DORGBR(l) LAPACK routine (version 1.1) DORGBR(l)
NAME
DORGBR - generate one of the matrices Q or P**T determined by DGEBRD when
reducing a real matrix A to bidiagonal form
SYNOPSIS
SUBROUTINE DORGBR( VECT, M, N, K, A, LDA, TAU, WORK, LWORK, INFO )
CHARACTER VECT
INTEGER INFO, K, LDA, LWORK, M, N
DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( LWORK )
PURPOSE
DORGBR generates one of the matrices Q or P**T determined by DGEBRD when
reducing a real matrix A to bidiagonal form: A = Q * B * P**T. Q and P**T
are defined as products of elementary reflectors H(i) or G(i) respectively.
If VECT = 'Q', A is assumed to have been an M-by-K matrix, and Q is of
order M:
if m >= k, Q = H(1) H(2) . . . H(k) and DORGBR returns the first n columns
of Q, where m >= n >= k;
if m < k, Q = H(1) H(2) . . . H(m-1) and DORGBR returns Q as an M-by-M
matrix.
If VECT = 'P', A is assumed to have been a K-by-N matrix, and P**T is of
order N:
if k < n, P**T = G(k) . . . G(2) G(1) and DORGBR returns the first m rows
of P**T, where n >= m >= k;
if k >= n, P**T = G(n-1) . . . G(2) G(1) and DORGBR returns P**T as an N-
by-N matrix.
ARGUMENTS
VECT (input) CHARACTER*1
Specifies whether the matrix Q or the matrix P**T is required, as
defined in the transformation applied by DGEBRD:
= 'Q': generate Q;
= 'P': generate P**T.
M (input) INTEGER
The number of rows of the matrix Q or P**T to be returned. M >= 0.
N (input) INTEGER
The number of columns of the matrix Q or P**T to be returned. N >=
0. If VECT = 'Q', M >= N >= min(M,K); if VECT = 'P', N >= M >=
min(N,K).
K (input) INTEGER
K >= 0. If VECT = 'Q', the number of columns in the original M-
by-K matrix reduced by DGEBRD. If VECT = 'P', the number of rows
in the original K-by-N matrix reduced by DGEBRD.
A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors, as
returned by DGEBRD. On exit, the M-by-N matrix Q or P**T.
LDA (input) INTEGER
The leading dimension of the array A. LDA >= max(1,M).
TAU (input) DOUBLE PRECISION array, dimension
(min(M,K)) if VECT = 'Q' (min(N,K)) if VECT = 'P' TAU(i) must con-
tain the scalar factor of the elementary reflector H(i) or G(i),
which determines Q or P**T, as returned by DGEBRD in its array
argument TAUQ or TAUP.
WORK (workspace) DOUBLE PRECISION array, dimension (LWORK)
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
LWORK (input) INTEGER
The dimension of the array WORK. LWORK >= max(1,min(M,N)). For
optimum performance LWORK >= min(M,N)*NB, where NB is the optimal
blocksize.
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
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value decomposition