code: def save(self, filename=None):
          
          if filename is None:
              filename = "morse_smale_complex.json"
          with open(filename, "w") as fp:
              fp.write(self.to_json())
docs: Saves a constructed Morse-Smale Complex in json file
              @ In, filename, a filename for storing the hierarchical
              merging of features and the base level partitions of the
              data