def test_s_shunt_element(self):
        """
        Shunt elements of admittance Y:

        ○---------○
            |
           [Y]
            |
        ○---------○

        have S matrix of the form:
        [ -Y Z0 / (Y Z0 + 2)     2/(Y Z0 + 2) ]
        [ 2/(Y Z0 + 2)          Z/Z0 / (Y Z0 + 2) ]
        """
        R = 1.0  # Ohm
        ntw = self.dummy_media.shunt(self.dummy_media.resistor(R)**self.dummy_media.short())
        Z0 = self.dummy_media.z0
        S11 = -(1/R*Z0) / (1/R*Z0 + 2)
        S21 = 2 / (1/R*Z0 + 2)
        npy.testing.assert_array_almost_equal(ntw.s[:,0,0], S11)
        npy.testing.assert_array_almost_equal(ntw.s[:,0,1], S21)
        npy.testing.assert_array_almost_equal(ntw.s[:,1,0], S21)
        npy.testing.assert_array_almost_equal(ntw.s[:,1,1], S11)