1 /*
2 * Copyright (C) 1998, 2000-2007, 2010, 2011, 2012, 2013 SINTEF ICT,
3 * Applied Mathematics, Norway.
4 *
5 * Contact information: E-mail: tor.dokken@sintef.no
6 * SINTEF ICT, Department of Applied Mathematics,
7 * P.O. Box 124 Blindern,
8 * 0314 Oslo, Norway.
9 *
10 * This file is part of SISL.
11 *
12 * SISL is free software: you can redistribute it and/or modify
13 * it under the terms of the GNU Affero General Public License as
14 * published by the Free Software Foundation, either version 3 of the
15 * License, or (at your option) any later version.
16 *
17 * SISL is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Affero General Public License for more details.
21 *
22 * You should have received a copy of the GNU Affero General Public
23 * License along with SISL. If not, see
24 * <http://www.gnu.org/licenses/>.
25 *
26 * In accordance with Section 7(b) of the GNU Affero General Public
27 * License, a covered work must retain the producer line in every data
28 * file that is created or manipulated using SISL.
29 *
30 * Other Usage
31 * You can be released from the requirements of the license by purchasing
32 * a commercial license. Buying such a license is mandatory as soon as you
33 * develop commercial activities involving the SISL library without
34 * disclosing the source code of your own applications.
35 *
36 * This file may be used in accordance with the terms contained in a
37 * written agreement between you and SINTEF ICT.
38 */
39
40 #include "sisl-copyright.h"
41
42 /*
43 *
44 * $Id: s6lusolp.c,v 1.2 2001-03-19 15:59:02 afr Exp $
45 *
46 */
47
48
49 #define S6LUSOLP
50
51 #include "sislP.h"
52
53 #if defined(SISLNEEDPROTOTYPES)
54 void
s6lusolp(double ea[],double eb[],int nl[],int im,int * jstat)55 s6lusolp(double ea[],double eb[],int nl[],int im,int *jstat)
56 #else
57 void s6lusolp(ea,eb,nl,im,jstat)
58 double ea[];
59 double eb[];
60 int nl[];
61 int im;
62 int *jstat;
63 #endif
64 /*
65 ************************************************************************
66 *
67 ***********************************************************************
68 *
69 * PURPOSE : Solve the equationsystem LU=eb by forth- and back-
70 * substitution. L and U are stored in ea.
71 *
72 *
73 * INPUT : ea - The factorized coeffecient-matrix.
74 * im - The number of equations.
75 * nl - Ordering of lines in the matrix.
76 *
77 *
78 * INPUT/OUTPUT : eb - the right side of the equationsystem and
79 * the found values for the unknowns.
80 *
81 * OUTPUT : jstat - Status variable.
82 * < 0 : Error
83 * = 0 : ok
84 * > 0 : Warning
85 *
86 *
87 * METHOD : Solve on the equation-system LU=eb.
88 *
89 *
90 * REFERENCES : Cheney & Kincaid : Numerical Mathematics and
91 * Computing.
92 *
93 *-
94 * CALLS :
95 *
96 * WRITTEN BY : Vibeke Skytt, SI, 86-10.
97 *
98 ************************************************************************
99 */
100 {
101 int kpos = 0; /* Position of error. */
102 int ki,kj; /* Counters. */
103 double *sx = SISL_NULL; /* Array used to keep solution of equation system
104 internally. */
105 double tdiv; /* Dividend in expression. */
106
107 /* Allocate space for local array. */
108
109 if ((sx = newarray(im,double)) == SISL_NULL) goto err101;
110
111 for (ki=0; ki<im-1; ki++)
112 {
113 /* Gauss on right side of equation */
114
115 for (kj=ki+1; kj<im; kj++)
116 eb[nl[kj]] -= eb[nl[ki]]*ea[ki+nl[kj]*im];
117 }
118
119 tdiv = ea[im-1+nl[im-1]*im];
120 if (DEQUAL(tdiv,DZERO)) goto warn1;
121 sx[im-1] = eb[nl[im-1]]/tdiv;
122
123 for (ki=im-2; ki>=0; ki--)
124 {
125 /* Backwards substitution. */
126
127 for (kj=ki+1; kj<im; kj++)
128 eb[nl[ki]] -= sx[kj]*ea[kj+nl[ki]*im];
129
130 tdiv = ea[ki+nl[ki]*im];
131 if (DEQUAL(tdiv,DZERO)) goto warn1;
132 sx[ki] = eb[nl[ki]]/tdiv;
133 }
134 for (ki=0; ki<im; ki++) eb[ki] = sx[ki];
135
136 /* Equation system solved. */
137
138 *jstat = 0;
139 goto out;
140
141 /* Singular equation system. */
142
143 warn1 : *jstat = 1;
144 goto out;
145
146 /* Error in space allocation. */
147
148 err101: *jstat = -101;
149 s6err("s6lusolp",*jstat,kpos);
150 goto out;
151
152 out:
153
154 /* Free space occupied by local array. */
155
156 if (sx != SISL_NULL) freearray(sx);
157
158 return;
159 }
160