I am trying to make use of the official example code of heevr routine in LAPACK. Once I changed the range parameter from 'V' to 'A' and commented out il and iu, the first two eigenvalues wrongly showed zero. Below is my tinily modified example code. I used icpc 13.1.3 and run in Linux. Thanks in advance.
#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, MKL_Complex16* a, MKL_INT lda );
extern void print_rmatrix( char* desc, MKL_INT m, MKL_INT n, double* a, MKL_INT lda );
/* Parameters */
#define N 4
#define LDA N
#define LDZ N
/* Main program */
int main() {
/* Locals */
MKL_INT n = N, lda = LDA, ldz = LDZ, il, iu, m, info;
double abstol, vl, vu;
/* Local arrays */
MKL_INT isuppz[N];
double w[N];
MKL_Complex16 z[LDZ*N];
MKL_Complex16 a[LDA*N] = {
{-2.16, 0.00}, {-0.16, 4.86}, {-7.23, 9.38}, {-0.04, -6.86},
{ 0.00, 0.00}, { 7.45, 0.00}, { 4.39, -6.29}, {-8.11, 4.41},
{ 0.00, 0.00}, { 0.00, 0.00}, {-9.03, 0.00}, {-6.89, 7.66},
{ 0.00, 0.00}, { 0.00, 0.00}, { 0.00, 0.00}, { 7.76, 0.00}
};
/* Executable statements */
printf( "LAPACKE_zheevr (column-major, high-level) Example Program Results\n" );
/* Negative abstol means using the default value */
abstol = -1.0;
/* Set VL, VU to compute eigenvalues in half-open (VL,VU] interval */
//vl = -5.0;
//vu = 5.0;
/* Solve eigenproblem */
info = LAPACKE_zheevr( LAPACK_COL_MAJOR, 'V', 'A', 'L', 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_rmatrix( "Selected eigenvalues", 1, m, w, 1 );
/* Print eigenvectors */
print_matrix( "Selected eigenvectors (stored columnwise)", n, m, z, ldz );
exit( 0 );
} /* End of LAPACKE_zheevr Example */
/* Auxiliary routine: printing a matrix */
void print_matrix( char* desc, MKL_INT m, MKL_INT n, MKL_Complex16* 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,%6.2f)", a[i+j*lda].real, a[i+j*lda].imag );
printf( "\n" );
}
}
/* Auxiliary routine: printing a real matrix */
void print_rmatrix( 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+j*lda] );
printf( "\n" );
}
}
