double precision function ddotf(n,dx,incx,dy,incy)

c

c     forms the dot product of two vectors.

c     uses unrolled loops for increments equal to one.

c     jack dongarra, linpack, 3/11/78.

c     modified 12/3/93, array(1) declarations changed to array(*)

c

      double precision dx(*),dy(*),dtemp

      integer i,incx,incy,ix,iy,m,mp1,n

c

      ddotf = 0.0d0

      dtemp = 0.0d0

      if(n.le.0)return

      if(incx.eq.1.and.incy.eq.1)go to 20

c

c        code for unequal increments or equal increments

c          not equal to 1

c

      ix = 1

      iy = 1

      if(incx.lt.0)ix = (-n+1)*incx + 1

      if(incy.lt.0)iy = (-n+1)*incy + 1

      do 10 i = 1,n

        dtemp = dtemp + dx(ix)*dy(iy)

        ix = ix + incx

        iy = iy + incy

   10 continue

      ddotf = dtemp

      return

c

c        code for both increments equal to 1

c

c

c        clean-up loop

c

   20 m = mod(n,5)

      if( m .eq. 0 ) go to 40

      do 30 i = 1,m

        dtemp = dtemp + dx(i)*dy(i)

   30 continue

      if( n .lt. 5 ) go to 60

   40 mp1 = m + 1

      do 50 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)

   50 continue

   60 ddotf = dtemp

      return

      end