zlaqps (l)  Linux Man Pages
zlaqps: computes a step of QR factorization with column pivoting of a complex MbyN matrix A by using Blas3
NAME
ZLAQPS  computes a step of QR factorization with column pivoting of a complex MbyN matrix A by using Blas3SYNOPSIS
 SUBROUTINE ZLAQPS(
 M, N, OFFSET, NB, KB, A, LDA, JPVT, TAU, VN1, VN2, AUXV, F, LDF )
 INTEGER KB, LDA, LDF, M, N, NB, OFFSET
 INTEGER JPVT( * )
 DOUBLE PRECISION VN1( * ), VN2( * )
 COMPLEX*16 A( LDA, * ), AUXV( * ), F( LDF, * ), TAU( * )
PURPOSE
ZLAQPS computes a step of QR factorization with column pivoting of a complex MbyN matrix A by using Blas3. It tries to factorize NB columns from A starting from the row OFFSET+1, and updates all of the matrix with Blas3 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.
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 A that have been factorized in previous steps.
 NB (input) INTEGER
 The number of columns to factorize.
 KB (output) INTEGER
 The number of columns actually factorized.
 A (input/output) COMPLEX*16 array, dimension (LDA,N)

On entry, the MbyN 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 (input) INTEGER
 The leading dimension of the array A. LDA >= max(1,M).
 JPVT (input/output) INTEGER array, dimension (N)
 JPVT(I) = K <==> Column K of the full matrix A has been permuted into position I in AP.
 TAU (output) COMPLEX*16 array, dimension (KB)
 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.
 AUXV (input/output) COMPLEX*16 array, dimension (NB)
 Auxiliar vector.
 F (input/output) COMPLEX*16 array, dimension (LDF,NB)
 Matrix Faq = L*Yaq*A.
 LDF (input) INTEGER
 The leading dimension of the array F. LDF >= max(1,N).
FURTHER DETAILS
Based on contributions by