src/HOL/Library/Polynomial.thy
 author kuncar Fri Dec 09 18:07:04 2011 +0100 (2011-12-09) changeset 45802 b16f976db515 parent 45694 4a8743618257 child 45928 874845660119 permissions -rw-r--r--
Quotient_Info stores only relation maps
1 (*  Title:      HOL/Library/Polynomial.thy
2     Author:     Brian Huffman
3     Author:     Clemens Ballarin
4 *)
6 header {* Univariate Polynomials *}
8 theory Polynomial
9 imports Main
10 begin
12 subsection {* Definition of type @{text poly} *}
14 definition "Poly = {f::nat \<Rightarrow> 'a::zero. \<exists>n. \<forall>i>n. f i = 0}"
16 typedef (open) 'a poly = "Poly :: (nat => 'a::zero) set"
17   morphisms coeff Abs_poly
18   unfolding Poly_def by auto
20 lemma expand_poly_eq: "p = q \<longleftrightarrow> (\<forall>n. coeff p n = coeff q n)"
21   by (simp add: coeff_inject [symmetric] fun_eq_iff)
23 lemma poly_ext: "(\<And>n. coeff p n = coeff q n) \<Longrightarrow> p = q"
27 subsection {* Degree of a polynomial *}
29 definition
30   degree :: "'a::zero poly \<Rightarrow> nat" where
31   "degree p = (LEAST n. \<forall>i>n. coeff p i = 0)"
33 lemma coeff_eq_0: "degree p < n \<Longrightarrow> coeff p n = 0"
34 proof -
35   have "coeff p \<in> Poly"
36     by (rule coeff)
37   hence "\<exists>n. \<forall>i>n. coeff p i = 0"
38     unfolding Poly_def by simp
39   hence "\<forall>i>degree p. coeff p i = 0"
40     unfolding degree_def by (rule LeastI_ex)
41   moreover assume "degree p < n"
42   ultimately show ?thesis by simp
43 qed
45 lemma le_degree: "coeff p n \<noteq> 0 \<Longrightarrow> n \<le> degree p"
46   by (erule contrapos_np, rule coeff_eq_0, simp)
48 lemma degree_le: "\<forall>i>n. coeff p i = 0 \<Longrightarrow> degree p \<le> n"
49   unfolding degree_def by (erule Least_le)
51 lemma less_degree_imp: "n < degree p \<Longrightarrow> \<exists>i>n. coeff p i \<noteq> 0"
52   unfolding degree_def by (drule not_less_Least, simp)
55 subsection {* The zero polynomial *}
57 instantiation poly :: (zero) zero
58 begin
60 definition
61   zero_poly_def: "0 = Abs_poly (\<lambda>n. 0)"
63 instance ..
64 end
66 lemma coeff_0 [simp]: "coeff 0 n = 0"
67   unfolding zero_poly_def
68   by (simp add: Abs_poly_inverse Poly_def)
70 lemma degree_0 [simp]: "degree 0 = 0"
71   by (rule order_antisym [OF degree_le le0]) simp
74   assumes "p \<noteq> 0" shows "coeff p (degree p) \<noteq> 0"
75 proof (cases "degree p")
76   case 0
77   from `p \<noteq> 0` have "\<exists>n. coeff p n \<noteq> 0"
79   then obtain n where "coeff p n \<noteq> 0" ..
80   hence "n \<le> degree p" by (rule le_degree)
81   with `coeff p n \<noteq> 0` and `degree p = 0`
82   show "coeff p (degree p) \<noteq> 0" by simp
83 next
84   case (Suc n)
85   from `degree p = Suc n` have "n < degree p" by simp
86   hence "\<exists>i>n. coeff p i \<noteq> 0" by (rule less_degree_imp)
87   then obtain i where "n < i" and "coeff p i \<noteq> 0" by fast
88   from `degree p = Suc n` and `n < i` have "degree p \<le> i" by simp
89   also from `coeff p i \<noteq> 0` have "i \<le> degree p" by (rule le_degree)
90   finally have "degree p = i" .
91   with `coeff p i \<noteq> 0` show "coeff p (degree p) \<noteq> 0" by simp
92 qed
94 lemma leading_coeff_0_iff [simp]: "coeff p (degree p) = 0 \<longleftrightarrow> p = 0"
98 subsection {* List-style constructor for polynomials *}
100 definition
101   pCons :: "'a::zero \<Rightarrow> 'a poly \<Rightarrow> 'a poly"
102 where
103   "pCons a p = Abs_poly (nat_case a (coeff p))"
105 syntax
106   "_poly" :: "args \<Rightarrow> 'a poly"  ("[:(_):]")
108 translations
109   "[:x, xs:]" == "CONST pCons x [:xs:]"
110   "[:x:]" == "CONST pCons x 0"
111   "[:x:]" <= "CONST pCons x (_constrain 0 t)"
113 lemma Poly_nat_case: "f \<in> Poly \<Longrightarrow> nat_case a f \<in> Poly"
114   unfolding Poly_def by (auto split: nat.split)
116 lemma coeff_pCons:
117   "coeff (pCons a p) = nat_case a (coeff p)"
118   unfolding pCons_def
119   by (simp add: Abs_poly_inverse Poly_nat_case coeff)
121 lemma coeff_pCons_0 [simp]: "coeff (pCons a p) 0 = a"
124 lemma coeff_pCons_Suc [simp]: "coeff (pCons a p) (Suc n) = coeff p n"
127 lemma degree_pCons_le: "degree (pCons a p) \<le> Suc (degree p)"
128 by (rule degree_le, simp add: coeff_eq_0 coeff_pCons split: nat.split)
130 lemma degree_pCons_eq:
131   "p \<noteq> 0 \<Longrightarrow> degree (pCons a p) = Suc (degree p)"
132 apply (rule order_antisym [OF degree_pCons_le])
133 apply (rule le_degree, simp)
134 done
136 lemma degree_pCons_0: "degree (pCons a 0) = 0"
137 apply (rule order_antisym [OF _ le0])
138 apply (rule degree_le, simp add: coeff_pCons split: nat.split)
139 done
141 lemma degree_pCons_eq_if [simp]:
142   "degree (pCons a p) = (if p = 0 then 0 else Suc (degree p))"
143 apply (cases "p = 0", simp_all)
144 apply (rule order_antisym [OF _ le0])
145 apply (rule degree_le, simp add: coeff_pCons split: nat.split)
146 apply (rule order_antisym [OF degree_pCons_le])
147 apply (rule le_degree, simp)
148 done
150 lemma pCons_0_0 [simp]: "pCons 0 0 = 0"
151 by (rule poly_ext, simp add: coeff_pCons split: nat.split)
153 lemma pCons_eq_iff [simp]:
154   "pCons a p = pCons b q \<longleftrightarrow> a = b \<and> p = q"
155 proof (safe)
156   assume "pCons a p = pCons b q"
157   then have "coeff (pCons a p) 0 = coeff (pCons b q) 0" by simp
158   then show "a = b" by simp
159 next
160   assume "pCons a p = pCons b q"
161   then have "\<forall>n. coeff (pCons a p) (Suc n) =
162                  coeff (pCons b q) (Suc n)" by simp
163   then show "p = q" by (simp add: expand_poly_eq)
164 qed
166 lemma pCons_eq_0_iff [simp]: "pCons a p = 0 \<longleftrightarrow> a = 0 \<and> p = 0"
167   using pCons_eq_iff [of a p 0 0] by simp
169 lemma Poly_Suc: "f \<in> Poly \<Longrightarrow> (\<lambda>n. f (Suc n)) \<in> Poly"
170   unfolding Poly_def
171   by (clarify, rule_tac x=n in exI, simp)
173 lemma pCons_cases [cases type: poly]:
174   obtains (pCons) a q where "p = pCons a q"
175 proof
176   show "p = pCons (coeff p 0) (Abs_poly (\<lambda>n. coeff p (Suc n)))"
177     by (rule poly_ext)
178        (simp add: Abs_poly_inverse Poly_Suc coeff coeff_pCons
179              split: nat.split)
180 qed
182 lemma pCons_induct [case_names 0 pCons, induct type: poly]:
183   assumes zero: "P 0"
184   assumes pCons: "\<And>a p. P p \<Longrightarrow> P (pCons a p)"
185   shows "P p"
186 proof (induct p rule: measure_induct_rule [where f=degree])
187   case (less p)
188   obtain a q where "p = pCons a q" by (rule pCons_cases)
189   have "P q"
190   proof (cases "q = 0")
191     case True
192     then show "P q" by (simp add: zero)
193   next
194     case False
195     then have "degree (pCons a q) = Suc (degree q)"
196       by (rule degree_pCons_eq)
197     then have "degree q < degree p"
198       using `p = pCons a q` by simp
199     then show "P q"
200       by (rule less.hyps)
201   qed
202   then have "P (pCons a q)"
203     by (rule pCons)
204   then show ?case
205     using `p = pCons a q` by simp
206 qed
209 subsection {* Recursion combinator for polynomials *}
211 function
212   poly_rec :: "'b \<Rightarrow> ('a::zero \<Rightarrow> 'a poly \<Rightarrow> 'b \<Rightarrow> 'b) \<Rightarrow> 'a poly \<Rightarrow> 'b"
213 where
214   poly_rec_pCons_eq_if [simp del]:
215     "poly_rec z f (pCons a p) = f a p (if p = 0 then z else poly_rec z f p)"
216 by (case_tac x, rename_tac q, case_tac q, auto)
218 termination poly_rec
219 by (relation "measure (degree \<circ> snd \<circ> snd)", simp)
222 lemma poly_rec_0:
223   "f 0 0 z = z \<Longrightarrow> poly_rec z f 0 = z"
224   using poly_rec_pCons_eq_if [of z f 0 0] by simp
226 lemma poly_rec_pCons:
227   "f 0 0 z = z \<Longrightarrow> poly_rec z f (pCons a p) = f a p (poly_rec z f p)"
228   by (simp add: poly_rec_pCons_eq_if poly_rec_0)
231 subsection {* Monomials *}
233 definition
234   monom :: "'a \<Rightarrow> nat \<Rightarrow> 'a::zero poly" where
235   "monom a m = Abs_poly (\<lambda>n. if m = n then a else 0)"
237 lemma coeff_monom [simp]: "coeff (monom a m) n = (if m=n then a else 0)"
238   unfolding monom_def
239   by (subst Abs_poly_inverse, auto simp add: Poly_def)
241 lemma monom_0: "monom a 0 = pCons a 0"
242   by (rule poly_ext, simp add: coeff_pCons split: nat.split)
244 lemma monom_Suc: "monom a (Suc n) = pCons 0 (monom a n)"
245   by (rule poly_ext, simp add: coeff_pCons split: nat.split)
247 lemma monom_eq_0 [simp]: "monom 0 n = 0"
248   by (rule poly_ext) simp
250 lemma monom_eq_0_iff [simp]: "monom a n = 0 \<longleftrightarrow> a = 0"
253 lemma monom_eq_iff [simp]: "monom a n = monom b n \<longleftrightarrow> a = b"
256 lemma degree_monom_le: "degree (monom a n) \<le> n"
257   by (rule degree_le, simp)
259 lemma degree_monom_eq: "a \<noteq> 0 \<Longrightarrow> degree (monom a n) = n"
260   apply (rule order_antisym [OF degree_monom_le])
261   apply (rule le_degree, simp)
262   done
265 subsection {* Addition and subtraction *}
268 begin
270 definition
271   plus_poly_def:
272     "p + q = Abs_poly (\<lambda>n. coeff p n + coeff q n)"
275   fixes f g :: "nat \<Rightarrow> 'a"
276   shows "\<lbrakk>f \<in> Poly; g \<in> Poly\<rbrakk> \<Longrightarrow> (\<lambda>n. f n + g n) \<in> Poly"
277   unfolding Poly_def
278   apply (clarify, rename_tac m n)
279   apply (rule_tac x="max m n" in exI, simp)
280   done
283   "coeff (p + q) n = coeff p n + coeff q n"
284   unfolding plus_poly_def
287 instance proof
288   fix p q r :: "'a poly"
289   show "(p + q) + r = p + (q + r)"
291   show "p + q = q + p"
293   show "0 + p = p"
295 qed
297 end
300 proof
301   fix p q r :: "'a poly"
302   assume "p + q = p + r" thus "q = r"
304 qed
307 begin
309 definition
310   uminus_poly_def:
311     "- p = Abs_poly (\<lambda>n. - coeff p n)"
313 definition
314   minus_poly_def:
315     "p - q = Abs_poly (\<lambda>n. coeff p n - coeff q n)"
317 lemma Poly_minus:
318   fixes f :: "nat \<Rightarrow> 'a"
319   shows "f \<in> Poly \<Longrightarrow> (\<lambda>n. - f n) \<in> Poly"
320   unfolding Poly_def by simp
322 lemma Poly_diff:
323   fixes f g :: "nat \<Rightarrow> 'a"
324   shows "\<lbrakk>f \<in> Poly; g \<in> Poly\<rbrakk> \<Longrightarrow> (\<lambda>n. f n - g n) \<in> Poly"
327 lemma coeff_minus [simp]: "coeff (- p) n = - coeff p n"
328   unfolding uminus_poly_def
329   by (simp add: Abs_poly_inverse coeff Poly_minus)
331 lemma coeff_diff [simp]:
332   "coeff (p - q) n = coeff p n - coeff q n"
333   unfolding minus_poly_def
334   by (simp add: Abs_poly_inverse coeff Poly_diff)
336 instance proof
337   fix p q :: "'a poly"
338   show "- p + p = 0"
340   show "p - q = p + - q"
341     by (simp add: expand_poly_eq diff_minus)
342 qed
344 end
347   "pCons a p + pCons b q = pCons (a + b) (p + q)"
348   by (rule poly_ext, simp add: coeff_pCons split: nat.split)
350 lemma minus_pCons [simp]:
351   "- pCons a p = pCons (- a) (- p)"
352   by (rule poly_ext, simp add: coeff_pCons split: nat.split)
354 lemma diff_pCons [simp]:
355   "pCons a p - pCons b q = pCons (a - b) (p - q)"
356   by (rule poly_ext, simp add: coeff_pCons split: nat.split)
358 lemma degree_add_le_max: "degree (p + q) \<le> max (degree p) (degree q)"
359   by (rule degree_le, auto simp add: coeff_eq_0)
362   "\<lbrakk>degree p \<le> n; degree q \<le> n\<rbrakk> \<Longrightarrow> degree (p + q) \<le> n"
363   by (auto intro: order_trans degree_add_le_max)
366   "\<lbrakk>degree p < n; degree q < n\<rbrakk> \<Longrightarrow> degree (p + q) < n"
367   by (auto intro: le_less_trans degree_add_le_max)
370   "degree p < degree q \<Longrightarrow> degree (p + q) = degree q"
371   apply (cases "q = 0", simp)
372   apply (rule order_antisym)
374   apply (rule le_degree)
376   done
379   "degree q < degree p \<Longrightarrow> degree (p + q) = degree p"
380   using degree_add_eq_right [of q p]
383 lemma degree_minus [simp]: "degree (- p) = degree p"
384   unfolding degree_def by simp
386 lemma degree_diff_le_max: "degree (p - q) \<le> max (degree p) (degree q)"
387   using degree_add_le [where p=p and q="-q"]
390 lemma degree_diff_le:
391   "\<lbrakk>degree p \<le> n; degree q \<le> n\<rbrakk> \<Longrightarrow> degree (p - q) \<le> n"
394 lemma degree_diff_less:
395   "\<lbrakk>degree p < n; degree q < n\<rbrakk> \<Longrightarrow> degree (p - q) < n"
398 lemma add_monom: "monom a n + monom b n = monom (a + b) n"
399   by (rule poly_ext) simp
401 lemma diff_monom: "monom a n - monom b n = monom (a - b) n"
402   by (rule poly_ext) simp
404 lemma minus_monom: "- monom a n = monom (-a) n"
405   by (rule poly_ext) simp
407 lemma coeff_setsum: "coeff (\<Sum>x\<in>A. p x) i = (\<Sum>x\<in>A. coeff (p x) i)"
408   by (cases "finite A", induct set: finite, simp_all)
410 lemma monom_setsum: "monom (\<Sum>x\<in>A. a x) n = (\<Sum>x\<in>A. monom (a x) n)"
411   by (rule poly_ext) (simp add: coeff_setsum)
414 subsection {* Multiplication by a constant *}
416 definition
417   smult :: "'a::comm_semiring_0 \<Rightarrow> 'a poly \<Rightarrow> 'a poly" where
418   "smult a p = Abs_poly (\<lambda>n. a * coeff p n)"
420 lemma Poly_smult:
421   fixes f :: "nat \<Rightarrow> 'a::comm_semiring_0"
422   shows "f \<in> Poly \<Longrightarrow> (\<lambda>n. a * f n) \<in> Poly"
423   unfolding Poly_def
424   by (clarify, rule_tac x=n in exI, simp)
426 lemma coeff_smult [simp]: "coeff (smult a p) n = a * coeff p n"
427   unfolding smult_def
428   by (simp add: Abs_poly_inverse Poly_smult coeff)
430 lemma degree_smult_le: "degree (smult a p) \<le> degree p"
431   by (rule degree_le, simp add: coeff_eq_0)
433 lemma smult_smult [simp]: "smult a (smult b p) = smult (a * b) p"
434   by (rule poly_ext, simp add: mult_assoc)
436 lemma smult_0_right [simp]: "smult a 0 = 0"
437   by (rule poly_ext, simp)
439 lemma smult_0_left [simp]: "smult 0 p = 0"
440   by (rule poly_ext, simp)
442 lemma smult_1_left [simp]: "smult (1::'a::comm_semiring_1) p = p"
443   by (rule poly_ext, simp)
446   "smult a (p + q) = smult a p + smult a q"
447   by (rule poly_ext, simp add: algebra_simps)
450   "smult (a + b) p = smult a p + smult b p"
451   by (rule poly_ext, simp add: algebra_simps)
453 lemma smult_minus_right [simp]:
454   "smult (a::'a::comm_ring) (- p) = - smult a p"
455   by (rule poly_ext, simp)
457 lemma smult_minus_left [simp]:
458   "smult (- a::'a::comm_ring) p = - smult a p"
459   by (rule poly_ext, simp)
461 lemma smult_diff_right:
462   "smult (a::'a::comm_ring) (p - q) = smult a p - smult a q"
463   by (rule poly_ext, simp add: algebra_simps)
465 lemma smult_diff_left:
466   "smult (a - b::'a::comm_ring) p = smult a p - smult b p"
467   by (rule poly_ext, simp add: algebra_simps)
469 lemmas smult_distribs =
471   smult_diff_left smult_diff_right
473 lemma smult_pCons [simp]:
474   "smult a (pCons b p) = pCons (a * b) (smult a p)"
475   by (rule poly_ext, simp add: coeff_pCons split: nat.split)
477 lemma smult_monom: "smult a (monom b n) = monom (a * b) n"
480 lemma degree_smult_eq [simp]:
481   fixes a :: "'a::idom"
482   shows "degree (smult a p) = (if a = 0 then 0 else degree p)"
483   by (cases "a = 0", simp, simp add: degree_def)
485 lemma smult_eq_0_iff [simp]:
486   fixes a :: "'a::idom"
487   shows "smult a p = 0 \<longleftrightarrow> a = 0 \<or> p = 0"
491 subsection {* Multiplication of polynomials *}
493 text {* TODO: move to SetInterval.thy *}
494 lemma setsum_atMost_Suc_shift:
495   fixes f :: "nat \<Rightarrow> 'a::comm_monoid_add"
496   shows "(\<Sum>i\<le>Suc n. f i) = f 0 + (\<Sum>i\<le>n. f (Suc i))"
497 proof (induct n)
498   case 0 show ?case by simp
499 next
500   case (Suc n) note IH = this
501   have "(\<Sum>i\<le>Suc (Suc n). f i) = (\<Sum>i\<le>Suc n. f i) + f (Suc (Suc n))"
502     by (rule setsum_atMost_Suc)
503   also have "(\<Sum>i\<le>Suc n. f i) = f 0 + (\<Sum>i\<le>n. f (Suc i))"
504     by (rule IH)
505   also have "f 0 + (\<Sum>i\<le>n. f (Suc i)) + f (Suc (Suc n)) =
506              f 0 + ((\<Sum>i\<le>n. f (Suc i)) + f (Suc (Suc n)))"
508   also have "(\<Sum>i\<le>n. f (Suc i)) + f (Suc (Suc n)) = (\<Sum>i\<le>Suc n. f (Suc i))"
509     by (rule setsum_atMost_Suc [symmetric])
510   finally show ?case .
511 qed
513 instantiation poly :: (comm_semiring_0) comm_semiring_0
514 begin
516 definition
517   times_poly_def:
518     "p * q = poly_rec 0 (\<lambda>a p pq. smult a q + pCons 0 pq) p"
520 lemma mult_poly_0_left: "(0::'a poly) * q = 0"
521   unfolding times_poly_def by (simp add: poly_rec_0)
523 lemma mult_pCons_left [simp]:
524   "pCons a p * q = smult a q + pCons 0 (p * q)"
525   unfolding times_poly_def by (simp add: poly_rec_pCons)
527 lemma mult_poly_0_right: "p * (0::'a poly) = 0"
528   by (induct p, simp add: mult_poly_0_left, simp)
530 lemma mult_pCons_right [simp]:
531   "p * pCons a q = smult a p + pCons 0 (p * q)"
534 lemmas mult_poly_0 = mult_poly_0_left mult_poly_0_right
536 lemma mult_smult_left [simp]: "smult a p * q = smult a (p * q)"
539 lemma mult_smult_right [simp]: "p * smult a q = smult a (p * q)"
543   fixes p q r :: "'a poly"
544   shows "(p + q) * r = p * r + q * r"
545   by (induct r, simp add: mult_poly_0,
548 instance proof
549   fix p q r :: "'a poly"
550   show 0: "0 * p = 0"
551     by (rule mult_poly_0_left)
552   show "p * 0 = 0"
553     by (rule mult_poly_0_right)
554   show "(p + q) * r = p * r + q * r"
556   show "(p * q) * r = p * (q * r)"
558   show "p * q = q * p"
559     by (induct p, simp add: mult_poly_0, simp)
560 qed
562 end
564 instance poly :: (comm_semiring_0_cancel) comm_semiring_0_cancel ..
566 lemma coeff_mult:
567   "coeff (p * q) n = (\<Sum>i\<le>n. coeff p i * coeff q (n-i))"
568 proof (induct p arbitrary: n)
569   case 0 show ?case by simp
570 next
571   case (pCons a p n) thus ?case
572     by (cases n, simp, simp add: setsum_atMost_Suc_shift
573                             del: setsum_atMost_Suc)
574 qed
576 lemma degree_mult_le: "degree (p * q) \<le> degree p + degree q"
577 apply (rule degree_le)
578 apply (induct p)
579 apply simp
580 apply (simp add: coeff_eq_0 coeff_pCons split: nat.split)
581 done
583 lemma mult_monom: "monom a m * monom b n = monom (a * b) (m + n)"
587 subsection {* The unit polynomial and exponentiation *}
589 instantiation poly :: (comm_semiring_1) comm_semiring_1
590 begin
592 definition
593   one_poly_def:
594     "1 = pCons 1 0"
596 instance proof
597   fix p :: "'a poly" show "1 * p = p"
598     unfolding one_poly_def
599     by simp
600 next
601   show "0 \<noteq> (1::'a poly)"
602     unfolding one_poly_def by simp
603 qed
605 end
607 instance poly :: (comm_semiring_1_cancel) comm_semiring_1_cancel ..
609 lemma coeff_1 [simp]: "coeff 1 n = (if n = 0 then 1 else 0)"
610   unfolding one_poly_def
611   by (simp add: coeff_pCons split: nat.split)
613 lemma degree_1 [simp]: "degree 1 = 0"
614   unfolding one_poly_def
615   by (rule degree_pCons_0)
617 text {* Lemmas about divisibility *}
619 lemma dvd_smult: "p dvd q \<Longrightarrow> p dvd smult a q"
620 proof -
621   assume "p dvd q"
622   then obtain k where "q = p * k" ..
623   then have "smult a q = p * smult a k" by simp
624   then show "p dvd smult a q" ..
625 qed
627 lemma dvd_smult_cancel:
628   fixes a :: "'a::field"
629   shows "p dvd smult a q \<Longrightarrow> a \<noteq> 0 \<Longrightarrow> p dvd q"
630   by (drule dvd_smult [where a="inverse a"]) simp
632 lemma dvd_smult_iff:
633   fixes a :: "'a::field"
634   shows "a \<noteq> 0 \<Longrightarrow> p dvd smult a q \<longleftrightarrow> p dvd q"
635   by (safe elim!: dvd_smult dvd_smult_cancel)
637 lemma smult_dvd_cancel:
638   "smult a p dvd q \<Longrightarrow> p dvd q"
639 proof -
640   assume "smult a p dvd q"
641   then obtain k where "q = smult a p * k" ..
642   then have "q = p * smult a k" by simp
643   then show "p dvd q" ..
644 qed
646 lemma smult_dvd:
647   fixes a :: "'a::field"
648   shows "p dvd q \<Longrightarrow> a \<noteq> 0 \<Longrightarrow> smult a p dvd q"
649   by (rule smult_dvd_cancel [where a="inverse a"]) simp
651 lemma smult_dvd_iff:
652   fixes a :: "'a::field"
653   shows "smult a p dvd q \<longleftrightarrow> (if a = 0 then q = 0 else p dvd q)"
654   by (auto elim: smult_dvd smult_dvd_cancel)
656 lemma degree_power_le: "degree (p ^ n) \<le> degree p * n"
657 by (induct n, simp, auto intro: order_trans degree_mult_le)
659 instance poly :: (comm_ring) comm_ring ..
661 instance poly :: (comm_ring_1) comm_ring_1 ..
663 instantiation poly :: (comm_ring_1) number_ring
664 begin
666 definition
667   "number_of k = (of_int k :: 'a poly)"
669 instance
670   by default (rule number_of_poly_def)
672 end
675 subsection {* Polynomials form an integral domain *}
677 lemma coeff_mult_degree_sum:
678   "coeff (p * q) (degree p + degree q) =
679    coeff p (degree p) * coeff q (degree q)"
680   by (induct p, simp, simp add: coeff_eq_0)
682 instance poly :: (idom) idom
683 proof
684   fix p q :: "'a poly"
685   assume "p \<noteq> 0" and "q \<noteq> 0"
686   have "coeff (p * q) (degree p + degree q) =
687         coeff p (degree p) * coeff q (degree q)"
688     by (rule coeff_mult_degree_sum)
689   also have "coeff p (degree p) * coeff q (degree q) \<noteq> 0"
690     using `p \<noteq> 0` and `q \<noteq> 0` by simp
691   finally have "\<exists>n. coeff (p * q) n \<noteq> 0" ..
692   thus "p * q \<noteq> 0" by (simp add: expand_poly_eq)
693 qed
695 lemma degree_mult_eq:
696   fixes p q :: "'a::idom poly"
697   shows "\<lbrakk>p \<noteq> 0; q \<noteq> 0\<rbrakk> \<Longrightarrow> degree (p * q) = degree p + degree q"
698 apply (rule order_antisym [OF degree_mult_le le_degree])
700 done
702 lemma dvd_imp_degree_le:
703   fixes p q :: "'a::idom poly"
704   shows "\<lbrakk>p dvd q; q \<noteq> 0\<rbrakk> \<Longrightarrow> degree p \<le> degree q"
705   by (erule dvdE, simp add: degree_mult_eq)
708 subsection {* Polynomials form an ordered integral domain *}
710 definition
711   pos_poly :: "'a::linordered_idom poly \<Rightarrow> bool"
712 where
713   "pos_poly p \<longleftrightarrow> 0 < coeff p (degree p)"
715 lemma pos_poly_pCons:
716   "pos_poly (pCons a p) \<longleftrightarrow> pos_poly p \<or> (p = 0 \<and> 0 < a)"
717   unfolding pos_poly_def by simp
719 lemma not_pos_poly_0 [simp]: "\<not> pos_poly 0"
720   unfolding pos_poly_def by simp
722 lemma pos_poly_add: "\<lbrakk>pos_poly p; pos_poly q\<rbrakk> \<Longrightarrow> pos_poly (p + q)"
723   apply (induct p arbitrary: q, simp)
725   done
727 lemma pos_poly_mult: "\<lbrakk>pos_poly p; pos_poly q\<rbrakk> \<Longrightarrow> pos_poly (p * q)"
728   unfolding pos_poly_def
729   apply (subgoal_tac "p \<noteq> 0 \<and> q \<noteq> 0")
730   apply (simp add: degree_mult_eq coeff_mult_degree_sum mult_pos_pos)
731   apply auto
732   done
734 lemma pos_poly_total: "p = 0 \<or> pos_poly p \<or> pos_poly (- p)"
735 by (induct p) (auto simp add: pos_poly_pCons)
737 instantiation poly :: (linordered_idom) linordered_idom
738 begin
740 definition
741   "x < y \<longleftrightarrow> pos_poly (y - x)"
743 definition
744   "x \<le> y \<longleftrightarrow> x = y \<or> pos_poly (y - x)"
746 definition
747   "abs (x::'a poly) = (if x < 0 then - x else x)"
749 definition
750   "sgn (x::'a poly) = (if x = 0 then 0 else if 0 < x then 1 else - 1)"
752 instance proof
753   fix x y :: "'a poly"
754   show "x < y \<longleftrightarrow> x \<le> y \<and> \<not> y \<le> x"
755     unfolding less_eq_poly_def less_poly_def
756     apply safe
757     apply simp
759     apply simp
760     done
761 next
762   fix x :: "'a poly" show "x \<le> x"
763     unfolding less_eq_poly_def by simp
764 next
765   fix x y z :: "'a poly"
766   assume "x \<le> y" and "y \<le> z" thus "x \<le> z"
767     unfolding less_eq_poly_def
768     apply safe
771     done
772 next
773   fix x y :: "'a poly"
774   assume "x \<le> y" and "y \<le> x" thus "x = y"
775     unfolding less_eq_poly_def
776     apply safe
778     apply simp
779     done
780 next
781   fix x y z :: "'a poly"
782   assume "x \<le> y" thus "z + x \<le> z + y"
783     unfolding less_eq_poly_def
784     apply safe
786     done
787 next
788   fix x y :: "'a poly"
789   show "x \<le> y \<or> y \<le> x"
790     unfolding less_eq_poly_def
791     using pos_poly_total [of "x - y"]
792     by auto
793 next
794   fix x y z :: "'a poly"
795   assume "x < y" and "0 < z"
796   thus "z * x < z * y"
797     unfolding less_poly_def
798     by (simp add: right_diff_distrib [symmetric] pos_poly_mult)
799 next
800   fix x :: "'a poly"
801   show "\<bar>x\<bar> = (if x < 0 then - x else x)"
802     by (rule abs_poly_def)
803 next
804   fix x :: "'a poly"
805   show "sgn x = (if x = 0 then 0 else if 0 < x then 1 else - 1)"
806     by (rule sgn_poly_def)
807 qed
809 end
811 text {* TODO: Simplification rules for comparisons *}
814 subsection {* Long division of polynomials *}
816 definition
817   pdivmod_rel :: "'a::field poly \<Rightarrow> 'a poly \<Rightarrow> 'a poly \<Rightarrow> 'a poly \<Rightarrow> bool"
818 where
819   "pdivmod_rel x y q r \<longleftrightarrow>
820     x = q * y + r \<and> (if y = 0 then q = 0 else r = 0 \<or> degree r < degree y)"
822 lemma pdivmod_rel_0:
823   "pdivmod_rel 0 y 0 0"
824   unfolding pdivmod_rel_def by simp
826 lemma pdivmod_rel_by_0:
827   "pdivmod_rel x 0 0 x"
828   unfolding pdivmod_rel_def by simp
830 lemma eq_zero_or_degree_less:
831   assumes "degree p \<le> n" and "coeff p n = 0"
832   shows "p = 0 \<or> degree p < n"
833 proof (cases n)
834   case 0
835   with `degree p \<le> n` and `coeff p n = 0`
836   have "coeff p (degree p) = 0" by simp
837   then have "p = 0" by simp
838   then show ?thesis ..
839 next
840   case (Suc m)
841   have "\<forall>i>n. coeff p i = 0"
842     using `degree p \<le> n` by (simp add: coeff_eq_0)
843   then have "\<forall>i\<ge>n. coeff p i = 0"
844     using `coeff p n = 0` by (simp add: le_less)
845   then have "\<forall>i>m. coeff p i = 0"
846     using `n = Suc m` by (simp add: less_eq_Suc_le)
847   then have "degree p \<le> m"
848     by (rule degree_le)
849   then have "degree p < n"
850     using `n = Suc m` by (simp add: less_Suc_eq_le)
851   then show ?thesis ..
852 qed
854 lemma pdivmod_rel_pCons:
855   assumes rel: "pdivmod_rel x y q r"
856   assumes y: "y \<noteq> 0"
857   assumes b: "b = coeff (pCons a r) (degree y) / coeff y (degree y)"
858   shows "pdivmod_rel (pCons a x) y (pCons b q) (pCons a r - smult b y)"
859     (is "pdivmod_rel ?x y ?q ?r")
860 proof -
861   have x: "x = q * y + r" and r: "r = 0 \<or> degree r < degree y"
862     using assms unfolding pdivmod_rel_def by simp_all
864   have 1: "?x = ?q * y + ?r"
865     using b x by simp
867   have 2: "?r = 0 \<or> degree ?r < degree y"
868   proof (rule eq_zero_or_degree_less)
869     show "degree ?r \<le> degree y"
870     proof (rule degree_diff_le)
871       show "degree (pCons a r) \<le> degree y"
872         using r by auto
873       show "degree (smult b y) \<le> degree y"
874         by (rule degree_smult_le)
875     qed
876   next
877     show "coeff ?r (degree y) = 0"
878       using `y \<noteq> 0` unfolding b by simp
879   qed
881   from 1 2 show ?thesis
882     unfolding pdivmod_rel_def
883     using `y \<noteq> 0` by simp
884 qed
886 lemma pdivmod_rel_exists: "\<exists>q r. pdivmod_rel x y q r"
887 apply (cases "y = 0")
888 apply (fast intro!: pdivmod_rel_by_0)
889 apply (induct x)
890 apply (fast intro!: pdivmod_rel_0)
891 apply (fast intro!: pdivmod_rel_pCons)
892 done
894 lemma pdivmod_rel_unique:
895   assumes 1: "pdivmod_rel x y q1 r1"
896   assumes 2: "pdivmod_rel x y q2 r2"
897   shows "q1 = q2 \<and> r1 = r2"
898 proof (cases "y = 0")
899   assume "y = 0" with assms show ?thesis
901 next
902   assume [simp]: "y \<noteq> 0"
903   from 1 have q1: "x = q1 * y + r1" and r1: "r1 = 0 \<or> degree r1 < degree y"
904     unfolding pdivmod_rel_def by simp_all
905   from 2 have q2: "x = q2 * y + r2" and r2: "r2 = 0 \<or> degree r2 < degree y"
906     unfolding pdivmod_rel_def by simp_all
907   from q1 q2 have q3: "(q1 - q2) * y = r2 - r1"
909   from r1 r2 have r3: "(r2 - r1) = 0 \<or> degree (r2 - r1) < degree y"
910     by (auto intro: degree_diff_less)
912   show "q1 = q2 \<and> r1 = r2"
913   proof (rule ccontr)
914     assume "\<not> (q1 = q2 \<and> r1 = r2)"
915     with q3 have "q1 \<noteq> q2" and "r1 \<noteq> r2" by auto
916     with r3 have "degree (r2 - r1) < degree y" by simp
917     also have "degree y \<le> degree (q1 - q2) + degree y" by simp
918     also have "\<dots> = degree ((q1 - q2) * y)"
919       using `q1 \<noteq> q2` by (simp add: degree_mult_eq)
920     also have "\<dots> = degree (r2 - r1)"
921       using q3 by simp
922     finally have "degree (r2 - r1) < degree (r2 - r1)" .
923     then show "False" by simp
924   qed
925 qed
927 lemma pdivmod_rel_0_iff: "pdivmod_rel 0 y q r \<longleftrightarrow> q = 0 \<and> r = 0"
928 by (auto dest: pdivmod_rel_unique intro: pdivmod_rel_0)
930 lemma pdivmod_rel_by_0_iff: "pdivmod_rel x 0 q r \<longleftrightarrow> q = 0 \<and> r = x"
931 by (auto dest: pdivmod_rel_unique intro: pdivmod_rel_by_0)
933 lemmas pdivmod_rel_unique_div = pdivmod_rel_unique [THEN conjunct1]
935 lemmas pdivmod_rel_unique_mod = pdivmod_rel_unique [THEN conjunct2]
937 instantiation poly :: (field) ring_div
938 begin
940 definition div_poly where
941   "x div y = (THE q. \<exists>r. pdivmod_rel x y q r)"
943 definition mod_poly where
944   "x mod y = (THE r. \<exists>q. pdivmod_rel x y q r)"
946 lemma div_poly_eq:
947   "pdivmod_rel x y q r \<Longrightarrow> x div y = q"
948 unfolding div_poly_def
949 by (fast elim: pdivmod_rel_unique_div)
951 lemma mod_poly_eq:
952   "pdivmod_rel x y q r \<Longrightarrow> x mod y = r"
953 unfolding mod_poly_def
954 by (fast elim: pdivmod_rel_unique_mod)
956 lemma pdivmod_rel:
957   "pdivmod_rel x y (x div y) (x mod y)"
958 proof -
959   from pdivmod_rel_exists
960     obtain q r where "pdivmod_rel x y q r" by fast
961   thus ?thesis
962     by (simp add: div_poly_eq mod_poly_eq)
963 qed
965 instance proof
966   fix x y :: "'a poly"
967   show "x div y * y + x mod y = x"
968     using pdivmod_rel [of x y]
970 next
971   fix x :: "'a poly"
972   have "pdivmod_rel x 0 0 x"
973     by (rule pdivmod_rel_by_0)
974   thus "x div 0 = 0"
975     by (rule div_poly_eq)
976 next
977   fix y :: "'a poly"
978   have "pdivmod_rel 0 y 0 0"
979     by (rule pdivmod_rel_0)
980   thus "0 div y = 0"
981     by (rule div_poly_eq)
982 next
983   fix x y z :: "'a poly"
984   assume "y \<noteq> 0"
985   hence "pdivmod_rel (x + z * y) y (z + x div y) (x mod y)"
986     using pdivmod_rel [of x y]
987     by (simp add: pdivmod_rel_def left_distrib)
988   thus "(x + z * y) div y = z + x div y"
989     by (rule div_poly_eq)
990 next
991   fix x y z :: "'a poly"
992   assume "x \<noteq> 0"
993   show "(x * y) div (x * z) = y div z"
994   proof (cases "y \<noteq> 0 \<and> z \<noteq> 0")
995     have "\<And>x::'a poly. pdivmod_rel x 0 0 x"
996       by (rule pdivmod_rel_by_0)
997     then have [simp]: "\<And>x::'a poly. x div 0 = 0"
998       by (rule div_poly_eq)
999     have "\<And>x::'a poly. pdivmod_rel 0 x 0 0"
1000       by (rule pdivmod_rel_0)
1001     then have [simp]: "\<And>x::'a poly. 0 div x = 0"
1002       by (rule div_poly_eq)
1003     case False then show ?thesis by auto
1004   next
1005     case True then have "y \<noteq> 0" and "z \<noteq> 0" by auto
1006     with `x \<noteq> 0`
1007     have "\<And>q r. pdivmod_rel y z q r \<Longrightarrow> pdivmod_rel (x * y) (x * z) q (x * r)"
1008       by (auto simp add: pdivmod_rel_def algebra_simps)
1009         (rule classical, simp add: degree_mult_eq)
1010     moreover from pdivmod_rel have "pdivmod_rel y z (y div z) (y mod z)" .
1011     ultimately have "pdivmod_rel (x * y) (x * z) (y div z) (x * (y mod z))" .
1012     then show ?thesis by (simp add: div_poly_eq)
1013   qed
1014 qed
1016 end
1018 lemma degree_mod_less:
1019   "y \<noteq> 0 \<Longrightarrow> x mod y = 0 \<or> degree (x mod y) < degree y"
1020   using pdivmod_rel [of x y]
1021   unfolding pdivmod_rel_def by simp
1023 lemma div_poly_less: "degree x < degree y \<Longrightarrow> x div y = 0"
1024 proof -
1025   assume "degree x < degree y"
1026   hence "pdivmod_rel x y 0 x"
1028   thus "x div y = 0" by (rule div_poly_eq)
1029 qed
1031 lemma mod_poly_less: "degree x < degree y \<Longrightarrow> x mod y = x"
1032 proof -
1033   assume "degree x < degree y"
1034   hence "pdivmod_rel x y 0 x"
1036   thus "x mod y = x" by (rule mod_poly_eq)
1037 qed
1039 lemma pdivmod_rel_smult_left:
1040   "pdivmod_rel x y q r
1041     \<Longrightarrow> pdivmod_rel (smult a x) y (smult a q) (smult a r)"
1044 lemma div_smult_left: "(smult a x) div y = smult a (x div y)"
1045   by (rule div_poly_eq, rule pdivmod_rel_smult_left, rule pdivmod_rel)
1047 lemma mod_smult_left: "(smult a x) mod y = smult a (x mod y)"
1048   by (rule mod_poly_eq, rule pdivmod_rel_smult_left, rule pdivmod_rel)
1050 lemma poly_div_minus_left [simp]:
1051   fixes x y :: "'a::field poly"
1052   shows "(- x) div y = - (x div y)"
1053   using div_smult_left [of "- 1::'a"] by simp
1055 lemma poly_mod_minus_left [simp]:
1056   fixes x y :: "'a::field poly"
1057   shows "(- x) mod y = - (x mod y)"
1058   using mod_smult_left [of "- 1::'a"] by simp
1060 lemma pdivmod_rel_smult_right:
1061   "\<lbrakk>a \<noteq> 0; pdivmod_rel x y q r\<rbrakk>
1062     \<Longrightarrow> pdivmod_rel x (smult a y) (smult (inverse a) q) r"
1063   unfolding pdivmod_rel_def by simp
1065 lemma div_smult_right:
1066   "a \<noteq> 0 \<Longrightarrow> x div (smult a y) = smult (inverse a) (x div y)"
1067   by (rule div_poly_eq, erule pdivmod_rel_smult_right, rule pdivmod_rel)
1069 lemma mod_smult_right: "a \<noteq> 0 \<Longrightarrow> x mod (smult a y) = x mod y"
1070   by (rule mod_poly_eq, erule pdivmod_rel_smult_right, rule pdivmod_rel)
1072 lemma poly_div_minus_right [simp]:
1073   fixes x y :: "'a::field poly"
1074   shows "x div (- y) = - (x div y)"
1075   using div_smult_right [of "- 1::'a"]
1078 lemma poly_mod_minus_right [simp]:
1079   fixes x y :: "'a::field poly"
1080   shows "x mod (- y) = x mod y"
1081   using mod_smult_right [of "- 1::'a"] by simp
1083 lemma pdivmod_rel_mult:
1084   "\<lbrakk>pdivmod_rel x y q r; pdivmod_rel q z q' r'\<rbrakk>
1085     \<Longrightarrow> pdivmod_rel x (y * z) q' (y * r' + r)"
1086 apply (cases "z = 0", simp add: pdivmod_rel_def)
1087 apply (cases "y = 0", simp add: pdivmod_rel_by_0_iff pdivmod_rel_0_iff)
1088 apply (cases "r = 0")
1089 apply (cases "r' = 0")
1091 apply (simp add: pdivmod_rel_def field_simps degree_mult_eq)
1092 apply (cases "r' = 0")
1093 apply (simp add: pdivmod_rel_def degree_mult_eq)
1094 apply (simp add: pdivmod_rel_def field_simps)
1096 done
1098 lemma poly_div_mult_right:
1099   fixes x y z :: "'a::field poly"
1100   shows "x div (y * z) = (x div y) div z"
1101   by (rule div_poly_eq, rule pdivmod_rel_mult, (rule pdivmod_rel)+)
1103 lemma poly_mod_mult_right:
1104   fixes x y z :: "'a::field poly"
1105   shows "x mod (y * z) = y * (x div y mod z) + x mod y"
1106   by (rule mod_poly_eq, rule pdivmod_rel_mult, (rule pdivmod_rel)+)
1108 lemma mod_pCons:
1109   fixes a and x
1110   assumes y: "y \<noteq> 0"
1111   defines b: "b \<equiv> coeff (pCons a (x mod y)) (degree y) / coeff y (degree y)"
1112   shows "(pCons a x) mod y = (pCons a (x mod y) - smult b y)"
1113 unfolding b
1114 apply (rule mod_poly_eq)
1115 apply (rule pdivmod_rel_pCons [OF pdivmod_rel y refl])
1116 done
1119 subsection {* GCD of polynomials *}
1121 function
1122   poly_gcd :: "'a::field poly \<Rightarrow> 'a poly \<Rightarrow> 'a poly" where
1123   "poly_gcd x 0 = smult (inverse (coeff x (degree x))) x"
1124 | "y \<noteq> 0 \<Longrightarrow> poly_gcd x y = poly_gcd y (x mod y)"
1125 by auto
1127 termination poly_gcd
1128 by (relation "measure (\<lambda>(x, y). if y = 0 then 0 else Suc (degree y))")
1129    (auto dest: degree_mod_less)
1131 declare poly_gcd.simps [simp del]
1133 lemma poly_gcd_dvd1 [iff]: "poly_gcd x y dvd x"
1134   and poly_gcd_dvd2 [iff]: "poly_gcd x y dvd y"
1135   apply (induct x y rule: poly_gcd.induct)
1137   apply (fastforce simp add: smult_dvd_iff dest: inverse_zero_imp_zero)
1138   apply (blast dest: dvd_mod_imp_dvd)
1139   done
1141 lemma poly_gcd_greatest: "k dvd x \<Longrightarrow> k dvd y \<Longrightarrow> k dvd poly_gcd x y"
1142   by (induct x y rule: poly_gcd.induct)
1143      (simp_all add: poly_gcd.simps dvd_mod dvd_smult)
1145 lemma dvd_poly_gcd_iff [iff]:
1146   "k dvd poly_gcd x y \<longleftrightarrow> k dvd x \<and> k dvd y"
1147   by (blast intro!: poly_gcd_greatest intro: dvd_trans)
1149 lemma poly_gcd_monic:
1150   "coeff (poly_gcd x y) (degree (poly_gcd x y)) =
1151     (if x = 0 \<and> y = 0 then 0 else 1)"
1152   by (induct x y rule: poly_gcd.induct)
1155 lemma poly_gcd_zero_iff [simp]:
1156   "poly_gcd x y = 0 \<longleftrightarrow> x = 0 \<and> y = 0"
1157   by (simp only: dvd_0_left_iff [symmetric] dvd_poly_gcd_iff)
1159 lemma poly_gcd_0_0 [simp]: "poly_gcd 0 0 = 0"
1160   by simp
1162 lemma poly_dvd_antisym:
1163   fixes p q :: "'a::idom poly"
1164   assumes coeff: "coeff p (degree p) = coeff q (degree q)"
1165   assumes dvd1: "p dvd q" and dvd2: "q dvd p" shows "p = q"
1166 proof (cases "p = 0")
1167   case True with coeff show "p = q" by simp
1168 next
1169   case False with coeff have "q \<noteq> 0" by auto
1170   have degree: "degree p = degree q"
1171     using `p dvd q` `q dvd p` `p \<noteq> 0` `q \<noteq> 0`
1172     by (intro order_antisym dvd_imp_degree_le)
1174   from `p dvd q` obtain a where a: "q = p * a" ..
1175   with `q \<noteq> 0` have "a \<noteq> 0" by auto
1176   with degree a `p \<noteq> 0` have "degree a = 0"
1178   with coeff a show "p = q"
1179     by (cases a, auto split: if_splits)
1180 qed
1182 lemma poly_gcd_unique:
1183   assumes dvd1: "d dvd x" and dvd2: "d dvd y"
1184     and greatest: "\<And>k. k dvd x \<Longrightarrow> k dvd y \<Longrightarrow> k dvd d"
1185     and monic: "coeff d (degree d) = (if x = 0 \<and> y = 0 then 0 else 1)"
1186   shows "poly_gcd x y = d"
1187 proof -
1188   have "coeff (poly_gcd x y) (degree (poly_gcd x y)) = coeff d (degree d)"
1189     by (simp_all add: poly_gcd_monic monic)
1190   moreover have "poly_gcd x y dvd d"
1191     using poly_gcd_dvd1 poly_gcd_dvd2 by (rule greatest)
1192   moreover have "d dvd poly_gcd x y"
1193     using dvd1 dvd2 by (rule poly_gcd_greatest)
1194   ultimately show ?thesis
1195     by (rule poly_dvd_antisym)
1196 qed
1198 interpretation poly_gcd: abel_semigroup poly_gcd
1199 proof
1200   fix x y z :: "'a poly"
1201   show "poly_gcd (poly_gcd x y) z = poly_gcd x (poly_gcd y z)"
1202     by (rule poly_gcd_unique) (auto intro: dvd_trans simp add: poly_gcd_monic)
1203   show "poly_gcd x y = poly_gcd y x"
1204     by (rule poly_gcd_unique) (simp_all add: poly_gcd_monic)
1205 qed
1207 lemmas poly_gcd_assoc = poly_gcd.assoc
1208 lemmas poly_gcd_commute = poly_gcd.commute
1209 lemmas poly_gcd_left_commute = poly_gcd.left_commute
1211 lemmas poly_gcd_ac = poly_gcd_assoc poly_gcd_commute poly_gcd_left_commute
1213 lemma poly_gcd_1_left [simp]: "poly_gcd 1 y = 1"
1214 by (rule poly_gcd_unique) simp_all
1216 lemma poly_gcd_1_right [simp]: "poly_gcd x 1 = 1"
1217 by (rule poly_gcd_unique) simp_all
1219 lemma poly_gcd_minus_left [simp]: "poly_gcd (- x) y = poly_gcd x y"
1220 by (rule poly_gcd_unique) (simp_all add: poly_gcd_monic)
1222 lemma poly_gcd_minus_right [simp]: "poly_gcd x (- y) = poly_gcd x y"
1223 by (rule poly_gcd_unique) (simp_all add: poly_gcd_monic)
1226 subsection {* Evaluation of polynomials *}
1228 definition
1229   poly :: "'a::comm_semiring_0 poly \<Rightarrow> 'a \<Rightarrow> 'a" where
1230   "poly = poly_rec (\<lambda>x. 0) (\<lambda>a p f x. a + x * f x)"
1232 lemma poly_0 [simp]: "poly 0 x = 0"
1233   unfolding poly_def by (simp add: poly_rec_0)
1235 lemma poly_pCons [simp]: "poly (pCons a p) x = a + x * poly p x"
1236   unfolding poly_def by (simp add: poly_rec_pCons)
1238 lemma poly_1 [simp]: "poly 1 x = 1"
1239   unfolding one_poly_def by simp
1241 lemma poly_monom:
1242   fixes a x :: "'a::{comm_semiring_1}"
1243   shows "poly (monom a n) x = a * x ^ n"
1244   by (induct n, simp add: monom_0, simp add: monom_Suc power_Suc mult_ac)
1246 lemma poly_add [simp]: "poly (p + q) x = poly p x + poly q x"
1247   apply (induct p arbitrary: q, simp)
1248   apply (case_tac q, simp, simp add: algebra_simps)
1249   done
1251 lemma poly_minus [simp]:
1252   fixes x :: "'a::comm_ring"
1253   shows "poly (- p) x = - poly p x"
1254   by (induct p, simp_all)
1256 lemma poly_diff [simp]:
1257   fixes x :: "'a::comm_ring"
1258   shows "poly (p - q) x = poly p x - poly q x"
1261 lemma poly_setsum: "poly (\<Sum>k\<in>A. p k) x = (\<Sum>k\<in>A. poly (p k) x)"
1262   by (cases "finite A", induct set: finite, simp_all)
1264 lemma poly_smult [simp]: "poly (smult a p) x = a * poly p x"
1265   by (induct p, simp, simp add: algebra_simps)
1267 lemma poly_mult [simp]: "poly (p * q) x = poly p x * poly q x"
1268   by (induct p, simp_all, simp add: algebra_simps)
1270 lemma poly_power [simp]:
1271   fixes p :: "'a::{comm_semiring_1} poly"
1272   shows "poly (p ^ n) x = poly p x ^ n"
1273   by (induct n, simp, simp add: power_Suc)
1276 subsection {* Synthetic division *}
1278 text {*
1279   Synthetic division is simply division by the
1280   linear polynomial @{term "x - c"}.
1281 *}
1283 definition
1284   synthetic_divmod :: "'a::comm_semiring_0 poly \<Rightarrow> 'a \<Rightarrow> 'a poly \<times> 'a"
1285 where
1286   "synthetic_divmod p c =
1287     poly_rec (0, 0) (\<lambda>a p (q, r). (pCons r q, a + c * r)) p"
1289 definition
1290   synthetic_div :: "'a::comm_semiring_0 poly \<Rightarrow> 'a \<Rightarrow> 'a poly"
1291 where
1292   "synthetic_div p c = fst (synthetic_divmod p c)"
1294 lemma synthetic_divmod_0 [simp]:
1295   "synthetic_divmod 0 c = (0, 0)"
1296   unfolding synthetic_divmod_def
1299 lemma synthetic_divmod_pCons [simp]:
1300   "synthetic_divmod (pCons a p) c =
1301     (\<lambda>(q, r). (pCons r q, a + c * r)) (synthetic_divmod p c)"
1302   unfolding synthetic_divmod_def
1305 lemma snd_synthetic_divmod: "snd (synthetic_divmod p c) = poly p c"
1306   by (induct p, simp, simp add: split_def)
1308 lemma synthetic_div_0 [simp]: "synthetic_div 0 c = 0"
1309   unfolding synthetic_div_def by simp
1311 lemma synthetic_div_pCons [simp]:
1312   "synthetic_div (pCons a p) c = pCons (poly p c) (synthetic_div p c)"
1313   unfolding synthetic_div_def
1314   by (simp add: split_def snd_synthetic_divmod)
1316 lemma synthetic_div_eq_0_iff:
1317   "synthetic_div p c = 0 \<longleftrightarrow> degree p = 0"
1318   by (induct p, simp, case_tac p, simp)
1320 lemma degree_synthetic_div:
1321   "degree (synthetic_div p c) = degree p - 1"
1322   by (induct p, simp, simp add: synthetic_div_eq_0_iff)
1324 lemma synthetic_div_correct:
1325   "p + smult c (synthetic_div p c) = pCons (poly p c) (synthetic_div p c)"
1326   by (induct p) simp_all
1328 lemma synthetic_div_unique_lemma: "smult c p = pCons a p \<Longrightarrow> p = 0"
1329 by (induct p arbitrary: a) simp_all
1331 lemma synthetic_div_unique:
1332   "p + smult c q = pCons r q \<Longrightarrow> r = poly p c \<and> q = synthetic_div p c"
1333 apply (induct p arbitrary: q r)
1334 apply (simp, frule synthetic_div_unique_lemma, simp)
1335 apply (case_tac q, force)
1336 done
1338 lemma synthetic_div_correct':
1339   fixes c :: "'a::comm_ring_1"
1340   shows "[:-c, 1:] * synthetic_div p c + [:poly p c:] = p"
1341   using synthetic_div_correct [of p c]
1344 lemma poly_eq_0_iff_dvd:
1345   fixes c :: "'a::idom"
1346   shows "poly p c = 0 \<longleftrightarrow> [:-c, 1:] dvd p"
1347 proof
1348   assume "poly p c = 0"
1349   with synthetic_div_correct' [of c p]
1350   have "p = [:-c, 1:] * synthetic_div p c" by simp
1351   then show "[:-c, 1:] dvd p" ..
1352 next
1353   assume "[:-c, 1:] dvd p"
1354   then obtain k where "p = [:-c, 1:] * k" by (rule dvdE)
1355   then show "poly p c = 0" by simp
1356 qed
1358 lemma dvd_iff_poly_eq_0:
1359   fixes c :: "'a::idom"
1360   shows "[:c, 1:] dvd p \<longleftrightarrow> poly p (-c) = 0"
1363 lemma poly_roots_finite:
1364   fixes p :: "'a::idom poly"
1365   shows "p \<noteq> 0 \<Longrightarrow> finite {x. poly p x = 0}"
1366 proof (induct n \<equiv> "degree p" arbitrary: p)
1367   case (0 p)
1368   then obtain a where "a \<noteq> 0" and "p = [:a:]"
1369     by (cases p, simp split: if_splits)
1370   then show "finite {x. poly p x = 0}" by simp
1371 next
1372   case (Suc n p)
1373   show "finite {x. poly p x = 0}"
1374   proof (cases "\<exists>x. poly p x = 0")
1375     case False
1376     then show "finite {x. poly p x = 0}" by simp
1377   next
1378     case True
1379     then obtain a where "poly p a = 0" ..
1380     then have "[:-a, 1:] dvd p" by (simp only: poly_eq_0_iff_dvd)
1381     then obtain k where k: "p = [:-a, 1:] * k" ..
1382     with `p \<noteq> 0` have "k \<noteq> 0" by auto
1383     with k have "degree p = Suc (degree k)"
1384       by (simp add: degree_mult_eq del: mult_pCons_left)
1385     with `Suc n = degree p` have "n = degree k" by simp
1386     then have "finite {x. poly k x = 0}" using `k \<noteq> 0` by (rule Suc.hyps)
1387     then have "finite (insert a {x. poly k x = 0})" by simp
1388     then show "finite {x. poly p x = 0}"
1390                del: mult_pCons_left)
1391   qed
1392 qed
1394 lemma poly_zero:
1395   fixes p :: "'a::{idom,ring_char_0} poly"
1396   shows "poly p = poly 0 \<longleftrightarrow> p = 0"
1397 apply (cases "p = 0", simp_all)
1398 apply (drule poly_roots_finite)
1399 apply (auto simp add: infinite_UNIV_char_0)
1400 done
1402 lemma poly_eq_iff:
1403   fixes p q :: "'a::{idom,ring_char_0} poly"
1404   shows "poly p = poly q \<longleftrightarrow> p = q"
1405   using poly_zero [of "p - q"]
1409 subsection {* Composition of polynomials *}
1411 definition
1412   pcompose :: "'a::comm_semiring_0 poly \<Rightarrow> 'a poly \<Rightarrow> 'a poly"
1413 where
1414   "pcompose p q = poly_rec 0 (\<lambda>a _ c. [:a:] + q * c) p"
1416 lemma pcompose_0 [simp]: "pcompose 0 q = 0"
1417   unfolding pcompose_def by (simp add: poly_rec_0)
1419 lemma pcompose_pCons:
1420   "pcompose (pCons a p) q = [:a:] + q * pcompose p q"
1421   unfolding pcompose_def by (simp add: poly_rec_pCons)
1423 lemma poly_pcompose: "poly (pcompose p q) x = poly p (poly q x)"
1424   by (induct p) (simp_all add: pcompose_pCons)
1426 lemma degree_pcompose_le:
1427   "degree (pcompose p q) \<le> degree p * degree q"
1428 apply (induct p, simp)
1429 apply (simp add: pcompose_pCons, clarify)
1431 apply (rule order_trans [OF degree_mult_le], simp)
1432 done
1435 subsection {* Order of polynomial roots *}
1437 definition
1438   order :: "'a::idom \<Rightarrow> 'a poly \<Rightarrow> nat"
1439 where
1440   "order a p = (LEAST n. \<not> [:-a, 1:] ^ Suc n dvd p)"
1442 lemma coeff_linear_power:
1443   fixes a :: "'a::comm_semiring_1"
1444   shows "coeff ([:a, 1:] ^ n) n = 1"
1445 apply (induct n, simp_all)
1446 apply (subst coeff_eq_0)
1447 apply (auto intro: le_less_trans degree_power_le)
1448 done
1450 lemma degree_linear_power:
1451   fixes a :: "'a::comm_semiring_1"
1452   shows "degree ([:a, 1:] ^ n) = n"
1453 apply (rule order_antisym)
1454 apply (rule ord_le_eq_trans [OF degree_power_le], simp)
1455 apply (rule le_degree, simp add: coeff_linear_power)
1456 done
1458 lemma order_1: "[:-a, 1:] ^ order a p dvd p"
1459 apply (cases "p = 0", simp)
1460 apply (cases "order a p", simp)
1461 apply (subgoal_tac "nat < (LEAST n. \<not> [:-a, 1:] ^ Suc n dvd p)")
1462 apply (drule not_less_Least, simp)
1463 apply (fold order_def, simp)
1464 done
1466 lemma order_2: "p \<noteq> 0 \<Longrightarrow> \<not> [:-a, 1:] ^ Suc (order a p) dvd p"
1467 unfolding order_def
1468 apply (rule LeastI_ex)
1469 apply (rule_tac x="degree p" in exI)
1470 apply (rule notI)
1471 apply (drule (1) dvd_imp_degree_le)
1472 apply (simp only: degree_linear_power)
1473 done
1475 lemma order:
1476   "p \<noteq> 0 \<Longrightarrow> [:-a, 1:] ^ order a p dvd p \<and> \<not> [:-a, 1:] ^ Suc (order a p) dvd p"
1477 by (rule conjI [OF order_1 order_2])
1479 lemma order_degree:
1480   assumes p: "p \<noteq> 0"
1481   shows "order a p \<le> degree p"
1482 proof -
1483   have "order a p = degree ([:-a, 1:] ^ order a p)"
1484     by (simp only: degree_linear_power)
1485   also have "\<dots> \<le> degree p"
1486     using order_1 p by (rule dvd_imp_degree_le)
1487   finally show ?thesis .
1488 qed
1490 lemma order_root: "poly p a = 0 \<longleftrightarrow> p = 0 \<or> order a p \<noteq> 0"
1491 apply (cases "p = 0", simp_all)
1492 apply (rule iffI)
1493 apply (rule ccontr, simp)
1494 apply (frule order_2 [where a=a], simp)
1497 apply (simp only: order_def)
1498 apply (drule not_less_Least, simp)
1499 done
1502 subsection {* Configuration of the code generator *}
1504 code_datatype "0::'a::zero poly" pCons
1506 declare pCons_0_0 [code_post]
1508 instantiation poly :: ("{zero, equal}") equal
1509 begin
1511 definition
1512   "HOL.equal (p::'a poly) q \<longleftrightarrow> p = q"
1514 instance proof
1515 qed (rule equal_poly_def)
1517 end
1519 lemma eq_poly_code [code]:
1520   "HOL.equal (0::_ poly) (0::_ poly) \<longleftrightarrow> True"
1521   "HOL.equal (0::_ poly) (pCons b q) \<longleftrightarrow> HOL.equal 0 b \<and> HOL.equal 0 q"
1522   "HOL.equal (pCons a p) (0::_ poly) \<longleftrightarrow> HOL.equal a 0 \<and> HOL.equal p 0"
1523   "HOL.equal (pCons a p) (pCons b q) \<longleftrightarrow> HOL.equal a b \<and> HOL.equal p q"
1526 lemma [code nbe]:
1527   "HOL.equal (p :: _ poly) p \<longleftrightarrow> True"
1528   by (fact equal_refl)
1530 lemmas coeff_code [code] =
1531   coeff_0 coeff_pCons_0 coeff_pCons_Suc
1533 lemmas degree_code [code] =
1534   degree_0 degree_pCons_eq_if
1536 lemmas monom_poly_code [code] =
1537   monom_0 monom_Suc
1540   "0 + q = (q :: _ poly)"
1541   "p + 0 = (p :: _ poly)"
1542   "pCons a p + pCons b q = pCons (a + b) (p + q)"
1543 by simp_all
1545 lemma minus_poly_code [code]:
1546   "- 0 = (0 :: _ poly)"
1547   "- pCons a p = pCons (- a) (- p)"
1548 by simp_all
1550 lemma diff_poly_code [code]:
1551   "0 - q = (- q :: _ poly)"
1552   "p - 0 = (p :: _ poly)"
1553   "pCons a p - pCons b q = pCons (a - b) (p - q)"
1554 by simp_all
1556 lemmas smult_poly_code [code] =
1557   smult_0_right smult_pCons
1559 lemma mult_poly_code [code]:
1560   "0 * q = (0 :: _ poly)"
1561   "pCons a p * q = smult a q + pCons 0 (p * q)"
1562 by simp_all
1564 lemmas poly_code [code] =
1565   poly_0 poly_pCons
1567 lemmas synthetic_divmod_code [code] =
1568   synthetic_divmod_0 synthetic_divmod_pCons
1570 text {* code generator setup for div and mod *}
1572 definition
1573   pdivmod :: "'a::field poly \<Rightarrow> 'a poly \<Rightarrow> 'a poly \<times> 'a poly"
1574 where
1575   "pdivmod x y = (x div y, x mod y)"
1577 lemma div_poly_code [code]: "x div y = fst (pdivmod x y)"
1578   unfolding pdivmod_def by simp
1580 lemma mod_poly_code [code]: "x mod y = snd (pdivmod x y)"
1581   unfolding pdivmod_def by simp
1583 lemma pdivmod_0 [code]: "pdivmod 0 y = (0, 0)"
1584   unfolding pdivmod_def by simp
1586 lemma pdivmod_pCons [code]:
1587   "pdivmod (pCons a x) y =
1588     (if y = 0 then (0, pCons a x) else
1589       (let (q, r) = pdivmod x y;
1590            b = coeff (pCons a r) (degree y) / coeff y (degree y)
1591         in (pCons b q, pCons a r - smult b y)))"
1592 apply (simp add: pdivmod_def Let_def, safe)
1593 apply (rule div_poly_eq)
1594 apply (erule pdivmod_rel_pCons [OF pdivmod_rel _ refl])
1595 apply (rule mod_poly_eq)
1596 apply (erule pdivmod_rel_pCons [OF pdivmod_rel _ refl])
1597 done
1599 lemma poly_gcd_code [code]:
1600   "poly_gcd x y =
1601     (if y = 0 then smult (inverse (coeff x (degree x))) x
1602               else poly_gcd y (x mod y))"