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