redhat man page for cunghr

CUNGHR(l)								 )								 CUNGHR(l)

NAME
       CUNGHR  -  generate  a complex unitary matrix Q which is defined as the product of IHI-ILO elementary reflectors of order N, as returned by
       CGEHRD

SYNOPSIS
       SUBROUTINE CUNGHR( N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO )

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

	   COMPLEX	  A( LDA, * ), TAU( * ), WORK( * )

PURPOSE
       CUNGHR generates a complex unitary matrix Q which is defined as the product of IHI-ILO elementary reflectors of order  N,  as  returned	by
       CGEHRD: Q = H(ilo) H(ilo+1) . . . H(ihi-1).

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 CGEHRD. 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) COMPLEX array, dimension (LDA,N)
	       On entry, the vectors which define the elementary reflectors, as returned by CGEHRD.  On exit, the N-by-N unitary matrix Q.

       LDA     (input) INTEGER
	       The leading dimension of the array A. LDA >= max(1,N).

       TAU     (input) COMPLEX array, dimension (N-1)
	       TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by CGEHRD.

       WORK    (workspace/output) COMPLEX array, dimension (LWORK)
	       On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

       LWORK   (input) INTEGER
	       The dimension of the array WORK. LWORK >= IHI-ILO.  For optimum performance LWORK >= (IHI-ILO)*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 							 CUNGHR(l)