Enumeration of dihypergraphs with specified degrees and edge types

Abstract: A dihypergraph consists of a set of vertices and a set of directed hyperedges, where each directed hyperedge is partitioned into a head and a tail. Directed hypergraphs are useful in many applications, including the study of chemical reactions or relational databases. We provide asymptotic formulae for the number of directed hypergraphs with given in-degree sequence, out-degree sequence, and the head and tail sizes of all directed hyperedges specified. Our formulae hold when none of the following parameters are too large: the maximum out-degree, the maximum in-degree, the maximum head size and the maximum tail size. If one of the four parameter sequences is near-regular, for example if each directed hyperedge has a tail of roughly the same size, then our formula is obtained using a simple argument based on existing asymptotic enumeration results for sparse bipartite graphs with given degree sequences. We also establish the same formula without the regularity assumption but with a larger relative error term, using a martingale argument.