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arXiv 2210.08620math.COcs.DM
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平面图的孪生宽度至多为 8,以及一些相关界

Twin-width of Planar Graphs is at most 8, and some Related Bounds

Petr Hliněný, Jan Jedelský

AI总结:

本文改进平面图孪生宽度上界至 8,并给出线性时间收缩序列,同时界定二部平面图、1-平面图和地图图。

摘要:

孪生宽度(twin-width)是由 Bonnet、Kim、Thomassé 和 Watrigant [FOCS 2020] 引入的一种结构宽度参数,并在图上逻辑和参数化算法领域具有有趣的应用。简而言之,孪生宽度的本质在于将给定图逐步归约(收缩序列)至单个顶点,同时保持顶点邻域之间的差异有限;它可以被视为广泛推广了其他若干传统结构参数。虽然已知许多自然图类具有有界的孪生宽度,但在非平凡情形下,已发表的孪生宽度上界往往“天文数字般巨大”。\n\n我们关注平面图;自孪生宽度引入以来,人们就知道平面图具有有界孪生宽度,但首个明确的“非天文数字”上界却经过一段时间才出现。具体而言,按照预印本出现的顺序,Jacob 和 Pilipczuk [arXiv,2022 年 1 月] 给出了至多 183 的界,Bonnet、Kwon 和 Wood [arXiv,2022 年 2 月] 给出了 583 的界。随后在 2022 年的 arXiv 手稿将该界改进至 37(Bekos 等人),以及 11 和 9(均由 Hliněný 给出)。我们进一步阐述后一类手稿中使用的方法,证明每个平面图的孪生宽度至多为 8,并在线性时间内构造一个见证收缩序列。值得注意的是,当前最佳的下界平面例子具有孪生宽度 7,由 Král 和 Lamaison [arXiv,2022 年 9 月] 给出。我们还证明了二部平面图和 1-平面图孪生宽度的明确小上界(分别为 6 和 16),以及地图图的上界(38)。所有这些结果的共同基础是使用一种新颖的、专门设计的平面图递归分解,该分解也可能在其他领域发挥作用。

英文摘要:

Twin-width is a structural width parameter introduced by Bonnet, Kim, Thomassé and Watrigant [FOCS 2020], and has interesting applications in the areas of logic on graphs and in parameterized algorithmics. Very briefly, the essence of twin-width is in a gradual reduction (a contraction sequence) of the given graph down to a single vertex while maintaining limited difference of neighbourhoods of the vertices, and it can be seen as widely generalizing several other traditional structural parameters. While for many natural graph classes it is known that their twin-width is bounded, published upper bounds on the twin-width in non-trivial cases are very often "astronomically large". We focus on planar graphs, which are known to have bounded twin-width already since the introduction of it, but it took some time for the first explicit "non-astronomical" upper bounds to come. Namely, in the order of preprint appearance, it was the bound of at most 183 by Jacob and Pilipczuk [arXiv, January 2022], and 583 by Bonnet, Kwon and Wood [arXiv, February 2022]. Subsequent arXiv manuscripts in 2022 improved the bound down to 37 (Bekos et al.), 11 and 9 (both by Hliněný). We further elaborate on the approach used in the latter manuscripts, proving that the twin-width of every planar graph is at most 8, and construct a witnessing contraction sequence in linear time. Note that the currently best lower-bound planar example is of twin-width 7, by Král and Lamaison [arXiv, September 2022]. We also prove small explicit upper bounds on the twin-width of bipartite planar and 1-planar graphs (6 and 16), and of map graphs (38). The common denominator of all these results is the use of a novel specially crafted recursive decomposition of planar graphs, which may be found useful also in other areas.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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