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84 lines
2 KiB
C
84 lines
2 KiB
C
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/*
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* Matrix operations library
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*
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* Copyright (C) 1999-2000
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* Thomas Sailer, <sailer@ife.ee.ethz.ch>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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/* AIX requires this to be the first thing in the file. */
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#ifndef __GNUC__
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# if HAVE_ALLOCA_H
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# include <alloca.h>
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# else
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# ifdef _AIX
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#pragma alloca
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# else
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# ifndef alloca /* predefined by HP cc +Olibcalls */
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char *alloca ();
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# endif
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# endif
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# endif
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#endif
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#include "mat.h"
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#include <math.h>
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#include <stdio.h>
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/*
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* This routine calculates A*c=b iteratively, using the Gauss-Seidel iteration method
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*/
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int frgaussseidel(const float *a, const float *b, float *c, unsigned int d, unsigned int iter)
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{
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float *adiag;
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unsigned int i, j, k;
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float s;
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adiag = alloca(d * sizeof(adiag[0]));
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/* initial vector */
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for (i = 0; i < d; i++)
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c[i] = 0;
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c[0] = 1;
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/* check for diagonal */
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for (i = 0; i < d; i++) {
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if (a[i*d+i] <= 0) {
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fprintf(stderr, "frgaussseidel: matrix diagonal not positive a[%u][%u]=%g\n", i, i, a[i*d+i]);
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return -1;
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}
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adiag[i] = 1 / a[i*d+i];
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}
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/* iteration */
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for (i = 0; i < iter; i++) {
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for (j = 0; j < d; j++) {
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s = b[j];
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for (k = 0; k < j; k++)
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s -= a[j*d+k] * c[k];
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for (k = j+1; k < d; k++)
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s -= a[j*d+k] * c[k];
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c[j] = s * adiag[j];
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}
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}
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return 0;
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}
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