docs: def store(self, filename=None, label=None, desc=None, date=None):
          """Store object to mat-file. TODO: determine format specification
          """
          date = date if date else datetime.now()
          date = date.replace(microsecond=0).isoformat()
          filename = filename if filename else date + '.mat'
  
          matfile = {
              'model': str(type(self)),
              'date': date,
              'dim': len(self.init_sol.shape),
              'dimlesses': self.coeffs,
              'init_solution': self.init_sol,
              'num_iters': self.num_iters,
              'num_nodes': self.num_nodes,
              'order': self.order,
              'originals': self.originals,
              'pumping': self.getPumping(),
              'spatial_step': self.dx,
              'time_step': self.dt,
          }
  
          if desc:
              matfile['desc'] = desc
          if label:
              matfile['label'] = label
  
          savemat(filename, matfile)