_interval_lt: |
|
858 |
"[| a < x; x < b |] |
|
859 |
==> \<exists>d::real. 0 < d & (\<forall>y. \<bar>x-y\<bar> < d --> a < y & y < b)" |
|
22998 | 860 |
apply (simp add: abs_less_iff) |
21164 | 861 |
apply (insert linorder_linear [of "x-a" "b-x"], safe) |
862 |
apply (rule_tac x = "x-a" in exI) |
|
863 |
apply (rule_tac [2] x = "b-x" in exI, auto) |
|
864 |
done |
|
865 |
||
866 |
lemma lemma_interval: "[| a < x; x < b |] ==> |
|
867 |
\<exists>d::real. 0 < d & (\<forall>y. \<bar>x-y\<bar> < d --> a \<le> y & y \<le> b)" |
|
868 |
apply (drule lemma_interval_lt, auto) |
|
869 |
apply (auto intro!: exI) |
|
870 |
done |
|
871 |
||
872 |
text{*Rolle's Theorem. |
|
873 |
If @{term f} is defined and continuous on the closed interval |
|
874 |
@{text "[a,b]"} and differentiable on the open interval @{text "(a,b)"}, |
|
875 |
and @{term "f(a) = f(b)"}, |
|
876 |
then there exists @{text "x0 \<in> (a,b)"} such that @{term "f'(x0) = 0"}*} |
|
877 |
theorem Rolle: |
|
878 |
assumes lt: "a < b" |
|
879 |
and eq: "f(a) = f(b)" |
|
880 |
and con: "\<forall>x. a \<le> x & x \<le> b --> isCont f x" |
|
881 |
and dif [rule_format]: "\<forall>x. a < x & x < b --> f differentiable x" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
882 |
shows "\<exists>z::real. a < z & z < b & DERIV f z :> 0" |
21164 | 883 |
proof - |
884 |
have le: "a \<le> b" using lt by simp |
|
885 |
from isCont_eq_Ub [OF le con] |
|
886 |
obtain x where x_max: "\<forall>z. a \<le> z \<and> z \<le> b \<longrightarrow> f z \<le> f x" |
|
887 |
and alex: "a \<le> x" and xleb: "x \<le> b" |
|
888 |
by blast |
|
889 |
from isCont_eq_Lb [OF le con] |
|
890 |
obtain x' where x'_min: "\<forall>z. a \<le> z \<and> z \<le> b \<longrightarrow> f x' \<le> f z" |
|
891 |
and alex': "a \<le> x'" and x'leb: "x' \<le> b" |
|
892 |
by blast |
|
893 |
show ?thesis |
|
894 |
proof cases |
|
895 |
assume axb: "a < x & x < b" |
|
896 |
--{*@{term f} attains its maximum within the interval*} |
|
897 |
hence ax: "a<x" and xb: "x<b" by auto |
|
898 |
from lemma_interval [OF ax xb] |
|
899 |
obtain d where d: "0<d" and bound: "\<forall>y. \<bar>x-y\<bar> < d \<longrightarrow> a \<le> y \<and> y \<le> b" |
|
900 |
by blast |
|
901 |
hence bound': "\<forall>y. \<bar>x-y\<bar> < d \<longrightarrow> f y \<le> f x" using x_max |
|
902 |
by blast |
|
903 |
from differentiableD [OF dif [OF axb]] |
|
904 |
obtain l where der: "DERIV f x :> l" .. |
|
905 |
have "l=0" by (rule DERIV_local_max [OF der d bound']) |
|
906 |
--{*the derivative at a local maximum is zero*} |
|
907 |
thus ?thesis using ax xb der by auto |
|
908 |
next |
|
909 |
assume notaxb: "~ (a < x & x < b)" |
|
910 |
hence xeqab: "x=a | x=b" using alex xleb by arith |
|
911 |
hence fb_eq_fx: "f b = f x" by (auto simp add: eq) |
|
912 |
show ?thesis |
|
913 |
proof cases |
|
914 |
assume ax'b: "a < x' & x' < b" |
|
915 |
--{*@{term f} attains its minimum within the interval*} |
|
916 |
hence ax': "a<x'" and x'b: "x'<b" by auto |
|
917 |
from lemma_interval [OF ax' x'b] |
|
918 |
obtain d where d: "0<d" and bound: "\<forall>y. \<bar>x'-y\<bar> < d \<longrightarrow> a \<le> y \<and> y \<le> b" |
|
919 |
by blast |
|
920 |
hence bound': "\<forall>y. \<bar>x'-y\<bar> < d \<longrightarrow> f x' \<le> f y" using x'_min |
|
921 |
by blast |
|
922 |
from differentiableD [OF dif [OF ax'b]] |
|
923 |
obtain l where der: "DERIV f x' :> l" .. |
|
924 |
have "l=0" by (rule DERIV_local_min [OF der d bound']) |
|
925 |
--{*the derivative at a local minimum is zero*} |
|
926 |
thus ?thesis using ax' x'b der by auto |
|
927 |
next |
|
928 |
assume notax'b: "~ (a < x' & x' < b)" |
|
929 |
--{*@{term f} is constant througout the interval*} |
|
930 |
hence x'eqab: "x'=a | x'=b" using alex' x'leb by arith |
|
931 |
hence fb_eq_fx': "f b = f x'" by (auto simp add: eq) |
|
932 |
from dense [OF lt] |
|
933 |
obtain r where ar: "a < r" and rb: "r < b" by blast |
|
934 |
from lemma_interval [OF ar rb] |
|
935 |
obtain d where d: "0<d" and bound: "\<forall>y. \<bar>r-y\<bar> < d \<longrightarrow> a \<le> y \<and> y \<le> b" |
|
936 |
by blast |
|
937 |
have eq_fb: "\<forall>z. a \<le> z --> z \<le> b --> f z = f b" |
|
938 |
proof (clarify) |
|
939 |
fix z::real |
|
940 |
assume az: "a \<le> z" and zb: "z \<le> b" |
|
941 |
show "f z = f b" |
|
942 |
proof (rule order_antisym) |
|
943 |
show "f z \<le> f b" by (simp add: fb_eq_fx x_max az zb) |
|
944 |
show "f b \<le> f z" by (simp add: fb_eq_fx' x'_min az zb) |
|
945 |
qed |
|
946 |
qed |
|
947 |
have bound': "\<forall>y. \<bar>r-y\<bar> < d \<longrightarrow> f r = f y" |
|
948 |
proof (intro strip) |
|
949 |
fix y::real |
|
950 |
assume lt: "\<bar>r-y\<bar> < d" |
|
951 |
hence "f y = f b" by (simp add: eq_fb bound) |
|
952 |
thus "f r = f y" by (simp add: eq_fb ar rb order_less_imp_le) |
|
953 |
qed |
|
954 |
from differentiableD [OF dif [OF conjI [OF ar rb]]] |
|
955 |
obtain l where der: "DERIV f r :> l" .. |
|
956 |
have "l=0" by (rule DERIV_local_const [OF der d bound']) |
|
957 |
--{*the derivative of a constant function is zero*} |
|
958 |
thus ?thesis using ar rb der by auto |
|
959 |
qed |
|
960 |
qed |
|
961 |
qed |
|
962 |
||
963 |
||
964 |
subsection{*Mean Value Theorem*} |
|
965 |
||
966 |
lemma lemma_MVT: |
|
967 |
"f a - (f b - f a)/(b-a) * a = f b - (f b - f a)/(b-a) * (b::real)" |
|
968 |
proof cases |
|
969 |
assume "a=b" thus ?thesis by simp |
|
970 |
next |
|
971 |
assume "a\<noteq>b" |
|
972 |
hence ba: "b-a \<noteq> 0" by arith |
|
973 |
show ?thesis |
|
974 |
by (rule real_mult_left_cancel [OF ba, THEN iffD1], |
|
975 |
simp add: right_diff_distrib, |
|
976 |
simp add: left_diff_distrib) |
|
977 |
qed |
|
978 |
||
979 |
theorem MVT: |
|
980 |
assumes lt: "a < b" |
|
981 |
and con: "\<forall>x. a \<le> x & x \<le> b --> isCont f x" |
|
982 |
and dif [rule_format]: "\<forall>x. a < x & x < b --> f differentiable x" |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
983 |
shows "\<exists>l z::real. a < z & z < b & DERIV f z :> l & |
21164 | 984 |
(f(b) - f(a) = (b-a) * l)" |
985 |
proof - |
|
986 |
let ?F = "%x. f x - ((f b - f a) / (b-a)) * x" |
|
987 |
have contF: "\<forall>x. a \<le> x \<and> x \<le> b \<longrightarrow> isCont ?F x" using con |
|
988 |
by (fast intro: isCont_diff isCont_const isCont_mult isCont_Id) |
|
989 |
have difF: "\<forall>x. a < x \<and> x < b \<longrightarrow> ?F differentiable x" |
|
990 |
proof (clarify) |
|
991 |
fix x::real |
|
992 |
assume ax: "a < x" and xb: "x < b" |
|
993 |
from differentiableD [OF dif [OF conjI [OF ax xb]]] |
|
994 |
obtain l where der: "DERIV f x :> l" .. |
|
995 |
show "?F differentiable x" |
|
996 |
by (rule differentiableI [where D = "l - (f b - f a)/(b-a)"], |
|
997 |
blast intro: DERIV_diff DERIV_cmult_Id der) |
|
998 |
qed |
|
999 |
from Rolle [where f = ?F, OF lt lemma_MVT contF difF] |
|
1000 |
obtain z where az: "a < z" and zb: "z < b" and der: "DERIV ?F z :> 0" |
|
1001 |
by blast |
|
1002 |
have "DERIV (%x. ((f b - f a)/(b-a)) * x) z :> (f b - f a)/(b-a)" |
|
1003 |
by (rule DERIV_cmult_Id) |
|
1004 |
hence derF: "DERIV (\<lambda>x. ?F x + (f b - f a) / (b - a) * x) z |
|
1005 |
:> 0 + (f b - f a) / (b - a)" |
|
1006 |
by (rule DERIV_add [OF der]) |
|
1007 |
show ?thesis |
|
1008 |
proof (intro exI conjI) |
|
1009 |
show "a < z" . |
|
1010 |
show "z < b" . |
|
1011 |
show "f b - f a = (b - a) * ((f b - f a)/(b-a))" by (simp) |
|
1012 |
show "DERIV f z :> ((f b - f a)/(b-a))" using derF by simp |
|
1013 |
qed |
|
1014 |
qed |
|
1015 |
||
1016 |
||
1017 |
text{*A function is constant if its derivative is 0 over an interval.*} |
|
1018 |
||
1019 |
lemma DERIV_isconst_end: |
|
1020 |
fixes f :: "real => real" |
|
1021 |
shows "[| a < b; |
|
1022 |
\<forall>x. a \<le> x & x \<le> b --> isCont f x; |
|
1023 |
\<forall>x. a < x & x < b --> DERIV f x :> 0 |] |
|
1024 |
==> f b = f a" |
|
1025 |
apply (drule MVT, assumption) |
|
1026 |
apply (blast intro: differentiableI) |
|
1027 |
apply (auto dest!: DERIV_unique simp add: diff_eq_eq) |
|
1028 |
done |
|
1029 |
||
1030 |
lemma DERIV_isconst1: |
|
1031 |
fixes f :: "real => real" |
|
1032 |
shows "[| a < b; |
|
1033 |
\<forall>x. a \<le> x & x \<le> b --> isCont f x; |
|
1034 |
\<forall>x. a < x & x < b --> DERIV f x :> 0 |] |
|
1035 |
==> \<forall>x. a \<le> x & x \<le> b --> f x = f a" |
|
1036 |
apply safe |
|
1037 |
apply (drule_tac x = a in order_le_imp_less_or_eq, safe) |
|
1038 |
apply (drule_tac b = x in DERIV_isconst_end, auto) |
|
1039 |
done |
|
1040 |
||
1041 |
lemma DERIV_isconst2: |
|
1042 |
fixes f :: "real => real" |
|
1043 |
shows "[| a < b; |
|
1044 |
\<forall>x. a \<le> x & x \<le> b --> isCont f x; |
|
1045 |
\<forall>x. a < x & x < b --> DERIV f x :> 0; |
|
1046 |
a \<le> x; x \<le> b |] |
|
1047 |
==> f x = f a" |
|
1048 |
apply (blast dest: DERIV_isconst1) |
|
1049 |
done |
|
1050 |
||
1051 |
lemma DERIV_isconst_all: |
|
1052 |
fixes f :: "real => real" |
|
1053 |
shows "\<forall>x. DERIV f x :> 0 ==> f(x) = f(y)" |
|
1054 |
apply (rule linorder_cases [of x y]) |
|
1055 |
apply (blast intro: sym DERIV_isCont DERIV_isconst_end)+ |
|
1056 |
done |
|
1057 |
||
1058 |
lemma DERIV_const_ratio_const: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
1059 |
fixes f :: "real => real" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
1060 |
shows "[|a \<noteq> b; \<forall>x. DERIV f x :> k |] ==> (f(b) - f(a)) = (b-a) * k" |
21164 | 1061 |
apply (rule linorder_cases [of a b], auto) |
1062 |
apply (drule_tac [!] f = f in MVT) |
|
1063 |
apply (auto dest: DERIV_isCont DERIV_unique simp add: differentiable_def) |
|
1064 |
apply (auto dest: DERIV_unique simp add: left_distrib diff_minus) |
|
1065 |
done |
|
1066 |
||
1067 |
lemma DERIV_const_ratio_const2: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
1068 |
fixes f :: "real => real" |
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
1069 |
shows "[|a \<noteq> b; \<forall>x. DERIV f x :> k |] ==> (f(b) - f(a))/(b-a) = k" |
21164 | 1070 |
apply (rule_tac c1 = "b-a" in real_mult_right_cancel [THEN iffD1]) |
1071 |
apply (auto dest!: DERIV_const_ratio_const simp add: mult_assoc) |
|
1072 |
done |
|
1073 |
||
1074 |
lemma real_average_minus_first [simp]: "((a + b) /2 - a) = (b-a)/(2::real)" |
|
1075 |
by (simp) |
|
1076 |
||
1077 |
lemma real_average_minus_second [simp]: "((b + a)/2 - a) = (b-a)/(2::real)" |
|
1078 |
by (simp) |
|
1079 |
||
1080 |
text{*Gallileo's "trick": average velocity = av. of end velocities*} |
|
1081 |
||
1082 |
lemma DERIV_const_average: |
|
1083 |
fixes v :: "real => real" |
|
1084 |
assumes neq: "a \<noteq> (b::real)" |
|
1085 |
and der: "\<forall>x. DERIV v x :> k" |
|
1086 |
shows "v ((a + b)/2) = (v a + v b)/2" |
|
1087 |
proof (cases rule: linorder_cases [of a b]) |
|
1088 |
case equal with neq show ?thesis by simp |
|
1089 |
next |
|
1090 |
case less |
|
1091 |
have "(v b - v a) / (b - a) = k" |
|
1092 |
by (rule DERIV_const_ratio_const2 [OF neq der]) |
|
1093 |
hence "(b-a) * ((v b - v a) / (b-a)) = (b-a) * k" by simp |
|
1094 |
moreover have "(v ((a + b) / 2) - v a) / ((a + b) / 2 - a) = k" |
|
1095 |
by (rule DERIV_const_ratio_const2 [OF _ der], simp add: neq) |
|
1096 |
ultimately show ?thesis using neq by force |
|
1097 |
next |
|
1098 |
case greater |
|
1099 |
have "(v b - v a) / (b - a) = k" |
|
1100 |
by (rule DERIV_const_ratio_const2 [OF neq der]) |
|
1101 |
hence "(b-a) * ((v b - v a) / (b-a)) = (b-a) * k" by simp |
|
1102 |
moreover have " (v ((b + a) / 2) - v a) / ((b + a) / 2 - a) = k" |
|
1103 |
by (rule DERIV_const_ratio_const2 [OF _ der], simp add: neq) |
|
1104 |
ultimately show ?thesis using neq by (force simp add: add_commute) |
|
1105 |
qed |
|
1106 |
||
1107 |
||
1108 |
text{*Dull lemma: an continuous injection on an interval must have a |
|
1109 |
strict maximum at an end point, not in the middle.*} |
|
1110 |
||
1111 |
lemma lemma_isCont_inj: |
|
1112 |
fixes f :: "real \<Rightarrow> real" |
|
1113 |
assumes d: "0 < d" |
|
1114 |
and inj [rule_format]: "\<forall>z. \<bar>z-x\<bar> \<le> d --> g(f z) = z" |
|
1115 |
and cont: "\<forall>z. \<bar>z-x\<bar> \<le> d --> isCont f z" |
|
1116 |
shows "\<exists>z. \<bar>z-x\<bar> \<le> d & f x < f z" |
|
1117 |
proof (rule ccontr) |
|
1118 |
assume "~ (\<exists>z. \<bar>z-x\<bar> \<le> d & f x < f z)" |
|
1119 |
hence all [rule_format]: "\<forall>z. \<bar>z - x\<bar> \<le> d --> f z \<le> f x" by auto |
|
1120 |
show False |
|
1121 |
proof (cases rule: linorder_le_cases [of "f(x-d)" "f(x+d)"]) |
|
1122 |
case le |
|
1123 |
from d cont all [of "x+d"] |
|
1124 |
have flef: "f(x+d) \<le> f x" |
|
1125 |
and xlex: "x - d \<le> x" |
|
1126 |
and cont': "\<forall>z. x - d \<le> z \<and> z \<le> x \<longrightarrow> isCont f z" |
|
1127 |
by (auto simp add: abs_if) |
|
1128 |
from IVT [OF le flef xlex cont'] |
|
1129 |
obtain x' where "x-d \<le> x'" "x' \<le> x" "f x' = f(x+d)" by blast |
|
1130 |
moreover |
|
1131 |
hence "g(f x') = g (f(x+d))" by simp |
|
1132 |
ultimately show False using d inj [of x'] inj [of "x+d"] |
|
22998 | 1133 |
by (simp add: abs_le_iff) |
21164 | 1134 |
next |
1135 |
case ge |
|
1136 |
from d cont all [of "x-d"] |
|
1137 |
have flef: "f(x-d) \<le> f x" |
|
1138 |
and xlex: "x \<le> x+d" |
|
1139 |
and cont': "\<forall>z. x \<le> z \<and> z \<le> x+d \<longrightarrow> isCont f z" |
|
1140 |
by (auto simp add: abs_if) |
|
1141 |
from IVT2 [OF ge flef xlex cont'] |
|
1142 |
obtain x' where "x \<le> x'" "x' \<le> x+d" "f x' = f(x-d)" by blast |
|
1143 |
moreover |
|
1144 |
hence "g(f x') = g (f(x-d))" by simp |
|
1145 |
ultimately show False using d inj [of x'] inj [of "x-d"] |
|
22998 | 1146 |
by (simp add: abs_le_iff) |
21164 | 1147 |
qed |
1148 |
qed |
|
1149 |
||
1150 |
||
1151 |
text{*Similar version for lower bound.*} |
|
1152 |
||
1153 |
lemma lemma_isCont_inj2: |
|
1154 |
fixes f g :: "real \<Rightarrow> real" |
|
1155 |
shows "[|0 < d; \<forall>z. \<bar>z-x\<bar> \<le> d --> g(f z) = z; |
|
1156 |
\<forall>z. \<bar>z-x\<bar> \<le> d --> isCont f z |] |
|
1157 |
==> \<exists>z. \<bar>z-x\<bar> \<le> d & f z < f x" |
|
1158 |
apply (insert lemma_isCont_inj |
|
1159 |
[where f = "%x. - f x" and g = "%y. g(-y)" and x = x and d = d]) |
|
1160 |
apply (simp add: isCont_minus linorder_not_le) |
|
1161 |
done |
|
1162 |
||
1163 |
text{*Show there's an interval surrounding @{term "f(x)"} in |
|
1164 |
@{text "f[[x - d, x + d]]"} .*} |
|
1165 |
||
1166 |
lemma isCont_inj_range: |
|
1167 |
fixes f :: "real \<Rightarrow> real" |
|
1168 |
assumes d: "0 < d" |
|
1169 |
and inj: "\<forall>z. \<bar>z-x\<bar> \<le> d --> g(f z) = z" |
|
1170 |
and cont: "\<forall>z. \<bar>z-x\<bar> \<le> d --> isCont f z" |
|
1171 |
shows "\<exists>e>0. \<forall>y. \<bar>y - f x\<bar> \<le> e --> (\<exists>z. \<bar>z-x\<bar> \<le> d & f z = y)" |
|
1172 |
proof - |
|
1173 |
have "x-d \<le> x+d" "\<forall>z. x-d \<le> z \<and> z \<le> x+d \<longrightarrow> isCont f z" using cont d |
|
22998 | 1174 |
by (auto simp add: abs_le_iff) |
21164 | 1175 |
from isCont_Lb_Ub [OF this] |
1176 |
obtain L M |
|
1177 |
where all1 [rule_format]: "\<forall>z. x-d \<le> z \<and> z \<le> x+d \<longrightarrow> L \<le> f z \<and> f z \<le> M" |
|
1178 |
and all2 [rule_format]: |
|
1179 |
"\<forall>y. L \<le> y \<and> y \<le> M \<longrightarrow> (\<exists>z. x-d \<le> z \<and> z \<le> x+d \<and> f z = y)" |
|
1180 |
by auto |
|
1181 |
with d have "L \<le> f x & f x \<le> M" by simp |
|
1182 |
moreover have "L \<noteq> f x" |
|
1183 |
proof - |
|
1184 |
from lemma_isCont_inj2 [OF d inj cont] |
|
1185 |
obtain u where "\<bar>u - x\<bar> \<le> d" "f u < f x" by auto |
|
1186 |
thus ?thesis using all1 [of u] by arith |
|
1187 |
qed |
|
1188 |
moreover have "f x \<noteq> M" |
|
1189 |
proof - |
|
1190 |
from lemma_isCont_inj [OF d inj cont] |
|
1191 |
obtain u where "\<bar>u - x\<bar> \<le> d" "f x < f u" by auto |
|
1192 |
thus ?thesis using all1 [of u] by arith |
|
1193 |
qed |
|
1194 |
ultimately have "L < f x & f x < M" by arith |
|
1195 |
hence "0 < f x - L" "0 < M - f x" by arith+ |
|
1196 |
from real_lbound_gt_zero [OF this] |
|
1197 |
obtain e where e: "0 < e" "e < f x - L" "e < M - f x" by auto |
|
1198 |
thus ?thesis |
|
1199 |
proof (intro exI conjI) |
|
1200 |
show "0<e" . |
|
1201 |
show "\<forall>y. \<bar>y - f x\<bar> \<le> e \<longrightarrow> (\<exists>z. \<bar>z - x\<bar> \<le> d \<and> f z = y)" |
|
1202 |
proof (intro strip) |
|
1203 |
fix y::real |
|
1204 |
assume "\<bar>y - f x\<bar> \<le> e" |
|
1205 |
with e have "L \<le> y \<and> y \<le> M" by arith |
|
1206 |
from all2 [OF this] |
|
1207 |
obtain z where "x - d \<le> z" "z \<le> x + d" "f z = y" by blast |
|
1208 |
thus "\<exists>z. \<bar>z - x\<bar> \<le> d \<and> f z = y" |
|
22998 | 1209 |
by (force simp add: abs_le_iff) |
21164 | 1210 |
qed |
1211 |
qed |
|
1212 |
qed |
|
1213 |
||
1214 |
||
1215 |
text{*Continuity of inverse function*} |
|
1216 |
||
1217 |
lemma isCont_inverse_function: |
|
1218 |
fixes f g :: "real \<Rightarrow> real" |
|
1219 |
assumes d: "0 < d" |
|
1220 |
and inj: "\<forall>z. \<bar>z-x\<bar> \<le> d --> g(f z) = z" |
|
1221 |
and cont: "\<forall>z. \<bar>z-x\<bar> \<le> d --> isCont f z" |
|
1222 |
shows "isCont g (f x)" |
|
1223 |
proof (simp add: isCont_iff LIM_eq) |
|
1224 |
show "\<forall>r. 0 < r \<longrightarrow> |
|
1225 |
(\<exists>s>0. \<forall>z. z\<noteq>0 \<and> \<bar>z\<bar> < s \<longrightarrow> \<bar>g(f x + z) - g(f x)\<bar> < r)" |
|
1226 |
proof (intro strip) |
|
1227 |
fix r::real |
|
1228 |
assume r: "0<r" |
|
1229 |
from real_lbound_gt_zero [OF r d] |
|
1230 |
obtain e where e: "0 < e" and e_lt: "e < r \<and> e < d" by blast |
|
1231 |
with inj cont |
|
1232 |
have e_simps: "\<forall>z. \<bar>z-x\<bar> \<le> e --> g (f z) = z" |
|
1233 |
"\<forall>z. \<bar>z-x\<bar> \<le> e --> isCont f z" by auto |
|
1234 |
from isCont_inj_range [OF e this] |
|
1235 |
obtain e' where e': "0 < e'" |
|
1236 |
and all: "\<forall>y. \<bar>y - f x\<bar> \<le> e' \<longrightarrow> (\<exists>z. \<bar>z - x\<bar> \<le> e \<and> f z = y)" |
|
1237 |
by blast |
|
1238 |
show "\<exists>s>0. \<forall>z. z\<noteq>0 \<and> \<bar>z\<bar> < s \<longrightarrow> \<bar>g(f x + z) - g(f x)\<bar> < r" |
|
1239 |
proof (intro exI conjI) |
|
1240 |
show "0<e'" . |
|
1241 |
show "\<forall>z. z \<noteq> 0 \<and> \<bar>z\<bar> < e' \<longrightarrow> \<bar>g (f x + z) - g (f x)\<bar> < r" |
|
1242 |
proof (intro strip) |
|
1243 |
fix z::real |
|
1244 |
assume z: "z \<noteq> 0 \<and> \<bar>z\<bar> < e'" |
|
1245 |
with e e_lt e_simps all [rule_format, of "f x + z"] |
|
1246 |
show "\<bar>g (f x + z) - g (f x)\<bar> < r" by force |
|
1247 |
qed |
|
1248 |
qed |
|
1249 |
qed |
|
1250 |
qed |
|
1251 |
||
1252 |
theorem GMVT: |
|
21784
e76faa6e65fd
changed (ns)deriv to take functions of type 'a::real_normed_field => 'a
huffman
parents:
21404
diff
changeset
|
1253 |
fixes a b :: real |
21164 | 1254 |
assumes alb: "a < b" |
1255 |
and fc: "\<forall>x. a \<le> x \<and> x \<le> b \<longrightarrow> isCont f x" |
|
1256 |
and fd: "\<forall>x. a < x \<and> x < b \<longrightarrow> f differentiable x" |
|
1257 |
and gc: "\<forall>x. a \<le> x \<and> x \<le> b \<longrightarrow> isCont g x" |
|
1258 |
and gd: "\<forall>x. a < x \<and> x < b \<longrightarrow> g differentiable x" |
|
1259 |
shows "\<exists>g'c f'c c. DERIV g c :> g'c \<and> DERIV f c :> f'c \<and> a < c \<and> c < b \<and> ((f b - f a) * g'c) = ((g b - g a) * f'c)" |
|
1260 |
proof - |
|
1261 |
let ?h = "\<lambda>x. (f b - f a)*(g x) - (g b - g a)*(f x)" |
|
1262 |
from prems have "a < b" by simp |
|
1263 |
moreover have "\<forall>x. a \<le> x \<and> x \<le> b \<longrightarrow> isCont ?h x" |
|
1264 |
proof - |
|
1265 |
have "\<forall>x. a <= x \<and> x <= b \<longrightarrow> isCont (\<lambda>x. f b - f a) x" by simp |
|
1266 |
with gc have "\<forall>x. a <= x \<and> x <= b \<longrightarrow> isCont (\<lambda>x. (f b - f a) * g x) x" |
|
1267 |
by (auto intro: isCont_mult) |
|
1268 |
moreover |
|
1269 |
have "\<forall>x. a <= x \<and> x <= b \<longrightarrow> isCont (\<lambda>x. g b - g a) x" by simp |
|
1270 |
with fc have "\<forall>x. a <= x \<and> x <= b \<longrightarrow> isCont (\<lambda>x. (g b - g a) * f x) x" |
|
1271 |
by (auto intro: isCont_mult) |
|
1272 |
ultimately show ?thesis |
|
1273 |
by (fastsimp intro: isCont_diff) |
|
1274 |
qed |
|
1275 |
moreover |
|
1276 |
have "\<forall>x. a < x \<and> x < b \<longrightarrow> ?h differentiable x" |
|
1277 |
proof - |
|
1278 |
have "\<forall>x. a < x \<and> x < b \<longrightarrow> (\<lambda>x. f b - f a) differentiable x" by (simp add: differentiable_const) |
|
1279 |
with gd have "\<forall>x. a < x \<and> x < b \<longrightarrow> (\<lambda>x. (f b - f a) * g x) differentiable x" by (simp add: differentiable_mult) |
|
1280 |
moreover |
|
1281 |
have "\<forall>x. a < x \<and> x < b \<longrightarrow> (\<lambda>x. g b - g a) differentiable x" by (simp add: differentiable_const) |
|
1282 |
with fd have "\<forall>x. a < x \<and> x < b \<longrightarrow> (\<lambda>x. (g b - g a) * f x) differentiable x" by (simp add: differentiable_mult) |
|
1283 |
ultimately show ?thesis by (simp add: differentiable_diff) |
|
1284 |
qed |
|
1285 |
ultimately have "\<exists>l z. a < z \<and> z < b \<and> DERIV ?h z :> l \<and> ?h b - ?h a = (b - a) * l" by (rule MVT) |
|
1286 |
then obtain l where ldef: "\<exists>z. a < z \<and> z < b \<and> DERIV ?h z :> l \<and> ?h b - ?h a = (b - a) * l" .. |
|
1287 |
then obtain c where cdef: "a < c \<and> c < b \<and> DERIV ?h c :> l \<and> ?h b - ?h a = (b - a) * l" .. |
|
1288 |
||
1289 |
from cdef have cint: "a < c \<and> c < b" by auto |
|
1290 |
with gd have "g differentiable c" by simp |
|
1291 |
hence "\<exists>D. DERIV g c :> D" by (rule differentiableD) |
|
1292 |
then obtain g'c where g'cdef: "DERIV g c :> g'c" .. |
|
1293 |
||
1294 |
from cdef have "a < c \<and> c < b" by auto |
|
1295 |
with fd have "f differentiable c" by simp |
|
1296 |
hence "\<exists>D. DERIV f c :> D" by (rule differentiableD) |
|
1297 |
then obtain f'c where f'cdef: "DERIV f c :> f'c" .. |
|
1298 |
||
1299 |
from cdef have "DERIV ?h c :> l" by auto |
|
1300 |
moreover |
|
1301 |
{ |
|
1302 |
from g'cdef have "DERIV (\<lambda>x. (f b - f a) * g x) c :> g'c * (f b - f a)" |
|
1303 |
apply (insert DERIV_const [where k="f b - f a"]) |
|
1304 |
apply (drule meta_spec [of _ c]) |
|
1305 |
apply (drule DERIV_mult [where f="(\<lambda>x. f b - f a)" and g=g]) |
|
1306 |
by simp_all |
|
1307 |
moreover from f'cdef have "DERIV (\<lambda>x. (g b - g a) * f x) c :> f'c * (g b - g a)" |
|
1308 |
apply (insert DERIV_const [where k="g b - g a"]) |
|
1309 |
apply (drule meta_spec [of _ c]) |
|
1310 |
apply (drule DERIV_mult [where f="(\<lambda>x. g b - g a)" and g=f]) |
|
1311 |
by simp_all |
|
1312 |
ultimately have "DERIV ?h c :> g'c * (f b - f a) - f'c * (g b - g a)" |
|
1313 |
by (simp add: DERIV_diff) |
|
1314 |
} |
|
1315 |
ultimately have leq: "l = g'c * (f b - f a) - f'c * (g b - g a)" by (rule DERIV_unique) |
|
1316 |
||
1317 |
{ |
|
1318 |
from cdef have "?h b - ?h a = (b - a) * l" by auto |
|
1319 |
also with leq have "\<dots> = (b - a) * (g'c * (f b - f a) - f'c * (g b - g a))" by simp |
|
1320 |
finally have "?h b - ?h a = (b - a) * (g'c * (f b - f a) - f'c * (g b - g a))" by simp |
|
1321 |
} |
|
1322 |
moreover |
|
1323 |
{ |
|
1324 |
have "?h b - ?h a = |
|
1325 |
((f b)*(g b) - (f a)*(g b) - (g b)*(f b) + (g a)*(f b)) - |
|
1326 |
((f b)*(g a) - (f a)*(g a) - (g b)*(f a) + (g a)*(f a))" |
|
22998 | 1327 |
by (simp add: mult_ac add_ac right_diff_distrib) |
21164 | 1328 |
hence "?h b - ?h a = 0" by auto |
1329 |
} |
|
1330 |
ultimately have "(b - a) * (g'c * (f b - f a) - f'c * (g b - g a)) = 0" by auto |
|
1331 |
with alb have "g'c * (f b - f a) - f'c * (g b - g a) = 0" by simp |
|
1332 |
hence "g'c * (f b - f a) = f'c * (g b - g a)" by simp |
|
1333 |
hence "(f b - f a) * g'c = (g b - g a) * f'c" by (simp add: mult_ac) |
|
1334 |
||
1335 |
with g'cdef f'cdef cint show ?thesis by auto |
|
1336 |
qed |
|
1337 |
||
1338 |
end |