saxpys Subroutine

      subroutine saxpys(a,x,is,y,n)
      implicit double precision (a-h,o-z)
      dimension x(*),y(*)
      if (a==0.D0) return
      ix=1
      do i=1,n
        y(i)=y(i)+a*x(ix)
        ix=ix+is
      end do
      end subroutine saxpys