Changing the low-energy boundary conditions of Table C.1 modifies the numerical result obtained for u. In this plot, the variations of the proton flux relative to the fiducial case of Fig. D.2 are displayed as a function of kinetic energy E_k. Notice that all conditions yield the same flux above 3 MeV. Close to the boundary, prescriptions L1 and L4 generate wiggles and the flux becomes inaccurate. Prescriptions L2 and L3 (fiducial) yield the same result.