SSTEV(3)              LAPACK driver routine (version 3.1)             SSTEV(3)



NAME
       SSTEV - all eigenvalues and, optionally, eigenvectors of a real symmet-
       ric tridiagonal matrix A

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

           CHARACTER     JOBZ

           INTEGER       INFO, LDZ, N

           REAL          D( * ), E( * ), WORK( * ), Z( LDZ, * )

PURPOSE
       SSTEV 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) REAL array, dimension (N)
               On  entry, the n diagonal elements of the tridiagonal matrix A.
               On exit, if INFO = 0, the eigenvalues in ascending order.

       E       (input/output) REAL array, dimension (N-1)
               On entry, the (n-1) subdiagonal  elements  of  the  tridiagonal
               matrix  A, stored in elements 1 to N-1 of E.  On exit, the con-
               tents of E are destroyed.

       Z       (output) REAL 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) REAL 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 illegal value
               > 0:  if INFO = i, the algorithm failed  to  converge;  i  off-
               diagonal elements of E did not converge to zero.



 LAPACK driver routine (version 3.N1o)vember 2006                        SSTEV(3)