get the adjustable (not fixed or tied) parameter names

        Returns
        -------
        adj_par_names : list
            list of adjustable (not fixed or tied) parameter names

def adj_par_names(self):
        """ get the adjustable (not fixed or tied) parameter names

        Returns
        -------
        adj_par_names : list
            list of adjustable (not fixed or tied) parameter names

        """
        adj_names = []
        for t,n in zip(self.parameter_data.partrans,
                       self.parameter_data.parnme):
            if t.lower() not in ["tied","fixed"]:
                adj_names.append(n)
        return adj_names