Evolutionary spatial games with mean-field interactions

We introduce a mean-field term to an evolutionary spatial game model.
Namely, we consider the game of Nowak and May, based on the Prisoner's
dilemma, and augment the game rules by a mean-field term. This way,
the agent operates based on local information from its neighbors and
non-local information via the mean-field coupling.
We simulate the model and construct the steady-state phase diagram,
which shows significant differences due to the mean-field term.