code: def kerr_lightring_velocity(chi):
      
      # If chi > 0.9996, the algorithm cannot solve the function
      if chi >= 0.9996:
          return brentq(kerr_lightring, 0, 0.8, args=(0.9996))
      else:
          return brentq(kerr_lightring, 0, 0.8, args=(chi))
docs: Return the velocity at the Kerr light ring