Burnside process on parking functions and Dyck paths

Abstract

Let $G$ be a finite group acting on a finite set $X$. This group action splits $X$ into disjoint orbits. The Burnside process is a Markov chain on $X$ which has a uniform stationary distribution when the chain is projected to orbits. We initiate the study of the Burnside process on Catalan structures. We consider two special cases: the first where the state space is the set of parking functions of length $n$ and $G = S_n$ is the symmetric group on $[n]$, such that $G$ acts by permuting coordinates, and the second where the state space is the set of labeled Dyck paths of length $2n$ and $G = S_n$ acts by permuting labels. The resulting Burnside processes give novel algorithms for sampling, respectively, an increasing parking function and a Dyck path approximately uniformly at random. Our main result shows that both processes are rapidly mixing, with mixing times upper bounded by $O(n \log n)$. As an application, we show how our Burnside process can be used to sample triangulations of an $(n+2)$-gon approximately uniformly at random.