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