dstev(3)

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, * )

PURPOSE

DSTEV computes all eigenvalues and, optionally, eigenvec

tors 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 eigenvalues 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 destroyed.

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 converge to zero.

LAPACK version 3.0 15 June 2000

DSTEV(3)