code: def nfwPot(self, R, Rs, rho0, r_trunc):
          
          x = R / Rs
          tau = float(r_trunc) / Rs
          hx = self._h(x, tau)
          return 2 * rho0 * Rs ** 3 * hx
docs: lensing potential of NFW profile
  
          :param R: radius of interest
          :type R: float/numpy array
          :param Rs: scale radius
          :type Rs: float
          :param rho0: density normalization (characteristic density)
          :type rho0: float
          :return: Epsilon(R) projected density at radius R