English

A weighted cycle-localization inequality

Combinatorics 2026-03-20 v1

Abstract

In 1959, Erd\H{o}s and Gallai showed that every 22-connected graph GG contains a cycle of length at least 2E(G)V(G)1\frac{2|E(G)|}{|V(G)|-1}. This result was subsequently extended to weighted graphs by Bondy and Fan in 1991. A natural local variant of this problem arises by considering, for each edge eE(G)e\in E(G), the quantity c(e)c(e), defined as the length of the longest cycle in GG containing ee (with c(e)=2c(e)=2 if ee is a bridge). Zhao and Zhang recently proved that for every graph GG on nn vertices satisfies eE(G)1c(e)n12.\sum_{e\in E(G)}\frac{1}{c(e)}\le \frac{n-1}{2}. In this note, we establish a weighted generalization of this inequality. For a weighted graph (G,w)(G,w) with positive edge weights, let Cw(e)C_w(e) denote the maximum weight of a cycle containing ee (setting Cw(e)=2w(e)C_w(e)=2w(e) if ee is a bridge). We prove that eE(G)w(e)Cw(e)n12. \sum_{e\in E(G)}\frac{w(e)}{C_w(e)}\le \frac{n-1}{2}. Our result can be viewed as a weighted local analogue of the Bondy-Fan theorem, thereby establishing a correspondence between the global and local perspectives. Furthermore, we present a broad class of graphs attaining equality and derive necessary conditions for equality.

Keywords

Cite

@article{arxiv.2603.18536,
  title  = {A weighted cycle-localization inequality},
  author = {Jiangdong Ai and Bin Chen and Ming Chen and Tianxiao Zhao},
  journal= {arXiv preprint arXiv:2603.18536},
  year   = {2026}
}
R2 v1 2026-07-01T11:27:32.537Z