Small Planar Hypohamiltonian Graphs

IF 0.9 3区 数学 Q2 MATHEMATICS
Cheng-Chen Tsai
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引用次数: 0

Abstract

A graph is hypohamiltonian if it is non-hamiltonian, but the deletion of every single vertex gives a Hamiltonian graph. Until now, the smallest known planar hypohamiltonian graph had 40 vertices, a result due to Jooyandeh, McKay, Östergård, Pettersson, and Zamfirescu. That result is here improved upon by two planar hypohamiltonian graphs on 34 vertices. We exploited a special subgraph contained in two graphs of Jooyandeh et al., and modified it to construct the two 34-vertex graphs and six planar hypohamiltonian graphs on 37 vertices. Each of the 34-vertex graphs has 26 cubic vertices, improving upon the result of Jooyandeh et al. that planar hypohamiltonian graphs have 30 cubic vertices. We use the 34-vertex graphs to construct hypohamiltonian graphs of order 34 with crossing number 1, improving the best-known bound of 36 due to Wiener. Whether there exists a planar hypohamiltonian graph on 41 vertices was an open question. We settled this question by applying an operation introduced by Thomassen to the 37-vertex graphs to obtain several planar hypohamiltonian graphs on 41 vertices. The 25 planar hypohamiltonian graphs on 40 vertices of Jooyandeh et al. have no nontrivial automorphisms. The result is here improved upon by six planar hypohamiltonian graphs on 40 vertices with nontrivial automorphisms.

小平面次哈密顿图
如果一个图是非哈密顿图,那么它就是次哈密顿图,但是删除每一个顶点会得到一个哈密顿图。到目前为止,已知最小的平面次哈密顿图有40个顶点,这是joooyandeh, McKay, Östergård, Pettersson和Zamfirescu的结果。这个结果在这里得到了两个平面的34个顶点的次哈密顿图的改进。我们利用了Jooyandeh等人的两个图中包含的一个特殊子图,并对其进行了修改,构造了两个34顶点图和六个37顶点的平面次哈密顿图。在Jooyandeh等人的平面次哈密顿图有30个立方顶点的结果的基础上,改进了34个顶点图的每个顶点有26个立方顶点。我们利用34顶点图构造了交次数为1的34阶次哈密顿图,改进了由Wiener提出的最著名的36界。是否存在41个顶点的平面次哈密顿图是一个悬而未决的问题。我们通过将Thomassen引入的运算应用于37顶点图,得到了41顶点上的几个平面次哈密顿图,从而解决了这个问题。Jooyandeh等在40个顶点上的25个平面次哈密顿图不存在非平凡自同构。这一结果在40个非平凡自同构顶点上的6个平面次哈密顿图的基础上得到了改进。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Graph Theory
Journal of Graph Theory 数学-数学
CiteScore
1.60
自引率
22.20%
发文量
130
审稿时长
6-12 weeks
期刊介绍: The Journal of Graph Theory is devoted to a variety of topics in graph theory, such as structural results about graphs, graph algorithms with theoretical emphasis, and discrete optimization on graphs. The scope of the journal also includes related areas in combinatorics and the interaction of graph theory with other mathematical sciences. A subscription to the Journal of Graph Theory includes a subscription to the Journal of Combinatorial Designs .
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