1 (* ========================================================================= *)
2 (* Bernoulli numbers and polynomials; sum of kth powers. *)
3 (* ========================================================================= *)
5 needs "Library/binomial.ml";;
6 needs "Library/analysis.ml";;
7 needs "Library/transc.ml";;
11 (* ------------------------------------------------------------------------- *)
12 (* A couple of basic lemmas about new-style sums. *)
13 (* ------------------------------------------------------------------------- *)
16 (`!a m n. m <= n + 1 ==> sum(m..n) (\i. a(i + 1) - a(i)) = a(n + 1) - a(m)`,
17 GEN_TAC THEN GEN_TAC THEN INDUCT_TAC THEN
18 REWRITE_TAC[SUM_CLAUSES_NUMSEG] THENL
19 [REWRITE_TAC[ARITH_RULE `m <= 0 + 1 <=> m = 0 \/ m = 1`] THEN
20 STRIP_TAC THEN ASM_REWRITE_TAC[ARITH; ADD_CLAUSES; REAL_SUB_REFL];
21 SIMP_TAC[ARITH_RULE `m <= SUC n + 1 <=> m <= n + 1 \/ m = SUC n + 1`] THEN
22 STRIP_TAC THEN ASM_SIMP_TAC[ADD1] THENL [REAL_ARITH_TAC; ALL_TAC] THEN
23 REWRITE_TAC[REAL_SUB_REFL; ARITH_RULE `~((n + 1) + 1 <= n + 1)`] THEN
24 MATCH_MP_TAC SUM_TRIV_NUMSEG THEN ARITH_TAC]);;
28 (!k. a <= k /\ k <= b ==> ((\x. f x k) diffl f'(k)) x)
29 ==> ((\x. sum(a..b) (f x)) diffl (sum(a..b) f')) x`,
30 REPLICATE_TAC 3 GEN_TAC THEN INDUCT_TAC THEN
31 REWRITE_TAC[SUM_CLAUSES_NUMSEG] THEN COND_CASES_TAC THEN
32 ASM_SIMP_TAC[ARITH; DIFF_CONST; SUM_TRIV_NUMSEG;
33 ARITH_RULE `~(a <= SUC b) ==> b < a`] THEN
34 DISCH_TAC THEN MATCH_MP_TAC DIFF_ADD THEN
35 ASM_SIMP_TAC[LE_REFL; ARITH_RULE `k <= b ==> k <= SUC b`]);;
37 (* ------------------------------------------------------------------------- *)
38 (* Bernoulli numbers. *)
39 (* ------------------------------------------------------------------------- *)
41 let bernoulli = define
42 `(bernoulli 0 = &1) /\
43 (!n. bernoulli(SUC n) =
44 --sum(0..n) (\j. &(binom(n + 2,j)) * bernoulli j) / (&n + &2))`;;
46 (* ------------------------------------------------------------------------- *)
47 (* A slightly tidier-looking form of the recurrence. *)
48 (* ------------------------------------------------------------------------- *)
51 (`!n. sum(0..n) (\j. &(binom(n + 1,j)) * bernoulli j) =
52 if n = 0 then &1 else &0`,
54 REWRITE_TAC[bernoulli; SUM_CLAUSES_NUMSEG; GSYM ADD1; ADD_CLAUSES; binom;
55 REAL_MUL_LID; LE_0; NOT_SUC] THEN
56 SIMP_TAC[BINOM_LT; ARITH_RULE `n < SUC n`; BINOM_REFL; REAL_ADD_LID] THEN
57 REWRITE_TAC[ADD_CLAUSES] THEN REWRITE_TAC[GSYM REAL_OF_NUM_ADD] THEN
58 REWRITE_TAC[ARITH_RULE `SUC(SUC n) = n + 2`] THEN
59 MATCH_MP_TAC(REAL_FIELD `x = &n + &2 ==> s + x * --s / (&n + &2) = &0`) THEN
60 REWRITE_TAC[ADD1; BINOM_TOP_STEP_REAL; ARITH_RULE `~(n = n + 1)`] THEN
61 REWRITE_TAC[BINOM_REFL] THEN REAL_ARITH_TAC);;
63 (* ------------------------------------------------------------------------- *)
64 (* Bernoulli polynomials. *)
65 (* ------------------------------------------------------------------------- *)
67 let bernpoly = new_definition
68 `bernpoly n x = sum(0..n) (\k. &(binom(n,k)) * bernoulli k * x pow (n - k))`;;
70 (* ------------------------------------------------------------------------- *)
71 (* The key derivative recurrence. *)
72 (* ------------------------------------------------------------------------- *)
74 let DIFF_BERNPOLY = prove
75 (`!n x. ((bernpoly (SUC n)) diffl (&(SUC n) * bernpoly n x)) x`,
77 GEN_REWRITE_TAC (RATOR_CONV o LAND_CONV) [GSYM ETA_AX] THEN
78 REWRITE_TAC[bernpoly; SUM_CLAUSES_NUMSEG; LE_0] THEN
79 GEN_REWRITE_TAC LAND_CONV [GSYM REAL_ADD_RID] THEN
80 MATCH_MP_TAC DIFF_ADD THEN REWRITE_TAC[SUB_REFL; real_pow; DIFF_CONST] THEN
81 REWRITE_TAC[GSYM SUM_LMUL] THEN MATCH_MP_TAC DIFF_SUM THEN
82 REPEAT STRIP_TAC THEN REWRITE_TAC[ADD1; BINOM_TOP_STEP_REAL] THEN
83 DIFF_TAC THEN ASM_SIMP_TAC[ARITH_RULE `k <= n ==> ~(k = n + 1)`] THEN
84 REWRITE_TAC[REAL_MUL_LZERO; REAL_ADD_LID] THEN
85 ASM_SIMP_TAC[ARITH_RULE `k <= n ==> (n + 1) - k - 1 = n - k`] THEN
86 ASM_SIMP_TAC[GSYM REAL_OF_NUM_SUB; ARITH_RULE `k <= n ==> k <= n + 1`] THEN
87 UNDISCH_TAC `k <= n:num` THEN
88 REWRITE_TAC[GSYM REAL_OF_NUM_ADD; GSYM REAL_OF_NUM_LE] THEN
89 ABBREV_TAC `z = x pow (n - k)` THEN CONV_TAC REAL_FIELD);;
91 (* ------------------------------------------------------------------------- *)
92 (* Hence the key stepping recurrence. *)
93 (* ------------------------------------------------------------------------- *)
95 let INTEGRALS_EQ = prove
96 (`!f g. (!x. ((\x. f(x) - g(x)) diffl &0) x) /\ f(&0) = g(&0)
99 MP_TAC(SPECL [`\x:real. f(x) - g(x)`; `x:real`; `&0`] DIFF_ISCONST_ALL) THEN
100 ASM_REWRITE_TAC[] THEN REAL_ARITH_TAC);;
102 let RECURRENCE_BERNPOLY = prove
103 (`!n x. bernpoly n (x + &1) - bernpoly n x = &n * x pow (n - 1)`,
105 [REWRITE_TAC[bernpoly; SUM_SING_NUMSEG; REAL_SUB_REFL; SUB_REFL;
106 real_pow; REAL_MUL_LZERO];
108 MATCH_MP_TAC INTEGRALS_EQ THEN CONJ_TAC THENL
109 [X_GEN_TAC `x:real` THEN FIRST_X_ASSUM(MP_TAC o SPEC `x:real`) THEN
110 ONCE_REWRITE_TAC[GSYM REAL_SUB_0] THEN
111 DISCH_THEN(MP_TAC o AP_TERM `(*) (&(SUC n))`) THEN
112 REWRITE_TAC[REAL_MUL_RZERO] THEN DISCH_THEN(SUBST1_TAC o SYM) THEN
113 REWRITE_TAC[REAL_SUB_LDISTRIB] THEN
114 REPEAT(MATCH_MP_TAC DIFF_SUB THEN CONJ_TAC) THEN
115 SIMP_TAC[SUC_SUB1; DIFF_CMUL; DIFF_POW; DIFF_BERNPOLY; ETA_AX] THEN
116 GEN_REWRITE_TAC LAND_CONV [GSYM REAL_MUL_RID] THEN
117 MATCH_MP_TAC DIFF_CHAIN THEN REWRITE_TAC[DIFF_BERNPOLY] THEN
118 DIFF_TAC THEN REAL_ARITH_TAC;
120 REWRITE_TAC[bernpoly; GSYM SUM_SUB_NUMSEG] THEN
121 REWRITE_TAC[REAL_ADD_LID; REAL_POW_ONE; GSYM REAL_SUB_LDISTRIB] THEN
122 REWRITE_TAC[SUM_CLAUSES_NUMSEG; LE_0; SUB_REFL; real_pow] THEN
123 REWRITE_TAC[REAL_SUB_REFL; REAL_MUL_RZERO; REAL_ADD_RID] THEN
124 SIMP_TAC[ARITH_RULE `i <= n ==> SUC n - i = SUC(n - i)`] THEN
125 REWRITE_TAC[real_pow; REAL_MUL_LZERO; REAL_SUB_RZERO; REAL_MUL_RID] THEN
126 REWRITE_TAC[BERNOULLI; ADD1] THEN
127 COND_CASES_TAC THEN ASM_REWRITE_TAC[ARITH; real_pow; REAL_MUL_LID] THEN
128 CONV_TAC SYM_CONV THEN REWRITE_TAC[REAL_ENTIRE; REAL_POW_EQ_0] THEN
129 ASM_REWRITE_TAC[ADD_SUB]);;
131 (* ------------------------------------------------------------------------- *)
132 (* Hence we get the main result. *)
133 (* ------------------------------------------------------------------------- *)
135 let SUM_OF_POWERS = prove
136 (`!n. sum(0..n) (\k. &k pow m) =
137 (bernpoly(SUC m) (&n + &1) - bernpoly(SUC m) (&0)) / (&m + &1)`,
138 GEN_TAC THEN ASM_SIMP_TAC[REAL_EQ_RDIV_EQ; REAL_ARITH `&0 < &n + &1`] THEN
139 ONCE_REWRITE_TAC[GSYM REAL_MUL_SYM] THEN
140 REWRITE_TAC[GSYM SUM_LMUL] THEN MATCH_MP_TAC EQ_TRANS THEN EXISTS_TAC
141 `sum(0..n) (\i. bernpoly (SUC m) (&(i + 1)) - bernpoly (SUC m) (&i))` THEN
143 [REWRITE_TAC[RECURRENCE_BERNPOLY; GSYM REAL_OF_NUM_ADD] THEN
144 REWRITE_TAC[GSYM REAL_OF_NUM_SUC; SUC_SUB1];
145 SIMP_TAC[SUM_DIFFS; LE_0] THEN REWRITE_TAC[REAL_OF_NUM_ADD]]);;
147 (* ------------------------------------------------------------------------- *)
148 (* Now explicit computations of the various terms on specific instances. *)
149 (* ------------------------------------------------------------------------- *)
153 (`sum(0..0) f = f 0 /\ sum(0..SUC n) f = sum(0..n) f + f(SUC n)`,
154 SIMP_TAC[SUM_CLAUSES_NUMSEG; LE_0]) in
155 let econv_0 = GEN_REWRITE_CONV I [CONJUNCT1 pth]
156 and econv_1 = GEN_REWRITE_CONV I [CONJUNCT2 pth] in
159 (LAND_CONV(RAND_CONV num_CONV) THENC econv_1 THENC
160 COMB2_CONV (RAND_CONV sconv) (RAND_CONV NUM_SUC_CONV))) tm in
165 (`a * b * x = FACT c ==> x = (FACT c) DIV (a * b)`,
166 REPEAT STRIP_TAC THEN CONV_TAC SYM_CONV THEN
167 MATCH_MP_TAC DIV_UNIQ THEN EXISTS_TAC `0` THEN CONJ_TAC THENL
168 [POP_ASSUM MP_TAC THEN ARITH_TAC;
169 POP_ASSUM MP_TAC THEN ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
170 SIMP_TAC[LT_NZ; MULT_ASSOC; MULT_CLAUSES] THEN
171 MESON_TAC[LT_NZ; FACT_LT]]) in
172 let match_pth = MATCH_MP pth
173 and binom_tm = `binom` in
175 let bop,lr = dest_comb tm in
176 if bop <> binom_tm then failwith "BINOM_CONV" else
177 let l,r = dest_pair lr in
178 let n = dest_numeral l and k = dest_numeral r in
180 let th = SPECL [l;r] BINOM_LT in
181 MP th (EQT_ELIM(NUM_LT_CONV(lhand(concl th))))
184 let th1 = match_pth(SPECL [mk_numeral d; r] BINOM_FACT) in
185 CONV_RULE NUM_REDUCE_CONV th1;;
188 let th_0,th_1 = CONJ_PAIR bernoulli
189 and b_tm = `bernoulli` in
190 let conv_1 = GEN_REWRITE_CONV I [th_1] in
192 if n <= 0 then [th_0] else
193 let bths = bconv (n - 1)
194 and tm = mk_comb(b_tm,mk_small_numeral n) in
195 (RAND_CONV num_CONV THENC conv_1 THENC
196 LAND_CONV(RAND_CONV SUM_CONV) THENC
197 ONCE_DEPTH_CONV BETA_CONV THENC
198 DEPTH_CONV(NUM_RED_CONV ORELSEC BINOM_CONV) THENC
199 GEN_REWRITE_CONV ONCE_DEPTH_CONV bths THENC
200 REAL_RAT_REDUCE_CONV) tm :: bths in
204 let b_tm = `bernoulli` in
205 fun tm -> let op,n = dest_comb tm in
206 if op <> b_tm or not(is_numeral n) then failwith "BERNOULLI_CONV"
207 else hd(BERNOULLIS(dest_small_numeral n));;
211 REWR_CONV bernpoly THENC SUM_CONV THENC
212 TOP_DEPTH_CONV BETA_CONV THENC NUM_REDUCE_CONV
214 ONCE_DEPTH_CONV BINOM_CONV THENC REAL_POLY_CONV in
216 let n = dest_small_numeral(lhand tm) in
217 let conv_2 = GEN_REWRITE_CONV ONCE_DEPTH_CONV (BERNOULLIS n) in
218 (conv_1 THENC conv_2 THENC conv_3) tm;;
222 (`sum(0..n) (\k. &k pow m) =
223 (\p. (p(&n + &1) - p(&0)) / (&m + &1))
224 (\x. bernpoly (SUC m) x)`,
225 REWRITE_TAC[SUM_OF_POWERS]) in
226 let conv_0 = REWR_CONV pth in
228 RAND_CONV(ABS_CONV(LAND_CONV NUM_SUC_CONV THENC BERNPOLY_CONV)) THENC
229 TOP_DEPTH_CONV BETA_CONV THENC
234 (`sum(0..n) (\k. &k pow p) = &m ==> nsum(0..n) (\k. k EXP p) = m`,
235 REWRITE_TAC[REAL_OF_NUM_POW; GSYM REAL_OF_NUM_SUM_NUMSEG;
237 let rule_1 = PART_MATCH (lhs o rand) pth in
239 let th1 = rule_1 tm in
240 let th2 = SOP_CONV(lhs(lhand(concl th1))) in
243 (* ------------------------------------------------------------------------- *)
244 (* The example Bernoulli bragged about. *)
245 (* ------------------------------------------------------------------------- *)
247 time SOP_NUM_CONV `nsum(0..1000) (\k. k EXP 10)`;;
249 (* ------------------------------------------------------------------------- *)
250 (* The general formulas for moderate powers. *)
251 (* ------------------------------------------------------------------------- *)
253 time SOP_CONV `sum(0..n) (\k. &k pow 0)`;;
254 time SOP_CONV `sum(0..n) (\k. &k pow 1)`;;
255 time SOP_CONV `sum(0..n) (\k. &k pow 2)`;;
256 time SOP_CONV `sum(0..n) (\k. &k pow 3)`;;
257 time SOP_CONV `sum(0..n) (\k. &k pow 4)`;;
258 time SOP_CONV `sum(0..n) (\k. &k pow 5)`;;
259 time SOP_CONV `sum(0..n) (\k. &k pow 6)`;;
260 time SOP_CONV `sum(0..n) (\k. &k pow 7)`;;
261 time SOP_CONV `sum(0..n) (\k. &k pow 8)`;;
262 time SOP_CONV `sum(0..n) (\k. &k pow 9)`;;
263 time SOP_CONV `sum(0..n) (\k. &k pow 10)`;;
264 time SOP_CONV `sum(0..n) (\k. &k pow 11)`;;
265 time SOP_CONV `sum(0..n) (\k. &k pow 12)`;;
266 time SOP_CONV `sum(0..n) (\k. &k pow 13)`;;
267 time SOP_CONV `sum(0..n) (\k. &k pow 14)`;;
268 time SOP_CONV `sum(0..n) (\k. &k pow 15)`;;
269 time SOP_CONV `sum(0..n) (\k. &k pow 16)`;;
270 time SOP_CONV `sum(0..n) (\k. &k pow 17)`;;
271 time SOP_CONV `sum(0..n) (\k. &k pow 18)`;;
272 time SOP_CONV `sum(0..n) (\k. &k pow 19)`;;
273 time SOP_CONV `sum(0..n) (\k. &k pow 20)`;;
274 time SOP_CONV `sum(0..n) (\k. &k pow 21)`;;