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2013
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# Gennadii Piftankin

Gubkina str. 8, Moscow, 119991 Russia
Steklov Mathematical Institute RAS

## Publications:

 Piftankin G. N., Treschev D. V. Coarse-grained entropy in dynamical systems 2010, vol. 15, no. 4-5, pp.  575-597 Abstract Let $M$ be the phase space of a physical system. Consider the dynamics, determined by the invertible map $T: M \to M$, preserving the measure $\mu$ on $M$. Let $\nu$ be another measure on $M$, $d\nu = \rho d\mu$. Gibbs introduced the quantity $s(\rho) = − \int \rho \log \rho d \mu$ as an analog of the thermodynamical entropy. We consider a modification of the Gibbs (fine-grained) entropy the so called coarse-grained entropy. First we obtain a formula for the difference between the coarse-grained and Gibbs entropy. The main term of the difference is expressed by a functional usually referenced to as the Fisher information. Then we consider the behavior of the coarse-grained entropy as a function of time. The dynamics transforms $\nu$ in the following way: $\nu \mapsto \nu_n$, $d\nu_n = \rho \circ T^{-n} d\mu$. Hence, we obtain the sequence of densities $\rho_n = \rho \circ T^{-n}$ and the corresponding values of the Gibbs and the coarse-grained entropy. We show that while the Gibbs entropy remains constant, the coarse-grained entropy has a tendency to a growth and this growth is determined by dynamical properties of the map $T$. Finally, we give numerical calculation of the coarse-grained entropy as a function of time for systems with various dynamical properties: integrable, chaotic and with mixed dynamics and compare these calculation with theoretical statements. Keywords: Gibbs entropy, nonequilibrium thermodynamics, Lyapunov exponents, Gibbs ensemble Citation: Piftankin G. N., Treschev D. V.,  Coarse-grained entropy in dynamical systems, Regular and Chaotic Dynamics, 2010, vol. 15, no. 4-5, pp. 575-597 DOI:10.1134/S156035471004012X