code: def nfw_physical2angle(self, M, c):
          
          rho0, Rs, r200 = self.nfwParam_physical(M, c)
          Rs_angle = Rs / self.D_d / const.arcsec  # Rs in arcsec
          theta_Rs = rho0 * (4 * Rs ** 2 * (1 + np.log(1. / 2.)))
          return Rs_angle,  theta_Rs / self.epsilon_crit / self.D_d / const.arcsec
docs: converts the physical mass and concentration parameter of an NFW profile into the lensing quantities
  
          :param M: mass enclosed 200 rho_crit in units of M_sun
          :param c: NFW concentration parameter (r200/r_s)
          :return: theta_Rs (observed bending angle at the scale radius, Rs_angle (angle at scale radius) (in units of arcsec)