DORGTR(3F)DORGTR(3F)NAME
DORGTR - generate a real orthogonal matrix Q which is defined as the
product of n-1 elementary reflectors of order N, as returned by DSYTRD
SYNOPSIS
SUBROUTINE DORGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
CHARACTER UPLO
INTEGER INFO, LDA, LWORK, N
DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( LWORK )
PURPOSE
DORGTR generates a real orthogonal matrix Q which is defined as the
product of n-1 elementary reflectors of order N, as returned by DSYTRD:
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
DSYTRD; = 'L': Lower triangle of A contains elementary reflectors
from DSYTRD.
N (input) INTEGER
The order of the matrix Q. N >= 0.
A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors, as
returned by DSYTRD. 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) DOUBLE PRECISION array, dimension (N-1)
TAU(i) must contain the scalar factor of the elementary reflector
H(i), as returned by DSYTRD.
WORK (workspace/output) 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,N-1). For
optimum performance LWORK >= (N-1)*NB, where NB is the optimal
blocksize.
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DORGTR(3F)DORGTR(3F)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
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