programming6/ruinv_8c_source.html

00001 /*  ruinv.c    CCMATH mathematics library source code.
00002  *
00003  *  Copyright (C)  2000   Daniel A. Atkinson    All rights reserved.
00004  *  This code may be redistributed under the terms of the GNU library
00005  *  public license (LGPL). ( See the lgpl.license file for details.)
00006  * ------------------------------------------------------------------------
00007  */
00008 int ruinv(double *a, int n)
00009 {
00010     int j;
00011
00012     double fabs();
00013
00014     double tt, z, *p, *q, *r, *s, *t;
00015
00016     for (j = 0, tt = 0., p = a; j < n; ++j, p += n + 1)
00017         if ((z = fabs(*p)) > tt)
00018             tt = z;
00019     tt *= 1.e-16;
00020     for (j = 0, p = a; j < n; ++j, p += n + 1) {
00021         if (fabs(*p) < tt)
00022             return -1;
00023         *p = 1. / *p;
00024         for (q = a + j, t = a; q < p; t += n + 1, q += n) {
00025             for (s = q, r = t, z = 0.; s < p; s += n)
00026                 z -= *s * *r++;
00027             *q = z * *p;
00028         }
00029     }
00030     return 0;
00031 }