English

Generalized Tur\'an problems for a matching and long cycles

Combinatorics 2024-12-30 v1

Abstract

Let F\mathscr{F} be a family of graphs. A graph GG is F\mathscr{F}-free if GG does not contain any FFF\in \mathcal{F} as a subgraph. The general Tur\'an number, denoted by ex(n,H,F)ex(n, H,\mathscr{F}), is the maximum number of copies of HH in an nn-vertex F\mathscr{F}-free graph. Then ex(n,K2,F)ex(n, K_2,\mathscr{F}), also denote by ex(n,F)ex(n, \mathscr{F}), is the Tur\'an number. Recently, Alon and Frankl determined the exact value of ex(n,{Kk,Ms+1})ex(n, \{K_{k},M_{s+1}\}), where KkK_{k} and Ms+1M_{s+1} are a complete graph on kk vertices and a matching of size s+1s +1, respectively. Then many results were obtained by extending KkK_{k} to a general fixed graph or family of graphs. Let CkC_k be a cycle of order kk. Denote Ck={Ck,Ck+1,}C_{\ge k}=\{C_k,C_{k+1},\ldots\}. In this paper, we determine the value of ex(n,Kr,{Ck,Ms+1})ex(n,K_r, \{C_{\ge k},M_{s+1}\}) for large enough nn and obtain the extremal graphs when kk is odd. Particularly, the exact value of ex(n,{Ck,Ms+1})ex(n, \{C_{\ge k},M_{s+1}\}) and the extremal graph are given for large enough nn.

Keywords

Cite

@article{arxiv.2412.18853,
  title  = {Generalized Tur\'an problems for a matching and long cycles},
  author = {Xiamiao Zhao and Mei Lu},
  journal= {arXiv preprint arXiv:2412.18853},
  year   = {2024}
}

Comments

15 pages, 2 figures

R2 v1 2026-06-28T20:48:41.224Z