# dlaqz2.f - Man Page

SRC/dlaqz2.f

## Synopsis

### Functions/Subroutines

subroutine dlaqz2 (ilq, ilz, k, istartm, istopm, ihi, a, lda, b, ldb, nq, qstart, q, ldq, nz, zstart, z, ldz)
DLAQZ2

## Function/Subroutine Documentation

### subroutine dlaqz2 (logical, intent(in) ilq, logical, intent(in) ilz, integer, intent(in) k, integer, intent(in) istartm, integer, intent(in) istopm, integer, intent(in) ihi, double precision, dimension( lda, * ) a, integer, intent(in) lda, double precision, dimension( ldb, * ) b, integer, intent(in) ldb, integer, intent(in) nq, integer, intent(in) qstart, double precision, dimension( ldq, * ) q, integer, intent(in) ldq, integer, intent(in) nz, integer, intent(in) zstart, double precision, dimension( ldz,                          * ) z, integer, intent(in) ldz)

DLAQZ2

Purpose:

`      DLAQZ2 chases a 2x2 shift bulge in a matrix pencil down a single position`
Parameters

ILQ

```          ILQ is LOGICAL
Determines whether or not to update the matrix Q```

ILZ

```          ILZ is LOGICAL
Determines whether or not to update the matrix Z```

K

```          K is INTEGER
Index indicating the position of the bulge.
On entry, the bulge is located in
(A(k+1:k+2,k:k+1),B(k+1:k+2,k:k+1)).
On exit, the bulge is located in
(A(k+2:k+3,k+1:k+2),B(k+2:k+3,k+1:k+2)).```

ISTARTM

`          ISTARTM is INTEGER`

ISTOPM

```          ISTOPM is INTEGER
Updates to (A,B) are restricted to
(istartm:k+3,k:istopm). It is assumed
without checking that istartm <= k+1 and
k+2 <= istopm```

IHI

`          IHI is INTEGER`

A

`          A is DOUBLE PRECISION array, dimension (LDA,N)`

LDA

```          LDA is INTEGER
The leading dimension of A as declared in
the calling procedure.```

B

`          B is DOUBLE PRECISION array, dimension (LDB,N)`

LDB

```          LDB is INTEGER
The leading dimension of B as declared in
the calling procedure.```

NQ

```          NQ is INTEGER
The order of the matrix Q```

QSTART

```          QSTART is INTEGER
Start index of the matrix Q. Rotations are applied
To columns k+2-qStart:k+4-qStart of Q.```

Q

`          Q is DOUBLE PRECISION array, dimension (LDQ,NQ)`

LDQ

```          LDQ is INTEGER
The leading dimension of Q as declared in
the calling procedure.```

NZ

```          NZ is INTEGER
The order of the matrix Z```

ZSTART

```          ZSTART is INTEGER
Start index of the matrix Z. Rotations are applied
To columns k+1-qStart:k+3-qStart of Z.```

Z

`          Z is DOUBLE PRECISION array, dimension (LDZ,NZ)`

LDZ

```          LDZ is INTEGER
The leading dimension of Q as declared in
the calling procedure.```
Author

Thijs Steel, KU Leuven

Date

May 2020

Definition at line 172 of file dlaqz2.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dlaqz2(3) is an alias of dlaqz2.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK