A stability result for almost perfect matchings

Abstract

Let $n,k,s$ be three integers and $\beta$ be a sufficiently small positive number such that $k\ge 3$, $0<1/n\ll \beta \ll 1/k$ and $ks+k\le n\le (1+\beta )ks+k-2$. A $k$-graph is called non-trivial if it has no isolated vertex. In this paper, we determine the maximum number of edges in a non-trivial $k$-graph with $n$ vertices and matching number at most $s$. This result confirms a conjecture proposed by Frankl (On non-trivial families without a perfect matching, \emph{European J. Combin.}, \textbf{84} (2020), 103044) for the case when $s$ is sufficiently large.