redhat man page for cungtr

CUNGTR(l)								 )								 CUNGTR(l)

NAME
       CUNGTR - generate a complex unitary matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by CHETRD

SYNOPSIS
       SUBROUTINE CUNGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )

	   CHARACTER	  UPLO

	   INTEGER	  INFO, LDA, LWORK, N

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

PURPOSE
       CUNGTR generates a complex unitary matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by CHETRD:
       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 CHETRD; = 'L': Lower triangle of A  contains  elementary	reflectors
	       from CHETRD.

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

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

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

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

       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 >= 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 							 CUNGTR(l)