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Diffstat (limited to 'test/monniaux/glpk-4.65/src/misc/fp2rat.c')
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diff --git a/test/monniaux/glpk-4.65/src/misc/fp2rat.c b/test/monniaux/glpk-4.65/src/misc/fp2rat.c new file mode 100644 index 00000000..4699bbd1 --- /dev/null +++ b/test/monniaux/glpk-4.65/src/misc/fp2rat.c @@ -0,0 +1,164 @@ +/* fp2rat.c (convert floating-point number to rational number) */ + +/*********************************************************************** +* This code is part of GLPK (GNU Linear Programming Kit). +* +* Copyright (C) 2000-2013 Andrew Makhorin, Department for Applied +* Informatics, Moscow Aviation Institute, Moscow, Russia. All rights +* reserved. E-mail: <mao@gnu.org>. +* +* GLPK is free software: you can redistribute it and/or modify it +* under the terms of the GNU General Public License as published by +* the Free Software Foundation, either version 3 of the License, or +* (at your option) any later version. +* +* GLPK is distributed in the hope that it will be useful, but WITHOUT +* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public +* License for more details. +* +* You should have received a copy of the GNU General Public License +* along with GLPK. If not, see <http://www.gnu.org/licenses/>. +***********************************************************************/ + +#include "env.h" +#include "misc.h" + +/*********************************************************************** +* NAME +* +* fp2rat - convert floating-point number to rational number +* +* SYNOPSIS +* +* #include "misc.h" +* int fp2rat(double x, double eps, double *p, double *q); +* +* DESCRIPTION +* +* Given a floating-point number 0 <= x < 1 the routine fp2rat finds +* its "best" rational approximation p / q, where p >= 0 and q > 0 are +* integer numbers, such that |x - p / q| <= eps. +* +* RETURNS +* +* The routine fp2rat returns the number of iterations used to achieve +* the specified precision eps. +* +* EXAMPLES +* +* For x = sqrt(2) - 1 = 0.414213562373095 and eps = 1e-6 the routine +* gives p = 408 and q = 985, where 408 / 985 = 0.414213197969543. +* +* BACKGROUND +* +* It is well known that every positive real number x can be expressed +* as the following continued fraction: +* +* x = b[0] + a[1] +* ------------------------ +* b[1] + a[2] +* ----------------- +* b[2] + a[3] +* ---------- +* b[3] + ... +* +* where: +* +* a[k] = 1, k = 0, 1, 2, ... +* +* b[k] = floor(x[k]), k = 0, 1, 2, ... +* +* x[0] = x, +* +* x[k] = 1 / frac(x[k-1]), k = 1, 2, 3, ... +* +* To find the "best" rational approximation of x the routine computes +* partial fractions f[k] by dropping after k terms as follows: +* +* f[k] = A[k] / B[k], +* +* where: +* +* A[-1] = 1, A[0] = b[0], B[-1] = 0, B[0] = 1, +* +* A[k] = b[k] * A[k-1] + a[k] * A[k-2], +* +* B[k] = b[k] * B[k-1] + a[k] * B[k-2]. +* +* Once the condition +* +* |x - f[k]| <= eps +* +* has been satisfied, the routine reports p = A[k] and q = B[k] as the +* final answer. +* +* In the table below here is some statistics obtained for one million +* random numbers uniformly distributed in the range [0, 1). +* +* eps max p mean p max q mean q max k mean k +* ------------------------------------------------------------- +* 1e-1 8 1.6 9 3.2 3 1.4 +* 1e-2 98 6.2 99 12.4 5 2.4 +* 1e-3 997 20.7 998 41.5 8 3.4 +* 1e-4 9959 66.6 9960 133.5 10 4.4 +* 1e-5 97403 211.7 97404 424.2 13 5.3 +* 1e-6 479669 669.9 479670 1342.9 15 6.3 +* 1e-7 1579030 2127.3 3962146 4257.8 16 7.3 +* 1e-8 26188823 6749.4 26188824 13503.4 19 8.2 +* +* REFERENCES +* +* W. B. Jones and W. J. Thron, "Continued Fractions: Analytic Theory +* and Applications," Encyclopedia on Mathematics and Its Applications, +* Addison-Wesley, 1980. */ + +int fp2rat(double x, double eps, double *p, double *q) +{ int k; + double xk, Akm1, Ak, Bkm1, Bk, ak, bk, fk, temp; + xassert(0.0 <= x && x < 1.0); + for (k = 0; ; k++) + { xassert(k <= 100); + if (k == 0) + { /* x[0] = x */ + xk = x; + /* A[-1] = 1 */ + Akm1 = 1.0; + /* A[0] = b[0] = floor(x[0]) = 0 */ + Ak = 0.0; + /* B[-1] = 0 */ + Bkm1 = 0.0; + /* B[0] = 1 */ + Bk = 1.0; + } + else + { /* x[k] = 1 / frac(x[k-1]) */ + temp = xk - floor(xk); + xassert(temp != 0.0); + xk = 1.0 / temp; + /* a[k] = 1 */ + ak = 1.0; + /* b[k] = floor(x[k]) */ + bk = floor(xk); + /* A[k] = b[k] * A[k-1] + a[k] * A[k-2] */ + temp = bk * Ak + ak * Akm1; + Akm1 = Ak, Ak = temp; + /* B[k] = b[k] * B[k-1] + a[k] * B[k-2] */ + temp = bk * Bk + ak * Bkm1; + Bkm1 = Bk, Bk = temp; + } + /* f[k] = A[k] / B[k] */ + fk = Ak / Bk; +#if 0 + print("%.*g / %.*g = %.*g", + DBL_DIG, Ak, DBL_DIG, Bk, DBL_DIG, fk); +#endif + if (fabs(x - fk) <= eps) + break; + } + *p = Ak; + *q = Bk; + return k; +} + +/* eof */ |