# RedHat 9 (Linux i386) - man page for ctrexc (redhat section l)

```CTREXC(l)								 )								 CTREXC(l)

NAME
CTREXC  -  reorder 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

SYNOPSIS
SUBROUTINE CTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO )

CHARACTER	  COMPQ

INTEGER	  IFST, ILST, INFO, LDQ, LDT, N

COMPLEX	  Q( LDQ, * ), T( LDT, * )

PURPOSE
CTREXC 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.

ARGUMENTS
COMPQ   (input) CHARACTER*1
= 'V':  update the matrix Q of Schur vectors;
= 'N':  do not update Q.

N       (input) INTEGER
The order of the matrix T. N >= 0.

T       (input/output) COMPLEX array, dimension (LDT,N)
On entry, the upper triangular matrix T.  On exit, the reordered upper triangular matrix.

LDT     (input) INTEGER
The leading dimension of the array T. LDT >= max(1,N).

Q       (input/output) COMPLEX array, dimension (LDQ,N)
On entry, if COMPQ = 'V', the matrix Q of Schur vectors.  On exit, if COMPQ = 'V', Q has been postmultiplied by the unitary  trans-
formation matrix Z which reorders T.  If COMPQ = 'N', Q is not referenced.

LDQ     (input) INTEGER
The leading dimension of the array Q.  LDQ >= max(1,N).

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.

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value

LAPACK version 3.0						   15 June 2000 							 CTREXC(l)```