dormbr (l) - Linux Manuals

NAME

DORMBR - VECT = aqQaq, DORMBR overwrites the general real M-by-N matrix C with SIDE = aqLaq SIDE = aqRaq TRANS = aqNaq

SYNOPSIS

SUBROUTINE DORMBR(
VECT, SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, LWORK, INFO )

CHARACTER SIDE, TRANS, VECT

INTEGER INFO, K, LDA, LDC, LWORK, M, N

DOUBLE PRECISION A( LDA, * ), C( LDC, * ), TAU( * ), WORK( * )

PURPOSE

If VECT = aqQaq, DORMBR overwrites the general real M-by-N matrix C with
SIDE aqLaq     SIDE aqRaq TRANS = aqNaq: Q * C C * Q TRANS = aqTaq: Q**T * C C * Q**T
If VECT = aqPaq, DORMBR overwrites the general real M-by-N matrix C with

SIDE aqLaq     SIDE aqRaq
TRANS = aqNaq: P * C C * P
TRANS = aqTaq: P**T * C C * P**T
Here Q and P**T are the orthogonal matrices 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) and G(i) respectively.
Let nq = m if SIDE = aqLaq and nq = n if SIDE = aqRaq. Thus nq is the order of the orthogonal matrix Q or P**T that is applied. If VECT = aqQaq, A is assumed to have been an NQ-by-K matrix: if nq >= k, Q = H(1) H(2) . . . H(k);
if nq < k, Q = H(1) H(2) . . . H(nq-1).
If VECT = aqPaq, A is assumed to have been a K-by-NQ matrix: if k < nq, P = G(1) G(2) . . . G(k);
if k >= nq, P = G(1) G(2) . . . G(nq-1).

ARGUMENTS

VECT (input) CHARACTER*1
= aqQaq: apply Q or Q**T;
= aqPaq: apply P or P**T.
SIDE (input) CHARACTER*1

= aqLaq: apply Q, Q**T, P or P**T from the Left;
= aqRaq: apply Q, Q**T, P or P**T from the Right.
TRANS (input) CHARACTER*1

= aqNaq: No transpose, apply Q or P;
= aqTaq: Transpose, apply Q**T or P**T.
M (input) INTEGER
The number of rows of the matrix C. M >= 0.
N (input) INTEGER
The number of columns of the matrix C. N >= 0.
K (input) INTEGER
If VECT = aqQaq, the number of columns in the original matrix reduced by DGEBRD. If VECT = aqPaq, the number of rows in the original matrix reduced by DGEBRD. K >= 0.
A (input) DOUBLE PRECISION array, dimension
(LDA,min(nq,K)) if VECT = aqQaq (LDA,nq) if VECT = aqPaq The vectors which define the elementary reflectors H(i) and G(i), whose products determine the matrices Q and P, as returned by DGEBRD.
LDA (input) INTEGER
The leading dimension of the array A. If VECT = aqQaq, LDA >= max(1,nq); if VECT = aqPaq, LDA >= max(1,min(nq,K)).
TAU (input) DOUBLE PRECISION array, dimension (min(nq,K))
TAU(i) must contain the scalar factor of the elementary reflector H(i) or G(i) which determines Q or P, as returned by DGEBRD in the array argument TAUQ or TAUP.
C (input/output) DOUBLE PRECISION array, dimension (LDC,N)
On entry, the M-by-N matrix C. On exit, C is overwritten by Q*C or Q**T*C or C*Q**T or C*Q or P*C or P**T*C or C*P or C*P**T.
LDC (input) INTEGER
The leading dimension of the array C. LDC >= max(1,M).
WORK (workspace/output) DOUBLE PRECISION array, dimension (MAX(1,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
LWORK (input) INTEGER
The dimension of the array WORK. If SIDE = aqLaq, LWORK >= max(1,N); if SIDE = aqRaq, LWORK >= max(1,M). For optimum performance LWORK >= N*NB if SIDE = aqLaq, and LWORK >= M*NB if SIDE = aqRaq, where NB is the optimal blocksize. If LWORK = -1, then a workspace query is assumed; the routine only calculates the optimal size of the WORK array, returns this value as the first entry of the WORK array, and no error message related to LWORK is issued by XERBLA.
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value