---
name: "ztrexc.f"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/ztrexc.f"
---

# ztrexc.f(3)

## NAME

SRC/ztrexc.f

## SYNOPSIS

### Functions/Subroutines

subroutine **ztrexc** (compq, n, t, ldt, q, ldq, ifst, ilst, info)\
 **ZTREXC**

## Function/Subroutine Documentation

### subroutine ztrexc (character compq, integer n, complex\*16, dimension( ldt, \* ) t, integer ldt, complex\*16, dimension( ldq, \* ) q, integer ldq, integer ifst, integer ilst, integer info)

**ZTREXC**

**Purpose:**

```
!>
!> ZTREXC 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
!> postmultiplying 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*16 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*16 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.

Definition at line **125** of file **ztrexc.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.