def lmfit_parameter_values(self, params):
        """
        `params` is a [`lmfit.Parameters`][1] object.

        Returns a tuple containing the values of the parameters in `params`.

        The order is determined by sorting the parameter keys alphabetically.

        [1]: http://lmfit.github.io/lmfit-py/parameters.html#the-parameters-class

        """
        return tuple( params[key].value for key in sorted(params) )