dsyev man page on Scientific

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DSYEV(1)	      LAPACK driver routine (version 3.2)	      DSYEV(1)

NAME
       DSYEV  -	 computes  all	eigenvalues and, optionally, eigenvectors of a
       real symmetric matrix A

SYNOPSIS
       SUBROUTINE DSYEV( JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, INFO )

	   CHARACTER	 JOBZ, UPLO

	   INTEGER	 INFO, LDA, LWORK, N

	   DOUBLE	 PRECISION A( LDA, * ), W( * ), WORK( * )

PURPOSE
       DSYEV computes all eigenvalues and, optionally, eigenvectors of a  real
       symmetric 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) 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 tri‐
	       angle (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) DOUBLE PRECISION array, dimension (N)
	       If INFO = 0, the eigenvalues in ascending order.

       WORK	 (workspace/output)   DOUBLE   PRECISION   array,    dimension
       (MAX(1,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	block‐
	       size  for  DSYTRD  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.

       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.

 LAPACK driver routine (version 3November 2008			      DSYEV(1)
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