English

Star-critical Ramsey numbers for cycles versus the complete graph on 5 vertices

Combinatorics 2019-01-30 v2

Abstract

Let GG, HH and KK represent three graphs without loops or parallel edges and nn represent an integer. Given any red blue coloring of the edges of GG, we say that K(G,H)K \rightarrow (G,H), if there exists red copy of GG in KK or a blue copy of HH in KK. Let KnK_n represent a complete graph on nn vertices, CnC_n a cycle on nn vertices and Sn=K1,nS_n=K_{1,n} a star on n+1n+1 vertices. The Ramsey number r(G,H)r(G, H) is defined as min{nKn(G,H)}\min\{n \mid K_n\rightarrow (G,H)\}. Likewise, the star-critical Ramsey number r(H,G)r_*(H, G) is defined min{kKr(G,H)1K1,k(H,G)}\min\{k \mid K_{r(G,H)-1} \sqcup K_{1,k} \rightarrow (H, G) \}. When n>3n >3, in this paper we show that r(Cn,K5)=3n1r_*(C_n,K_5)=3n-1 except r(C4,K5)=13r_*(C_4,K_5)=13. We also characterize all Ramsey critical r(Cn,K5)r(C_n,K_5) graphs.

Keywords

Cite

@article{arxiv.1901.04802,
  title  = {Star-critical Ramsey numbers for cycles versus the complete graph on 5 vertices},
  author = {Chula J. Jayawardene},
  journal= {arXiv preprint arXiv:1901.04802},
  year   = {2019}
}

Comments

23 pages, 15 figures