return a dictionary of  parameter names in each parameter group.

        Returns:
            dictionary

def pars_in_groups(self):
        """
        return a dictionary of  parameter names in each parameter group.

        Returns:
            dictionary
        """
        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