DLAQP2(3S)DLAQP2(3S)NAMEDLAQP2 - 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( * )
IMPLEMENTATION
These routines are part of the SCSL Scientific Library and can be loaded
using either the -lscs or the -lscs_mp option. The -lscs_mp option
directs the linker to use the multi-processor version of the library.
When linking to SCSL with -lscs or -lscs_mp, the default integer size is
4 bytes (32 bits). Another version of SCSL is available in which integers
are 8 bytes (64 bits). This version allows the user access to larger
memory sizes and helps when porting legacy Cray codes. It can be loaded
by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
only one of the two versions; 4-byte integer and 8-byte integer library
calls cannot be mixed.
PURPOSEDLAQP2 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.
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DLAQP2(3S)DLAQP2(3S)
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
SEE ALSOINTRO_LAPACK(3S), INTRO_SCSL(3S)
This man page is available only online.
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