redhat man page for sorgtr

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	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 elementary 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 block-
	       size.

	       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)