1D advection test for radiative transfer. Test that your method is TVD and the propagation speed of the photons is correct. The ICs set up three photon groups: - The first is a top hat function initial distribution where outside values are zero. - The second is a top hat function initial distribution where outside values are nonzero. This distinction is important to test because photon energies can't be negative, so these cases need to be tested individually. - the third is a smooth Gaussian. This way, you can test multiple initial condition scenarios simultaneously. There are no stars to act as sources. Also make sure that you choose your photon frequencies in a way that doesn't interact with gas! The ICs are created to be compatible with GEAR_RT and SPHM1RT. Recommended configuration: GEAR_RT (with gizmo-mfv solver): --with-rt=GEAR_3 --with-rt-riemann-solver=GLF --with-hydro-dimension=1 --with-hydro=gizmo-mfv \ --with-riemann-solver=hllc --with-stars=GEAR --with-feedback=none --with-grackle=$GRACKLE_ROOT GEAR_RT (with sphenix SPH solver): --with-rt=GEAR_3 --with-rt-riemann-solver=GLF --with-hydro-dimension=1 --with-hydro=sphenix --with-stars=GEAR --with-feedback=none --with-grackle=$GRACKLE_ROOT SPHM1RT: --with-rt=SPHM1RT_4 --with-hydro-dimension=1 --with-stars=basic --with-sundials=$SUNDIALS_ROOT IMPORTANT: Need SUNDIALS version = 5 . SUNDIALS_ROOT is the root directory that contains the lib and include directories, e.g. on cosma: SUNDIALS_ROOT=/cosma/local/sundials/5.1.0/ Note that in SPHM1RT any (SPH) hydro scheme is compatible. Note that if you want to use a reduced speed of light for this test, you also need to adapt the fluxes in the initial conditions! They are generated assuming that the speed of light is not reduced.