dsteqr.f man page

dsteqr.f —

Synopsis

Functions/Subroutines

subroutine dsteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO)
DSTEQR

Function/Subroutine Documentation

subroutine dsteqr (characterCOMPZ, integerN, double precision, dimension( * )D, double precision, dimension( * )E, double precision, dimension( ldz, * )Z, integerLDZ, double precision, dimension( * )WORK, integerINFO)

DSTEQR

Purpose:

DSTEQR computes all eigenvalues and, optionally, eigenvectors of a
symmetric tridiagonal matrix using the implicit QL or QR method.
The eigenvectors of a full or band symmetric matrix can also be found
if DSYTRD or DSPTRD or DSBTRD has been used to reduce this matrix to
tridiagonal form.

Parameters:

COMPZ

COMPZ is CHARACTER*1
= 'N':  Compute eigenvalues only.
= 'V':  Compute eigenvalues and eigenvectors of the original
        symmetric matrix.  On entry, Z must contain the
        orthogonal matrix used to reduce the original matrix
        to tridiagonal form.
= 'I':  Compute eigenvalues and eigenvectors of the
        tridiagonal matrix.  Z is initialized to the identity
        matrix.

N

N is INTEGER
The order of the matrix.  N >= 0.

D

D is DOUBLE PRECISION array, dimension (N)
On entry, the diagonal elements of the tridiagonal matrix.
On exit, if INFO = 0, the eigenvalues in ascending order.

E

E is DOUBLE PRECISION array, dimension (N-1)
On entry, the (n-1) subdiagonal elements of the tridiagonal
matrix.
On exit, E has been destroyed.

Z

Z is DOUBLE PRECISION array, dimension (LDZ, N)
On entry, if  COMPZ = 'V', then Z contains the orthogonal
matrix used in the reduction to tridiagonal form.
On exit, if INFO = 0, then if  COMPZ = 'V', Z contains the
orthonormal eigenvectors of the original symmetric matrix,
and if COMPZ = 'I', Z contains the orthonormal eigenvectors
of the symmetric tridiagonal matrix.
If COMPZ = 'N', then Z is not referenced.

LDZ

LDZ is INTEGER
The leading dimension of the array Z.  LDZ >= 1, and if
eigenvectors are desired, then  LDZ >= max(1,N).

WORK

WORK is DOUBLE PRECISION array, dimension (max(1,2*N-2))
If COMPZ = 'N', then WORK is not referenced.

INFO

INFO is INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value
> 0:  the algorithm has failed to find all the eigenvalues in
      a total of 30*N iterations; if INFO = i, then i
      elements of E have not converged to zero; on exit, D
      and E contain the elements of a symmetric tridiagonal
      matrix which is orthogonally similar to the original
      matrix.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

November 2011

Definition at line 132 of file dsteqr.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

dsteqr(3) is an alias of dsteqr.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK