Explorations of ternary cellular automata and ternary density classification problems

Abstract: While binary nearest-neighbour cellar automata (CA) have been studied in detail and from many different angles, the same cannot be said about ternary (three-state) CA rules. We present some results of our explorations of a small subset of the vast space of ternary rules, namely rules possessing additive invariants. We first enumerate rules with four different additive invariants, and then we investigate if any of them could be used to construct a two-rule solution of generalized density classification problem (DCP). We show that neither simple nor absolute classification is possible with a pair of ternary rules where the first rule is all-conserving and the second one is reducible to two states. Similar negative result holds for another version of DCP we propose: symmetric interval-wise DCP. Finally we show an example of a pair of rules which solve non-symmetric interval-wise DCP for initial configurations containing at least one zero.