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LAPACKE_dsyevr Example Program in C for Row Major Data Layout
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/*
LAPACKE_dsyevr Example.
=======================
Program computes the smallest eigenvalues and the corresponding
eigenvectors of a real symmetric matrix A using the Relatively Robust
Representations, where A is:
0.67 -0.20 0.19 -1.06 0.46
-0.20 3.82 -0.13 1.06 -0.48
0.19 -0.13 3.27 0.11 1.10
-1.06 1.06 0.11 5.86 -0.98
0.46 -0.48 1.10 -0.98 3.54
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_dsyevr (row-major, high-level) Example Program Results
The total number of eigenvalues found: 3
Selected eigenvalues
0.43 2.14 3.37
Selected eigenvectors (stored columnwise)
-0.98 -0.01 -0.08
0.01 0.02 -0.93
0.04 -0.69 -0.07
-0.18 0.19 0.31
0.07 0.69 -0.13
*/
#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 isuppz[N];
double w[N], z[LDZ*N];
double a[LDA*N] = {
0.67, -0.20, 0.19, -1.06, 0.46,
0.00, 3.82, -0.13, 1.06, -0.48,
0.00, 0.00, 3.27, 0.11, 1.10,
0.00, 0.00, 0.00, 5.86, -0.98,
0.00, 0.00, 0.00, 0.00, 3.54
};
/* Executable statements */
printf( "LAPACKE_dsyevr (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_dsyevr( LAPACK_ROW_MAJOR, 'V', 'I', 'U', n, a, lda,
vl, vu, il, iu, abstol, &m, w, z, ldz, isuppz );
/* 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_dsyevr 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: DSYEVR Example