# ctrexc.f man page

ctrexc.f

## 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

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