code: def spacings(self):
          
          result_invsq = (self.reciprocal**2).sum(axis=0)
          result = np.zeros(3, float)
          for i in range(3):
              if result_invsq[i] > 0:
                  result[i] = result_invsq[i]**(-0.5)
          return result
docs: Computes the distances between neighboring crystal planes