Generating infinite monoids of cellular automata

Abstract

For a group [Formula: see text] and a set [Formula: see text], let End[Formula: see text] be the monoid of all cellular automata over [Formula: see text], and let Aut[Formula: see text] be its group of units. By establishing a characterization of surjunctive groups in terms of the monoid End[Formula: see text], we prove that the rank of End[Formula: see text] (i.e. the smallest cardinality of a generating set) is equal to the rank of Aut[Formula: see text] plus the relative rank of Aut[Formula: see text] in End[Formula: see text], and that the latter is infinite when [Formula: see text] has an infinite decreasing chain of normal subgroups of finite index, condition which is satisfied, for example, for any infinite residually finite group. Moreover, when [Formula: see text] is a vector space over a field [Formula: see text], we study the monoid [Formula: see text] of all linear cellular automata over [Formula: see text] and its group of units [Formula: see text]. We show that if [Formula: see text] is an indicable group and [Formula: see text] is finite-dimensional, then [Formula: see text] is not finitely generated; however, for any finitely generated indicable group [Formula: see text], the group [Formula: see text] is finitely generated if and only if [Formula: see text] is finite.