zlaqp2 (3)  Linux Manuals
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.
NN is INTEGER The number of columns of the matrix A. N >= 0.
OFFSETOFFSET is INTEGER The number of rows of the matrix A that must be pivoted but no factorized. OFFSET >= 0.
AA is COMPLEX*16 array, dimension (LDA,N) On entry, the MbyN 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.
LDALDA is INTEGER The leading dimension of the array A. LDA >= max(1,M).
JPVTJPVT is INTEGER array, dimension (N) On entry, if JPVT(i) .ne. 0, the ith column of A is permuted to the front of A*P (a leading column); if JPVT(i) = 0, the ith column of A is a free column. On exit, if JPVT(i) = k, then the ith column of A*P was the kth column of A.
TAUTAU is COMPLEX*16 array, dimension (min(M,N)) The scalar factors of the elementary reflectors.
VN1VN1 is DOUBLE PRECISION array, dimension (N) The vector with the partial column norms.
VN2VN2 is DOUBLE PRECISION array, dimension (N) The vector with the exact column norms.
WORKWORK 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. QuintanaOrti, 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
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