Tight upper bound on the maximum anti-forcing numbers of graphs

Abstract

Let $G$ be a simple graph with a perfect matching. Deng and Zhang showed thatthe maximum anti-forcing number of $G$ is no more than the cyclomatic number.In this paper, we get a novel upper bound on the maximum anti-forcing number of$G$ and investigate the extremal graphs. If $G$ has a perfect matching $M$whose anti-forcing number attains this upper bound, then we say $G$ is anextremal graph and $M$ is a nice perfect matching. We obtain an equivalentcondition for the nice perfect matchings of $G$ and establish a one-to-onecorrespondence between the nice perfect matchings and the edge-involutions of$G$, which are the automorphisms $\alpha$ of order two such that $v$ and$\alpha(v)$ are adjacent for every vertex $v$. We demonstrate that all extremalgraphs can be constructed from $K_2$ by implementing two expansion operations,and $G$ is extremal if and only if one factor in a Cartesian decomposition of$G$ is extremal. As examples, we have that all perfect matchings of thecomplete graph $K_{2n}$ and the complete bipartite graph $K_{n, n}$ are nice.Also we show that the hypercube $Q_n$, the folded hypercube $FQ_n$ ($n\geq4$)and the enhanced hypercube $Q_{n, k}$ ($0\leq k\leq n-4$) have exactly $n$,$n+1$ and $n+1$ nice perfect matchings respectively.Comment: 15 pages, 7 figure