# ctrexc.f man page

ctrexc.f —

## Synopsis

### Functions/Subroutines

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

## Function/Subroutine Documentation

### subroutine ctrexc (characterCOMPQ, integerN, complex, dimension( ldt, * )T, integerLDT, complex, dimension( ldq, * )Q, integerLDQ, integerIFST, integerILST, integerINFO)

**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.
```

*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 >= 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:**

November 2011

Definition at line 125 of file ctrexc.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

ctrexc(3) is an alias of ctrexc.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK