def cartesian_from_miller(h, k, l)

      if self.miller_to_cart
        self.miller_to_cart*Vector[h, k, l]
      else
        nil
      end
    end
def cartesian_from_miller(h, k, l)

      if self.miller_to_cart
        self.miller_to_cart*Vector[h, k, l]
      else
        nil
      end
    end
Given a miller index (h,k,l),
 return a vector in cartesian coordinates pointing in that direction