code: def pars_in_groups(self):
          
          pargp = self.par_groups
          allpars = dict()
          for cpg in pargp:
              allpars[cpg] = [i for i in self.parameter_data.loc[self.parameter_data.pargp == cpg, 'parnme']]
          return allpars
docs: return a dictionary of  parameter names in each parameter group.
  
          Returns:
              dictionary