def nfwPot(self, R, Rs, rho0, r_trunc):
        """
        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
        """
        x = R / Rs
        tau = float(r_trunc) / Rs
        hx = self._h(x, tau)
        return 2 * rho0 * Rs ** 3 * hx