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Asymptotic density of graphs excluding disconnected minors
Journal of Combinatorial Theory Series B ( IF 1.2 ) Pub Date : 2020-09-23 , DOI: 10.1016/j.jctb.2020.09.007
Rohan Kapadia , Sergey Norin , Yingjie Qian

For a graph H, letc(H)=limnmax|E(G)|n, where the maximum is taken over all graphs G on n vertices not containing H as a minor. Thus c(H) is the asymptotic maximum density of graphs not containing H as a minor. Employing a structural lemma due to Eppstein, we prove new upper bounds on c(H) for disconnected graphs H. In particular, we determine c(H) whenever H is a union of cycles. Finally, we investigate the behaviour of c(sKr) for fixed r, where sKr denotes the union of s disjoint copies of the complete graph on r vertices. Improving on a result of Thomason, we show thatc(sKr)=s(r1)1fors=ω(logrloglogr), andc(sKr)>s(r1)1fors=o(logrloglogr).



中文翻译:

图的渐近密度,不包括未连接的未成年人

对于图H,让CH=ñ最高|ËG|ñ其中在不包含H作为次要元素的n个顶点上的所有图G上取最大值。从而CH是不含次要元素H的图的渐近最大密度。利用因普斯坦的结构引理,我们证明了新的上界CH断开连接图^ h。特别是,我们确定CH每当H是周期的并集时。最后,我们调查了Csķ[R对于固定r,其中sķ[R表示在r个顶点上完整图的s个不相交副本的并集。通过对Thomason的改进,我们表明Csķ[R=s[R-1个-1个对于s=ω日志[R日志日志[RCsķ[R>s[R-1个-1个对于s=Ø日志[R日志日志[R

更新日期:2020-09-23
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