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Subdivisions of digraphs in tournaments
Journal of Combinatorial Theory Series B ( IF 1.2 ) Pub Date : 2020-09-25 , DOI: 10.1016/j.jctb.2020.09.006
António Girão , Kamil Popielarz , Richard Snyder

We show that for every positive integer k, any tournament with minimum out-degree at least (2+o(1))k2 contains a subdivision of the complete directed graph on k vertices, where each path of the subdivision has length at most 3. This result is best possible on the minimum out-degree condition (up to a multiplicative factor of 8), and it is tight with respect to the length of the paths. It may be viewed as a directed analogue of a theorem proved by Bollobás and Thomason, and independently by Komlós and Szemerédi, concerning subdivisions of cliques in graphs with sufficiently high average degree. We also consider the following problem: given k, what is the smallest positive integer f(k) such that any f(k)-vertex tournament contains a 1-subdivision of the transitive tournament on k vertices? We show that f(k)=O(k2log3k) which is best possible up to the logarithmic factors.



中文翻译:

锦标赛中有向图的细分

我们显示出,对于每个正整数k,任何具有最小出学位的比赛至少2+Ø1个ķ2包含一个完整的有向图在k个顶点上的细分,该细分的每个路径的长度最大为3。在最小向外度条件下(乘数最大为8),此结果是最好的,并且它很紧关于路径的长度。可以将其视为由Bollobás和Thomason证明的定理的有向类似物,并且可以由Komlós和Szemerédi独立地证明,该定理涉及具有足够高平均度的图中的集团细分。我们还考虑以下问题:给定k,最小正整数是多少Fķ 这样任何 Fķ-vertex竞赛在k个顶点上包含传递竞赛的1细分?我们证明Fķ=Øķ2日志3ķ 根据对数因子,这是最可能的。

更新日期:2020-09-26
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