Compute the stress transfer function.

        Parameters
        ----------
        lin : :class:`~site.Location`
            Location of input
        lout : :class:`~site.Location`
            Location of output. Note that this would typically be midheight
            of the layer.

def calc_stress_tf(self, lin, lout, damped):
        """Compute the stress transfer function.

        Parameters
        ----------
        lin : :class:`~site.Location`
            Location of input
        lout : :class:`~site.Location`
            Location of output. Note that this would typically be midheight
            of the layer.

        """
        tf = self.calc_strain_tf(lin, lout)
        if damped:
            # Scale by complex shear modulus to include the influence of
            # damping
            tf *= lout.layer.comp_shear_mod
        else:
            tf *= lout.layer.shear_mod

        return tf