Enumerating simplicial decompositions of surfaces with boundaries

Abstract

It is well-known that the triangulations of the disc with $n+2$ vertices on its boundary are counted by the $n$th Catalan number $C(n)=\frac{1}{n+1}\left(\genfrac{}{}{0ex}{}{2n}{n}\right)$. This paper deals with the generalisation of this problem to any arbitrary compact surface $S$ with boundaries. We obtain the asymptotic number of simplicial decompositions of the surface $S$ with $n$ vertices on its boundary. More generally, we determine the asymptotic number of dissections of $S$ when the faces are $\delta$-gons with $\delta$ belonging to a set of admissible degrees $\Delta \subseteq \{3,4,5,...\}$. We also give the limit laws of certain parameters of such dissections.