SORGBR(l) ) SORGBR(l)
SORGBR - generate one of the real orthogonal matrices Q or P**T determined by SGEBRD when
reducing a real matrix A to bidiagonal form
SUBROUTINE SORGBR( VECT, M, N, K, A, LDA, TAU, WORK, LWORK, INFO )
INTEGER INFO, K, LDA, LWORK, M, N
REAL A( LDA, * ), TAU( * ), WORK( * )
SORGBR generates one of the real orthogonal matrices Q or P**T determined by SGEBRD 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 SORGBR returns the first n columns of Q, where m
>= n >= k;
if m < k, Q = H(1) H(2) . . . H(m-1) and SORGBR 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 SORGBR 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 SORGBR returns P**T as an N-by-N matrix.
VECT (input) CHARACTER*1
Specifies whether the matrix Q or the matrix P**T is required, as defined in the
transformation applied by SGEBRD:
= '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
If VECT = 'Q', the number of columns in the original M-by-K matrix reduced by SGE-
BRD. If VECT = 'P', the number of rows in the original K-by-N matrix reduced by
SGEBRD. K >= 0.
A (input/output) REAL array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors, as returned by SGE-
BRD. 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) REAL array, dimension
(min(M,K)) if VECT = 'Q' (min(N,K)) if VECT = 'P' TAU(i) must contain the scalar
factor of the elementary reflector H(i) or G(i), which determines Q or P**T, as
returned by SGEBRD in its array argument TAUQ or TAUP.
WORK (workspace/output) REAL 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 perfor-
mance LWORK >= min(M,N)*NB, 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
LAPACK version 3.0 15 June 2000 SORGBR(l)