csteqr(3)

NAME

csteqr.f –

SYNOPSIS

Functions/Subroutines

subroutine csteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO)
CSTEQR

Function/Subroutine Documentation

subroutine csteqr (characterCOMPZ, integerN, real, dimension( * )D, real, dimension( * )E, complex, dimension( ldz, * )Z, integerLDZ, real, dimension( * )WORK, integerINFO)

CSTEQR

Purpose:

 CSTEQR 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 CHETRD or CHPTRD or CHBTRD 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 REAL 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 REAL 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 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 REAL 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 csteqr.f.

Author

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