DLAQP2(l) ) DLAQP2(l)NAME
DLAQP2 - compute a QR factorization with column pivoting of the block
A(OFFSET+1:M,1:N)
SYNOPSIS
SUBROUTINE DLAQP2( M, N, OFFSET, A, LDA, JPVT, TAU, VN1, VN2, WORK )
INTEGER LDA, M, N, OFFSET
INTEGER JPVT( * )
DOUBLE PRECISION A( LDA, * ), TAU( * ), VN1( * ), VN2( * ),
WORK( * )
PURPOSE
DLAQP2 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) DOUBLE PRECISION 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 (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 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 (output) DOUBLE PRECISION 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) DOUBLE PRECISION 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 DLAQP2(l)
