The Minimum Number of Plane Graphs for Sets with Small Hulls

Abstract

Let $\mathcal{P}$ be a set of $n$ points in $\mathbb{R}^2$, with a convex hull of size $O(n/\log n)$. We prove that $Ω(12.24^n)$ plane graphs can be drawn on $\mathcal{P}$, the first non-trivial bound for this problem. We also show that a random plane graph, uniformly chosen from the set of all plane graphs of $\mathcal{P}$, has at most $n/12.24$ isolated vertices. This improves upon a previous bound of $n/10.18$. Our analysis is based on studying the expected vertex potentials in a random plane graph. The potential of a vertex is its degree plus the number of vertices visible from it. We show that this quantity can be used to study numbers of plane graphs.