This example runs a cosmological simulation using 32^3 particles with
the gas density set to the mean baryonic density and no fluctuations
(i.e. sigma_8 == 0). The simulation is run without gravity to prevent
any numerical fluctuation from growing. 

The gas is cooling/heating via its interaction with the UV background
set by the cooling model. In practice, the gas will follow the
equilibirum temperature of the model at all z and only be affected by
reionization. Assuming primoridal abundance, the temperature of the
gas at different redshifts can be compared to temperatures inferred
from observations of the Lyman-alpha forrest. The plotting script runs
this comparison once the simulation has completed.

Within the EAGLE cooling model, interesting changes are to switch
on/off the Helium II reionisation (or change its redshift) as well as
the position and amount of energy injected by Hydrogen
reionisation. The parameters given the YAML file are the ones used for
actual EAGLE galaxy formation runs.