Parameterize the eit instance by supplying one
        SIP spectrum and the area to apply to.

        Parameters
        ----------
        xmin : float
            Minimum x coordinate of the area
        xmax : float
            Maximum x coordinate of the area
        zmin : float
            Minimum z coordinate of the area
        zmax : float
            Maximum z coordinate of the area
        spectrum : sip_response
            SIP spectrum to use for parameterization

def set_area_to_sip_signature(self, xmin, xmax, zmin, zmax, spectrum):
        """Parameterize the eit instance by supplying one
        SIP spectrum and the area to apply to.

        Parameters
        ----------
        xmin : float
            Minimum x coordinate of the area
        xmax : float
            Maximum x coordinate of the area
        zmin : float
            Minimum z coordinate of the area
        zmax : float
            Maximum z coordinate of the area
        spectrum : sip_response
            SIP spectrum to use for parameterization

        """
        assert isinstance(spectrum, (sip_response, sip_response2))
        assert np.all(self.frequencies == spectrum.frequencies)
        for frequency, rmag, rpha in zip(
                self.frequencies, spectrum.rmag, spectrum.rpha):
            td = self.tds[frequency]
            pidm, pidp = td.a['forward_model']
            td.parman.modify_area(pidm, xmin, xmax, zmin, zmax, rmag)
            td.parman.modify_area(pidp, xmin, xmax, zmin, zmax, rpha)