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arXiv 0907.1591math.CO
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有限和无限可平面图及有界亏格图的谱半径

Spectral radius of finite and infinite planar graphs and of graphs of bounded genus

Zdenek Dvorak, Bojan Mohar

摘要:

众所周知,最大度为$D$的树的谱半径不能超过$2\sqrt{D-1}$。本文对任意可平面图和有界亏格图给出了类似的界。证明了顶点度为$D\ge 4$的平面图$G$的谱半径$ρ(G)$满足$\sqrt{D}\le ρ(G)\le \sqrt{8D-16}+7.75$ .这个结果是最好的可能的加法常数-我们构造了一个(无限)平面图的最大程度$D$,其谱半径是$\sqrt{8D-16}$。这推广和改进了以前的几个结果,并解决了一个开放的问题,提出了汤姆海耶斯。对于有界亏格的图,也得到了类似的界。对于每个$k$,这些界限可以通过排除$K_{2,k}$作为子图来改进。特别地,5-连通图的上界得到了加强。我们的所有结果都适用于有限和无限图。最后,我们改进了第一部分中介绍的图分解方法,并将其应用于双曲平面的曲面细分。我们推导出接近真实值的谱半径的界,即使在最简单的情况下,我们得到一个重要的改进已知的结果,在一阶项和非平凡的估计二阶渐近的定期镶嵌类型$\{p,q\}$。

英文摘要:

It is well known that the spectral radius of a tree whose maximum degree is $D$ cannot exceed $2\sqrt{D-1}$. In this paper we derive similar bounds for arbitrary planar graphs and for graphs of bounded genus. It is proved that a the spectral radius $ρ(G)$ of a planar graph $G$ of maximum vertex degree $D\ge 4$ satisfies $\sqrt{D}\le ρ(G)\le \sqrt{8D-16}+7.75$. This result is best possible up to the additive constant--we construct an (infinite) planar graph of maximum degree $D$, whose spectral radius is $\sqrt{8D-16}$. This generalizes and improves several previous results and solves an open problem proposed by Tom Hayes. Similar bounds are derived for graphs of bounded genus. For every $k$, these bounds can be improved by excluding $K_{2,k}$ as a subgraph. In particular, the upper bound is strengthened for 5-connected graphs. All our results hold for finite as well as for infinite graphs. At the end we enhance the graph decomposition method introduced in the first part of the paper and apply it to tessellations of the hyperbolic plane. We derive bounds on the spectral radius that are close to the true value, and even in the simplest case of regular tessellations of type $\{p,q\}$ we derive an essential improvement over known results, obtaining exact estimates in the first order term and non-trivial estimates for the second order asymptotics.

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