Cellular automata models of reaction-diffusion and excitable media capture essential aspects of natural media in a computationally tractable form. A cellular automaton is a lattice of uniform finite automata. The automata evolve in a discrete time and take their states from a finite set. All automata of the lattice update their states simultaneously. Every automaton calculates its next state depending on the states of its closest neighbors.
We refer a reader to an excellent book by Chopard and Droz (1999) to gain background knowledge on cellular automata simulations of physical phenomena; see also Adamatzky (2001) for specific cellularautomaton models of reaction-diffusion computing.