Quick comment on the options relating to parallelization, controlled using vfoptions.parallel:
parallel=2 corresponds to gpu parallelization
parallel=1 corresponds to parallel cpus
parallel=0 uses just a single cpu
(you are unlikely to ever want to use parallel=0, it is there in case you are doing something more advanced and want to control at which level parallelization occurs)
For simulating the agent distribution there are no options [because it uses the Tan improvement which is always best done with sparse cpu matrices]
By default, VFI Toolkit asks if your computer if it has a gpu, if yes it sets parallel=2, if no it sets parallel=1. Note that most features beyond the very basics require gpu.
[Edit: updated late 2023 to reflect that now all agent distribution is done with Tan improvement there are no longer any relevant ‘parallel’ options for this]