.TH ZTREXC 1 "November 2006" " LAPACK routine (version 3.1) " " LAPACK routine (version 3.1) "
.SH NAME
ZTREXC - the Schur factorization of a complex matrix A = Q*T*Q**H, so that the diagonal element of T with row index IFST is moved to row ILST
.SH SYNOPSIS
.TP 19
SUBROUTINE ZTREXC(
COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO )
.TP 19
.ti +4
CHARACTER
COMPQ
.TP 19
.ti +4
INTEGER
IFST, ILST, INFO, LDQ, LDT, N
.TP 19
.ti +4
COMPLEX*16
Q( LDQ, * ), T( LDT, * )
.SH PURPOSE
ZTREXC reorders the Schur factorization of a complex matrix
A = Q*T*Q**H, so that the diagonal element of T with row index IFST
is moved to row ILST.
The Schur form T is reordered by a unitary similarity transformation
Z**H*T*Z, and optionally the matrix Q of Schur vectors is updated by
postmultplying it with Z.
.br
.SH ARGUMENTS
.TP 8
COMPQ (input) CHARACTER*1
= \(aqV\(aq: update the matrix Q of Schur vectors;
.br
= \(aqN\(aq: do not update Q.
.TP 8
N (input) INTEGER
The order of the matrix T. N >= 0.
.TP 8
T (input/output) COMPLEX*16 array, dimension (LDT,N)
On entry, the upper triangular matrix T.
On exit, the reordered upper triangular matrix.
.TP 8
LDT (input) INTEGER
The leading dimension of the array T. LDT >= max(1,N).
.TP 8
Q (input/output) COMPLEX*16 array, dimension (LDQ,N)
On entry, if COMPQ = \(aqV\(aq, the matrix Q of Schur vectors.
On exit, if COMPQ = \(aqV\(aq, Q has been postmultiplied by the
unitary transformation matrix Z which reorders T.
If COMPQ = \(aqN\(aq, Q is not referenced.
.TP 8
LDQ (input) INTEGER
The leading dimension of the array Q. LDQ >= max(1,N).
.TP 8
IFST (input) INTEGER
ILST (input) INTEGER
Specify the reordering of the diagonal elements of T:
The element with row index IFST is moved to row ILST by a
sequence of transpositions between adjacent elements.
1 <= IFST <= N; 1 <= ILST <= N.
.TP 8
INFO (output) INTEGER
= 0: successful exit
.br
< 0: if INFO = -i, the i-th argument had an illegal value