Runs a uniform cosmological box with imposed abundances for a set of elements entering the Grackle cooling. The simulation is run with the Grackle thermochemistry, down to redhift 0 where the resulting abundances are compared with predictions. To run, configure swift with: ./configure --with-cooling=grackle_3 --with-grackle=$GRACKLE_ROOT Note : the script getPrimordialAbundances.py helps in the setting of the initial abundances.