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SYSV Example Program in C
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/*
SSYSV Example.
==============
The program computes the solution to the system of linear equations
with a real symmetric matrix A and multiple right-hand sides B,
where A is the coefficient matrix:
-5.86 3.99 -5.93 -2.82 7.69
3.99 4.46 2.58 4.42 4.61
-5.93 2.58 -8.52 8.57 7.69
-2.82 4.42 8.57 3.72 8.07
7.69 4.61 7.69 8.07 9.83
and B is the right-hand side matrix:
1.32 -6.33 -8.77
2.22 1.69 -8.33
0.12 -1.56 9.54
-6.41 -9.49 9.56
6.33 -3.67 7.48
Description.
============
The routine solves for X the real system of linear equations A*X = B,
where A is an n-by-n symmetric matrix, the columns of matrix B are
individual right-hand sides, and the columns of X are the corresponding
solutions.
The diagonal pivoting method is used to factor A as A = U*D*UT or
A = L*D*LT , where U (or L) is a product of permutation and unit upper
(lower) triangular matrices, and D is symmetric and block diagonal with
1-by-1 and 2-by-2 diagonal blocks.
The factored form of A is then used to solve the system of equations A*X = B.
Example Program Results.
========================
SSYSV Example Program Results
Solution
1.17 0.52 -0.86
-0.71 1.05 -4.90
-0.63 -0.52 0.99
-0.33 0.43 1.22
0.83 -1.22 1.96
Details of factorization
-5.86 0.00 0.00 0.00 0.00
-0.68 7.18 0.00 0.00 0.00
1.01 -0.20 -2.82 0.00 0.00
0.48 0.35 11.93 4.21 0.00
-1.31 1.37 0.02 0.16 6.22
Pivot indices
1 2 -4 -4 5
*/
#include <stdlib.h>
#include <stdio.h>
/* SSYSV prototype */
extern void ssysv( char* uplo, int* n, int* nrhs, float* a, int* lda,
int* ipiv, float* b, int* ldb, float* work, int* lwork, int* info );
/* Auxiliary routines prototypes */
extern void print_matrix( char* desc, int m, int n, float* a, int lda );
extern void print_int_vector( char* desc, int n, int* a );
/* Parameters */
#define N 5
#define NRHS 3
#define LDA N
#define LDB N
/* Main program */
int main() {
/* Locals */
int n = N, nrhs = NRHS, lda = LDA, ldb = LDB, info, lwork;
float wkopt;
float* work;
/* Local arrays */
int ipiv[N];
float a[LDA*N] = {
-5.86f, 3.99f, -5.93f, -2.82f, 7.69f,
0.00f, 4.46f, 2.58f, 4.42f, 4.61f,
0.00f, 0.00f, -8.52f, 8.57f, 7.69f,
0.00f, 0.00f, 0.00f, 3.72f, 8.07f,
0.00f, 0.00f, 0.00f, 0.00f, 9.83f
};
float b[LDB*NRHS] = {
1.32f, 2.22f, 0.12f, -6.41f, 6.33f,
-6.33f, 1.69f, -1.56f, -9.49f, -3.67f,
-8.77f, -8.33f, 9.54f, 9.56f, 7.48f
};
/* Executable statements */
printf( " SSYSV Example Program Results\n" );
/* Query and allocate the optimal workspace */
lwork = -1;
ssysv( "Lower", &n, &nrhs, a, &lda, ipiv, b, &ldb, &wkopt, &lwork, &info );
lwork = (int)wkopt;
work = (float*)malloc( lwork*sizeof(float) );
/* Solve the equations A*X = B */
ssysv( "Lower", &n, &nrhs, a, &lda, ipiv, b, &ldb, work, &lwork, &info );
/* Check for the exact singularity */
if( info > 0 ) {
printf( "The element of the diagonal factor " );
printf( "D(%i,%i) is zero, so that D is singular;\n", info, info );
printf( "the solution could not be computed.\n" );
exit( 1 );
}
/* Print solution */
print_matrix( "Solution", n, nrhs, b, ldb );
/* Print details of factorization */
print_matrix( "Details of factorization", n, n, a, lda );
/* Print pivot indices */
print_int_vector( "Pivot indices", n, ipiv );
/* Free workspace */
free( (void*)work );
exit( 0 );
} /* End of SSYSV Example */
/* Auxiliary routine: printing a matrix */
void print_matrix( char* desc, int m, int n, float* a, int lda ) {
int i, j;
printf( "\n %s\n", desc );
for( i = 0; i < m; i++ ) {
for( j = 0; j < n; j++ ) printf( " %6.2f", a[i+j*lda] );
printf( "\n" );
}
}
/* Auxiliary routine: printing a vector of integers */
void print_int_vector( char* desc, int n, int* a ) {
int j;
printf( "\n %s\n", desc );
for( j = 0; j < n; j++ ) printf( " %6i", a[j] );
printf( "\n" );
}
Parent topic: SSYSV Example