code: def diff_matrix(array_1, array_2, cell_size):
      
      array_1_norm = np.array(array_1) / np.array(cell_size, dtype=float)[None,:]
      array_2_norm = np.array(array_2) / np.array(cell_size, dtype=float)[None,:]
  
      return array_2_norm - array_1_norm
docs: :param array_1: supercell scaled positions respect unit cell
      :param array_2: supercell scaled positions respect unit cell
      :param cell_size: diference between arrays accounting for periodicity
      :return: