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On the computability of rotation sets and their entropies

Published online by Cambridge University Press:  10 August 2018

MICHAEL A. BURR
Affiliation:
Department of Mathematical Sciences, Clemson University, Clemson, SC 29634, USA email burr2@clemson.edu, schmoll@clemson.edu
MARTIN SCHMOLL
Affiliation:
Department of Mathematical Sciences, Clemson University, Clemson, SC 29634, USA email burr2@clemson.edu, schmoll@clemson.edu
CHRISTIAN WOLF
Affiliation:
Department of Mathematics, The City College of New York and CUNY Graduate Center, New York, NY 10031, USA email cwolf@ccny.cuny.edu
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Abstract

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Let $f:X\rightarrow X$ be a continuous dynamical system on a compact metric space $X$ and let $\unicode[STIX]{x1D6F7}:X\rightarrow \mathbb{R}^{m}$ be an $m$-dimensional continuous potential. The (generalized) rotation set $\text{Rot}(\unicode[STIX]{x1D6F7})$ is defined as the set of all $\unicode[STIX]{x1D707}$-integrals of $\unicode[STIX]{x1D6F7}$, where $\unicode[STIX]{x1D707}$ runs over all invariant probability measures. Analogous to the classical topological entropy, one can associate the localized entropy $\unicode[STIX]{x210B}(w)$ to each $w\in \text{Rot}(\unicode[STIX]{x1D6F7})$. In this paper, we study the computability of rotation sets and localized entropy functions by deriving conditions that imply their computability. Then we apply our results to study the case where $f$ is a subshift of finite type. We prove that $\text{Rot}(\unicode[STIX]{x1D6F7})$ is computable and that $\unicode[STIX]{x210B}(w)$ is computable in the interior of the rotation set. Finally, we construct an explicit example that shows that, in general, $\unicode[STIX]{x210B}$ is not continuous on the boundary of the rotation set when considered as a function of $\unicode[STIX]{x1D6F7}$ and $w$. In particular, $\unicode[STIX]{x210B}$ is, in general, not computable at the boundary of $\text{Rot}(\unicode[STIX]{x1D6F7})$.

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Type
Original Article
Copyright
© Cambridge University Press, 2018