redhat man page for zungtr

ZUNGTR(l)								 )								 ZUNGTR(l)

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

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

	   CHARACTER	  UPLO

	   INTEGER	  INFO, LDA, LWORK, N

	   COMPLEX*16	  A( LDA, * ), TAU( * ), WORK( * )

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

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

       A       (input/output) COMPLEX*16 array, dimension (LDA,N)
	       On entry, the vectors which define the elementary reflectors, as returned by ZHETRD.  On exit, the N-by-N unitary matrix Q.

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

       TAU     (input) COMPLEX*16 array, dimension (N-1)
	       TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by ZHETRD.

       WORK    (workspace/output) COMPLEX*16 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 							 ZUNGTR(l)