SSYEV(l) LAPACK driver routine (version 1.1) 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 sym-
metric 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 triangu-
lar part of A contains the lower triangular part of the matrix A.
On exit, if JOBZ = 'V', then if INFO = 0, A contains the orthonor-
mal 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) 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.
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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