def add_homogeneous_model(self, magnitude, phase=0):
        """Add a homogeneous resistivity model to the tomodir. This is useful
        for synthetic measurements.

        Parameters
        ----------
        magnitude : float
            magnitude [Ohm m] value of the homogeneous model
        phase : float, optional
            phase [mrad] value of the homogeneous model


        Returns
        -------
        pid_mag : int
            ID value of the parameter set of the magnitude model
        pid_pha : int
            ID value of the parameter set of the phase model

        Note that the parameter sets are automatically registered as the
        forward models for magnitude and phase values.
        """
        if self.assignments['forward_model'] is not None:
            print('model already set, will overwrite')

        # generate distributions
        magnitude_model = np.ones(self.grid.nr_of_elements) * magnitude
        phase_model = np.ones(self.grid.nr_of_elements) * phase
        pid_mag = self.parman.add_data(magnitude_model)
        pid_pha = self.parman.add_data(phase_model)

        self.assignments['forward_model'] = [pid_mag, pid_pha]
        return pid_mag, pid_pha