def third_parameter(self, singular_value):
        """get the omitted parameter contribution to parameter error variance
             at a singular value (G * omitted_jco * Sigma_(omitted_pars) * omitted_jco^T * G^T)

        Parameters
        ----------
        singular_value : int
            singular value to calc third term at

        Returns
        -------
        third_parameter : pyemu.Cov
            0.0 if need_omitted is False

        """
        if self.__need_omitted is False:
            return 0.0
        self.log("calc third term parameter @" + str(singular_value))
        GZo = self.G(singular_value) * self.omitted_jco
        result = GZo * self.omitted_parcov * GZo.T
        self.log("calc third term parameter @" + str(singular_value))
        return result