DORGHR(3)
generates a real orthogonal matrix Q which is defined as the product of IHIILO elementary reflectors of order N, as returned by DGEHRD
SYNOPSIS
 SUBROUTINE DORGHR(

N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO )

INTEGER
IHI, ILO, INFO, LDA, LWORK, N

DOUBLE
PRECISION A( LDA, * ), TAU( * ), WORK( * )
PURPOSE
DORGHR generates a real orthogonal matrix Q which is defined as the
product of IHIILO elementary reflectors of order N, as returned by
DGEHRD:
Q = H(ilo) H(ilo+1) . . . H(ihi1).
ARGUMENTS
 N (input) INTEGER

The order of the matrix Q. N >= 0.
 ILO (input) INTEGER

IHI (input) INTEGER
ILO and IHI must have the same values as in the previous call
of DGEHRD. Q is equal to the unit matrix except in the
submatrix Q(ilo+1:ihi,ilo+1:ihi).
1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
 A (input/output) DOUBLE PRECISION array, dimension (LDA,N)

On entry, the vectors which define the elementary reflectors,
as returned by DGEHRD.
On exit, the NbyN orthogonal matrix Q.
 LDA (input) INTEGER

The leading dimension of the array A. LDA >= max(1,N).
 TAU (input) DOUBLE PRECISION array, dimension (N1)

TAU(i) must contain the scalar factor of the elementary
reflector H(i), as returned by DGEHRD.
 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. LWORK >= IHIILO.
For optimum performance LWORK >= (IHIILO)*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 ith argument had an illegal value