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NAME
     dstev - compute all eigenvalues and,  optionally,  eigenvec-
     tors of a real symmetric tridiagonal matrix A

SYNOPSIS
     SUBROUTINE DSTEV( JOBZ, N, D, E, Z, LDZ, WORK, INFO )

     CHARACTER JOBZ

     INTEGER INFO, LDZ, N

     DOUBLE PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )



     #include <sunperf.h>

     void dstev(char jobz, int n, double *d,  double  *e,  double
               *dz, int ldz, int *info) ;

PURPOSE
     DSTEV computes all eigenvalues and, optionally, eigenvectors
     of a real symmetric tridiagonal matrix A.


ARGUMENTS
     JOBZ      (input) CHARACTER*1
               = 'N':  Compute eigenvalues only;
               = 'V':  Compute eigenvalues and eigenvectors.

     N         (input) INTEGER
               The order of the matrix.  N >= 0.

     D         (input/output) DOUBLE PRECISION  array,  dimension
               (N)
               On entry, the n diagonal elements of the tridiago-
               nal  matrix  A.   On exit, if INFO = 0, the eigen-
               values in ascending order.

     E         (input/output) DOUBLE PRECISION  array,  dimension
               (N)
               On entry, the (n-1) subdiagonal  elements  of  the
               tridiagonal  matrix A, stored in elements 1 to N-1
               of E; E(N) need not be set, but  is  used  by  the
               routine.   On  exit,  the  contents  of E are des-
               troyed.

     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  D(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
               (max(1,2*N-2))
               If JOBZ = 'N', WORK is not referenced.

     INFO      (output) INTEGER
               = 0:  successful exit
               < 0:  if INFO = -i, the i-th argument had an ille-
               gal value
               > 0:  if INFO = i, the algorithm  failed  to  con-
               verge;  i  off-diagonal elements of E did not con-
               verge to zero.

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