ruinv.c

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/*  ruinv.c    CCMATH mathematics library source code.
 *
 *  Copyright (C)  2000   Daniel A. Atkinson    All rights reserved.
 *  This code may be redistributed under the terms of the GNU library
 *  public license (LGPL). ( See the lgpl.license file for details.)
 * ------------------------------------------------------------------------
 */
int ruinv(double *a, int n)
{
    int j;

    double fabs();

    double tt, z, *p, *q, *r, *s, *t;

    for (j = 0, tt = 0., p = a; j < n; ++j, p += n + 1)
        if ((z = fabs(*p)) > tt)
            tt = z;
    tt *= 1.e-16;
    for (j = 0, p = a; j < n; ++j, p += n + 1) {
        if (fabs(*p) < tt)
            return -1;
        *p = 1. / *p;
        for (q = a + j, t = a; q < p; t += n + 1, q += n) {
            for (s = q, r = t, z = 0.; s < p; s += n)
                z -= *s * *r++;
            *q = z * *p;
        }
    }
    return 0;
}