docs: def display_dp_matrix_attr(dp_matrix, attr_name):
      """
      show a value assocciated with an attribute for each
      DataProperty instance in the dp_matrix
      """
  
      print()
      print("---------- {:s} ----------".format(attr_name))
      for dp_list in dp_matrix:
          print([getattr(dp, attr_name) for dp in dp_list])