zsteqr.f man page

zsteqr.f —

Synopsis

Functions/Subroutines

subroutine zsteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO)
ZSTEQR

Function/Subroutine Documentation

subroutine zsteqr (characterCOMPZ, integerN, double precision, dimension( * )D, double precision, dimension( * )E, complex*16, dimension( ldz, * )Z, integerLDZ, double precision, dimension( * )WORK, integerINFO)

ZSTEQR

Purpose:

ZSTEQR 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 complex Hermitian matrix can also
be found if ZHETRD or ZHPTRD or ZHBTRD 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
        Hermitian matrix.  On entry, Z must contain the
        unitary 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 COMPLEX*16 array, dimension (LDZ, N)
On entry, if  COMPZ = 'V', then Z contains the unitary
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 Hermitian 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 unitarily 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 133 of file zsteqr.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

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

Sat Nov 16 2013 Version 3.4.2 LAPACK