1 (* ========================================================================= *)
2 (* Derivation of Machin's formula and other similar ones. *)
3 (* ========================================================================= *)
5 needs "Library/transc.ml";;
7 let REAL_LE_1_POW2 = prove
9 REWRITE_TAC[REAL_OF_NUM_POW; REAL_OF_NUM_LE; ARITH_RULE `1 <= n <=> 0 < n`;
12 let REAL_LT_1_POW2 = prove
13 (`!n. &1 < &2 pow n <=> ~(n = 0)`,
14 GEN_TAC THEN ASM_CASES_TAC `n = 0` THEN ASM_REWRITE_TAC[] THEN
15 CONV_TAC REAL_RAT_REDUCE_CONV THEN
16 SUBST1_TAC(SYM(REAL_RAT_REDUCE_CONV `&2 pow 0`)) THEN
17 MATCH_MP_TAC REAL_POW_MONO_LT THEN
18 REWRITE_TAC[REAL_OF_NUM_LT] THEN POP_ASSUM MP_TAC THEN ARITH_TAC);;
20 let REAL_POW2_CLAUSES = prove
21 (`(!n. &0 <= &2 pow n) /\
22 (!n. &0 < &2 pow n) /\
23 (!n. &0 <= inv(&2 pow n)) /\
24 (!n. &0 < inv(&2 pow n)) /\
25 (!n. inv(&2 pow n) <= &1) /\
26 (!n. &1 - inv(&2 pow n) <= &1) /\
27 (!n. &1 <= &2 pow n) /\
28 (!n. &1 < &2 pow n <=> ~(n = 0)) /\
29 (!n. &0 <= &1 - inv(&2 pow n)) /\
30 (!n. &0 <= &2 pow n - &1) /\
31 (!n. &0 < &1 - inv(&2 pow n) <=> ~(n = 0))`,
32 SIMP_TAC[REAL_LE_1_POW2; REAL_LT_1_POW2; REAL_SUB_LE; REAL_SUB_LT;
34 SIMP_TAC[REAL_LE_INV_EQ; REAL_LT_INV_EQ; REAL_POW_LT; REAL_POW_LE;
35 REAL_OF_NUM_LE; REAL_OF_NUM_LT; ARITH;
36 REAL_ARITH `&1 - x <= &1 <=> &0 <= x`] THEN
37 GEN_TAC THEN ASM_CASES_TAC `n = 0` THEN ASM_REWRITE_TAC[] THEN
38 CONV_TAC REAL_RAT_REDUCE_CONV THEN
39 MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC `inv(&2 pow 1)` THEN
40 ASM_SIMP_TAC[REAL_LE_INV2; REAL_POW_MONO; REAL_POW_LT; REAL_OF_NUM_LT; ARITH;
41 REAL_OF_NUM_LE; ARITH_RULE `1 <= n <=> ~(n = 0)`] THEN
42 CONV_TAC REAL_RAT_REDUCE_CONV);;
44 let REAL_POW2_THM = prove
47 (&1 < &2 pow n <=> ~(n = 0)) /\
48 (&2 pow m <= &2 pow n <=> m <= n) /\
49 (&2 pow m < &2 pow n <=> m < n) /\
50 (inv(&2 pow m) <= inv(&2 pow n) <=> n <= m) /\
51 (inv(&2 pow m) < inv(&2 pow n) <=> n < m)`,
52 REWRITE_TAC[REAL_POW2_CLAUSES] THEN
53 SUBGOAL_THEN `!m n. &2 pow m <= &2 pow n <=> m <= n` ASSUME_TAC THENL
54 [REPEAT GEN_TAC THEN EQ_TAC THEN
55 SIMP_TAC[REAL_POW_MONO; REAL_OF_NUM_LE; ARITH] THEN
56 CONV_TAC CONTRAPOS_CONV THEN
57 SIMP_TAC[REAL_NOT_LE; REAL_NOT_LT; REAL_POW_MONO_LT; REAL_OF_NUM_LT;
58 NOT_LE; ARITH]; ALL_TAC] THEN
59 ASM_REWRITE_TAC[GSYM REAL_NOT_LE] THEN REWRITE_TAC[GSYM NOT_LE] THEN
60 SUBGOAL_THEN `!m n. inv(&2 pow m) <= inv(&2 pow n) <=> &2 pow n <= &2 pow m`
61 (fun th -> ASM_REWRITE_TAC[th]) THEN
62 REPEAT GEN_TAC THEN EQ_TAC THEN
63 SIMP_TAC[REAL_LE_INV2; REAL_POW2_CLAUSES] THEN
64 CONV_TAC CONTRAPOS_CONV THEN
65 SIMP_TAC[REAL_NOT_LE; REAL_LT_INV2; REAL_POW2_CLAUSES]);;
67 (* ------------------------------------------------------------------------- *)
68 (* Compound errors given bounds in assumptions. *)
69 (* ------------------------------------------------------------------------- *)
71 let BOUND_SUMPROD_RULE =
72 let pth_add = REAL_ARITH
73 `abs(x1) <= b1 /\ abs(x2) <= b2 ==> abs(x1 + x2) <= b1 + b2`
74 and pth_sub = REAL_ARITH
75 `abs(x1) <= b1 /\ abs(x2) <= b2 ==> abs(x1 - x2) <= b1 + b2`
77 (`abs(x1) <= b1 /\ abs(x2) <= b2 ==> abs(x1 * x2) <= b1 * b2`,
78 REWRITE_TAC[REAL_ABS_MUL] THEN
79 SIMP_TAC[REAL_LE_MUL2; REAL_ABS_POS])
80 and pth_neg = REAL_ARITH
81 `abs(x1) <= b1 ==> abs(--x1) <= b1`
83 (`abs(x) <= b1 ==> abs(x pow n) <= b1 pow n`,
84 REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[REAL_ABS_POW] THEN
85 MATCH_MP_TAC REAL_POW_LE2 THEN ASM_REWRITE_TAC[REAL_ABS_POS])
86 and pth_abs = REAL_ARITH `abs(x) <= b ==> abs(abs(x)) <= b`
87 and pth_triv = REAL_ARITH `abs(x) <= abs(x)`
89 let rec BOUND_SUMPROD_RULE (asl,w) =
91 try tryfind (fun (_,th) -> if rator(concl th) = tm then th
95 (fun pth -> pth,PART_MATCH (rator o rand) pth tm)
97 let th1 = BOUND_SUMPROD_RULE (asl,lhand(concl th)) in
100 let pth = INST [funpow 3 rand tm,n_tm] pth_pow in
101 let th = PART_MATCH (rator o rand) pth tm in
102 let th1 = BOUND_SUMPROD_RULE (asl,lhand(concl th)) in
103 MATCH_MP (INST [funpow 3 rand tm,n_tm] pth_pow) th1
104 with Failure _ -> try
106 (fun pth -> pth,PART_MATCH (rator o rand) pth tm)
107 [pth_add; pth_sub; pth_mul] in
108 let trm = lhand(concl th) in
109 let th1 = BOUND_SUMPROD_RULE (asl,lhand trm)
110 and th2 = BOUND_SUMPROD_RULE (asl,rand trm) in
111 MATCH_MP pth (CONJ th1 th2)
113 PART_MATCH rator pth_triv tm in
116 let BOUND_SUMPROD_TAC =
119 REAL_ARITH `x <= a ==> (!b. a <= b ==> x <= b) /\
120 (!b. a < b ==> x < b)` in
122 let th1,th2 = CONJ_PAIR(MATCH_MP pth th) in
123 MATCH_MP_TAC th1 ORELSE MATCH_MP_TAC th2
124 and le_tm = `(<=):real->real->bool` in
126 let l,r = dest_comb w in
127 let gv = genvar(type_of r) in
128 let tm = mk_comb(mk_comb(le_tm,rand l),gv) in
129 let th = BOUND_SUMPROD_RULE(asl,tm) in
132 (* ------------------------------------------------------------------------- *)
133 (* Power series for atn. *)
134 (* ------------------------------------------------------------------------- *)
136 let REAL_ATN_POWSER_SUMMABLE = prove
138 ==> summable (\n. (if EVEN n then &0
139 else --(&1) pow ((n - 1) DIV 2) / &n) * x pow n)`,
140 REPEAT STRIP_TAC THEN MATCH_MP_TAC SER_COMPAR THEN
141 EXISTS_TAC `\n. abs(x) pow n` THEN CONJ_TAC THENL
142 [EXISTS_TAC `0` THEN REPEAT STRIP_TAC THEN REWRITE_TAC[] THEN
144 SIMP_TAC[REAL_POW_LE; REAL_MUL_LZERO; REAL_ABS_POS; REAL_ABS_NUM] THEN
145 REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_DIV; REAL_ABS_NEG; REAL_ABS_POW] THEN
146 REWRITE_TAC[REAL_ABS_NUM; REAL_POW_ONE; REAL_MUL_LID] THEN
147 REWRITE_TAC[real_div; REAL_MUL_LID] THEN
148 ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN REWRITE_TAC[GSYM real_div] THEN
149 MATCH_MP_TAC REAL_LE_LDIV THEN
150 CONJ_TAC THENL [ASM_MESON_TAC[REAL_OF_NUM_LT; EVEN; LT_NZ]; ALL_TAC] THEN
151 GEN_REWRITE_TAC LAND_CONV [GSYM REAL_MUL_RID] THEN
152 MATCH_MP_TAC REAL_LE_LMUL THEN
153 SIMP_TAC[REAL_POW_LE; REAL_ABS_POS] THEN
154 ASM_MESON_TAC[REAL_OF_NUM_LE; EVEN; ARITH_RULE `1 <= n <=> ~(n = 0)`];
156 REWRITE_TAC[summable] THEN EXISTS_TAC `inv(&1 - abs x)` THEN
157 MATCH_MP_TAC GP THEN ASM_REWRITE_TAC[REAL_ABS_ABS]);;
159 let REAL_ATN_POWSER_DIFFS_SUMMABLE = prove
161 ==> summable (\n. diffs (\n. (if EVEN n then &0
162 else --(&1) pow ((n - 1) DIV 2) / &n)) n *
164 REPEAT STRIP_TAC THEN REWRITE_TAC[diffs] THEN
165 MATCH_MP_TAC SER_COMPAR THEN
166 EXISTS_TAC `\n. abs(x) pow n` THEN CONJ_TAC THENL
167 [EXISTS_TAC `0` THEN REPEAT STRIP_TAC THEN REWRITE_TAC[] THEN
169 SIMP_TAC[REAL_POW_LE; REAL_MUL_LZERO; REAL_MUL_RZERO;
170 REAL_ABS_POS; REAL_ABS_NUM] THEN
171 SIMP_TAC[REAL_MUL_ASSOC; REAL_DIV_LMUL; REAL_OF_NUM_EQ; NOT_SUC] THEN
172 REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_DIV; REAL_ABS_NEG; REAL_ABS_POW] THEN
173 REWRITE_TAC[REAL_ABS_NUM; REAL_POW_ONE; REAL_MUL_LID; REAL_LE_REFL];
175 REWRITE_TAC[summable] THEN EXISTS_TAC `inv(&1 - abs x)` THEN
176 MATCH_MP_TAC GP THEN ASM_REWRITE_TAC[REAL_ABS_ABS]);;
178 let REAL_ATN_POWSER_DIFFS_SUM = prove
180 ==> (\n. diffs (\n. (if EVEN n then &0
181 else --(&1) pow ((n - 1) DIV 2) / &n)) n * x pow n)
182 sums (inv(&1 + x pow 2))`,
183 REPEAT STRIP_TAC THEN
184 FIRST_ASSUM(MP_TAC o MATCH_MP REAL_ATN_POWSER_DIFFS_SUMMABLE) THEN
185 DISCH_THEN(fun th -> MP_TAC(MATCH_MP SUMMABLE_SUM th) THEN
186 MP_TAC(MATCH_MP SER_PAIR th)) THEN
188 `(\n. sum (2 * n,2) (\n. diffs
189 (\n. (if EVEN n then &0
190 else --(&1) pow ((n - 1) DIV 2) / &n)) n * x pow n)) =
191 (\n. --(x pow 2) pow n)`
194 CONV_TAC(LAND_CONV(LAND_CONV(RAND_CONV(TOP_DEPTH_CONV num_CONV)))) THEN
195 REWRITE_TAC[sum; diffs; ADD_CLAUSES; EVEN_MULT; ARITH_EVEN; EVEN] THEN
196 REWRITE_TAC[REAL_ADD_LID; REAL_ADD_RID; REAL_MUL_LZERO;
198 SIMP_TAC[ARITH_RULE `SUC n - 1 = n`; DIV_MULT; ARITH_EQ] THEN
199 SIMP_TAC[REAL_MUL_ASSOC; REAL_DIV_LMUL; REAL_OF_NUM_EQ; NOT_SUC] THEN
200 ONCE_REWRITE_TAC[GSYM REAL_POW_POW] THEN
201 REWRITE_TAC[GSYM REAL_POW_MUL] THEN
202 REWRITE_TAC[REAL_MUL_LNEG; REAL_MUL_LID]; ALL_TAC] THEN
203 SUBGOAL_THEN `(\n. --(x pow 2) pow n) sums inv (&1 + x pow 2)` MP_TAC THENL
204 [ONCE_REWRITE_TAC[REAL_ARITH `&1 + x = &1 - (--x)`] THEN
206 REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_POW] THEN
207 GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
208 ASM_SIMP_TAC[REAL_POW_2; REAL_LT_MUL2; REAL_ABS_POS]; ALL_TAC] THEN
209 MESON_TAC[SUM_UNIQ]);;
211 let REAL_ATN_POWSER_DIFFS_DIFFS_SUMMABLE = prove
215 (\n. (if EVEN n then &0
216 else --(&1) pow ((n - 1) DIV 2) / &n))) n * x pow n)`,
217 REPEAT STRIP_TAC THEN REWRITE_TAC[diffs] THEN
218 MATCH_MP_TAC SER_COMPAR THEN
219 EXISTS_TAC `\n. &(SUC n) * abs(x) pow n` THEN CONJ_TAC THENL
220 [EXISTS_TAC `0` THEN REPEAT STRIP_TAC THEN
221 REWRITE_TAC[REAL_ABS_NUM; REAL_ABS_MUL; GSYM REAL_MUL_ASSOC] THEN
222 MATCH_MP_TAC REAL_LE_LMUL THEN REWRITE_TAC[REAL_POS] THEN
224 SIMP_TAC[REAL_POW_LE; REAL_MUL_LZERO; REAL_MUL_RZERO;
225 REAL_ABS_POS; REAL_ABS_NUM] THEN
226 REWRITE_TAC[REAL_ABS_DIV; REAL_ABS_NUM; REAL_MUL_ASSOC] THEN
227 SIMP_TAC[REAL_DIV_LMUL; REAL_OF_NUM_EQ; NOT_SUC] THEN
228 REWRITE_TAC[REAL_ABS_POW; REAL_ABS_NEG; REAL_POW_ONE; REAL_MUL_LID;
229 REAL_ABS_NUM; REAL_LE_REFL]; ALL_TAC] THEN
230 MATCH_MP_TAC SER_RATIO THEN
231 SUBGOAL_THEN `?c. abs(x) < c /\ c < &1` STRIP_ASSUME_TAC THENL
232 [EXISTS_TAC `(&1 + abs(x)) / &2` THEN
233 SIMP_TAC[REAL_LT_LDIV_EQ; REAL_LT_RDIV_EQ; REAL_OF_NUM_LT; ARITH] THEN
234 UNDISCH_TAC `abs(x) < &1` THEN REAL_ARITH_TAC; ALL_TAC] THEN
235 EXISTS_TAC `c:real` THEN ASM_REWRITE_TAC[] THEN
236 SUBGOAL_THEN `?N. !n. n >= N ==> &(SUC(SUC n)) * abs(x) <= &(SUC n) * c`
237 STRIP_ASSUME_TAC THENL
239 EXISTS_TAC `N:num` THEN REPEAT STRIP_TAC THEN
240 REWRITE_TAC[real_pow; REAL_ABS_MUL; REAL_MUL_ASSOC] THEN
241 MATCH_MP_TAC REAL_LE_RMUL THEN REWRITE_TAC[REAL_ABS_POS] THEN
242 REWRITE_TAC[REAL_ABS_NUM; REAL_ABS_ABS] THEN
243 GEN_REWRITE_TAC RAND_CONV [REAL_MUL_SYM] THEN ASM_SIMP_TAC[]] THEN
244 ASM_CASES_TAC `x = &0` THENL
245 [ASM_REWRITE_TAC[REAL_ABS_NUM; REAL_MUL_RZERO] THEN
246 EXISTS_TAC `0` THEN REPEAT STRIP_TAC THEN MATCH_MP_TAC REAL_LE_MUL THEN
247 REWRITE_TAC[REAL_POS] THEN UNDISCH_TAC `abs(x) < c` THEN REAL_ARITH_TAC;
249 ASM_SIMP_TAC[GSYM REAL_LE_RDIV_EQ; GSYM REAL_ABS_NZ] THEN
250 REWRITE_TAC[real_div; GSYM REAL_MUL_ASSOC] THEN
251 REWRITE_TAC[GSYM real_div] THEN
252 REWRITE_TAC[ADD1; GSYM REAL_OF_NUM_ADD] THEN
253 ONCE_REWRITE_TAC[REAL_ARITH `x + &1 <= y <=> &1 <= y - x * &1`] THEN
254 REWRITE_TAC[GSYM REAL_SUB_LDISTRIB] THEN
255 SUBGOAL_THEN `?N. &1 <= &N * (c / abs x - &1)` STRIP_ASSUME_TAC THENL
257 EXISTS_TAC `N:num` THEN REWRITE_TAC[GE] THEN REPEAT STRIP_TAC THEN
258 FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_ARITH
259 `&1 <= x ==> x <= y ==> &1 <= y`)) THEN
260 MATCH_MP_TAC REAL_LE_RMUL THEN
261 ASM_SIMP_TAC[REAL_ARITH `a <= b ==> a <= b + &1`;
262 REAL_OF_NUM_LE; REAL_LE_RADD] THEN
263 REWRITE_TAC[REAL_LE_SUB_LADD; REAL_ADD_LID] THEN
264 ASM_SIMP_TAC[REAL_LE_RDIV_EQ; GSYM REAL_ABS_NZ; REAL_MUL_LID;
265 REAL_LT_IMP_LE]] THEN
266 ASM_SIMP_TAC[GSYM REAL_LE_LDIV_EQ; REAL_LT_SUB_LADD; REAL_ADD_LID;
267 REAL_LT_RDIV_EQ; GSYM REAL_ABS_NZ; REAL_MUL_LID;
270 let REAL_ATN_POWSER_DIFFL = prove
272 ==> ((\x. suminf (\n. (if EVEN n then &0
273 else --(&1) pow ((n - 1) DIV 2) / &n) * x pow n))
274 diffl (inv(&1 + x pow 2))) x`,
275 REPEAT STRIP_TAC THEN
276 FIRST_ASSUM(MP_TAC o MATCH_MP REAL_ATN_POWSER_DIFFS_SUM) THEN
277 DISCH_THEN(SUBST1_TAC o MATCH_MP SUM_UNIQ) THEN
278 MATCH_MP_TAC TERMDIFF THEN
279 SUBGOAL_THEN `?K. abs(x) < abs(K) /\ abs(K) < &1` STRIP_ASSUME_TAC THENL
280 [EXISTS_TAC `(&1 + abs(x)) / &2` THEN
281 SIMP_TAC[REAL_LT_LDIV_EQ; REAL_ABS_DIV; REAL_ABS_NUM;
282 REAL_LT_RDIV_EQ; REAL_OF_NUM_LT; ARITH] THEN
283 UNDISCH_TAC `abs(x) < &1` THEN REAL_ARITH_TAC; ALL_TAC] THEN
284 EXISTS_TAC `K:real` THEN ASM_REWRITE_TAC[] THEN
285 ASM_SIMP_TAC[REAL_ATN_POWSER_SUMMABLE; REAL_ATN_POWSER_DIFFS_SUMMABLE;
286 REAL_ATN_POWSER_DIFFS_DIFFS_SUMMABLE]);;
288 let REAL_ATN_POWSER = prove
290 ==> (\n. (if EVEN n then &0
291 else --(&1) pow ((n - 1) DIV 2) / &n) * x pow n)
293 REPEAT STRIP_TAC THEN
294 FIRST_ASSUM(MP_TAC o MATCH_MP REAL_ATN_POWSER_SUMMABLE) THEN
295 DISCH_THEN(MP_TAC o MATCH_MP SUMMABLE_SUM) THEN
297 `suminf (\n. (if EVEN n then &0
298 else --(&1) pow ((n - 1) DIV 2) / &n) * x pow n) = atn(x)`
299 (fun th -> REWRITE_TAC[th]) THEN
300 ONCE_REWRITE_TAC[REAL_ARITH `(a = b) <=> (a - b = &0)`] THEN
302 `suminf (\n. (if EVEN n then &0
303 else --(&1) pow ((n - 1) DIV 2) / &n) * &0 pow n) -
306 [MATCH_MP_TAC(REAL_ARITH `(a = &0) /\ (b = &0) ==> (a - b = &0)`) THEN
308 [CONV_TAC SYM_CONV THEN MATCH_MP_TAC SUM_UNIQ THEN
309 MP_TAC(SPEC `&0` GP) THEN
310 REWRITE_TAC[REAL_ABS_NUM; REAL_OF_NUM_LT; ARITH] THEN
311 DISCH_THEN(MP_TAC o SPEC `&0` o MATCH_MP SER_CMUL) THEN
312 REWRITE_TAC[REAL_MUL_LZERO] THEN
313 MATCH_MP_TAC(TAUT `(a = b) ==> a ==> b`) THEN
314 AP_THM_TAC THEN AP_TERM_TAC THEN ABS_TAC THEN
315 COND_CASES_TAC THEN ASM_REWRITE_TAC[REAL_MUL_LZERO] THEN
316 CONV_TAC SYM_CONV THEN
317 REWRITE_TAC[REAL_ENTIRE; REAL_POW_EQ_0] THEN ASM_MESON_TAC[EVEN];
318 GEN_REWRITE_TAC (LAND_CONV o RAND_CONV) [GSYM TAN_0] THEN
319 MATCH_MP_TAC TAN_ATN THEN
320 SIMP_TAC[PI2_BOUNDS; REAL_ARITH `&0 < x ==> --x < &0`]];
322 ASM_CASES_TAC `x = &0` THEN ASM_REWRITE_TAC[] THEN
323 DISCH_THEN(fun th -> GEN_REWRITE_TAC RAND_CONV [SYM th]) THEN
324 MP_TAC(SPEC `\x. suminf (\n. (if EVEN n then &0
326 else --(&1) pow ((n - 1) DIV 2) / &n) * x pow n) -
327 atn x` DIFF_ISCONST_END_SIMPLE) THEN
328 FIRST_ASSUM(DISJ_CASES_TAC o MATCH_MP (REAL_ARITH
329 `~(x = &0) ==> &0 < x \/ x < &0`))
331 [DISCH_THEN(MP_TAC o SPECL [`&0`; `x:real`]);
332 CONV_TAC(RAND_CONV SYM_CONV) THEN
333 DISCH_THEN(MP_TAC o SPECL [`x:real`; `&0`])] THEN
334 (REWRITE_TAC[] THEN DISCH_THEN MATCH_MP_TAC THEN
335 ASM_REWRITE_TAC[] THEN
336 X_GEN_TAC `u:real` THEN REPEAT STRIP_TAC THEN
337 SUBGOAL_THEN `abs(u) < &1` (MP_TAC o MATCH_MP REAL_ATN_POWSER_DIFFL) THENL
338 [POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN REAL_ARITH_TAC;
340 DISCH_THEN(MP_TAC o C CONJ (SPEC `u:real` DIFF_ATN)) THEN
341 DISCH_THEN(MP_TAC o MATCH_MP DIFF_SUB) THEN
342 REWRITE_TAC[REAL_SUB_REFL]));;
344 (* ------------------------------------------------------------------------- *)
345 (* A more Taylor-like version with a simply bounded remainder term. *)
346 (* ------------------------------------------------------------------------- *)
348 let MCLAURIN_ATN_SIMPLE = prove
349 (`!x n k. abs(x) <= inv(&2 pow k) /\ ~(k = 0)
351 sum(0,n) (\m. (if EVEN m then &0
352 else --(&1) pow ((m - 1) DIV 2) / &m) *
354 <= &2 * abs(x) pow n`,
355 REPEAT STRIP_TAC THEN SUBGOAL_THEN `abs(x) < &1` ASSUME_TAC THENL
356 [MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC `inv(&2 pow k)` THEN
357 ASM_REWRITE_TAC[REAL_ARITH `a < &1 <=> &0 < &1 - a`; REAL_POW2_CLAUSES];
359 FIRST_ASSUM(MP_TAC o MATCH_MP REAL_ATN_POWSER) THEN
360 DISCH_THEN(fun th -> ASSUME_TAC(SYM(MATCH_MP SUM_UNIQ th)) THEN
361 MP_TAC(MATCH_MP SUM_SUMMABLE th)) THEN
362 DISCH_THEN(MP_TAC o MATCH_MP SER_OFFSET) THEN
363 DISCH_THEN(MP_TAC o SPEC `n:num`) THEN ASM_REWRITE_TAC[] THEN
364 DISCH_THEN(MP_TAC o MATCH_MP SUM_UNIQ) THEN
365 MATCH_MP_TAC(REAL_ARITH
366 `abs(r) <= e ==> (f - s = r) ==> abs(f - s) <= e`) THEN
368 `(\m. abs(x) pow (m + n)) sums (abs(x) pow n) * inv(&1 - abs(x))`
370 [FIRST_ASSUM(MP_TAC o MATCH_MP GP o MATCH_MP (REAL_ARITH
371 `abs(x) < &1 ==> abs(abs x) < &1`)) THEN
372 DISCH_THEN(MP_TAC o SPEC `abs(x) pow n` o MATCH_MP SER_CMUL) THEN
373 ONCE_REWRITE_TAC[ADD_SYM] THEN REWRITE_TAC[GSYM REAL_POW_ADD];
375 MATCH_MP_TAC REAL_LE_TRANS THEN
376 EXISTS_TAC `suminf (\m. abs(x) pow (m + n))` THEN CONJ_TAC THENL
378 FIRST_ASSUM(SUBST1_TAC o SYM o MATCH_MP SUM_UNIQ) THEN
379 GEN_REWRITE_TAC RAND_CONV [REAL_MUL_SYM] THEN
380 MATCH_MP_TAC REAL_LE_LMUL THEN SIMP_TAC[REAL_ABS_POS; REAL_POW_LE] THEN
381 GEN_REWRITE_TAC RAND_CONV [GSYM REAL_INV_INV] THEN
382 MATCH_MP_TAC REAL_LE_INV2 THEN
383 ONCE_REWRITE_TAC[REAL_ARITH `a <= &1 - b <=> b <= &1 - a`] THEN
384 CONV_TAC REAL_RAT_REDUCE_CONV THEN
385 MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `inv(&2 pow k)` THEN
386 ASM_REWRITE_TAC[] THEN REWRITE_TAC[real_div; REAL_MUL_LID] THEN
387 MATCH_MP_TAC REAL_LE_INV2 THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
388 GEN_REWRITE_TAC LAND_CONV [GSYM REAL_POW_1] THEN
389 ASM_SIMP_TAC[REAL_POW_MONO; REAL_OF_NUM_LE; ARITH;
390 ARITH_RULE `~(k = 0) ==> 1 <= k`]] THEN
392 `!m. abs((if EVEN (m + n) then &0
393 else --(&1) pow (((m + n) - 1) DIV 2) / &(m + n)) *
395 <= abs(x) pow (m + n)`
397 [GEN_TAC THEN COND_CASES_TAC THEN
398 SIMP_TAC[REAL_MUL_LZERO; REAL_ABS_NUM; REAL_POW_LE; REAL_ABS_POS] THEN
399 REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_DIV; REAL_ABS_POW; REAL_ABS_NEG] THEN
400 REWRITE_TAC[REAL_ABS_NUM; REAL_POW_ONE; REAL_MUL_LID] THEN
401 GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
402 MATCH_MP_TAC REAL_LE_RMUL THEN SIMP_TAC[REAL_POW_LE; REAL_ABS_POS] THEN
403 REWRITE_TAC[real_div; REAL_MUL_LID] THEN
404 GEN_REWRITE_TAC RAND_CONV [GSYM REAL_INV_1] THEN
405 MATCH_MP_TAC REAL_LE_INV2 THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
406 REWRITE_TAC[REAL_OF_NUM_LE; ARITH_RULE `1 <= n <=> ~(n = 0)`] THEN
407 ASM_MESON_TAC[EVEN]; ALL_TAC] THEN
408 MATCH_MP_TAC REAL_LE_TRANS THEN
410 `suminf (\m. abs((if EVEN (m + n) then &0
411 else --(&1) pow (((m + n) - 1) DIV 2) / &(m + n)) *
412 x pow (m + n)))` THEN
414 [MATCH_MP_TAC SER_ABS THEN MATCH_MP_TAC SER_COMPARA THEN
415 EXISTS_TAC `\m. abs(x) pow (m + n)` THEN
416 ASM_REWRITE_TAC[] THEN ASM_MESON_TAC[SUM_SUMMABLE]; ALL_TAC] THEN
417 MATCH_MP_TAC SER_LE THEN ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
418 [MATCH_MP_TAC SER_COMPARA THEN
419 EXISTS_TAC `\m. abs(x) pow (m + n)` THEN
420 ASM_REWRITE_TAC[]; ALL_TAC] THEN
421 ASM_MESON_TAC[SUM_SUMMABLE]);;
423 let MCLAURIN_ATN_APPROX = prove
424 (`!x n k. abs(x) <= inv(&2 pow k) /\ ~(k = 0)
426 sum(0,n) (\m. (if EVEN m then &0
427 else --(&1) pow ((m - 1) DIV 2) / &m) *
429 <= inv(&2 pow (n * k - 1))`,
430 REPEAT STRIP_TAC THEN ASM_CASES_TAC `n = 0` THENL
431 [ASM_REWRITE_TAC[sum; REAL_SUB_RZERO; MULT_CLAUSES; SUB_0] THEN
432 MP_TAC(SPECL [`x:real`; `2`; `k:num`] MCLAURIN_ATN_SIMPLE) THEN
433 ASM_REWRITE_TAC[] THEN
434 MATCH_MP_TAC(REAL_ARITH
435 `abs(y) + d <= e ==> abs(x - y) <= d ==> abs(x) <= e`) THEN
436 CONV_TAC(ONCE_DEPTH_CONV REAL_SUM_CONV) THEN
437 REWRITE_TAC[real_pow; REAL_POW_1] THEN CONV_TAC NUM_REDUCE_CONV THEN
438 CONV_TAC REAL_RAT_REDUCE_CONV THEN
439 REWRITE_TAC[real_div; REAL_MUL_LID; REAL_INV_1; REAL_ADD_LID] THEN
440 SUBGOAL_THEN `abs(x) <= inv(&2)` ASSUME_TAC THENL
441 [MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `inv(&2 pow k)` THEN
442 ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LE_INV2 THEN
443 CONV_TAC REAL_RAT_REDUCE_CONV THEN
444 CONV_TAC REAL_RAT_REDUCE_CONV THEN
445 GEN_REWRITE_TAC LAND_CONV [GSYM REAL_POW_1] THEN
446 ASM_SIMP_TAC[REAL_POW_MONO; REAL_OF_NUM_LE; ARITH;
447 ARITH_RULE `~(k = 0) ==> 1 <= k`];
449 MATCH_MP_TAC REAL_LE_TRANS THEN
450 EXISTS_TAC `inv(&2) + &2 * inv(&2) pow 2` THEN
451 CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN REWRITE_TAC[REAL_POW_1] THEN
452 MATCH_MP_TAC REAL_LE_ADD2 THEN ASM_REWRITE_TAC[] THEN
453 ASM_SIMP_TAC[REAL_LE_LMUL_EQ; REAL_OF_NUM_LT; ARITH;
454 REAL_POW_LE2; REAL_OF_NUM_LE; REAL_ABS_POS];
456 MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&2 * abs(x) pow n` THEN
458 [MATCH_MP_TAC MCLAURIN_ATN_SIMPLE THEN ASM_MESON_TAC[]; ALL_TAC] THEN
459 ASM_SIMP_TAC[REAL_POW_SUB; REAL_OF_NUM_EQ; ARITH_EQ;
460 ARITH_RULE `1 <= x <=> ~(x = 0)`; MULT_EQ_0] THEN
461 REWRITE_TAC[REAL_INV_DIV; REAL_POW_1] THEN REWRITE_TAC[real_div] THEN
462 SIMP_TAC[REAL_LE_LMUL_EQ; REAL_OF_NUM_LT; ARITH] THEN
463 ONCE_REWRITE_TAC[MULT_SYM] THEN REWRITE_TAC[GSYM REAL_POW_POW] THEN
464 ONCE_REWRITE_TAC[GSYM REAL_POW_INV] THEN MATCH_MP_TAC REAL_POW_LE2 THEN
465 ASM_REWRITE_TAC[REAL_ABS_POS]);;
467 (* ------------------------------------------------------------------------- *)
468 (* Rules to return approximations to atn(x) good to 2^-p given |x| <= 2^-k. *)
469 (* ------------------------------------------------------------------------- *)
471 let mclaurin_atn_rule,MCLAURIN_ATN_RULE =
476 and le_tm = `(<=):real->real->bool`
477 and pow2_tm = `(pow) (&2)` in
478 let pth = SPECL [x_tm; n_tm; k_tm] MCLAURIN_ATN_APPROX
479 and CLEAN_RULE = REWRITE_RULE[real_pow]
480 and MATCH_REAL_LE_TRANS = MATCH_MP REAL_LE_TRANS
483 let mclaurin_atn_rule k0 p0 =
484 if k0 = 0 then failwith "mclaurin_atn_rule: must have |x| <= 1/2" else
487 let n = Num.int_of_num(ceiling_num ((p +/ k) // k)) in
488 let ns = if n mod 2 = 0 then 0--(n - 1) else 0--(n - 2) in
489 map (fun m -> if m mod 2 = 0 then num_0 else
490 (if (m - 1) mod 4 = 0 then I else minus_num)
492 and MCLAURIN_ATN_RULE k0 p0 =
493 if k0 = 0 then failwith "MCLAURIN_ATN_RULE: must have |x| <= 1/2" else
496 let n = ceiling_num ((p +/ k) // k) in
497 let th1 = INST [mk_numeral k,k_tm; mk_numeral n,n_tm] pth in
498 let th2 = ASSUME (lhand(lhand(concl th1)))
499 and th3 = EQF_ELIM(NUM_REDUCE_CONV(rand(rand(lhand(concl th1))))) in
500 let th4 = MP th1 (CONJ th2 th3) in
501 let th5 = CONV_RULE(ONCE_DEPTH_CONV REAL_HORNER_SUM_CONV) th4 in
502 let th6 = CLEAN_RULE th5 in
503 let th7 = CONV_RULE (NUM_REDUCE_CONV THENC LAND_CONV REAL_RAT_REDUCE_CONV)
505 let tm1 = mk_comb(inv_tm,mk_comb(pow2_tm,mk_numeral p)) in
506 let tm2 = mk_comb(mk_comb(le_tm,rand(concl th7)),tm1) in
507 let th8 = EQT_ELIM((NUM_REDUCE_CONV THENC REAL_RAT_REDUCE_CONV) tm2) in
508 let th9 = MATCH_REAL_LE_TRANS (CONJ th7 th8) in
509 GEN x_tm (DISCH_ALL th9) in
510 mclaurin_atn_rule,MCLAURIN_ATN_RULE;;
512 (* ------------------------------------------------------------------------- *)
513 (* Lemmas for Machin-type formulas. *)
514 (* ------------------------------------------------------------------------- *)
516 let TAN_ADD_ATN_SIDECOND = prove
517 (`!x y. ~(x * y = &1) ==> ~(cos(atn x + atn y) = &0)`,
518 REPEAT GEN_TAC THEN DISCH_TAC THEN
519 REWRITE_TAC[COS_ADD; REAL_ARITH `(a - b = &0) <=> (a = b)`] THEN
520 DISCH_THEN(MP_TAC o AP_TERM `(*) (inv(cos(atn x)))`) THEN
521 SIMP_TAC[REAL_MUL_ASSOC; REAL_MUL_LINV; COS_ATN_NZ; REAL_MUL_LID] THEN
522 DISCH_THEN(MP_TAC o AP_TERM `(*) (inv(cos(atn y)))`) THEN
523 SIMP_TAC[REAL_MUL_LINV; COS_ATN_NZ; REAL_MUL_LID; GSYM REAL_MUL_ASSOC] THEN
524 ONCE_REWRITE_TAC[AC REAL_MUL_AC `a * b * c * d = (c * b) * (d * a)`] THEN
525 ASM_REWRITE_TAC[GSYM tan; GSYM real_div; ATN_TAN]);;
528 (`!x y. ~(x * y = &1) /\
529 abs(atn x + atn y) < pi / &2
530 ==> (atn(x) + atn(y) = atn((x + y) / (&1 - x * y)))`,
531 REPEAT STRIP_TAC THEN
532 SUBGOAL_THEN `tan(atn(x) + atn(y)) = (x + y) / (&1 - x * y)` MP_TAC THENL
533 [ASM_SIMP_TAC[ATN_TAN; TAN_ADD; COS_ATN_NZ; TAN_ADD_ATN_SIDECOND];
534 DISCH_THEN(SUBST1_TAC o SYM) THEN CONV_TAC SYM_CONV THEN
535 ASM_SIMP_TAC[TAN_ATN; REAL_ARITH `abs(x) < e ==> --e < x /\ x < e`]]);;
537 let ATN_ADD_SMALL_LEMMA_POS = prove
538 (`!x y. &0 < y /\ x * y < &1
539 ==> atn(x) + atn(y) < pi / &2`,
540 REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM REAL_LT_SUB_LADD] THEN
541 SUBGOAL_THEN `pi / &2 - atn y = atn(tan(pi / &2 - atn y))` SUBST1_TAC THENL
542 [CONV_TAC SYM_CONV THEN MATCH_MP_TAC TAN_ATN THEN
543 MATCH_MP_TAC(REAL_ARITH
544 `&0 < x /\ x < a ==> --a < a - x /\ a - x < a`) THEN
545 REWRITE_TAC[ATN_BOUNDS] THEN
546 GEN_REWRITE_TAC LAND_CONV [GSYM ATN_0] THEN
547 ASM_SIMP_TAC[ATN_MONO_LT];
548 MATCH_MP_TAC ATN_MONO_LT THEN REWRITE_TAC[TAN_COT; ATN_TAN] THEN
549 GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
550 ASM_SIMP_TAC[GSYM real_div; REAL_LT_RDIV_EQ; REAL_LT_IMP_NZ]]);;
552 let ATN_ADD_SMALL_LEMMA = prove
553 (`!x y. abs(x * y) < &1 ==> abs(atn(x) + atn(y)) < pi / &2`,
554 REPEAT STRIP_TAC THEN
555 MATCH_MP_TAC(REAL_ARITH
556 `--a < x /\ x < a /\ --a < y /\ y < a /\
557 (&0 < y ==> x + y < a) /\
558 (&0 < --y ==> --x + --y < a)
559 ==> abs(x + y) < a`) THEN
560 REWRITE_TAC[ATN_BOUNDS] THEN CONJ_TAC THEN
561 REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM ATN_NEG] THEN
562 MATCH_MP_TAC ATN_ADD_SMALL_LEMMA_POS THEN
563 ASM_SIMP_TAC[REAL_ARITH `abs(x) < &1 ==> x < &1`;
564 REAL_ARITH `--x * -- y = x * y`] THEN
565 FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_ARITH
566 `&0 < y ==> (z <= &0 ==> y <= &0) ==> &0 < z`)) THEN
567 MATCH_MP_TAC(REAL_ARITH
568 `(y < &0 ==> z < &0) /\ ((y = &0) ==> (z = &0))
569 ==> y <= &0 ==> z <= &0`) THEN
570 SIMP_TAC[ATN_0; GSYM ATN_NEG] THEN
571 GEN_REWRITE_TAC (RAND_CONV o RAND_CONV) [GSYM ATN_0] THEN
572 SIMP_TAC[ATN_MONO_LT]);;
574 let ATN_ADD_SMALL = prove
575 (`!x y. abs(x * y) < &1
576 ==> (atn(x) + atn(y) = atn((x + y) / (&1 - x * y)))`,
577 REPEAT STRIP_TAC THEN MATCH_MP_TAC ATN_ADD THEN
578 ASM_SIMP_TAC[ATN_ADD_SMALL_LEMMA] THEN
579 POP_ASSUM MP_TAC THEN REAL_ARITH_TAC);;
582 let match_fn = PART_MATCH (lhand o rand) ATN_ADD_SMALL in
586 (COMB2_CONV REAL_RAT_REDUCE_CONV
587 (RAND_CONV REAL_RAT_REDUCE_CONV)) o
589 fun tm -> if is_ratconst(rand(rand tm)) &
590 is_ratconst(rand(lhand tm))
592 else failwith "ATN_ADD_CONV: Atn of nonconstant";;
596 (`(&0 * atn(x) = &0) /\
597 (&1 * atn(x) = atn(x))`,
598 REWRITE_TAC[REAL_MUL_LZERO; REAL_MUL_LID])
599 and pth_0,pth_1 = (CONJ_PAIR o prove)
600 (`(&(NUMERAL(BIT0 n)) * atn(x) =
601 &(NUMERAL n) * atn(x) + &(NUMERAL n) * atn(x)) /\
602 (&(NUMERAL(BIT1 n)) * atn(x) =
603 atn(x) + &(NUMERAL n) * atn(x) + &(NUMERAL n) * atn(x))`,
604 REWRITE_TAC[REAL_MUL_LZERO; REAL_MUL_LID] THEN
605 REWRITE_TAC[NUMERAL; BIT0; BIT1] THEN
606 REWRITE_TAC[GSYM REAL_OF_NUM_ADD; GSYM REAL_OF_NUM_SUC] THEN
608 let rewr_base = GEN_REWRITE_CONV I [pth_base]
609 and rewr_0 = GEN_REWRITE_CONV I [pth_0]
610 and rewr_1 = GEN_REWRITE_CONV I [pth_1] in
611 let rec ATN_CMUL_CONV tm =
612 if not (is_ratconst(rand(rand tm))) then failwith "ATN_CMUL_CONV" else
613 try rewr_base tm with Failure _ ->
614 try let th1 = rewr_0 tm in
615 let tm1 = rand(concl th1) in
616 let th2 = ATN_CMUL_CONV(rand tm1) in
617 let th3 = MK_COMB(AP_TERM (rator(rator tm1)) th2,th2) in
618 let th4 = TRANS th3 (ATN_ADD_CONV(rand(concl th3))) in
621 let th1 = rewr_1 tm in
622 let tm1 = rand(rand(concl th1)) in
623 let th2 = ATN_CMUL_CONV(rand tm1) in
624 let th3 = MK_COMB(AP_TERM (rator(rator tm1)) th2,th2) in
625 let th4 = TRANS th3 (ATN_ADD_CONV(rand(concl th3))) in
626 let th5 = AP_TERM (rator(rand(concl th1))) th4 in
627 let th6 = TRANS th5 (ATN_ADD_CONV(rand(concl th5))) in
633 (`(atn(x) - atn(y) = atn(x) + atn(--y))`,
634 REWRITE_TAC[real_sub; ATN_NEG]) in
635 GEN_REWRITE_CONV I [pth] THENC
636 RAND_CONV(RAND_CONV REAL_RAT_NEG_CONV) THENC
640 DEPTH_CONV(ATN_ADD_CONV ORELSEC ATN_SUB_CONV ORELSEC ATN_CMUL_CONV);;
642 let MACHIN_RULE tm = SYM(TRANS (MACHIN_CONV tm) ATN_1);;
644 let MACHIN_1 = time MACHIN_RULE `&4 * atn(&1 / &5) - atn(&1 / &239)`;;
645 let MACHIN_2 = time MACHIN_RULE `atn(&1 / &2) + atn(&1 / &3)`;;
646 let MACHIN_3 = time MACHIN_RULE `&2 * atn(&1 / &2) - atn(&1 / &7)`;;
647 let MACHIN_4 = time MACHIN_RULE `&2 * atn(&1 / &3) + atn(&1 / &7)`;;
649 let EULER = time MACHIN_RULE `&5 * atn(&1 / &7) + &2 * atn (&3 / &79)`;;
651 let GAUSS_MACHIN = time MACHIN_RULE
652 `&12 * atn(&1 / &18) + &8 * atn (&1 / &57) - &5 * atn(&1 / &239)`;;
654 let STRASSNITZKY_MACHIN = time MACHIN_RULE
655 `atn(&1 / &2) + atn (&1 / &5) + atn(&1 / &8)`;;
657 let MACHINLIKE_1 = time MACHIN_RULE
658 `&6 * atn(&1 / &8) + &2 * atn(&1 / &57) + atn(&1 / &239)`;;
659 let MACHINLIKE_2 = time MACHIN_RULE
660 `&4 * atn(&1 / &5) - &1 * atn(&1 / &70) + atn(&1 / &99)`;;
661 let MACHINLIKE_3 = time MACHIN_RULE
662 `&1 * atn(&1 / &2) + &1 * atn(&1 / &5) + atn(&1 / &8)`;;
663 let MACHINLIKE_4 = time MACHIN_RULE
664 `&8 * atn(&1 / &10) - &1 * atn(&1 / &239) - &4 * atn(&1 / &515)`;;
665 let MACHINLIKE_5 = time MACHIN_RULE
666 `&5 * atn(&1 / &7) + &4 * atn(&1 / &53) + &2 * atn(&1 / &4443)`;;
668 (***** Hopefully this one would work, but it takes a long time
670 let HWANG_MACHIN = time MACHIN_RULE
671 `&183 * atn(&1 / &239) + &32 * atn(&1 / &1023) -
672 &68 * atn(&1 / &5832) + &12 * atn(&1 / &110443) -
673 &12 * atn(&1 / &4841182) - &100 * atn(&1 / &6826318)`;;
677 (* ------------------------------------------------------------------------- *)
678 (* Approximate the arctan of a rational number. *)
679 (* ------------------------------------------------------------------------- *)
683 else hd l +/ (x */ POLY (tl l) x);;
685 let atn_approx_conv,ATN_APPROX_CONV =
690 let rec log_2 x = if x <=/ num_1 then log_2 (num_2 */ x) -/ num_1
691 else if x >/ num_2 then log_2 (x // num_2) +/ num_1
694 (`!p. abs(atn(&0) - &0) <= inv(&2 pow p)`,
695 SIMP_TAC[ATN_0; REAL_SUB_REFL; REAL_ABS_NUM; REAL_LE_INV_EQ;
696 REAL_POW_LE; REAL_POS]) in
697 let atn_approx_conv p r =
698 if r =/ num_0 then num_0 else
699 let k = Num.int_of_num(minus_num(log_2(abs_num r))) in
700 if k < 1 then failwith "atn_approx_conv: argument too big" else
701 let rats = mclaurin_atn_rule k p in
703 and ATN_APPROX_CONV p tm =
704 let atm,rtm = dest_comb tm in
705 if atm <> atn_tm then failwith "ATN_APPROX_CONV" else
706 let r = rat_of_term rtm in
707 if r =/ num_0 then SPEC (mk_small_numeral p) pth else
708 let k = Num.int_of_num(minus_num(log_2(abs_num r))) in
709 if k < 1 then failwith "ATN_APPROX_CONV: argument too big" else
710 let th1 = MCLAURIN_ATN_RULE k p in
711 let th2 = SPEC rtm th1 in
712 let th3 = MP th2 (EQT_ELIM(REAL_RAT_REDUCE_CONV(lhand(concl th2)))) in
713 CONV_RULE(LAND_CONV(RAND_CONV(RAND_CONV REAL_RAT_REDUCE_CONV))) th3 in
714 atn_approx_conv,ATN_APPROX_CONV;;
716 (* ------------------------------------------------------------------------- *)
717 (* Approximate pi using this and a Machin-type formula. *)
718 (* ------------------------------------------------------------------------- *)
720 let pi_approx_rule,PI_APPROX_RULE =
721 let const_1_8 = Int 1 // Int 8
722 and const_1_57 = Int 1 // Int 57
723 and const_1_239 = Int 1 // Int 239
724 and const_24 = Int 24
727 and tm_1_8 = `atn(&1 / &8)`
728 and tm_1_57 = `atn(&1 / &57)`
729 and tm_1_239 = `atn(&1 / &239)`
732 and p_tm = `p:num` in
736 abs(atn(&1 / &8) - a1) <= inv(&2 pow q1) /\
737 abs(atn(&1 / &57) - a2) <= inv(&2 pow q2) /\
738 abs(atn(&1 / &239) - a3) <= inv(&2 pow q2)
739 ==> abs(pi - (&24 * a1 + &8 * a2 + &4 * a3)) <= inv(&2 pow p)`,
740 DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
741 DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
742 ASM_REWRITE_TAC[] THEN POP_ASSUM_LIST(K ALL_TAC) THEN STRIP_TAC THEN
743 MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN EXISTS_TAC `abs(inv(&2 pow 2))` THEN
744 SIMP_TAC[REAL_POW2_CLAUSES; REAL_ARITH `&0 < x ==> &0 < abs(x)`] THEN
745 REWRITE_TAC[GSYM REAL_ABS_MUL] THEN
746 REWRITE_TAC[REAL_ABS_INV; REAL_ABS_POW; REAL_ABS_NUM] THEN
747 REWRITE_TAC[GSYM REAL_INV_MUL; GSYM REAL_POW_ADD] THEN
748 CONV_TAC REAL_RAT_REDUCE_CONV THEN
749 REWRITE_TAC[REAL_SUB_LDISTRIB; REAL_ADD_LDISTRIB; REAL_MUL_ASSOC] THEN
750 CONV_TAC REAL_RAT_REDUCE_CONV THEN
751 REWRITE_TAC[real_div; REAL_MUL_LID] THEN
752 GEN_REWRITE_TAC (LAND_CONV o RAND_CONV o LAND_CONV) [REAL_MUL_SYM] THEN
753 REWRITE_TAC[GSYM real_div; MACHINLIKE_1] THEN
754 REWRITE_TAC[REAL_ARITH `(x1 + x2 + x3) - (y1 + y2 + y3) =
755 (x1 - y1) + (x2 - y2) + (x3 - y3)`] THEN
756 REWRITE_TAC[GSYM REAL_SUB_LDISTRIB] THEN BOUND_SUMPROD_TAC THEN
757 GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [ADD_SYM] THEN
758 REWRITE_TAC[REAL_POW_ADD; REAL_INV_MUL; REAL_MUL_ASSOC] THEN
759 SIMP_TAC[GSYM REAL_ADD_RDISTRIB; REAL_LE_RMUL_EQ; REAL_POW2_CLAUSES] THEN
760 CONV_TAC REAL_RAT_REDUCE_CONV) in
761 let pi_approx_rule p =
764 let a1 = atn_approx_conv q1 const_1_8
765 and a2 = atn_approx_conv q2 const_1_57
766 and a3 = atn_approx_conv q2 const_1_239 in
767 const_24 */ a1 +/ const_8 */ a2 +/ const_4 */ a3
768 and PI_APPROX_RULE p =
771 let th1 = ATN_APPROX_CONV q1 tm_1_8
772 and th2 = ATN_APPROX_CONV q2 tm_1_57
773 and th3 = ATN_APPROX_CONV q2 tm_1_239 in
774 let th4 = INST [mk_small_numeral p,p_tm;
775 mk_small_numeral q1,q1_tm;
776 mk_small_numeral q2,q2_tm] pth in
777 let th5 = EQT_ELIM(NUM_REDUCE_CONV(lhand(lhand(concl th4))))
778 and th6 = EQT_ELIM(NUM_REDUCE_CONV(lhand(rand(lhand(concl th4))))) in
779 let th7 = MATCH_MP th4 (end_itlist CONJ [th5; th6; th1; th2; th3]) in
780 CONV_RULE(LAND_CONV(RAND_CONV(RAND_CONV REAL_RAT_REDUCE_CONV))) th7 in
781 pi_approx_rule,PI_APPROX_RULE;;
783 (* ------------------------------------------------------------------------- *)
784 (* A version that yields a fraction with power of two denominator. *)
785 (* ------------------------------------------------------------------------- *)
787 let pi_approx_binary_rule,PI_APPROX_BINARY_RULE =
789 (`abs(x - r) <= inv(&2 pow (SUC p))
790 ==> !a. abs(&2 pow p * r - a) <= inv(&2)
791 ==> abs(x - a / &2 pow p) <= inv(&2 pow p)`,
792 REPEAT STRIP_TAC THEN
793 FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_ARITH
794 `abs(x - r) <= q ==> abs(r - r') <= p - q ==> abs(x - r') <= p`)) THEN
795 MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN EXISTS_TAC `abs(&2 pow p)` THEN
796 SIMP_TAC[REAL_ARITH `&0 < x ==> &0 < abs(x)`; REAL_POW2_THM] THEN
797 REWRITE_TAC[GSYM REAL_ABS_MUL; REAL_SUB_LDISTRIB] THEN
798 SIMP_TAC[REAL_ABS_POW; REAL_ABS_NUM; GSYM real_div;
799 REAL_DIV_LMUL; REAL_LT_IMP_NZ; REAL_POW2_CLAUSES;
800 REAL_DIV_POW2; REAL_OF_NUM_EQ; ARITH_EQ;
801 LE_REFL; ARITH_RULE `~(SUC p <= p)`;
802 ARITH_RULE `SUC p - p = 1`; SUB_REFL] THEN
803 UNDISCH_TAC `abs (&2 pow p * r - a) <= inv (&2)` THEN
804 CONV_TAC NUM_REDUCE_CONV THEN CONV_TAC REAL_RAT_REDUCE_CONV)
806 let pi_approx_binary_rule p =
807 let ppow = power_num num_2 (Int p) in
808 let r = pi_approx_rule (p + 1) in
809 let a = round_num (ppow */ r) in
811 and PI_APPROX_BINARY_RULE p =
812 let ppow = power_num num_2 (Int p) in
813 let th1 = PI_APPROX_RULE (p + 1) in
814 let th2 = CONV_RULE(funpow 3 RAND_CONV num_CONV) th1 in
815 let r = rat_of_term(rand(rand(lhand(concl th2)))) in
816 let th3 = SPEC (mk_realintconst(round_num(ppow */ r))) (MATCH_MP pth th2) in
817 let th4 = MP th3 (EQT_ELIM(REAL_RAT_REDUCE_CONV(lhand(concl th3)))) in
818 CONV_RULE(LAND_CONV(RAND_CONV(RAND_CONV REAL_RAT_REDUCE_CONV))) th4 in
819 pi_approx_binary_rule,PI_APPROX_BINARY_RULE;;
821 (* ------------------------------------------------------------------------- *)
822 (* Rule to expand atn(r) for rational r into more easily calculable bits. *)
823 (* ------------------------------------------------------------------------- *)
825 let ATN_EXPAND_CONV =
829 and eighth = Int 1 // Int 8
831 and eighth_tm = `&1 / &8`
832 and mk_mul = mk_binop `(*)`
833 and mk_add = mk_binop `(+)`
837 let x' = (x -/ eighth) // (num_1 +/ x */ eighth) in
839 if abs_num(x') </ abs_num(x) then (x',n+1) else (x,n)
840 else homein (n + 1) x' in
843 let ltm,rtm = dest_comb tm in
844 if ltm <> atn_tm then failwith "ATN_EXPAND_CONV" else
845 let r = rat_of_term rtm in
846 let (x,n) = home_in r in
847 let xtm = mk_add (mk_mul (mk_comb(amp_tm,mk_small_numeral n))
848 (mk_comb(atn_tm,eighth_tm)))
849 (mk_comb(atn_tm,term_of_rat x)) in
850 SYM(MACHIN_CONV xtm);;