r_shift Subroutine

      subroutine r_shift(r,n,k)
      implicit double precision (a-h,o-z)
      dimension r(*)
      if (k>0) then
        do i=1,n
          r(i)=r(i+k)
        end do
      else if (k<0) then
        do i=n,1,-1
          r(i)=r(i+k)
        end do
      end if
      end subroutine r_shift