code: def nfwParam_physical(self, M, c):
          
          r200 = self.nfw_param.r200_M(M * self.h) / self.h * self.a_z(self.z_lens)  # physical radius r200
          rho0 = self.nfw_param.rho0_c(c) * self.h**2 / self.a_z(self.z_lens)**3 # physical density in M_sun/Mpc**3
          Rs = r200/c
          return rho0, Rs, r200
docs: returns the NFW parameters in physical units
          :param M: physical mass in M_sun
          :param c: concentration
          :return: