The entropy theory of symbolic extensions

• 成果类型: Article
• 署名作者: Boyle, M; Downarowicz, T
• 署名单位: University System of Maryland; University of Maryland College Park; Wroclaw University of Science & Technology
• 刊物名称: INVENTIONES MATHEMATICAE
• ISSN/ISSBN: 0020-9910
• DOI: 10.1007/s00222-003-0335-2
• 发表日期: 2004
• 页码: 119-161
• 关键词: variational principle; Conditional entropy; transformations; covers

摘要

Fix a topological system (X, T), with its space K(X, T) of T-Invariant Borel probabilities. If (Y, S) is a symbolic system (subshift) and phi : (Y, S) (X, T) is a topological extension (factor map), then the function h(ext)(phi) on K(X, T) which assigns to each mu the maximal entropy of a measure nu on Y mapping to mu is called the extension entropy function of phi. The infimum of such functions over all symbolic extensions is called the symbolic extension entropy function and is denoted by h(sex). In this paper we completely characterize these functions in terms of functional analytic properties of an entropy structure on (X, T). The entropy structure H is a sequence of entropy functions h(k) defined with respect to a refining sequence of partitions of X (or of X x Z, for some auxiliary system (Z, R) with simple dynamics) whose boundaries have measure zero for all the invariant Borel probabilities. We develop the functional analysis and computational techniques to produce many dynamical examples; for instance, we resolve in the negative the question of whether the infimum of the topological entropies of symbolic extensions of (X, T) must always be attained, and we show that the maximum value of h(sex) need not be achieved at an ergodic measure. We exhibit several characterizations of the asymptotically h-expansive systems of Misiurewicz, which emerge as a fundamental natural class in the context of the entropy structure. The results of this paper are required for the Downarowicz-Newhouse results [DN] on smooth dynamical systems.