dspev man page on Scientific

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

NAME
       DSPEV - computes all the eigenvalues and, optionally, eigenvectors of a
       real symmetric matrix A in packed storage

SYNOPSIS
       SUBROUTINE DSPEV( JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, INFO )

	   CHARACTER	 JOBZ, UPLO

	   INTEGER	 INFO, LDZ, N

	   DOUBLE	 PRECISION AP( * ), W( * ), WORK( * ), Z( LDZ, * )

PURPOSE
       DSPEV computes all the eigenvalues and, optionally, eigenvectors	 of  a
       real symmetric matrix A in packed storage.

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.

       AP      (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
	       On  entry,  the upper or lower triangle of the symmetric matrix
	       A, packed columnwise in a linear array.	The j-th column	 of  A
	       is  stored  in  the  array AP as follows: if UPLO = 'U', AP(i +
	       (j-1)*j/2) =  A(i,j)  for  1<=i<=j;  if	UPLO  =	 'L',  AP(i  +
	       (j-1)*(2*n-j)/2)	 =  A(i,j)  for j<=i<=n.  On exit, AP is over‐
	       written by values generated during the reduction to tridiagonal
	       form.   If  UPLO = 'U', the diagonal and first superdiagonal of
	       the tridiagonal matrix T overwrite the  corresponding  elements
	       of  A, and if UPLO = 'L', the diagonal and first subdiagonal of
	       T overwrite the corresponding elements of A.

       W       (output) DOUBLE PRECISION array, dimension (N)
	       If INFO = 0, the eigenvalues in ascending order.

       Z       (output) DOUBLE PRECISION array, dimension (LDZ, N)
	       If JOBZ = 'V', then if INFO = 0,	 Z  contains  the  orthonormal
	       eigenvectors of the matrix A, with the i-th column of Z holding
	       the eigenvector associated with W(i).  If JOBZ = 'N', then Z is
	       not referenced.

       LDZ     (input) INTEGER
	       The  leading dimension of the array Z.  LDZ >= 1, and if JOBZ =
	       'V', LDZ >= max(1,N).

       WORK    (workspace) DOUBLE PRECISION array, dimension (3*N)

       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			      DSPEV(1)
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