docs: def store(self, filename=None, label=None, desc=None, date=None):
          """Store object to mat-file. TODO: determine format specification
          """
          date = datetime.now() if date is None else date
          filename = filename if filename else date.replace(microsecond=0).isoformat() + '.mat'
  
          def storeWithFileLikeObject(file_like):
              content = {
                  'elapsed_time': self.elapsed_time,
                  'solution': self.solution,
                  'version': version(),
              }
              self.model.store(file_like, label, desc, date)
              savemat(file_like, content, appendmat=True)
  
          if isinstance(filename, file):
              storeWithFileLikeObject(filename)
          else:
              with open(filename, 'wb') as f:
                  storeWithFileLikeObject(f)