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LAPACKE_dsyevx Example Program in C for Row Major Data Layout
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/*
LAPACKE_dsyevx Example.
=======================
Program computes the smallest eigenvalues and the corresponding
eigenvectors of a real symmetric matrix A:
6.29 -0.39 0.61 1.18 -0.08
-0.39 7.19 0.81 1.19 -0.08
0.61 0.81 5.48 -3.13 0.22
1.18 1.19 -3.13 3.79 -0.26
-0.08 -0.08 0.22 -0.26 0.83
Description.
============
The routine computes selected eigenvalues and, optionally, eigenvectors of
an n-by-n real symmetric matrix A. The eigenvector v(j) of A satisfies
A*v(j) = lambda(j)*v(j)
where lambda(j) is its eigenvalue. The computed eigenvectors are
orthonormal.
Eigenvalues and eigenvectors can be selected by specifying either a range
of values or a range of indices for the desired eigenvalues.
Example Program Results.
========================
LAPACKE_dsyevx (row-major, high-level) Example Program Results
The total number of eigenvalues found: 3
Selected eigenvalues
0.71 0.82 6.58
Selected eigenvectors (stored columnwise)
0.22 0.09 -0.95
0.21 0.08 -0.04
-0.52 -0.22 -0.29
-0.73 -0.21 -0.09
-0.32 0.94 0.01
*/
#include <stdlib.h>
#include <stdio.h>
#include "mkl_lapacke.h"
/* Auxiliary routines prototypes */
extern void print_matrix( char* desc, MKL_INT m, MKL_INT n, double* a, MKL_INT lda );
/* Parameters */
#define N 5
#define NSELECT 3
#define LDA N
#define LDZ NSELECT
/* Main program */
int main() {
/* Locals */
MKL_INT n = N, il, iu, m, lda = LDA, ldz = LDZ, info;
double abstol, vl, vu;
/* Local arrays */
MKL_INT ifail[N];
double w[N], z[LDZ*N];
double a[LDA*N] = {
6.29, -0.39, 0.61, 1.18, -0.08,
0.00, 7.19, 0.81, 1.19, -0.08,
0.00, 0.00, 5.48, -3.13, 0.22,
0.00, 0.00, 0.00, 3.79, -0.26,
0.00, 0.00, 0.00, 0.00, 0.83
};
/* Executable statements */
printf( "LAPACKE_dsyevx (row-major, high-level) Example Program Results\n" );
/* Negative abstol means using the default value */
abstol = -1.0;
/* Set il, iu to compute NSELECT smallest eigenvalues */
il = 1;
iu = NSELECT;
/* Solve eigenproblem */
info = LAPACKE_dsyevx( LAPACK_ROW_MAJOR, 'V', 'I', 'U', n, a, lda,
vl, vu, il, iu, abstol, &m, w, z, ldz, ifail );
/* Check for convergence */
if( info > 0 ) {
printf( "The algorithm failed to compute eigenvalues.\n" );
exit( 1 );
}
/* Print the number of eigenvalues found */
printf( "\n The total number of eigenvalues found:%2i\n", m );
/* Print eigenvalues */
print_matrix( "Selected eigenvalues", 1, m, w, 1 );
/* Print eigenvectors */
print_matrix( "Selected eigenvectors (stored columnwise)", n, m, z, ldz );
exit( 0 );
} /* End of LAPACKE_dsyevx Example */
/* Auxiliary routine: printing a matrix */
void print_matrix( char* desc, MKL_INT m, MKL_INT n, double* a, MKL_INT lda ) {
MKL_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*lda+j] );
printf( "\n" );
}
}
Parent topic: DSYEVX Example