Multiplicity of topological systems

Abstract

We define the topological multiplicity of an invertible topological system (X, T ) as the minimal number $k$ of real continuous functions $f_1, \cdots , f_k$ such that the functions $f_i\circ T^n$, $n \in \mathbb Z$, $1 \leq i \leq k$, span a dense linear vector space in the space of real continuous functions on $X$ endowed with the supremum norm. We study some properties of topological systems with finite multiplicity. After giving some examples, we investigate the multiplicity of subshifts with linear growth complexity.