Uniform Random Planar Graphs with Degree Constraints

Abstract

Random planar graphs have been the subject of much recent work. Many basic properties of the standard uniform random planar graph P_{n}, by which we mean a graph chosen uniformly at random from the set of all planar graphs with vertex set {1,2,...,n}, are now known, and variations on this standard random graph are also attracting interest. Prominent among the work on P_{n} have been asymptotic results for the probability that P_{n} will be connected or contain given components/subgraphs. Such progress has been achieved through a combination of counting arguments and a generating function approach. More recently, attention has turned to P_{n,m}, the graph taken uniformly at random from the set of all planar graphs on {1,2,...,n} with exactly m(n) edges (this can be thought of as a uniform random planar graph with a constraint on the average degree). The case when m(n) = qn for fixed q in (1,3) has been investigated, and results obtained for the events that P_{n,qn} will be connected and that P_{n,qn} will contain given subgraphs. In Part I of this thesis, we use elementary counting arguments to extend the current knowledge of P_{n,m}. We investigate the probability that P_{n,m} will contain given components, the probability that P_{n,m} will contain given subgraphs, and the probability that P_{n,m} will be connected, all for general m(n), and show that there is different behaviour depending on which `region' the ratio m(n)/n falls into. In Part II, we investigate the same three topics for a uniform random planar graph with constraints on the maximum and minimum degrees.