# zlaqp2(3) [centos man page]

```zlaqp2.f(3)							      LAPACK							       zlaqp2.f(3)

NAME
zlaqp2.f -

SYNOPSIS
Functions/Subroutines
subroutine zlaqp2 (M, N, OFFSET, A, LDA, JPVT, TAU, VN1, VN2, WORK)
ZLAQP2 computes a QR factorization with column pivoting of the matrix block.

Function/Subroutine Documentation
subroutine zlaqp2 (integerM, integerN, integerOFFSET, complex*16, dimension( lda, * )A, integerLDA, integer, dimension( * )JPVT, complex*16,
dimension( * )TAU, double precision, dimension( * )VN1, double precision, dimension( * )VN2, complex*16, dimension( * )WORK)
ZLAQP2 computes a QR factorization with column pivoting of the matrix block.

Purpose:

ZLAQP2 computes a QR factorization with column pivoting of
the block A(OFFSET+1:M,1:N).
The 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 the matrix A that must be pivoted
but no factorized. OFFSET >= 0.

A

A is COMPLEX*16 array, dimension (LDA,N)
On entry, the M-by-N matrix A.
On exit, the upper triangle of block A(OFFSET+1:M,1:N) is
the triangular factor obtained; the elements in block
A(OFFSET+1:M,1:N) below the diagonal, together with the
array TAU, represent the orthogonal matrix Q as a product of
elementary reflectors. Block A(1:OFFSET,1:N) has been
accordingly pivoted, but no factorized.

LDA

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

JPVT

JPVT is INTEGER array, dimension (N)
On entry, if JPVT(i) .ne. 0, the i-th column of A is permuted
to the front of A*P (a leading column); if JPVT(i) = 0,
the i-th column of A is a free column.
On exit, if JPVT(i) = k, then the i-th column of A*P
was the k-th column of A.

TAU

TAU is COMPLEX*16 array, dimension (min(M,N))
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.

WORK

WORK is COMPLEX*16 array, dimension (N)

Author:
Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:
September 2012

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 149 of file zlaqp2.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       zlaqp2.f(3)```

## Check Out this Related Man Page

```ZLAQP2(l)								 )								 ZLAQP2(l)

NAME
ZLAQP2 - compute a QR factorization with column pivoting of the block A(OFFSET+1:M,1:N)

SYNOPSIS
SUBROUTINE ZLAQP2( M, N, OFFSET, A, LDA, JPVT, TAU, VN1, VN2, WORK )

INTEGER	  LDA, M, N, OFFSET

INTEGER	  JPVT( * )

DOUBLE	  PRECISION VN1( * ), VN2( * )

COMPLEX*16	  A( LDA, * ), TAU( * ), WORK( * )

PURPOSE
ZLAQP2  computes  a QR factorization with column pivoting of the block A(OFFSET+1:M,1:N). The block A(1:OFFSET,1:N) is accordingly pivoted,
but not factorized.

ARGUMENTS
M       (input) INTEGER
The number of rows of the matrix A. M >= 0.

N       (input) INTEGER
The number of columns of the matrix A. N >= 0.

OFFSET  (input) INTEGER
The number of rows of the matrix A that must be pivoted but no factorized. OFFSET >= 0.

A       (input/output) COMPLEX*16 array, dimension (LDA,N)
On entry, the M-by-N matrix A.  On exit, the upper triangle of block A(OFFSET+1:M,1:N) is the triangular factor obtained; the  ele-
ments in block A(OFFSET+1:M,1:N) below the diagonal, together with the array TAU, represent the orthogonal matrix Q as a product of
elementary reflectors. Block A(1:OFFSET,1:N) has been accordingly pivoted, but no factorized.

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

JPVT    (input/output) INTEGER array, dimension (N)
On entry, if JPVT(i) .ne. 0, the i-th column of A is permuted to the front of A*P (a leading column); if JPVT(i) = 0, the i-th col-
umn of A is a free column.  On exit, if JPVT(i) = k, then the i-th column of A*P was the k-th column of A.

TAU     (output) COMPLEX*16 array, dimension (min(M,N))
The scalar factors of the elementary reflectors.

VN1     (input/output) DOUBLE PRECISION array, dimension (N)
The vector with the partial column norms.

VN2     (input/output) DOUBLE PRECISION array, dimension (N)
The vector with the exact column norms.

WORK    (workspace) COMPLEX*16 array, dimension (N)

FURTHER DETAILS
Based on contributions by
G. Quintana-Orti, Depto. de Informatica, Universidad Jaime I, Spain
X. Sun, Computer Science Dept., Duke University, USA

LAPACK version 3.0						   15 June 2000 							 ZLAQP2(l)```
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