DSTEV(3f)

NAME
DSTEV - all eigenvalues and, optionally, eigenvectors 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, 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 tridiagonal matrix A. On exit, if INFO = 0, the eigenvalues in ascending order.

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