code: def I_R_simga2(self, R, kwargs_mass, kwargs_light, kwargs_anisotropy):
          
          R = max(R, self._min_integrate)
          if self._log_int is True:
              min_log = np.log10(R+0.001)
              max_log = np.log10(self._max_integrate)
              r_array = np.logspace(min_log, max_log, self._interp_grid_num)
              dlog_r = (np.log10(r_array[2]) - np.log10(r_array[1])) * np.log(10)
              IR_sigma2_dr = self._integrand_A15(r_array, R, kwargs_mass, kwargs_light, kwargs_anisotropy) * dlog_r * r_array
          else:
              r_array = np.linspace(R+0.001, self._max_integrate, self._interp_grid_num)
              dr = r_array[2] - r_array[1]
              IR_sigma2_dr = self._integrand_A15(r_array, R, kwargs_mass, kwargs_light, kwargs_anisotropy) * dr
          IR_sigma2 = np.sum(IR_sigma2_dr)
          return IR_sigma2
docs: equation A15 in Mamon&Lokas 2005 as a logarithmic numerical integral (if option is chosen)
          modulo pre-factor 2*G
  
          :param R: 2d projected radius (in angular units)
          :param kwargs_mass: mass model parameters (following lenstronomy lens model conventions)
          :param kwargs_light: deflector light parameters (following lenstronomy light model conventions)
          :param kwargs_anisotropy: anisotropy parameters, may vary according to anisotropy type chosen.
              We refer to the Anisotropy() class for details on the parameters.
          :return: integral of A15 in Mamon&Lokas 2005