smooth_cutoff Subroutine

pure subroutine smooth_cutoff(r, cutoff, width, sw, dswdr)
   real(wp), intent(in) :: r
   real(wp), intent(in) :: cutoff
   real(wp), intent(in) :: width
   real(wp), intent(out) :: sw
   real(wp), intent(out) :: dswdr

   real(wp) :: inner, x

   if (width <= 0.0_wp .or. width >= cutoff) then
      sw = 1.0_wp
      dswdr = 0.0_wp
   else
      inner = cutoff - width
      if (r <= inner) then
         sw = 1.0_wp
         dswdr = 0.0_wp
      else if (r >= cutoff) then
         sw = 0.0_wp
         dswdr = 0.0_wp
      else
         x = (cutoff - r) / width
         sw = x**3 * (10.0_wp + x*(-15.0_wp + 6.0_wp*x))
         dswdr = -30.0_wp * x**2 * (1.0_wp - x)**2 / width
      end if
   end if
end subroutine smooth_cutoff