Compensation functions for factors of shifts of finite type

Abstract

We consider an infinite-to-one factor map from an irreducible shift of finite type X to a sofic shift Y. A compensation function relates equilibrium states on X to equilibrium states on Y. The p-Dini condition is given as a way of measuring the smoothness of a continuous function, with 1-Dini corresponding to functions with summable variation. Two types of compensation functions are defined in terms of this condition. We show that the relative equilibrium states of a 1-Dini function f over a fully supported invariant measure on Y are themselves fully supported, and have positive relative entropy. We then show that there exists a compensation function which is p-Dini for all p > 1 which has relative equilibrium states supported on a finite-to-one subfactor.