csteqr-f(3)

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

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

 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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