NAME

dsyev - compute all eigenvalues and, optionally, eigenvectors of a real symmetric matrix A

SYNOPSIS

SUBROUTINE DSYEV( JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, INFO )

CHARACTER JOBZ, UPLO

INTEGER INFO, LDA, LWORK, N

DOUBLE PRECISION A( LDA, ∗ ), W( ∗ ), WORK( ∗ )

#include <sunperf.h>

void dsyev(char jobz, char uplo, int n, double ∗da, int lda, double ∗w, int ∗info) ;

PURPOSE

DSYEV computes all eigenvalues and, optionally, eigenvectors of a real symmetric matrix A. 
 

ARGUMENTS

JOBZ (input) CHARACTER∗1
= ’N’:  Compute eigenvalues only;
= ’V’:  Compute eigenvalues and eigenvectors.

UPLO (input) CHARACTER∗1
= ’U’:  Upper triangle of A is stored;
= ’L’:  Lower triangle of A is stored.

N (input) INTEGER
The order of the matrix A.  N >= 0.

A (input/output) DOUBLE PRECISION array, dimension (LDA, N)
On entry, the symmetric matrix A.  If UPLO = ’U’, the leading N-by-N upper triangular part of A contains the upper triangular part of the matrix A.  If UPLO = ’L’, the leading N-by-N lower triangular part of A contains the lower triangular part of the matrix A. On exit, if JOBZ = ’V’, then if INFO = 0, A contains the orthonormal eigenvectors of the matrix A. If JOBZ = ’N’, then on exit the lower triangle (if UPLO=’L’) or the upper triangle (if UPLO=’U’) of A, including the diagonal, is destroyed.

LDA (input) INTEGER
The leading dimension of the array A.  LDA >= max(1,N).

W (output) DOUBLE PRECISION array, dimension (N)
If INFO = 0, the eigenvalues in ascending order.

WORK (workspace/output) DOUBLE PRECISION array, dimension (LWORK)
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

LWORK (input) INTEGER
The length of the array WORK.  LWORK >= max(1,3∗N-1). For optimal efficiency, LWORK >= (NB+2)∗N, where NB is the blocksize for DSYTRD returned by ILAENV.

INFO (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value
> 0:  if INFO = i, the algorithm failed to converge; i off-diagonal elements of an intermediate tridiagonal form did not converge to zero.

SunOS WorkShop_5.0  —  Last change: 10 Dec 1998