```      SUBROUTINE CUNG2R( M, N, K, A, LDA, TAU, WORK, INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
INTEGER            INFO, K, LDA, M, N
*     ..
*     .. Array Arguments ..
COMPLEX            A( LDA, * ), TAU( * ), WORK( * )
*     ..
*
*  Purpose
*  =======
*
*  CUNG2R generates an m by n complex matrix Q with orthonormal columns,
*  which is defined as the first n columns of a product of k elementary
*  reflectors of order m
*
*        Q  =  H(1) H(2) . . . H(k)
*
*  as returned by CGEQRF.
*
*  Arguments
*  =========
*
*  M       (input) INTEGER
*          The number of rows of the matrix Q. M >= 0.
*
*  N       (input) INTEGER
*          The number of columns of the matrix Q. M >= N >= 0.
*
*  K       (input) INTEGER
*          The number of elementary reflectors whose product defines the
*          matrix Q. N >= K >= 0.
*
*  A       (input/output) COMPLEX array, dimension (LDA,N)
*          On entry, the i-th column must contain the vector which
*          defines the elementary reflector H(i), for i = 1,2,...,k, as
*          returned by CGEQRF in the first k columns of its array
*          argument A.
*          On exit, the m by n matrix Q.
*
*  LDA     (input) INTEGER
*          The first dimension of the array A. LDA >= max(1,M).
*
*  TAU     (input) COMPLEX array, dimension (K)
*          TAU(i) must contain the scalar factor of the elementary
*          reflector H(i), as returned by CGEQRF.
*
*  WORK    (workspace) COMPLEX array, dimension (N)
*
*  INFO    (output) INTEGER
*          = 0: successful exit
*          < 0: if INFO = -i, the i-th argument has an illegal value
*
*  =====================================================================
*
*     .. Parameters ..
COMPLEX            ONE, ZERO
PARAMETER          ( ONE = ( 1.0E+0, 0.0E+0 ),
\$                   ZERO = ( 0.0E+0, 0.0E+0 ) )
*     ..
*     .. Local Scalars ..
INTEGER            I, J, L
*     ..
*     .. External Subroutines ..
EXTERNAL           CLARF, CSCAL, XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          MAX
*     ..
*     .. Executable Statements ..
*
*     Test the input arguments
*
INFO = 0
IF( M.LT.0 ) THEN
INFO = -1
ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
INFO = -2
ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
INFO = -3
ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
INFO = -5
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'CUNG2R', -INFO )
RETURN
END IF
*
*     Quick return if possible
*
IF( N.LE.0 )
\$   RETURN
*
*     Initialise columns k+1:n to columns of the unit matrix
*
DO 20 J = K + 1, N
DO 10 L = 1, M
A( L, J ) = ZERO
10    CONTINUE
A( J, J ) = ONE
20 CONTINUE
*
DO 40 I = K, 1, -1
*
*        Apply H(i) to A(i:m,i:n) from the left
*
IF( I.LT.N ) THEN
A( I, I ) = ONE
CALL CLARF( 'Left', M-I+1, N-I, A( I, I ), 1, TAU( I ),
\$                  A( I, I+1 ), LDA, WORK )
END IF
IF( I.LT.M )
\$      CALL CSCAL( M-I, -TAU( I ), A( I+1, I ), 1 )
A( I, I ) = ONE - TAU( I )
*
*        Set A(1:i-1,i) to zero
*
DO 30 L = 1, I - 1
A( L, I ) = ZERO
30    CONTINUE
40 CONTINUE
RETURN
*
*     End of CUNG2R
*
END

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