NAME

sstev - compute all eigenvalues and, optionally, eigenvectors of a real symmetric 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, ∗ )

#include <sunperf.h>

void sstev(char jobz, int n, float ∗d, float ∗e, float ∗sz, int ldz, int ∗info) ;

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)
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 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.

SunOS 5.0  —  Last change: 10 Dec 1998