359 lines
10 KiB
Fortran
359 lines
10 KiB
Fortran
*> \brief \b DLAQPS computes a step of QR factorization with column pivoting of a real m-by-n matrix A by using BLAS level 3.
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download DLAQPS + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlaqps.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlaqps.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlaqps.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE DLAQPS( M, N, OFFSET, NB, KB, A, LDA, JPVT, TAU, VN1,
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* VN2, AUXV, F, LDF )
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*
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* .. Scalar Arguments ..
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* INTEGER KB, LDA, LDF, M, N, NB, OFFSET
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* ..
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* .. Array Arguments ..
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* INTEGER JPVT( * )
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* DOUBLE PRECISION A( LDA, * ), AUXV( * ), F( LDF, * ), TAU( * ),
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* $ VN1( * ), VN2( * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> DLAQPS computes a step of QR factorization with column pivoting
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*> of a real M-by-N matrix A by using Blas-3. It tries to factorize
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*> NB columns from A starting from the row OFFSET+1, and updates all
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*> of the matrix with Blas-3 xGEMM.
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*>
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*> In some cases, due to catastrophic cancellations, it cannot
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*> factorize NB columns. Hence, the actual number of factorized
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*> columns is returned in KB.
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*>
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*> Block A(1:OFFSET,1:N) is accordingly pivoted, but not factorized.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] M
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*> \verbatim
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*> M is INTEGER
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*> The number of rows of the matrix A. M >= 0.
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The number of columns of the matrix A. N >= 0
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*> \endverbatim
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*>
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*> \param[in] OFFSET
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*> \verbatim
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*> OFFSET is INTEGER
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*> The number of rows of A that have been factorized in
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*> previous steps.
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*> \endverbatim
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*>
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*> \param[in] NB
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*> \verbatim
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*> NB is INTEGER
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*> The number of columns to factorize.
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*> \endverbatim
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*>
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*> \param[out] KB
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*> \verbatim
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*> KB is INTEGER
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*> The number of columns actually factorized.
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*> \endverbatim
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*>
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*> \param[in,out] A
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*> \verbatim
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*> A is DOUBLE PRECISION array, dimension (LDA,N)
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*> On entry, the M-by-N matrix A.
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*> On exit, block A(OFFSET+1:M,1:KB) is the triangular
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*> factor obtained and block A(1:OFFSET,1:N) has been
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*> accordingly pivoted, but no factorized.
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*> The rest of the matrix, block A(OFFSET+1:M,KB+1:N) has
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*> been updated.
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*> \endverbatim
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*>
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*> \param[in] LDA
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*> \verbatim
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*> LDA is INTEGER
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*> The leading dimension of the array A. LDA >= max(1,M).
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*> \endverbatim
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*>
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*> \param[in,out] JPVT
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*> \verbatim
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*> JPVT is INTEGER array, dimension (N)
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*> JPVT(I) = K <==> Column K of the full matrix A has been
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*> permuted into position I in AP.
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*> \endverbatim
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*>
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*> \param[out] TAU
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*> \verbatim
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*> TAU is DOUBLE PRECISION array, dimension (KB)
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*> The scalar factors of the elementary reflectors.
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*> \endverbatim
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*>
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*> \param[in,out] VN1
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*> \verbatim
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*> VN1 is DOUBLE PRECISION array, dimension (N)
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*> The vector with the partial column norms.
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*> \endverbatim
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*>
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*> \param[in,out] VN2
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*> \verbatim
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*> VN2 is DOUBLE PRECISION array, dimension (N)
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*> The vector with the exact column norms.
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*> \endverbatim
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*>
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*> \param[in,out] AUXV
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*> \verbatim
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*> AUXV is DOUBLE PRECISION array, dimension (NB)
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*> Auxiliar vector.
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*> \endverbatim
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*>
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*> \param[in,out] F
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*> \verbatim
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*> F is DOUBLE PRECISION array, dimension (LDF,NB)
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*> Matrix F**T = L*Y**T*A.
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*> \endverbatim
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*>
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*> \param[in] LDF
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*> \verbatim
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*> LDF is INTEGER
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*> The leading dimension of the array F. LDF >= max(1,N).
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \date September 2012
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*
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*> \ingroup doubleOTHERauxiliary
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*
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*> \par Contributors:
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* ==================
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*>
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*> G. Quintana-Orti, Depto. de Informatica, Universidad Jaime I, Spain
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*> X. Sun, Computer Science Dept., Duke University, USA
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*> \n
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*> Partial column norm updating strategy modified on April 2011
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*> Z. Drmac and Z. Bujanovic, Dept. of Mathematics,
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*> University of Zagreb, Croatia.
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*
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*> \par References:
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* ================
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*>
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*> LAPACK Working Note 176
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*
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*> \htmlonly
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*> <a href="http://www.netlib.org/lapack/lawnspdf/lawn176.pdf">[PDF]</a>
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*> \endhtmlonly
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*
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* =====================================================================
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SUBROUTINE DLAQPS( M, N, OFFSET, NB, KB, A, LDA, JPVT, TAU, VN1,
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$ VN2, AUXV, F, LDF )
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*
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* -- LAPACK auxiliary routine (version 3.4.2) --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* September 2012
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*
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* .. Scalar Arguments ..
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INTEGER KB, LDA, LDF, M, N, NB, OFFSET
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* ..
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* .. Array Arguments ..
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INTEGER JPVT( * )
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DOUBLE PRECISION A( LDA, * ), AUXV( * ), F( LDF, * ), TAU( * ),
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$ VN1( * ), VN2( * )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO, ONE
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PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
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* ..
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* .. Local Scalars ..
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INTEGER ITEMP, J, K, LASTRK, LSTICC, PVT, RK
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DOUBLE PRECISION AKK, TEMP, TEMP2, TOL3Z
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* ..
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* .. External Subroutines ..
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EXTERNAL DGEMM, DGEMV, DLARFG, DSWAP
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, DBLE, MAX, MIN, NINT, SQRT
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* ..
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* .. External Functions ..
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INTEGER IDAMAX
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DOUBLE PRECISION DLAMCH, DNRM2
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EXTERNAL IDAMAX, DLAMCH, DNRM2
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* ..
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* .. Executable Statements ..
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*
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LASTRK = MIN( M, N+OFFSET )
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LSTICC = 0
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K = 0
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TOL3Z = SQRT(DLAMCH('Epsilon'))
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*
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* Beginning of while loop.
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*
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10 CONTINUE
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IF( ( K.LT.NB ) .AND. ( LSTICC.EQ.0 ) ) THEN
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K = K + 1
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RK = OFFSET + K
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*
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* Determine ith pivot column and swap if necessary
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*
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PVT = ( K-1 ) + IDAMAX( N-K+1, VN1( K ), 1 )
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IF( PVT.NE.K ) THEN
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CALL DSWAP( M, A( 1, PVT ), 1, A( 1, K ), 1 )
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CALL DSWAP( K-1, F( PVT, 1 ), LDF, F( K, 1 ), LDF )
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ITEMP = JPVT( PVT )
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JPVT( PVT ) = JPVT( K )
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JPVT( K ) = ITEMP
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VN1( PVT ) = VN1( K )
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VN2( PVT ) = VN2( K )
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END IF
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*
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* Apply previous Householder reflectors to column K:
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* A(RK:M,K) := A(RK:M,K) - A(RK:M,1:K-1)*F(K,1:K-1)**T.
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*
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IF( K.GT.1 ) THEN
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CALL DGEMV( 'No transpose', M-RK+1, K-1, -ONE, A( RK, 1 ),
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$ LDA, F( K, 1 ), LDF, ONE, A( RK, K ), 1 )
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END IF
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*
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* Generate elementary reflector H(k).
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*
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IF( RK.LT.M ) THEN
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CALL DLARFG( M-RK+1, A( RK, K ), A( RK+1, K ), 1, TAU( K ) )
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ELSE
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CALL DLARFG( 1, A( RK, K ), A( RK, K ), 1, TAU( K ) )
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END IF
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*
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AKK = A( RK, K )
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A( RK, K ) = ONE
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*
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* Compute Kth column of F:
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*
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* Compute F(K+1:N,K) := tau(K)*A(RK:M,K+1:N)**T*A(RK:M,K).
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*
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IF( K.LT.N ) THEN
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CALL DGEMV( 'Transpose', M-RK+1, N-K, TAU( K ),
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$ A( RK, K+1 ), LDA, A( RK, K ), 1, ZERO,
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$ F( K+1, K ), 1 )
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END IF
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*
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* Padding F(1:K,K) with zeros.
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*
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DO 20 J = 1, K
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F( J, K ) = ZERO
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20 CONTINUE
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*
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* Incremental updating of F:
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* F(1:N,K) := F(1:N,K) - tau(K)*F(1:N,1:K-1)*A(RK:M,1:K-1)**T
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* *A(RK:M,K).
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*
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IF( K.GT.1 ) THEN
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CALL DGEMV( 'Transpose', M-RK+1, K-1, -TAU( K ), A( RK, 1 ),
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$ LDA, A( RK, K ), 1, ZERO, AUXV( 1 ), 1 )
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*
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CALL DGEMV( 'No transpose', N, K-1, ONE, F( 1, 1 ), LDF,
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$ AUXV( 1 ), 1, ONE, F( 1, K ), 1 )
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END IF
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*
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* Update the current row of A:
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* A(RK,K+1:N) := A(RK,K+1:N) - A(RK,1:K)*F(K+1:N,1:K)**T.
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*
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IF( K.LT.N ) THEN
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CALL DGEMV( 'No transpose', N-K, K, -ONE, F( K+1, 1 ), LDF,
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$ A( RK, 1 ), LDA, ONE, A( RK, K+1 ), LDA )
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END IF
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*
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* Update partial column norms.
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*
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IF( RK.LT.LASTRK ) THEN
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DO 30 J = K + 1, N
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IF( VN1( J ).NE.ZERO ) THEN
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*
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* NOTE: The following 4 lines follow from the analysis in
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* Lapack Working Note 176.
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*
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TEMP = ABS( A( RK, J ) ) / VN1( J )
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TEMP = MAX( ZERO, ( ONE+TEMP )*( ONE-TEMP ) )
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TEMP2 = TEMP*( VN1( J ) / VN2( J ) )**2
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IF( TEMP2 .LE. TOL3Z ) THEN
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VN2( J ) = DBLE( LSTICC )
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LSTICC = J
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ELSE
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VN1( J ) = VN1( J )*SQRT( TEMP )
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END IF
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END IF
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30 CONTINUE
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END IF
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*
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A( RK, K ) = AKK
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*
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* End of while loop.
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*
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GO TO 10
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END IF
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KB = K
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RK = OFFSET + KB
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*
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* Apply the block reflector to the rest of the matrix:
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* A(OFFSET+KB+1:M,KB+1:N) := A(OFFSET+KB+1:M,KB+1:N) -
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* A(OFFSET+KB+1:M,1:KB)*F(KB+1:N,1:KB)**T.
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*
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IF( KB.LT.MIN( N, M-OFFSET ) ) THEN
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CALL DGEMM( 'No transpose', 'Transpose', M-RK, N-KB, KB, -ONE,
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$ A( RK+1, 1 ), LDA, F( KB+1, 1 ), LDF, ONE,
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$ A( RK+1, KB+1 ), LDA )
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END IF
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*
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* Recomputation of difficult columns.
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*
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40 CONTINUE
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IF( LSTICC.GT.0 ) THEN
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ITEMP = NINT( VN2( LSTICC ) )
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VN1( LSTICC ) = DNRM2( M-RK, A( RK+1, LSTICC ), 1 )
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*
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* NOTE: The computation of VN1( LSTICC ) relies on the fact that
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* SNRM2 does not fail on vectors with norm below the value of
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* SQRT(DLAMCH('S'))
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*
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VN2( LSTICC ) = VN1( LSTICC )
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LSTICC = ITEMP
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GO TO 40
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END IF
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*
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RETURN
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*
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* End of DLAQPS
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*
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END
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