code: def mass_fraction_within_radius(self, kwargs_lens, center_x, center_y, theta_E, numPix=100):
          
          x_grid, y_grid = util.make_grid(numPix=numPix, deltapix=2.*theta_E / numPix)
          x_grid += center_x
          y_grid += center_y
          mask = mask_util.mask_sphere(x_grid, y_grid, center_x, center_y, theta_E)
          kappa_list = []
          for i in range(len(kwargs_lens)):
              kappa = self.LensModel.kappa(x_grid, y_grid, kwargs_lens, k=i)
              kappa_mean = np.sum(kappa * mask) / np.sum(mask)
              kappa_list.append(kappa_mean)
          return kappa_list
docs: computes the mean convergence of all the different lens model components within a spherical aperture
  
          :param kwargs_lens: lens model keyword argument list
          :param center_x: center of the aperture
          :param center_y: center of the aperture
          :param theta_E: radius of aperture
          :return: list of average convergences for all the model components