solvps.c

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/*  solvps.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.)
 * ------------------------------------------------------------------------
 */
#include "ccmath.h"
int solvps(double *a, double *b, int n)
{
    double *p, *q, *r, *s, t;
 
    int j, k;
 
    for (j = 0, p = a; j < n; ++j, p += n + 1) {
        for (q = a + j * n; q < p; ++q)
            *p -= *q * *q;
        if (*p <= 0.)
            return -1;
        *p = sqrt(*p);
        for (k = j + 1, q = p + n; k < n; ++k, q += n) {
            for (r = a + j * n, s = a + k * n, t = 0.; r < p;)
                t += *r++ * *s++;
            *q -= t;
            *q /= *p;
        }
    }
    for (j = 0, p = a; j < n; ++j, p += n + 1) {
        for (k = 0, q = a + j * n; k < j;)
            b[j] -= b[k++] * *q++;
        b[j] /= *p;
    }
    for (j = n - 1, p = a + n * n - 1; j >= 0; --j, p -= n + 1) {
        for (k = j + 1, q = p + n; k < n; q += n)
            b[j] -= b[k++] * *q;
        b[j] /= *p;
    }
    return 0;
}