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RedHat 9 (Linux i386) - man page for ssyevd (redhat section l)

SSYEVD(l)					)					SSYEVD(l)

NAME
       SSYEVD  - compute all eigenvalues and, optionally, eigenvectors of a real symmetric matrix
       A

SYNOPSIS
       SUBROUTINE SSYEVD( JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, IWORK, LIWORK, INFO )

	   CHARACTER	  JOBZ, UPLO

	   INTEGER	  INFO, LDA, LIWORK, LWORK, N

	   INTEGER	  IWORK( * )

	   REAL 	  A( LDA, * ), W( * ), WORK( * )

PURPOSE
       SSYEVD 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 arith-
       metic. 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, SSYEVD needs N**2 more workspace than SSYEVX.

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 trian-
	       gular 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.

       LWORK   (input) 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 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.

       IWORK   (workspace/output) INTEGER array, dimension (LIWORK)
	       On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.

       LIWORK  (input) 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 size of the IWORK array, returns this value as  the  first  entry  of  the
	       IWORK array, and no error message related to LIWORK is issued by XERBLA.

       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.

FURTHER DETAILS
       Based on contributions by
	  Jeff Rutter, Computer Science Division, University of California
	  at Berkeley, USA
       Modified by Francoise Tisseur, University of Tennessee.

LAPACK version 3.0			   15 June 2000 				SSYEVD(l)


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