# zlaqps.f man page

zlaqps.f

## Synopsis

### Functions/Subroutines

subroutine zlaqps (M, N, OFFSET, NB, KB, A, LDA, JPVT, TAU, VN1, VN2, AUXV, F, LDF)
ZLAQPS computes a step of QR factorization with column pivoting of a real m-by-n matrix A by using BLAS level 3.

## Function/Subroutine Documentation

### subroutine zlaqps (integer M, integer N, integer OFFSET, integer NB, integer KB, complex*16, dimension( lda, * ) A, integer LDA, integer, dimension( * ) JPVT, complex*16, dimension( * ) TAU, double precision, dimension( * ) VN1, double precision, dimension( * ) VN2, complex*16, dimension( * ) AUXV, complex*16, dimension( ldf, * ) F, integer LDF)

ZLAQPS computes a step of QR factorization with column pivoting of a real m-by-n matrix A by using BLAS level 3.

Purpose:

``` ZLAQPS computes a step of QR factorization with column pivoting
of a complex M-by-N matrix A by using Blas-3.  It tries to factorize
NB columns from A starting from the row OFFSET+1, and updates all
of the matrix with Blas-3 xGEMM.

In some cases, due to catastrophic cancellations, it cannot
factorize NB columns.  Hence, the actual number of factorized
columns is returned in KB.

Block A(1:OFFSET,1:N) is accordingly pivoted, but not factorized.```
Parameters:

M

```          M is INTEGER
The number of rows of the matrix A. M >= 0.```

N

```          N is INTEGER
The number of columns of the matrix A. N >= 0```

OFFSET

```          OFFSET is INTEGER
The number of rows of A that have been factorized in
previous steps.```

NB

```          NB is INTEGER
The number of columns to factorize.```

KB

```          KB is INTEGER
The number of columns actually factorized.```

A

```          A is COMPLEX*16 array, dimension (LDA,N)
On entry, the M-by-N matrix A.
On exit, block A(OFFSET+1:M,1:KB) is the triangular
factor obtained and block A(1:OFFSET,1:N) has been
accordingly pivoted, but no factorized.
The rest of the matrix, block A(OFFSET+1:M,KB+1:N) has
been updated.```

LDA

```          LDA is INTEGER
The leading dimension of the array A. LDA >= max(1,M).```

JPVT

```          JPVT is INTEGER array, dimension (N)
JPVT(I) = K <==> Column K of the full matrix A has been
permuted into position I in AP.```

TAU

```          TAU is COMPLEX*16 array, dimension (KB)
The scalar factors of the elementary reflectors.```

VN1

```          VN1 is DOUBLE PRECISION array, dimension (N)
The vector with the partial column norms.```

VN2

```          VN2 is DOUBLE PRECISION array, dimension (N)
The vector with the exact column norms.```

AUXV

```          AUXV is COMPLEX*16 array, dimension (NB)
Auxiliar vector.```

F

```          F is COMPLEX*16 array, dimension (LDF,NB)
Matrix F**H = L * Y**H * A.```

LDF

```          LDF is INTEGER
The leading dimension of the array F. LDF >= max(1,N).```
Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

December 2016

Contributors:

G. Quintana-Orti, Depto. de Informatica, Universidad Jaime I, Spain X. Sun, Computer Science Dept., Duke University, USA
Partial column norm updating strategy modified on April 2011 Z. Drmac and Z. Bujanovic, Dept. of Mathematics, University of Zagreb, Croatia.

References:

LAPACK Working Note 176

Definition at line 179 of file zlaqps.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Tue Nov 14 2017 Version 3.8.0 LAPACK