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边临界图和推广扇的拉姆齐数

Ramsey numbers of edge-critical graphs versus large generalized fans

  • 摘要: 给定两个图GH,拉姆齐数R(G,H)是最小的正整数N,使得对K_N的边的任意一种2染色图中或包含一个红色图G或包含一个蓝色图H。记K_N-1\sqcup K_1,\, k是通过在K_N-1外添加一个顶点并连接K_N-1k个顶点所得到的图。对一个色数为k+1的图G,如果它含一条边使得\chi(G-e)=k,则称G为边临界图。前人对图拉姆齐数进行了大量研究。本文证明了对给定的色数为k+1的边临界图G,当k\geq 2, t\geq 2n 足够大时, R(G, K_1+nK_t)=knt+1 并且 r_*(G,K_1+nK_t)=(k-1)nt+t

     

    Abstract: Given two graphs G and H, the Ramsey number R(G,H) is the smallest positive integer N such that every 2-coloring of the edges of K_N contains either a red G or a blue H. Let K_N-1\sqcup K_1,\,k be the graph obtained from K_N-1 by adding a new vertex v connecting k vertices of K_N-1. A graph G with \chi(G)=k+1 is called edge-critical if G contains an edge e such that \chi(G-e)=k. A considerable amount of research has been conducted by previous scholars on Ramsey numbers of graphs. In this study, we show that for an edge-critical graph G with \chi(G)=k+1, when k\geq 2, t\geq 2, and n is sufficiently large, R(G, K_1+nK_t)=knt+1 and r_*(G,K_1+nK_t)=(k-1)nt+t.

     

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