dsyevd()

subroutine dsyevd	(	character	jobz,
		character	uplo,
		integer	n,
		double precision, dimension( lda, * )	a,
		integer	lda,
		double precision, dimension( * )	w,
		double precision, dimension( * )	work,
		integer	lwork,
		integer, dimension( * )	iwork,
		integer	liwork,
		integer	info )

DSYEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices

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Purpose:

!>
!> DSYEVD computes all eigenvalues and, optionally, eigenvectors of a
!> real symmetric matrix A. If eigenvectors are desired, it uses a
!> divide and conquer algorithm.
!>
!> Because of large use of BLAS of level 3, DSYEVD needs N**2 more
!> workspace than DSYEVX.
!> 

Parameters

[in]	JOBZ	!> JOBZ is CHARACTER*1 !> = 'N': Compute eigenvalues only; !> = 'V': Compute eigenvalues and eigenvectors. !>
[in]	UPLO	!> UPLO is CHARACTER*1 !> = 'U': Upper triangle of A is stored; !> = 'L': Lower triangle of A is stored. !>
[in]	N	!> N is INTEGER !> The order of the matrix A. N >= 0. !>
[in,out]	A	!> A is 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. !>
[in]	LDA	!> LDA is INTEGER !> The leading dimension of the array A. LDA >= max(1,N). !>
[out]	W	!> W is DOUBLE PRECISION array, dimension (N) !> If INFO = 0, the eigenvalues in ascending order. !>
[out]	WORK	!> WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK)) !> On exit, if INFO = 0, WORK(1) returns the optimal LWORK. !>
[in]	LWORK	!> LWORK is INTEGER !> The dimension of the array WORK. !> If N <= 1, LWORK must be at least 1. !> If JOBZ = 'N' and N > 1, LWORK must be at least 2*N+1. !> If JOBZ = 'V' and N > 1, LWORK must be at least !> 1 + 6*N + 2*N**2. !> !> If LWORK = -1, then a workspace query is assumed; the routine !> only calculates the optimal sizes of the WORK and IWORK !> arrays, returns these values as the first entries of the WORK !> and IWORK arrays, and no error message related to LWORK or !> LIWORK is issued by XERBLA. !>
[out]	IWORK	!> IWORK is INTEGER array, dimension (MAX(1,LIWORK)) !> On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK. !>
[in]	LIWORK	!> LIWORK is INTEGER !> The dimension of the array IWORK. !> If N <= 1, LIWORK must be at least 1. !> If JOBZ = 'N' and N > 1, LIWORK must be at least 1. !> If JOBZ = 'V' and N > 1, LIWORK must be at least 3 + 5*N. !> !> If LIWORK = -1, then a workspace query is assumed; the !> routine only calculates the optimal sizes of the WORK and !> IWORK arrays, returns these values as the first entries of !> the WORK and IWORK arrays, and no error message related to !> LWORK or LIWORK is issued by XERBLA. !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -i, the i-th argument had an illegal value !> > 0: if INFO = i and JOBZ = 'N', then the algorithm failed !> to converge; i off-diagonal elements of an intermediate !> tridiagonal form did not converge to zero; !> if INFO = i and JOBZ = 'V', then the algorithm failed !> to compute an eigenvalue while working on the submatrix !> lying in rows and columns INFO/(N+1) through !> mod(INFO,N+1). !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Contributors:

Jeff Rutter, Computer Science Division, University of California at Berkeley, USA
Modified by Francoise Tisseur, University of Tennessee
Modified description of INFO. Sven, 16 Feb 05.