SUBROUTINE SGERF  ( M, N, ALPHA, X, INCX, Y, INCY, A, LDA )

*     .. Scalar Arguments ..

      REAL               ALPHA

      INTEGER            INCX, INCY, LDA, M, N

*     .. Array Arguments ..

      REAL               A( LDA, * ), X( * ), Y( * )

*     ..

*

*  Purpose

*  =======

*

*  SGER   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.

*

*  Parameters

*  ==========

*

*  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  - REAL            .

*           On entry, ALPHA specifies the scalar alpha.

*           Unchanged on exit.

*

*  X      - REAL             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      - REAL             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      - REAL             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 ..

      REAL               ZERO

      PARAMETER        ( ZERO = 0.0E+0 )

*     .. Local Scalars ..

      REAL               TEMP

      INTEGER            I, INFO, IX, J, JY, KX

*     .. External Subroutines ..

      EXTERNAL           XERBLA

*     .. Intrinsic Functions ..

      INTRINSIC          MAX

*     ..

*     .. Executable Statements ..

*

*     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( 'SGER  ', 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 SGER  .

*

      END