On the number of linear multipartite hypergraphs with given size

Abstract

For any given integer $r⩾3$, let $k=k(n)$ be an integer with $r⩽k⩽n$. A hypergraph is $r$-uniform if each edge is a set of $r$ vertices, and is said to be linear if two edges intersect in at most one vertex. Let $A_1,\dots ,A_k$ be a given $k$-partition of $[n]$ with $|A_i|=n_i⩾1$. An $r$-uniform hypergraph $H$ is called {\it $k$-partite} if each edge $e$ satisfies $|e\cap A_i|⩽1$ for $1⩽i⩽k$. In this paper, the number of linear $k$-partite $r$-uniform hypergraphs on $n\to \infty$ vertices is determined asymptotically when the number of edges is $m(n)=o(n^{\frac{4}{3}})$. For $k=n$, it is the number of linear $r$-uniform hypergraphs on vertex set $[n]$ with $m=o(n^{\frac{4}{3}})$ edges.

accepted by Graphs and Combinatorics. arXiv admin note: text overlap with arXiv:2007.12490