Subsequently we let the particle distribution relax by evolving it isothermally within the slab.
Relaxation is necessary to decrease the numerical noise introduced by the random distribution.
We now have an ensemble of particles which does not possess any prefered directions and which represents a gas of constant density and temperature. Mass in units, where the total mass in the slab is unity. The test was performed for a total number of particles. Here, t is measured in units of the time necessary for the ionization front to cross the volume.