A principle in dynamic coarse graining–Onsager principle and its applications
Center of Soft Matter Physics and its Applications, Beihang University, Beijing, China
Received: 19 April 2016
Revised: 9 June 2016
Published online: 18 July 2016
Dynamic coarse graining is a procedure to map a dynamical system with large degrees of freedom to a system with smaller degrees of freedom by properly choosing coarse grained variables. This procedure has been conducted mainly by empiricisms. In this paper, I will discuss a theoretical principle which may be useful for this procedure. I will discuss how to choose coarse grained variables (or slow variables), and how to set up their evolution equations. To this end, I will review the classical example of dynamic coarse graining, i.e., the Brownian motion theory, and show a variational principle for the evolution of the slow variables. The principle, called the Onsager principle, is useful not only to derive the evolution equations, but also to solve the problems.
© EDP Sciences, Springer-Verlag, 2016