DSTEV(3F)DSTEV(3F)NAMEDSTEV - compute 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, * )
PURPOSEDSTEV 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)
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 illegal value
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DSTEV(3F)DSTEV(3F)
> 0: if INFO = i, the algorithm failed to converge; i off-
diagonal elements of E did not converge to zero.
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