      SUBROUTINE ZUNMR2( SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC,
     $                   WORK, INFO )
*
*  -- LAPACK routine (version 3.0) --
*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
*     Courant Institute, Argonne National Lab, and Rice University
*     September 30, 1994
*
*     .. Scalar Arguments ..
      CHARACTER          SIDE, TRANS
      INTEGER            INFO, K, LDA, LDC, M, N
*     ..
*     .. Array Arguments ..
      COMPLEX*16         A( LDA, * ), C( LDC, * ), TAU( * ), WORK( * )
*     ..
*
*  Purpose
*  =======
*
*  ZUNMR2 overwrites the general complex m-by-n matrix C with
*
*        Q * C  if SIDE = 'L' and TRANS = 'N', or
*
*        Q'* C  if SIDE = 'L' and TRANS = 'C', or
*
*        C * Q  if SIDE = 'R' and TRANS = 'N', or
*
*        C * Q' if SIDE = 'R' and TRANS = 'C',
*
*  where Q is a complex unitary matrix defined as the product of k
*  elementary reflectors
*
*        Q = H(1)' H(2)' . . . H(k)'
*
*  as returned by ZGERQF. Q is of order m if SIDE = 'L' and of order n
*  if SIDE = 'R'.
*
*  Arguments
*  =========
*
*  SIDE    (input) CHARACTER*1
*          = 'L': apply Q or Q' from the Left
*          = 'R': apply Q or Q' from the Right
*
*  TRANS   (input) CHARACTER*1
*          = 'N': apply Q  (No transpose)
*          = 'C': apply Q' (Conjugate transpose)
*
*  M       (input) INTEGER
*          The number of rows of the matrix C. M >= 0.
*
*  N       (input) INTEGER
*          The number of columns of the matrix C. N >= 0.
*
*  K       (input) INTEGER
*          The number of elementary reflectors whose product defines
*          the matrix Q.
*          If SIDE = 'L', M >= K >= 0;
*          if SIDE = 'R', N >= K >= 0.
*
*  A       (input) COMPLEX*16 array, dimension
*                               (LDA,M) if SIDE = 'L',
*                               (LDA,N) if SIDE = 'R'
*          The i-th row must contain the vector which defines the
*          elementary reflector H(i), for i = 1,2,...,k, as returned by
*          ZGERQF in the last k rows of its array argument A.
*          A is modified by the routine but restored on exit.
*
*  LDA     (input) INTEGER
*          The leading dimension of the array A. LDA >= max(1,K).
*
*  TAU     (input) COMPLEX*16 array, dimension (K)
*          TAU(i) must contain the scalar factor of the elementary
*          reflector H(i), as returned by ZGERQF.
*
*  C       (input/output) COMPLEX*16 array, dimension (LDC,N)
*          On entry, the m-by-n matrix C.
*          On exit, C is overwritten by Q*C or Q'*C or C*Q' or C*Q.
*
*  LDC     (input) INTEGER
*          The leading dimension of the array C. LDC >= max(1,M).
*
*  WORK    (workspace) COMPLEX*16 array, dimension
*                                   (N) if SIDE = 'L',
*                                   (M) if SIDE = 'R'
*
*  INFO    (output) INTEGER
*          = 0: successful exit
*          < 0: if INFO = -i, the i-th argument had an illegal value
*
*  =====================================================================
*
*     .. Parameters ..
      COMPLEX*16         ONE
      PARAMETER          ( ONE = ( 1.0D+0, 0.0D+0 ) )
*     ..
*     .. Local Scalars ..
      LOGICAL            LEFT, NOTRAN
      INTEGER            I, I1, I2, I3, MI, NI, NQ
      COMPLEX*16         AII, TAUI
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           LSAME
*     ..
*     .. External Subroutines ..
      EXTERNAL           XERBLA, ZLACGV, ZLARF
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          DCONJG, MAX
*     ..
*     .. Executable Statements ..
*
*     Test the input arguments
*
      INFO = 0
      LEFT = LSAME( SIDE, 'L' )
      NOTRAN = LSAME( TRANS, 'N' )
*
*     NQ is the order of Q
*
      IF( LEFT ) THEN
         NQ = M
      ELSE
         NQ = N
      END IF
      IF( .NOT.LEFT .AND. .NOT.LSAME( SIDE, 'R' ) ) THEN
         INFO = -1
      ELSE IF( .NOT.NOTRAN .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
         INFO = -2
      ELSE IF( M.LT.0 ) THEN
         INFO = -3
      ELSE IF( N.LT.0 ) THEN
         INFO = -4
      ELSE IF( K.LT.0 .OR. K.GT.NQ ) THEN
         INFO = -5
      ELSE IF( LDA.LT.MAX( 1, K ) ) THEN
         INFO = -7
      ELSE IF( LDC.LT.MAX( 1, M ) ) THEN
         INFO = -10
      END IF
      IF( INFO.NE.0 ) THEN
         CALL XERBLA( 'ZUNMR2', -INFO )
         RETURN
      END IF
*
*     Quick return if possible
*
      IF( M.EQ.0 .OR. N.EQ.0 .OR. K.EQ.0 )
     $   RETURN
*
      IF( ( LEFT .AND. .NOT.NOTRAN .OR. .NOT.LEFT .AND. NOTRAN ) ) THEN
         I1 = 1
         I2 = K
         I3 = 1
      ELSE
         I1 = K
         I2 = 1
         I3 = -1
      END IF
*
      IF( LEFT ) THEN
         NI = N
      ELSE
         MI = M
      END IF
*
      DO 10 I = I1, I2, I3
         IF( LEFT ) THEN
*
*           H(i) or H(i)' is applied to C(1:m-k+i,1:n)
*
            MI = M - K + I
         ELSE
*
*           H(i) or H(i)' is applied to C(1:m,1:n-k+i)
*
            NI = N - K + I
         END IF
*
*        Apply H(i) or H(i)'
*
         IF( NOTRAN ) THEN
            TAUI = DCONJG( TAU( I ) )
         ELSE
            TAUI = TAU( I )
         END IF
         CALL ZLACGV( NQ-K+I-1, A( I, 1 ), LDA )
         AII = A( I, NQ-K+I )
         A( I, NQ-K+I ) = ONE
         CALL ZLARF( SIDE, MI, NI, A( I, 1 ), LDA, TAUI, C, LDC, WORK )
         A( I, NQ-K+I ) = AII
         CALL ZLACGV( NQ-K+I-1, A( I, 1 ), LDA )
   10 CONTINUE
      RETURN
*
*     End of ZUNMR2
*
      END
