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Some tight lower bounds for Turán problems via constructions of multi-hypergraphs
European Journal of Combinatorics ( IF 1.0 ) Pub Date : 2020-05-30 , DOI: 10.1016/j.ejc.2020.103161
Zixiang Xu , Tao Zhang , Gennian Ge

Recently, several hypergraph Turán problems were solved by the powerful random algebraic method. However, the random algebraic method usually requires some parameters to be very large, hence we are concerned about how these Turán numbers depend on such large parameters of the forbidden hypergraphs. In this paper, we determine the dependence on such specified large constant for several hypergraph Turán problems. More specifically, for complete r-partite r-uniform hypergraphs, we show that if sr is sufficiently larger than s1,s2,,sr1, then exr(n,Ks1,s2,,sr(r))=Θ(sr1s1s2sr1nr1s1s2sr1).For complete bipartite r-uniform hypergraphs, we prove that if s is sufficiently larger than t, we have exr(n,Ks,t(r))=Θ(s1tnr1t).In particular, our results imply that the famous Kővári–Sós–Turán’s upper bound ex(n,Ks,t)=O(t1sn21s) has the correct dependence on large t. The main approach is to construct random multi-hypergraph via a variant of random algebraic method.



中文翻译:

通过多重超图的构造来解决Turán问题的一些紧下界

最近,通过强大的随机代数方法解决了一些超图Turán问题。但是,随机代数方法通常要求某些参数非常大,因此我们担心这些Turán数如何取决于禁止超图的如此大参数。在本文中,我们确定了几个超图Turán问题对这样指定的大常数的依赖性。更具体地说,完整[R-部分 [R-一致的超图,我们证明 s[R 足够大于 s1个s2s[R-1个 然后 [Rñķs1个s2s[R[R=Θs[R1个s1个s2s[R-1个ñ[R-1个s1个s2s[R-1个对于完全二分 [R-一致超图,我们证明 s 足够大于 Ť 我们有 [RñķsŤ[R=Θs1个Ťñ[R-1个Ť特别是,我们的结果暗示着著名的克瓦里(Kővári–Sós–Turán)的上限 ñķsŤ=ØŤ1个sñ2-1个s 正确依赖大 Ť。主要方法是通过随机代数方法的变体构造随机多超级图。

更新日期:2020-05-30
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