def _compute_term_3(self, C, mag, R):
        """
        (a12 + a13.*M + a14.*M.*M + a15.*M.*M.*M).*(d(r).^2)
        """
        return (
            (C['a12'] + C['a13'] * mag + C['a14'] * np.power(mag, 2) +
             C['a15'] * np.power(mag, 3)) * np.power(R, 2)
        )