code: def potential_from_grid(self, grid):
          
          eta = (1.0 / self.scale_radius) * self.grid_to_grid_radii(grid) + 0j
          return np.real(2.0 * self.scale_radius * self.kappa_s * self.potential_func_sph(eta))
docs: Calculate the potential at a given set of arc-second gridded coordinates.
  
          Parameters
          ----------
          grid : grids.RegularGrid
              The grid of (y,x) arc-second coordinates the deflection angles are computed on.