double precision function ddot	(	integer	N,
		double precision, dimension(*)	DX,
		integer	INCX,
		double precision, dimension(*)	DY,
		integer	INCY
	)

DDOT

Purpose:

    DDOT forms the dot product of two vectors.
    uses unrolled loops for increments equal to one.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date

December 2016

Further Details:

     jack dongarra, linpack, 3/11/78.
     modified 12/3/93, array(1) declarations changed to array(*)

Definition at line 53 of file ddot.f.

*
*  -- Reference BLAS level1 routine (version 3.7.0) --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     December 2016
*
*     .. Scalar Arguments ..
      INTEGER incx,incy,n
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION dx(*),dy(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION dtemp
      INTEGER i,ix,iy,m,mp1
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC mod
*     ..
      ddot = 0.0d0
      dtemp = 0.0d0
      IF (n.LE.0) RETURN
      IF (incx.EQ.1 .AND. incy.EQ.1) THEN
*
*        code for both increments equal to 1
*
*
*        clean-up loop
*
         m = mod(n,5)
         IF (m.NE.0) THEN
            DO i = 1,m
               dtemp = dtemp + dx(i)*dy(i)
            END DO
            IF (n.LT.5) THEN
               ddot=dtemp
            RETURN
            END IF
         END IF
         mp1 = m + 1
         DO i = mp1,n,5
          dtemp = dtemp + dx(i)*dy(i) + dx(i+1)*dy(i+1) +
     $            dx(i+2)*dy(i+2) + dx(i+3)*dy(i+3) + dx(i+4)*dy(i+4)
         END DO
      ELSE
*
*        code for unequal increments or equal increments
*          not equal to 1
*
         ix = 1
         iy = 1
         IF (incx.LT.0) ix = (-n+1)*incx + 1
         IF (incy.LT.0) iy = (-n+1)*incy + 1
         DO i = 1,n
            dtemp = dtemp + dx(ix)*dy(iy)
            ix = ix + incx
            iy = iy + incy
         END DO
      END IF
      ddot = dtemp
      RETURN

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