indexer for fixed status

        Returns
        -------
        fixed_indexer : pandas.Series

def fixed_indexer(self):
        """ indexer for fixed status

        Returns
        -------
        fixed_indexer : pandas.Series

        """
        #isfixed = self.pst.parameter_data.partrans == "fixed"
        isfixed = self.pst.parameter_data.partrans.\
            apply(lambda x : x in ["fixed","tied"])
        return isfixed.values