SORGTR - generate a real orthogonal matrix Q which is
defined as the product of n-1 elementary reflectors of
order N, as returned by SSYTRD
SYNOPSIS
SUBROUTINE SORGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO
)
CHARACTER UPLO
INTEGER INFO, LDA, LWORK, N
REAL A( LDA, * ), TAU( * ), WORK( * )
PURPOSE
SORGTR generates a real orthogonal matrix Q which is
defined as the product of n-1 elementary reflectors of
order N, as returned by SSYTRD: if UPLO = 'U', Q = H(n-1)
. . . H(2) H(1),
if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
ARGUMENTS
UPLO (input) CHARACTER*1
= 'U': Upper triangle of A contains elementary
reflectors from SSYTRD; = 'L': Lower triangle of A
contains elementary reflectors from SSYTRD.
N (input) INTEGER
The order of the matrix Q. N >= 0.
A (input/output) REAL array, dimension (LDA,N)
On entry, the vectors which define the elementary
reflectors, as returned by SSYTRD. On exit, the
N-by-N orthogonal matrix Q.
LDA (input) INTEGER
The leading dimension of the array A. LDA >=
max(1,N).
TAU (input) REAL array, dimension (N-1)
TAU(i) must contain the scalar factor of the ele
mentary reflector H(i), as returned by SSYTRD.
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,N-1). For optimum performance LWORK >=
(N-1)*NB, where NB is the optimal blocksize.
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 ille
gal value
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