Over time, the CPM has evolved from a specific model of cell sorting to a general framework with many extensions, some of which are partially or entirely off-lattice. Various cell behaviours, such as chemotaxis, elongation and haptotaxis can be incorporated by extending either the Hamiltonian, H, or the change in energy Δ Δ H . Auxiliary sub-lattices may be used to include additional spatial information, such as the concentrations of chemicals.