We start by defining what a cellular automaton is and then consider some standard examples, mainly developed within the physical sciences. These can be adapted to model phenomena such as the spread of gossip and the formation of cliques. This leads us to a more detailed consideration of some social science models, on ethnic segregation, relations between political states and attitude change. Finally, we show how CA models can be programmed. In social simulations, cells may represent individuals or collective actors such as countries.
Time advances through the simulation in discrete steps.
After each time step, the state of each cell may change. The state of a cell at any time step is determined by a set of rules which specify how that state depends on the previous state of that cell and the states of the cell's immediate neighbours. The same rules are used to update the state of every cell in the grid. The model is therefore homogeneous with respect to the rules. Because the rules only make reference to the states of other cells in a cell's neighbourhood, cellular automata are best used to model situations where the interactions are local.