CHEEV - compute all eigenvalues and, optionally, eigenvec
tors of a complex Hermitian matrix A
SYNOPSIS
SUBROUTINE CHEEV( JOBZ, UPLO, N, A, LDA, W, WORK, LWORK,
RWORK, INFO )
CHARACTER JOBZ, UPLO
INTEGER INFO, LDA, LWORK, N
REAL RWORK( * ), W( * )
COMPLEX A( LDA, * ), WORK( * )
PURPOSE
CHEEV computes all eigenvalues and, optionally, eigenvec
tors of a complex Hermitian 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) COMPLEX array, dimension (LDA, N)
On entry, the Hermitian matrix A. If UPLO = 'U',
the leading N-by-N upper triangular part of A con
tains 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) COMPLEX array, dimension
(LWORK)
LWORK.
LWORK (input) INTEGER
The length of the array WORK. LWORK >=
max(1,2*N-1). For optimal efficiency, LWORK >=
(NB+1)*N, where NB is the blocksize for CHETRD
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.
RWORK (workspace) REAL array, dimension (max(1, 3*N-2))
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille
gal value
> 0: if INFO = i, the algorithm failed to con
verge; i off-diagonal elements of an intermediate
tridiagonal form did not converge to zero.
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