csteqr (l)  Linux Manuals
csteqr: computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method
Command to display csteqr
manual in Linux: $ man l csteqr
NAME
CSTEQR  computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method
SYNOPSIS
 SUBROUTINE CSTEQR(

COMPZ, N, D, E, Z, LDZ, WORK, INFO )

CHARACTER
COMPZ

INTEGER
INFO, LDZ, N

REAL
D( * ), E( * ), WORK( * )

COMPLEX
Z( LDZ, * )
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.
ARGUMENTS
 COMPZ (input) CHARACTER*1

= aqNaq: Compute eigenvalues only.
= aqVaq: 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.
= aqIaq: Compute eigenvalues and eigenvectors of the
tridiagonal matrix. Z is initialized to the identity
matrix.
 N (input) INTEGER

The order of the matrix. N >= 0.
 D (input/output) REAL array, dimension (N)

On entry, the diagonal elements of the tridiagonal matrix.
On exit, if INFO = 0, the eigenvalues in ascending order.
 E (input/output) REAL array, dimension (N1)

On entry, the (n1) subdiagonal elements of the tridiagonal
matrix.
On exit, E has been destroyed.
 Z (input/output) COMPLEX array, dimension (LDZ, N)

On entry, if COMPZ = aqVaq, then Z contains the unitary
matrix used in the reduction to tridiagonal form.
On exit, if INFO = 0, then if COMPZ = aqVaq, Z contains the
orthonormal eigenvectors of the original Hermitian matrix,
and if COMPZ = aqIaq, Z contains the orthonormal eigenvectors
of the symmetric tridiagonal matrix.
If COMPZ = aqNaq, then Z is not referenced.
 LDZ (input) INTEGER

The leading dimension of the array Z. LDZ >= 1, and if
eigenvectors are desired, then LDZ >= max(1,N).
 WORK (workspace) REAL array, dimension (max(1,2*N2))

If COMPZ = aqNaq, then WORK is not referenced.
 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith 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.
Pages related to csteqr
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 cstegr (l)  computes selected eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix T
 cstein (l)  computes the eigenvectors of a real symmetric tridiagonal matrix T corresponding to specified eigenvalues, using inverse iteration
 cstemr (l)  computes selected eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix T
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 cspcon (l)  estimates the reciprocal of the condition number (in the 1norm) of a complex symmetric packed matrix A using the factorization A = U*D*U**T or A = L*D*L**T computed by CSPTRF