forked from lijiext/lammps
382 lines
14 KiB
Fortran
382 lines
14 KiB
Fortran
*> \brief \b DLABRD reduces the first nb rows and columns of a general matrix to a bidiagonal form.
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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 DLABRD + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlabrd.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/dlabrd.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/dlabrd.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 DLABRD( M, N, NB, A, LDA, D, E, TAUQ, TAUP, X, LDX, Y,
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* LDY )
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*
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* .. Scalar Arguments ..
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* INTEGER LDA, LDX, LDY, M, N, NB
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* ..
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* .. Array Arguments ..
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* DOUBLE PRECISION A( LDA, * ), D( * ), E( * ), TAUP( * ),
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* $ TAUQ( * ), X( LDX, * ), Y( LDY, * )
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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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*> DLABRD reduces the first NB rows and columns of a real general
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*> m by n matrix A to upper or lower bidiagonal form by an orthogonal
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*> transformation Q**T * A * P, and returns the matrices X and Y which
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*> are needed to apply the transformation to the unreduced part of A.
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*>
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*> If m >= n, A is reduced to upper bidiagonal form; if m < n, to lower
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*> bidiagonal form.
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*>
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*> This is an auxiliary routine called by DGEBRD
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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 in the matrix A.
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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 in the matrix A.
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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 leading rows and columns of A to be reduced.
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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 general matrix to be reduced.
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*> On exit, the first NB rows and columns of the matrix are
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*> overwritten; the rest of the array is unchanged.
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*> If m >= n, elements on and below the diagonal in the first NB
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*> columns, with the array TAUQ, represent the orthogonal
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*> matrix Q as a product of elementary reflectors; and
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*> elements above the diagonal in the first NB rows, with the
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*> array TAUP, represent the orthogonal matrix P as a product
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*> of elementary reflectors.
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*> If m < n, elements below the diagonal in the first NB
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*> columns, with the array TAUQ, represent the orthogonal
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*> matrix Q as a product of elementary reflectors, and
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*> elements on and above the diagonal in the first NB rows,
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*> with the array TAUP, represent the orthogonal matrix P as
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*> a product of elementary reflectors.
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*> See Further Details.
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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[out] D
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*> \verbatim
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*> D is DOUBLE PRECISION array, dimension (NB)
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*> The diagonal elements of the first NB rows and columns of
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*> the reduced matrix. D(i) = A(i,i).
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*> \endverbatim
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*>
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*> \param[out] E
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*> \verbatim
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*> E is DOUBLE PRECISION array, dimension (NB)
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*> The off-diagonal elements of the first NB rows and columns of
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*> the reduced matrix.
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*> \endverbatim
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*>
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*> \param[out] TAUQ
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*> \verbatim
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*> TAUQ is DOUBLE PRECISION array dimension (NB)
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*> The scalar factors of the elementary reflectors which
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*> represent the orthogonal matrix Q. See Further Details.
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*> \endverbatim
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*>
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*> \param[out] TAUP
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*> \verbatim
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*> TAUP is DOUBLE PRECISION array, dimension (NB)
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*> The scalar factors of the elementary reflectors which
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*> represent the orthogonal matrix P. See Further Details.
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*> \endverbatim
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*>
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*> \param[out] X
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*> \verbatim
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*> X is DOUBLE PRECISION array, dimension (LDX,NB)
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*> The m-by-nb matrix X required to update the unreduced part
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*> of A.
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*> \endverbatim
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*>
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*> \param[in] LDX
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*> \verbatim
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*> LDX is INTEGER
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*> The leading dimension of the array X. LDX >= max(1,M).
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*> \endverbatim
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*>
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*> \param[out] Y
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*> \verbatim
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*> Y is DOUBLE PRECISION array, dimension (LDY,NB)
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*> The n-by-nb matrix Y required to update the unreduced part
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*> of A.
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*> \endverbatim
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*>
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*> \param[in] LDY
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*> \verbatim
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*> LDY is INTEGER
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*> The leading dimension of the array Y. LDY >= 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 Further Details:
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* =====================
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*>
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*> \verbatim
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*>
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*> The matrices Q and P are represented as products of elementary
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*> reflectors:
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*>
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*> Q = H(1) H(2) . . . H(nb) and P = G(1) G(2) . . . G(nb)
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*>
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*> Each H(i) and G(i) has the form:
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*>
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*> H(i) = I - tauq * v * v**T and G(i) = I - taup * u * u**T
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*>
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*> where tauq and taup are real scalars, and v and u are real vectors.
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*>
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*> If m >= n, v(1:i-1) = 0, v(i) = 1, and v(i:m) is stored on exit in
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*> A(i:m,i); u(1:i) = 0, u(i+1) = 1, and u(i+1:n) is stored on exit in
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*> A(i,i+1:n); tauq is stored in TAUQ(i) and taup in TAUP(i).
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*>
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*> If m < n, v(1:i) = 0, v(i+1) = 1, and v(i+1:m) is stored on exit in
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*> A(i+2:m,i); u(1:i-1) = 0, u(i) = 1, and u(i:n) is stored on exit in
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*> A(i,i+1:n); tauq is stored in TAUQ(i) and taup in TAUP(i).
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*>
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*> The elements of the vectors v and u together form the m-by-nb matrix
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*> V and the nb-by-n matrix U**T which are needed, with X and Y, to apply
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*> the transformation to the unreduced part of the matrix, using a block
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*> update of the form: A := A - V*Y**T - X*U**T.
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*>
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*> The contents of A on exit are illustrated by the following examples
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*> with nb = 2:
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*>
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*> m = 6 and n = 5 (m > n): m = 5 and n = 6 (m < n):
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*>
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*> ( 1 1 u1 u1 u1 ) ( 1 u1 u1 u1 u1 u1 )
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*> ( v1 1 1 u2 u2 ) ( 1 1 u2 u2 u2 u2 )
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*> ( v1 v2 a a a ) ( v1 1 a a a a )
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*> ( v1 v2 a a a ) ( v1 v2 a a a a )
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*> ( v1 v2 a a a ) ( v1 v2 a a a a )
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*> ( v1 v2 a a a )
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*>
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*> where a denotes an element of the original matrix which is unchanged,
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*> vi denotes an element of the vector defining H(i), and ui an element
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*> of the vector defining G(i).
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*> \endverbatim
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*>
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* =====================================================================
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SUBROUTINE DLABRD( M, N, NB, A, LDA, D, E, TAUQ, TAUP, X, LDX, Y,
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$ LDY )
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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 LDA, LDX, LDY, M, N, NB
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION A( LDA, * ), D( * ), E( * ), TAUP( * ),
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$ TAUQ( * ), X( LDX, * ), Y( LDY, * )
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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 = 0.0D0, ONE = 1.0D0 )
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* ..
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* .. Local Scalars ..
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INTEGER I
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* ..
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* .. External Subroutines ..
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EXTERNAL DGEMV, DLARFG, DSCAL
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MIN
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* ..
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* .. Executable Statements ..
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*
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* Quick return if possible
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*
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IF( M.LE.0 .OR. N.LE.0 )
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$ RETURN
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*
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IF( M.GE.N ) THEN
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*
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* Reduce to upper bidiagonal form
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*
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DO 10 I = 1, NB
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*
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* Update A(i:m,i)
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*
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CALL DGEMV( 'No transpose', M-I+1, I-1, -ONE, A( I, 1 ),
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$ LDA, Y( I, 1 ), LDY, ONE, A( I, I ), 1 )
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CALL DGEMV( 'No transpose', M-I+1, I-1, -ONE, X( I, 1 ),
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$ LDX, A( 1, I ), 1, ONE, A( I, I ), 1 )
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*
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* Generate reflection Q(i) to annihilate A(i+1:m,i)
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*
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CALL DLARFG( M-I+1, A( I, I ), A( MIN( I+1, M ), I ), 1,
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$ TAUQ( I ) )
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D( I ) = A( I, I )
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IF( I.LT.N ) THEN
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A( I, I ) = ONE
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*
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* Compute Y(i+1:n,i)
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*
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CALL DGEMV( 'Transpose', M-I+1, N-I, ONE, A( I, I+1 ),
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$ LDA, A( I, I ), 1, ZERO, Y( I+1, I ), 1 )
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CALL DGEMV( 'Transpose', M-I+1, I-1, ONE, A( I, 1 ), LDA,
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$ A( I, I ), 1, ZERO, Y( 1, I ), 1 )
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CALL DGEMV( 'No transpose', N-I, I-1, -ONE, Y( I+1, 1 ),
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$ LDY, Y( 1, I ), 1, ONE, Y( I+1, I ), 1 )
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CALL DGEMV( 'Transpose', M-I+1, I-1, ONE, X( I, 1 ), LDX,
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$ A( I, I ), 1, ZERO, Y( 1, I ), 1 )
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CALL DGEMV( 'Transpose', I-1, N-I, -ONE, A( 1, I+1 ),
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$ LDA, Y( 1, I ), 1, ONE, Y( I+1, I ), 1 )
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CALL DSCAL( N-I, TAUQ( I ), Y( I+1, I ), 1 )
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*
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* Update A(i,i+1:n)
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*
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CALL DGEMV( 'No transpose', N-I, I, -ONE, Y( I+1, 1 ),
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$ LDY, A( I, 1 ), LDA, ONE, A( I, I+1 ), LDA )
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CALL DGEMV( 'Transpose', I-1, N-I, -ONE, A( 1, I+1 ),
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$ LDA, X( I, 1 ), LDX, ONE, A( I, I+1 ), LDA )
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*
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* Generate reflection P(i) to annihilate A(i,i+2:n)
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*
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CALL DLARFG( N-I, A( I, I+1 ), A( I, MIN( I+2, N ) ),
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$ LDA, TAUP( I ) )
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E( I ) = A( I, I+1 )
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A( I, I+1 ) = ONE
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*
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* Compute X(i+1:m,i)
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*
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CALL DGEMV( 'No transpose', M-I, N-I, ONE, A( I+1, I+1 ),
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$ LDA, A( I, I+1 ), LDA, ZERO, X( I+1, I ), 1 )
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CALL DGEMV( 'Transpose', N-I, I, ONE, Y( I+1, 1 ), LDY,
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$ A( I, I+1 ), LDA, ZERO, X( 1, I ), 1 )
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CALL DGEMV( 'No transpose', M-I, I, -ONE, A( I+1, 1 ),
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$ LDA, X( 1, I ), 1, ONE, X( I+1, I ), 1 )
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CALL DGEMV( 'No transpose', I-1, N-I, ONE, A( 1, I+1 ),
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$ LDA, A( I, I+1 ), LDA, ZERO, X( 1, I ), 1 )
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CALL DGEMV( 'No transpose', M-I, I-1, -ONE, X( I+1, 1 ),
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$ LDX, X( 1, I ), 1, ONE, X( I+1, I ), 1 )
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CALL DSCAL( M-I, TAUP( I ), X( I+1, I ), 1 )
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END IF
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10 CONTINUE
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ELSE
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*
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* Reduce to lower bidiagonal form
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*
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DO 20 I = 1, NB
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*
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* Update A(i,i:n)
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*
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CALL DGEMV( 'No transpose', N-I+1, I-1, -ONE, Y( I, 1 ),
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$ LDY, A( I, 1 ), LDA, ONE, A( I, I ), LDA )
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CALL DGEMV( 'Transpose', I-1, N-I+1, -ONE, A( 1, I ), LDA,
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$ X( I, 1 ), LDX, ONE, A( I, I ), LDA )
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*
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* Generate reflection P(i) to annihilate A(i,i+1:n)
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*
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CALL DLARFG( N-I+1, A( I, I ), A( I, MIN( I+1, N ) ), LDA,
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$ TAUP( I ) )
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D( I ) = A( I, I )
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IF( I.LT.M ) THEN
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A( I, I ) = ONE
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*
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* Compute X(i+1:m,i)
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*
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CALL DGEMV( 'No transpose', M-I, N-I+1, ONE, A( I+1, I ),
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$ LDA, A( I, I ), LDA, ZERO, X( I+1, I ), 1 )
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CALL DGEMV( 'Transpose', N-I+1, I-1, ONE, Y( I, 1 ), LDY,
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$ A( I, I ), LDA, ZERO, X( 1, I ), 1 )
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CALL DGEMV( 'No transpose', M-I, I-1, -ONE, A( I+1, 1 ),
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$ LDA, X( 1, I ), 1, ONE, X( I+1, I ), 1 )
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CALL DGEMV( 'No transpose', I-1, N-I+1, ONE, A( 1, I ),
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$ LDA, A( I, I ), LDA, ZERO, X( 1, I ), 1 )
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CALL DGEMV( 'No transpose', M-I, I-1, -ONE, X( I+1, 1 ),
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$ LDX, X( 1, I ), 1, ONE, X( I+1, I ), 1 )
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CALL DSCAL( M-I, TAUP( I ), X( I+1, I ), 1 )
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*
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* Update A(i+1:m,i)
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*
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CALL DGEMV( 'No transpose', M-I, I-1, -ONE, A( I+1, 1 ),
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$ LDA, Y( I, 1 ), LDY, ONE, A( I+1, I ), 1 )
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CALL DGEMV( 'No transpose', M-I, I, -ONE, X( I+1, 1 ),
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$ LDX, A( 1, I ), 1, ONE, A( I+1, I ), 1 )
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*
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* Generate reflection Q(i) to annihilate A(i+2:m,i)
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*
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CALL DLARFG( M-I, A( I+1, I ), A( MIN( I+2, M ), I ), 1,
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$ TAUQ( I ) )
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E( I ) = A( I+1, I )
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A( I+1, I ) = ONE
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*
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* Compute Y(i+1:n,i)
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*
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CALL DGEMV( 'Transpose', M-I, N-I, ONE, A( I+1, I+1 ),
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$ LDA, A( I+1, I ), 1, ZERO, Y( I+1, I ), 1 )
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CALL DGEMV( 'Transpose', M-I, I-1, ONE, A( I+1, 1 ), LDA,
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$ A( I+1, I ), 1, ZERO, Y( 1, I ), 1 )
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CALL DGEMV( 'No transpose', N-I, I-1, -ONE, Y( I+1, 1 ),
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$ LDY, Y( 1, I ), 1, ONE, Y( I+1, I ), 1 )
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CALL DGEMV( 'Transpose', M-I, I, ONE, X( I+1, 1 ), LDX,
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$ A( I+1, I ), 1, ZERO, Y( 1, I ), 1 )
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CALL DGEMV( 'Transpose', I, N-I, -ONE, A( 1, I+1 ), LDA,
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$ Y( 1, I ), 1, ONE, Y( I+1, I ), 1 )
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CALL DSCAL( N-I, TAUQ( I ), Y( I+1, I ), 1 )
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END IF
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20 CONTINUE
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END IF
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RETURN
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*
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* End of DLABRD
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*
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END
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