SORGTR(l) ) SORGTR(l)NAME
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 reflec‐
tors 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 elementary reflec‐
tor 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.
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 SORGTR(l)
