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Finite entropy for multidimensional cellular automata

Published online by Cambridge University Press:  01 August 2008

School of Mathematical Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel (email:


Let where is a countable group and S is a finite set. A cellular automaton (CA) is an endomorphism T:XX (continuous, commuting with the action of ). Shereshevsky [Expansiveness, entropy and polynomial growth for groups acting on subshifts by automorphisms. Indag. Math. (N.S.)4(2) (1993), 203–210] proved that for with d>1 no CA can be forward expansive, raising the following conjecture: for , d>1, the topological entropy of any CA is either zero or infinite. Morris and Ward [Entropy bounds for endomorphisms commuting with K actions. Israel J. Math. 106 (1998), 1–11] proved this for linear CAs, leaving the original conjecture open. We show that this conjecture is false, proving that for any d there exists a d-dimensional CA with finite, non-zero topological entropy. We also discuss a measure-theoretic counterpart of this question for measure-preserving CAs.

Research Article
Copyright © 2008 Cambridge University Press

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