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RedHat 9 (Linux i386) - man page for dorgtr (redhat section l)

DORGTR(l)					)					DORGTR(l)

NAME
       DORGTR  -  generate a real orthogonal matrix Q which is defined as the product of n-1 ele-
       mentary 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( * )

PURPOSE
       DORGTR generates a real orthogonal matrix Q which is defined as the product of n-1 elemen-
       tary  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.

	       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 				DORGTR(l)


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