DSTEV(3)
computes 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.
