SSYEV(3F)SSYEV(3F)NAMESSYEV - 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( * )
PURPOSESSYEV 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.
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SSYEV(3F)SSYEV(3F)
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.
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.
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