zgeru.f

          SUBROUTINE ZGERU(M,N,ALPHA,X,INCX,Y,INCY,A,LDA)
    *     .. Scalar Arguments ..
          DOUBLE COMPLEX ALPHA
          INTEGER INCX,INCY,LDA,M,N
    *     ..
    *     .. Array Arguments ..
          DOUBLE COMPLEX A(LDA,*),X(*),Y(*)
    *     ..
    *
    *  Purpose
    *  =======
    *
    *  ZGERU  performs the rank 1 operation
    *
    *     A := alpha*x*y' + A,
    *
    *  where alpha is a scalar, x is an m element vector, y is an n element
    *  vector and A is an m by n matrix.
    *
    *  Arguments
    *  ==========
    *
    *  M      - INTEGER.
    *           On entry, M specifies the number of rows of the matrix A.
    *           M must be at least zero.
    *           Unchanged on exit.
    *
    *  N      - INTEGER.
    *           On entry, N specifies the number of columns of the matrix A.
    *           N must be at least zero.
    *           Unchanged on exit.
    *
    *  ALPHA  - COMPLEX*16      .
    *           On entry, ALPHA specifies the scalar alpha.
    *           Unchanged on exit.
    *
    *  X      - COMPLEX*16       array of dimension at least
    *           ( 1 + ( m - 1 )*abs( INCX ) ).
    *           Before entry, the incremented array X must contain the m
    *           element vector x.
    *           Unchanged on exit.
    *
    *  INCX   - INTEGER.
    *           On entry, INCX specifies the increment for the elements of
    *           X. INCX must not be zero.
    *           Unchanged on exit.
    *
    *  Y      - COMPLEX*16       array of dimension at least
    *           ( 1 + ( n - 1 )*abs( INCY ) ).
    *           Before entry, the incremented array Y must contain the n
    *           element vector y.
    *           Unchanged on exit.
    *
    *  INCY   - INTEGER.
    *           On entry, INCY specifies the increment for the elements of
    *           Y. INCY must not be zero.
    *           Unchanged on exit.
    *
    *  A      - COMPLEX*16       array of DIMENSION ( LDA, n ).
    *           Before entry, the leading m by n part of the array A must
    *           contain the matrix of coefficients. On exit, A is
    *           overwritten by the updated matrix.
    *
    *  LDA    - INTEGER.
    *           On entry, LDA specifies the first dimension of A as declared
    *           in the calling (sub) program. LDA must be at least
    *           max( 1, m ).
    *           Unchanged on exit.
    *
    *
    *  Level 2 Blas routine.
    *
    *  -- Written on 22-October-1986.
    *     Jack Dongarra, Argonne National Lab.
    *     Jeremy Du Croz, Nag Central Office.
    *     Sven Hammarling, Nag Central Office.
    *     Richard Hanson, Sandia National Labs.
    *
    *
    *     .. Parameters ..
          DOUBLE COMPLEX ZERO
          PARAMETER (ZERO= (0.0D+0,0.0D+0))
    *     ..
    *     .. Local Scalars ..
          DOUBLE COMPLEX TEMP
          INTEGER I,INFO,IX,J,JY,KX
    *     ..
    *     .. External Subroutines ..
          EXTERNAL XERBLA
    *     ..
    *     .. Intrinsic Functions ..
          INTRINSIC MAX
    *     ..
    *
    *     Test the input parameters.
    *
          INFO = 0
          IF (M.LT.0) THEN
              INFO = 1
          ELSE IF (N.LT.0) THEN
              INFO = 2
          ELSE IF (INCX.EQ.0) THEN
              INFO = 5
          ELSE IF (INCY.EQ.0) THEN
              INFO = 7
          ELSE IF (LDA.LT.MAX(1,M)) THEN
              INFO = 9
          END IF
          IF (INFO.NE.0) THEN
              CALL XERBLA('ZGERU ',INFO)
              RETURN
          END IF
    *
    *     Quick return if possible.
    *
          IF ((M.EQ.0) .OR. (N.EQ.0) .OR. (ALPHA.EQ.ZERO)) RETURN
    *
    *     Start the operations. In this version the elements of A are
    *     accessed sequentially with one pass through A.
    *
          IF (INCY.GT.0) THEN
              JY = 1
          ELSE
              JY = 1 - (N-1)*INCY
          END IF
          IF (INCX.EQ.1) THEN
              DO 20 J = 1,N
                  IF (Y(JY).NE.ZERO) THEN
                      TEMP = ALPHA*Y(JY)
                      DO 10 I = 1,M
                          A(I,J) = A(I,J) + X(I)*TEMP
       10             CONTINUE
                  END IF
                  JY = JY + INCY
       20     CONTINUE
          ELSE
              IF (INCX.GT.0) THEN
                  KX = 1
              ELSE
                  KX = 1 - (M-1)*INCX
              END IF
              DO 40 J = 1,N
                  IF (Y(JY).NE.ZERO) THEN
                      TEMP = ALPHA*Y(JY)
                      IX = KX
                      DO 30 I = 1,M
                          A(I,J) = A(I,J) + X(IX)*TEMP
                          IX = IX + INCX
       30             CONTINUE
                  END IF
                  JY = JY + INCY
       40     CONTINUE
          END IF
    *
          RETURN
    *
    *     End of ZGERU .
    *
          END