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arXiv 2403.04401math.CO
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关于$(r,c)$-常数图、平面图和循环图

On $(r,c)$-constant, planar and circulant graphs

Yair Caro, Xandru Mifsud

AI总结:

本文研究$(r,c)$-常数图,完全确定了$(r,c)$-平面图的存在性及最小阶,给出$(r,c)$-循环图的存在性条件,还明确了小参数范围内$(r,c)$-常数图的存在情况并搭建了公开数据库。

摘要:

本文研究$(r,c)$-常数图,这类图是$r$-正则图,且每个顶点的开邻域诱导出的子图恰好包含$c$条边。$(r,c)$-图族包含顶点传递图(尤其是Cayley图)、常链接图(有时称为局部同构图)、$(r,b)$-正则图、强正则图等多种图类。\n 该图族近期在文献[arXiv:2312.08777]中被提出,是构造翻转图的重要工具(相关研究见arXiv:2312.08777、arXiv:2401.02315)。\n 本文主要围绕以下三方面展开研究:\n 一、$(r,c)$-平面图的存在性与不存在性。我们完全确定了这类图的存在与不存在的所有情形,并给出了存在情形下的最小阶数。\n 二、$(r,c)$-循环图的存在性。我们证明当$c \equiv 2 \\\\ (\mathrm{mod} \\\\ 3)$时,不存在$(r,c)$-循环图;当$c \equiv 0, 1 \\\\ (\mathrm{mod} \\\\ 3)$、$c > 0$且$r \geq 6 + \sqrt{\frac{8c - 5}{3}}$时,存在$(r,c)$-循环图。此外,当$c = 0$且$r \geq 1$时,$(r,0)$-循环图存在。\n 三、小型$(r,c)$-常数图的存在性与不存在性。我们给出了$0 \leq c \leq \binom{r}{2}$且$r \leq 6$范围内,已找到的最小阶图的完整表格,同时确定了该范围内所有$(r,c)$-常数图不存在的情形。我们还建立了一个包含不同$r$、$c$和阶数的$(r,c)$-常数图公开数据库。

英文摘要:

This paper concerns $(r,c)$-constant graphs, which are $r$-regular graphs in which the subgraph induced by the open neighbourhood of every vertex has precisely $c$ edges. The family of $(r,c)$-graphs contains vertex-transitive graphs (and in particular Cayley graphs), graphs with constant link (sometimes called locally isomorphic graphs), $(r,b)$-regular graphs, strongly regular graphs, and much more. This family was recently introduced in [arXiv:2312.08777] serving as important tool in constructing flip graphs [arXiv:2312.08777, arXiv:2401.02315]. In this paper we shall mainly deal with the following: i. Existence and non-existence of $(r, c)$-planar graphs. We completely determine the cases of existence and non-existence of such graphs and supply the smallest order in the case when they exist. ii. We consider the existence of $(r, c)$-circulant graphs. We prove that for $c \equiv 2 \ (\mathrm{mod} \ 3)$ no $(r,c)$-circulant graph exists and that for $c \equiv 0, 1 \ (\mathrm{mod} \ 3)$, $c > 0$ and $r \geq 6 + \sqrt{\frac{8c - 5}{3}}$ there exists $(r,c)$-circulant graphs. Moreover for $c = 0$ and $r \geq 1$, $(r, 0)$-circulants exist. iii. We consider the existence and non-existence of small $(r,c)$-constant graphs, supplying a complete table of the smallest order of graphs we found for $0 \leq c \leq \binom{r}{2}$ and $r \leq 6$. We shall also determine all the cases in this range for which $(r,c)$-constant graphs don't exist. We establish a public database of $(r,c)$-constant graphs for varying $r$, $c$ and order.

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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