CR proton flux Φ_p is plotted as a function of kinetic energy E_k. The long dashed-dotted and solid black curves stand respectively for the approximations u⁰ and u_loss. The exact solution u is derived numerically assuming boundary conditions L3 and H4. The long dashed orange and short dashed purple curves correspond to different methods used to solve transport Eq. (4). Protons are injected with a rate where N_p = 5.8 × 10⁻¹¹ protons cm⁻³ GeV⁻¹ Myr⁻¹ and α = 2.3. With these values, we get Φ_p in rough agreement with the Voyager 1 (Stone et al. 2013), PAMELA (Adriani et al. 2011) and AMS-02 (Aguilar et al. 2015a) data.