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arXiv 2008.03173math.CO
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5-正则图中的哈密顿圈和1-因子

Hamiltonian cycles and 1-factors in 5-regular graphs

Nico Van Cleemput, Carol T. Zamfirescu

摘要:

证明了对任意整数$g \ge 0$和$k \in \{ 0, \ldots, 10 \}$,存在无穷多个含1-因子分解的亏格为$g$的5-正则图,其中恰好有$k$对1-因子是完美的,即构成一个哈密顿圈.对于$g = 0$,这解决了1964年的Kotzig问题。受Kotzig和Labelle的“婚姻”操作的启发,我们讨论了两种胶合技术,旨在产生高循环边连通图。证明了存在无穷多个平面5-连通5-正则图,其中每个1-因子分解都有零个完美对。另一方面,利用四色定理和Brinkmann与第一作者的一个结果,证明了每个平面4-连通5-正则图在其哈密顿圈上满足一个条件时,都有线性数目的1-因子分解,每个分解至少包含一个完美对.我们还证明了满足更强条件的平面5-连通5-正则图包含最多9个完美对的1-因子分解,由此,每一个允许最多10个完美对的1-因子分解的平面5-连通5-正则图至少有两个边Kempe等价类.最后给出了平面5-正则图的边Kempe等价类的进一步结果。

英文摘要:

It is proven that for any integer $g \ge 0$ and $k \in \{ 0, \ldots, 10 \}$, there exist infinitely many 5-regular graphs of genus $g$ containing a 1-factorisation with exactly $k$ pairs of 1-factors that are perfect, i.e. form a hamiltonian cycle. For $g = 0$, this settles a problem of Kotzig from 1964. Motivated by Kotzig and Labelle's "marriage" operation, we discuss two gluing techniques aimed at producing graphs of high cyclic edge-connectivity. We prove that there exist infinitely many planar 5-connected 5-regular graphs in which every 1-factorisation has zero perfect pairs. On the other hand, by the Four Colour Theorem and a result of Brinkmann and the first author, every planar 4-connected 5-regular graph satisfying a condition on its hamiltonian cycles has a linear number of 1-factorisations each containing at least one perfect pair. We also prove that every planar 5-connected 5-regular graph satisfying a stronger condition contains a 1-factorisation with at most nine perfect pairs, whence, every such graph admitting a 1-factorisation with ten perfect pairs has at least two edge-Kempe equivalence classes. The paper concludes with further results on edge-Kempe equivalence classes in planar 5-regular graphs.

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