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Extremal problems for multigraphs
Journal of Combinatorial Theory Series B ( IF 1.4 ) Pub Date : 2021-12-23 , DOI: 10.1016/j.jctb.2021.12.003
A. Nicholas Day , Victor Falgas-Ravry , Andrew Treglown

An (n,s,q)-graph is an n-vertex multigraph in which every s-set of vertices spans at most q edges. Turán-type questions on the maximum of the sum of the edge multiplicities in such multigraphs have been studied since the 1990s. More recently, Mubayi and Terry (2019) [13] posed the problem of determining the maximum of the product of the edge multiplicities in (n,s,q)-graphs. We give a general lower bound construction for this problem for many pairs (s,q), which we conjecture is asymptotically best possible. We prove various general cases of our conjecture, and in particular we settle a conjecture of Mubayi and Terry on the (s,q)=(4,6a+3) case of the problem (for a2); this in turn answers a question of Alon. We also determine the asymptotic behaviour of the problem for ‘sparse’ multigraphs (i.e. when q2(s2)). Finally we introduce some tools that are likely to be useful for attacking the problem in general.



中文翻译:

多重图的极值问题

一个 (n,,q)-graph 是一个n -顶点多重图,其中每个s -顶点集最多跨越q 条边。自 1990 年代以来,已经研究了关于此类多重图中边多重性总和的最大值的 Turán 类型问题。最近,Mubayi 和 Terry (2019) [13] 提出了确定边缘多重性乘积的最大值的问题(n,,q)-图表。我们为这个问题的许多对给出了一个一般的下界构造(,q),我们推测这是渐近最好的。我们证明了我们猜想的各种一般情况,特别是我们解决了穆巴伊和特里的猜想(,q)=(4,6一个+3) 问题的情况(对于 一个2); 这反过来回答了阿隆的一个问题。我们还确定了“稀疏”多重图问题的渐近行为(即,当q2(2))。最后,我们介绍一些可能对解决一般问题有用的工具。

更新日期:2021-12-23
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