DSYEVD (3) Linux Manual Page

dsyevd.f –

Synopsis

Functions/Subroutines

subroutine dsyevd (JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, IWORK, LIWORK, INFO)
DSYEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices

Function/Subroutine Documentation

subroutine dsyevd (characterJOBZ, characterUPLO, integerN, double precision, dimension( lda, * )A, integerLDA, double precision, dimension( * )W, double precision, dimension( * )WORK, integerLWORK, integer, dimension( * )IWORK, integerLIWORK, integerINFO)

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

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.

 The divide and conquer algorithm makes very mild assumptions about

 floating point arithmetic. It will work on machines with a guard

 digit in add/subtract, or on those binary machines without guard

 digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or

 Cray-2. It could conceivably fail on hexadecimal or decimal machines

 without guard digits, but we know of none.

 Because of large use of BLAS of level 3, DSYEVD needs N**2 more

 workspace than DSYEVX.

 

Parameters:

JOBZ

 JOBZ is CHARACTER*1

 = ‘N’: Compute eigenvalues only;

 = ‘V’: Compute eigenvalues and eigenvectors.

UPLO

 UPLO is CHARACTER*1

 = ‘U’: Upper triangle of A is stored;

 = ‘L’: Lower triangle of A is stored.

N

 N is INTEGER

 The order of the matrix A. N >= 0.

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.

LDA

 LDA is INTEGER

 The leading dimension of the array A. LDA >= max(1,N).

W

 W is DOUBLE PRECISION array, dimension (N)

 If INFO = 0, the eigenvalues in ascending order.

WORK

 WORK is DOUBLE PRECISION array,

 dimension (LWORK)

 On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

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.

IWORK

 IWORK is INTEGER array, dimension (MAX(1,LIWORK))

 On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.

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.

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.

Date:

September 2012

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. 

 

Definition at line 185 of file dsyevd.f.

Author

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