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 transformation 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 2.0  —  08 October 1994