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arXiv 1107.4829math.COcs.DM
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图正则性的界与移除引理

Bounds for graph regularity and removal lemmas

David Conlon, Jacob Fox

摘要:

本文证明了,对于任意正整数k,存在一个图,它的顶点被均匀划分为k个部分,其中至少有ck^2/ \log^* k对部分不是ε-正则的,其中c,ε>0是绝对常数.这个界限是紧的常数c和地址的问题高尔斯的数量不规则对Szemerédi的规律性引理。为了获得对不规则对的一些控制,另一个正则性引理,称为强正则性引理,由阿隆,费舍尔,Krivelevich和Szegedy开发。对于这个引理,我们证明了一个关于强正则引理中部分个数的Wowzer型下界,它在Ackermann族中比塔函数高一级,本质上与上界相匹配.另一方面,对于导出图移除引理,强正则引理的标准应用,我们找到了一个不同的证明,它产生了一个塔型界。我们还讨论了几个相关的正则性引理的界,包括Frieze和Kannan的弱正则性引理以及最近建立的正则逼近定理。特别地,我们证明了具有近似参数ε的弱划分可能需要多达2^{Ω(ε^{-2})}个部分。这是紧到隐含常数,并解决了一个问题的研究Lovász和Szegedy。

英文摘要:

We show, for any positive integer k, that there exists a graph in which any equitable partition of its vertices into k parts has at least ck^2/\log^* k pairs of parts which are not ε-regular, where c,ε>0 are absolute constants. This bound is tight up to the constant c and addresses a question of Gowers on the number of irregular pairs in Szemerédi's regularity lemma. In order to gain some control over irregular pairs, another regularity lemma, known as the strong regularity lemma, was developed by Alon, Fischer, Krivelevich, and Szegedy. For this lemma, we prove a lower bound of wowzer-type, which is one level higher in the Ackermann hierarchy than the tower function, on the number of parts in the strong regularity lemma, essentially matching the upper bound. On the other hand, for the induced graph removal lemma, the standard application of the strong regularity lemma, we find a different proof which yields a tower-type bound. We also discuss bounds on several related regularity lemmas, including the weak regularity lemma of Frieze and Kannan and the recently established regular approximation theorem. In particular, we show that a weak partition with approximation parameter εmay require as many as 2^{Ω(ε^{-2})} parts. This is tight up to the implied constant and solves a problem studied by Lovász and Szegedy.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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