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/*
* Copyright (C) 1998, 2000-2007, 2010, 2011, 2012, 2013 SINTEF ICT,
* Applied Mathematics, Norway.
*
* Contact information: E-mail: tor.dokken@sintef.no
* SINTEF ICT, Department of Applied Mathematics,
* P.O. Box 124 Blindern,
* 0314 Oslo, Norway.
*
* This file is part of SISL.
*
* SISL is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* SISL 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public
* License along with SISL. If not, see
* <http://www.gnu.org/licenses/>.
*
* In accordance with Section 7(b) of the GNU Affero General Public
* License, a covered work must retain the producer line in every data
* file that is created or manipulated using SISL.
*
* Other Usage
* You can be released from the requirements of the license by purchasing
* a commercial license. Buying such a license is mandatory as soon as you
* develop commercial activities involving the SISL library without
* disclosing the source code of your own applications.
*
* This file may be used in accordance with the terms contained in a
* written agreement between you and SINTEF ICT.
*/
#include "sisl-copyright.h"
/*
*
* $Id: s6lusolp.c,v 1.2 2001-03-19 15:59:02 afr Exp $
*
*/
#define S6LUSOLP
#include "sislP.h"
#if defined(SISLNEEDPROTOTYPES)
void
s6lusolp(double ea[],double eb[],int nl[],int im,int *jstat)
#else
void s6lusolp(ea,eb,nl,im,jstat)
double ea[];
double eb[];
int nl[];
int im;
int *jstat;
#endif
/*
************************************************************************
*
***********************************************************************
*
* PURPOSE : Solve the equationsystem LU=eb by forth- and back-
* substitution. L and U are stored in ea.
*
*
* INPUT : ea - The factorized coeffecient-matrix.
* im - The number of equations.
* nl - Ordering of lines in the matrix.
*
*
* INPUT/OUTPUT : eb - the right side of the equationsystem and
* the found values for the unknowns.
*
* OUTPUT : jstat - Status variable.
* < 0 : Error
* = 0 : ok
* > 0 : Warning
*
*
* METHOD : Solve on the equation-system LU=eb.
*
*
* REFERENCES : Cheney & Kincaid : Numerical Mathematics and
* Computing.
*
*-
* CALLS :
*
* WRITTEN BY : Vibeke Skytt, SI, 86-10.
*
************************************************************************
*/
{
int kpos = 0; /* Position of error. */
int ki,kj; /* Counters. */
double *sx = SISL_NULL; /* Array used to keep solution of equation system
internally. */
double tdiv; /* Dividend in expression. */
/* Allocate space for local array. */
if ((sx = newarray(im,double)) == SISL_NULL) goto err101;
for (ki=0; ki<im-1; ki++)
{
/* Gauss on right side of equation */
for (kj=ki+1; kj<im; kj++)
eb[nl[kj]] -= eb[nl[ki]]*ea[ki+nl[kj]*im];
}
tdiv = ea[im-1+nl[im-1]*im];
if (DEQUAL(tdiv,DZERO)) goto warn1;
sx[im-1] = eb[nl[im-1]]/tdiv;
for (ki=im-2; ki>=0; ki--)
{
/* Backwards substitution. */
for (kj=ki+1; kj<im; kj++)
eb[nl[ki]] -= sx[kj]*ea[kj+nl[ki]*im];
tdiv = ea[ki+nl[ki]*im];
if (DEQUAL(tdiv,DZERO)) goto warn1;
sx[ki] = eb[nl[ki]]/tdiv;
}
for (ki=0; ki<im; ki++) eb[ki] = sx[ki];
/* Equation system solved. */
*jstat = 0;
goto out;
/* Singular equation system. */
warn1 : *jstat = 1;
goto out;
/* Error in space allocation. */
err101: *jstat = -101;
s6err("s6lusolp",*jstat,kpos);
goto out;
out:
/* Free space occupied by local array. */
if (sx != SISL_NULL) freearray(sx);
return;
}
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