1. A data processor for processing data of a plurality of sites of a lattice to simulate an interactive process across the lattice, the data processor comprising: storage means for storing element representations of plural elements, including moving elements of plural possible energy states, for each of plural sites of a lattice; interaction processing means for processing, for each lattice site, the element representations to generate second element representations which reflect a transfer of energy between elements of different energy states; and move processing means for processing the representations across the lattice to generate new representations which reflect movement of elements in the lattice to new sites.