# ctrexc.f - Man Page

## Synopsis

### Functions/Subroutines

subroutine **ctrexc** (COMPQ, **N**, T, LDT, Q, LDQ, IFST, ILST, INFO)**CTREXC**

## Function/Subroutine Documentation

### subroutine ctrexc (character COMPQ, integer N, complex, dimension( ldt, * ) T, integer LDT, complex, dimension( ldq, * ) Q, integer LDQ, integer IFST, integer ILST, integer INFO)

**CTREXC**

**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.

**Parameters:***COMPQ*COMPQ is CHARACTER*1 = 'V': update the matrix Q of Schur vectors; = 'N': do not update Q.

*N*N is INTEGER The order of the matrix T. N >= 0. If N == 0 arguments ILST and IFST may be any value.

*T*T is COMPLEX array, dimension (LDT,N) On entry, the upper triangular matrix T. On exit, the reordered upper triangular matrix.

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

*Q*Q is 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*LDQ is INTEGER The leading dimension of the array Q. LDQ >= 1, and if COMPQ = 'V', LDQ >= max(1,N).

*IFST*IFST is INTEGER

*ILST*ILST is 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*INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value

**Author:**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**December 2016

Definition at line 128 of file ctrexc.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page ctrexc(3) is an alias of ctrexc.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK