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Hamiltonian cycles above expectation in r-graphs and quasi-random r-graphs
Journal of Combinatorial Theory Series B ( IF 1.4 ) Pub Date : 2021-12-17 , DOI: 10.1016/j.jctb.2021.12.002
Raphael Yuster 1
Affiliation  

Let Hr(n,p) denote the maximum number of Hamiltonian cycles in an n-vertex r-graph with density p(0,1). The expected number of Hamiltonian cycles in the random r-graph model Gr(n,p) is E(n,p)=pn(n1)!/2 and in the random graph model Gr(n,m) with m=p(nr) it is, in fact, slightly smaller than E(n,p).

For graphs, H2(n,p) is proved to be only larger than E(n,p) by a polynomial factor and it is an open problem whether a quasi-random graph with density p can be larger than E(n,p) by a polynomial factor.

For hypergraphs (i.e. r3) the situation is drastically different. For all r3 it is proved that Hr(n,p) is larger than E(n,p) by an exponential factor and, moreover, there are quasi-random r-graphs with density p whose number of Hamiltonian cycles is larger than E(n,p) by an exponential factor.



中文翻译:

r-graphs 和 quasi-random r-graphs 中超出预期的哈密顿循环

Hr(n,p)表示具有密度n顶点r图中的哈密顿循环的最大数量p(0,1). 随机r- graph 模型中哈密顿循环的预期数量Gr(n,p)(n,p)=pn(n-1)/2 并在随机图模型中 Gr(n,)=p(nr) 事实上,它比 (n,p).

对于图形, H2(n,p) 被证明只大于 (n,p)通过多项式因子,密度为p的拟随机图是否可以大于(n,p) 由多项式因子。

对于超图(即 r3)情况大不相同。对所有人r3 事实证明 Hr(n,p) 大于 (n,p)通过指数因子,此外,存在密度为p的准随机r图,其哈密顿循环的数量大于(n,p) 由指数因子。

更新日期:2021-12-17
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