A function of the single independent variable after
        partially evaluating `scipy_data_fitting.Fit.function` at
        the `scipy_data_fitting.Fit.fitted_parameters`.

def fitted_function(self):
        """
        A function of the single independent variable after
        partially evaluating `scipy_data_fitting.Fit.function` at
        the `scipy_data_fitting.Fit.fitted_parameters`.
        """
        function = self.function
        fitted_parameters = self.fitted_parameters
        return lambda x: function(x, *fitted_parameters)