def VoltageAmplifierThreePortDenom(G, Zi, Zo):
    """symbolic three port voltage amplifier denominator
    @param G string voltage gain
    @param Zi string input impedance
    @param Zo string output impedance
    @return the denominator element common in the s-parameter matrix as a string
    containing LaTeX or ASCII strings for each element.
    @note strings can be any valid LaTeX
    @note this is the symbolic version of SignalIntegrity.Lib.Devices.VoltageAmplifier.VoltageAmplifierThreePort
    @see VoltageAmplifierThreePortWithoutDenom
    """
    D = ('-' + Zo + '\\cdot ' + Zi + '-2\\cdot ' + Zo +
        '\\cdot Z0-2\\cdot ' + Zi + '\\cdot Z0-3\\cdot Z0^2+' + G +
        '\\cdot ' + Zi + '\\cdot Z0')
    return D
