redhat man page for ssyev

SSYEV(l)								 )								  SSYEV(l)

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

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

	   CHARACTER	 JOBZ, UPLO

	   INTEGER	 INFO, LDA, LWORK, N

	   REAL 	 A( LDA, * ), W( * ), WORK( * )

PURPOSE
       SSYEV 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) REAL 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) REAL array, dimension (N)
	       If INFO = 0, the eigenvalues in ascending order.

       WORK    (workspace/output) REAL 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
	       SSYTRD returned by ILAENV.

	       If  LWORK  =  -1,  then	a workspace query is assumed; the routine only calculates the optimal size of the WORK array, returns this
	       value as the first entry of the WORK array, and no error message related to LWORK is issued by XERBLA.

       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.

LAPACK version 3.0						   15 June 2000 							  SSYEV(l)