get the number of adjustable parameters (not fixed or tied)

        Returns
        -------
        npar_adj : int
            the number of adjustable parameters

def npar_adj(self):
        """get the number of adjustable parameters (not fixed or tied)

        Returns
        -------
        npar_adj : int
            the number of adjustable parameters

        """
        pass
        np = 0
        for t in self.parameter_data.partrans:
            if t not in ["fixed", "tied"]:
                np += 1
        return np