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ZSYSV Example Program in C
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/*
ZSYSV Example.
==============
The program computes the solution to the system of linear equations
with a complex symmetric matrix A and multiple right-hand sides B,
where A is the coefficient matrix:
( 9.99, -4.73) ( -5.68, -0.80) ( -8.94, 1.32) ( -9.42, 2.05)
( -5.68, -0.80) ( -8.01, 4.61) ( 1.64, -6.29) ( 6.79, -2.17)
( -8.94, 1.32) ( 1.64, -6.29) ( 9.04, 3.96) ( -4.51, -7.54)
( -9.42, 2.05) ( 6.79, -2.17) ( -4.51, -7.54) ( 0.40, 4.06)
and B is the right-hand side matrix:
( 5.71, -1.20) ( 2.84, -0.18)
( -7.70, 6.47) ( -8.29, -1.72)
( 3.77, -7.40) ( -4.28, -8.25)
( -3.78, 0.33) ( -2.70, -0.39)
Description.
============
The routine solves for X the complex 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.
========================
ZSYSV Example Program Results
Solution
( 0.13, 0.13) ( 0.63, 0.34)
( 0.32, -0.07) ( 0.61, 0.21)
( -0.26, -0.44) ( -0.01, -0.10)
( -0.40, 0.51) ( 0.21, 0.02)
Details of factorization
(-16.42, 1.69) ( -0.53, 0.35) ( 0.36, 0.41) ( -0.78, 0.49)
( 0.00, 0.00) ( 3.69, 0.64) (-16.58, -1.61) ( -0.10, -0.65)
( 0.00, 0.00) ( 0.00, 0.00) ( 1.02, -3.74) ( -0.73, -0.52)
( 0.00, 0.00) ( 0.00, 0.00) ( 0.00, 0.00) ( 9.04, 3.96)
Pivot indices
1 -1 -1 3
*/
#include <stdlib.h>
#include <stdio.h>
/* Complex datatype */
struct _dcomplex { double re, im; };
typedef struct _dcomplex dcomplex;
/* ZSYSV prototype */
extern void zsysv( char* uplo, int* n, int* nrhs, dcomplex* a, int* lda,
int* ipiv, dcomplex* b, int* ldb, dcomplex* work, int* lwork, int* info );
/* Auxiliary routines prototypes */
extern void print_matrix( char* desc, int m, int n, dcomplex* a, int lda );
extern void print_int_vector( char* desc, int n, int* a );
/* Parameters */
#define N 4
#define NRHS 2
#define LDA N
#define LDB N
/* Main program */
int main() {
/* Locals */
int n = N, nrhs = NRHS, lda = LDA, ldb = LDB, info, lwork;
dcomplex wkopt;
dcomplex* work;
/* Local arrays */
int ipiv[N];
dcomplex a[LDA*N] = {
{ 9.99, -4.73}, { 0.00, 0.00}, { 0.00, 0.00}, { 0.00, 0.00},
{-5.68, -0.80}, {-8.01, 4.61}, { 0.00, 0.00}, { 0.00, 0.00},
{-8.94, 1.32}, { 1.64, -6.29}, { 9.04, 3.96}, { 0.00, 0.00},
{-9.42, 2.05}, { 6.79, -2.17}, {-4.51, -7.54}, { 0.40, 4.06}
};
dcomplex b[LDB*NRHS] = {
{ 5.71, -1.20}, {-7.70, 6.47}, { 3.77, -7.40}, {-3.78, 0.33},
{ 2.84, -0.18}, {-8.29, -1.72}, {-4.28, -8.25}, {-2.70, -0.39}
};
/* Executable statements */
printf( " ZSYSV Example Program Results\n" );
/* Query and allocate the optimal workspace */
lwork = -1;
zsysv( "Upper", &n, &nrhs, a, &lda, ipiv, b, &ldb, &wkopt, &lwork, &info );
lwork = (int)wkopt.re;
work = (dcomplex*)malloc( lwork*sizeof(dcomplex) );
/* Solve the equations A*X = B */
zsysv( "Upper", &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 ZSYSV Example */
/* Auxiliary routine: printing a matrix */
void print_matrix( char* desc, int m, int n, dcomplex* 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,%6.2f)", a[i+j*lda].re, a[i+j*lda].im );
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: ZSYSV Example