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      SUBROUTINE ZGETRFF( M, N, A, LDA, IPIV, INFO )
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*
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*  -- LAPACK routine (version 3.0) --
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*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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*     Courant Institute, Argonne National Lab, and Rice University
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*     September 30, 1994
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*
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*     .. Scalar Arguments ..
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      INTEGER            INFO, LDA, M, N
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*     ..
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*     .. Array Arguments ..
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      INTEGER            IPIV( * )
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      COMPLEX*16         A( LDA, * )
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*     ..
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*
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*  Purpose
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*  =======
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*
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*  ZGETRF computes an LU factorization of a general M-by-N matrix A
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*  using partial pivoting with row interchanges.
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*
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*  The factorization has the form
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*     A = P * L * U
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*  where P is a permutation matrix, L is lower triangular with unit
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*  diagonal elements (lower trapezoidal if m > n), and U is upper
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*  triangular (upper trapezoidal if m < n).
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*
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*  This is the right-looking Level 3 BLAS version of the algorithm.
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*
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*  Arguments
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*  =========
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*
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*  M       (input) INTEGER
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*          The number of rows of the matrix A.  M >= 0.
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*
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*  N       (input) INTEGER
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*          The number of columns of the matrix A.  N >= 0.
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*
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*  A       (input/output) COMPLEX*16 array, dimension (LDA,N)
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*          On entry, the M-by-N matrix to be factored.
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*          On exit, the factors L and U from the factorization
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*          A = P*L*U; the unit diagonal elements of L are not stored.
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*
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*  LDA     (input) INTEGER
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*          The leading dimension of the array A.  LDA >= max(1,M).
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*
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*  IPIV    (output) INTEGER array, dimension (min(M,N))
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*          The pivot indices; for 1 <= i <= min(M,N), row i of the
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*          matrix was interchanged with row IPIV(i).
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*
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*  INFO    (output) INTEGER
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*          = 0:  successful exit
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*          < 0:  if INFO = -i, the i-th argument had an illegal value
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*          > 0:  if INFO = i, U(i,i) is exactly zero. The factorization
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*                has been completed, but the factor U is exactly
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*                singular, and division by zero will occur if it is used
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*                to solve a system of equations.
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*
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*  =====================================================================
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*
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*     .. Parameters ..
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      COMPLEX*16         ONE
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      PARAMETER          ( ONE = ( 1.0D+0, 0.0D+0 ) )
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*     ..
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*     .. Local Scalars ..
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      INTEGER            I, IINFO, J, JB, NB
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*     ..
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*     .. External Subroutines ..
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      EXTERNAL           XERBLA, ZGEMM, ZGETF2, ZLASWP, ZTRSM
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*     ..
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*     .. Intrinsic Functions ..
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      INTRINSIC          MAX, MIN
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*     ..
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*     .. Executable Statements ..
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*
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*     Test the input parameters.
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*
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      INFO = 0
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      IF( M.LT.0 ) THEN
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         INFO = -1
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      ELSE IF( N.LT.0 ) THEN
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         INFO = -2
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      ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
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         INFO = -4
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      END IF
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      IF( INFO.NE.0 ) THEN
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         CALL XERBLA( 'ZGETRF', -INFO )
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         RETURN
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      END IF
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*
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*     Quick return if possible
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*
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      IF( M.EQ.0 .OR. N.EQ.0 )
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     $   RETURN
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*
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*     Determine the block size for this environment.
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*
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      NB = 64
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      IF( NB.LE.1 .OR. NB.GE.MIN( M, N ) ) THEN
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*
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*        Use unblocked code.
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*
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         CALL ZGETF2( M, N, A, LDA, IPIV, INFO )
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      ELSE
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*
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*        Use blocked code.
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*
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         DO 20 J = 1, MIN( M, N ), NB
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            JB = MIN( MIN( M, N )-J+1, NB )
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*
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*           Factor diagonal and subdiagonal blocks and test for exact
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*           singularity.
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*
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            CALL ZGETF2( M-J+1, JB, A( J, J ), LDA, IPIV( J ), IINFO )
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*
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*           Adjust INFO and the pivot indices.
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*
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            IF( INFO.EQ.0 .AND. IINFO.GT.0 )
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     $         INFO = IINFO + J - 1
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            DO 10 I = J, MIN( M, J+JB-1 )
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               IPIV( I ) = J - 1 + IPIV( I )
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   10       CONTINUE
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*
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*           Apply interchanges to columns 1:J-1.
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*
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            CALL ZLASWP( J-1, A, LDA, J, J+JB-1, IPIV, 1 )
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*
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            IF( J+JB.LE.N ) THEN
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*
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*              Apply interchanges to columns J+JB:N.
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*
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               CALL ZLASWP( N-J-JB+1, A( 1, J+JB ), LDA, J, J+JB-1,
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     $                      IPIV, 1 )
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*
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*              Compute block row of U.
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*
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               CALL ZTRSM( 'Left', 'Lower', 'No transpose', 'Unit', JB,
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     $                     N-J-JB+1, ONE, A( J, J ), LDA, A( J, J+JB ),
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     $                     LDA )
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               IF( J+JB.LE.M ) THEN
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*
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*                 Update trailing submatrix.
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*
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                  CALL ZGEMM( 'No transpose', 'No transpose', M-J-JB+1,
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     $                        N-J-JB+1, JB, -ONE, A( J+JB, J ), LDA,
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     $                        A( J, J+JB ), LDA, ONE, A( J+JB, J+JB ),
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     $                        LDA )
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               END IF
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            END IF
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   20    CONTINUE
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      END IF
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      RETURN
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*
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*     End of ZGETRF
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*
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      END