无 C 2 k + 1 图形的最小度稳定性

IF 0.9 3区 数学 Q2 MATHEMATICS
Xiaoli Yuan, Yuejian Peng
{"title":"无 C 2 k + 1 图形的最小度稳定性","authors":"Xiaoli Yuan,&nbsp;Yuejian Peng","doi":"10.1002/jgt.23086","DOIUrl":null,"url":null,"abstract":"<p>We consider the minimum degree stability of graphs forbidding odd cycles: What is the tight bound on the minimum degree to guarantee that the structure of a <span></span><math>\n <semantics>\n <mrow>\n <msub>\n <mi>C</mi>\n \n <mrow>\n <mn>2</mn>\n \n <mi>k</mi>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n </msub>\n </mrow>\n <annotation> ${C}_{2k+1}$</annotation>\n </semantics></math>-free graph inherits from the extremal graph (a balanced complete bipartite graph)? Andrásfai, Erdős, and Sós showed that if a <span></span><math>\n <semantics>\n <mrow>\n <mo>{</mo>\n \n <msub>\n <mi>C</mi>\n \n <mn>3</mn>\n </msub>\n \n <mo>,</mo>\n \n <msub>\n <mi>C</mi>\n \n <mn>5</mn>\n </msub>\n \n <mo>,</mo>\n \n <mtext>…</mtext>\n \n <mo>,</mo>\n \n <msub>\n <mi>C</mi>\n \n <mrow>\n <mn>2</mn>\n \n <mi>k</mi>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n </msub>\n \n <mo>}</mo>\n </mrow>\n <annotation> $\\{{C}_{3},{C}_{5},\\ldots ,{C}_{2k+1}\\}$</annotation>\n </semantics></math>-free graph on <span></span><math>\n <semantics>\n <mrow>\n <mi>n</mi>\n </mrow>\n <annotation> $n$</annotation>\n </semantics></math> vertices has minimum degree greater than <span></span><math>\n <semantics>\n <mrow>\n <mfrac>\n <mn>2</mn>\n \n <mrow>\n <mn>2</mn>\n \n <mi>k</mi>\n \n <mo>+</mo>\n \n <mn>3</mn>\n </mrow>\n </mfrac>\n \n <mi>n</mi>\n </mrow>\n <annotation> $\\frac{2}{2k+3}n$</annotation>\n </semantics></math>, then it is bipartite. Häggkvist showed that for <span></span><math>\n <semantics>\n <mrow>\n <mi>k</mi>\n \n <mo>∈</mo>\n \n <mrow>\n <mo>{</mo>\n \n <mrow>\n <mn>1</mn>\n \n <mo>,</mo>\n \n <mn>2</mn>\n \n <mo>,</mo>\n \n <mn>3</mn>\n \n <mo>,</mo>\n \n <mn>4</mn>\n </mrow>\n \n <mo>}</mo>\n </mrow>\n </mrow>\n <annotation> $k\\in \\{1,2,3,4\\}$</annotation>\n </semantics></math>, if a <span></span><math>\n <semantics>\n <mrow>\n <msub>\n <mi>C</mi>\n \n <mrow>\n <mn>2</mn>\n \n <mi>k</mi>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n </msub>\n </mrow>\n <annotation> ${C}_{2k+1}$</annotation>\n </semantics></math>-free graph on <span></span><math>\n <semantics>\n <mrow>\n <mi>n</mi>\n </mrow>\n <annotation> $n$</annotation>\n </semantics></math> vertices has minimum degree greater than <span></span><math>\n <semantics>\n <mrow>\n <mfrac>\n <mn>2</mn>\n \n <mrow>\n <mn>2</mn>\n \n <mi>k</mi>\n \n <mo>+</mo>\n \n <mn>3</mn>\n </mrow>\n </mfrac>\n \n <mi>n</mi>\n </mrow>\n <annotation> $\\frac{2}{2k+3}n$</annotation>\n </semantics></math>, then it is bipartite. Häggkvist also pointed out that this result cannot be extended to <span></span><math>\n <semantics>\n <mrow>\n <mi>k</mi>\n \n <mo>≥</mo>\n \n <mn>5</mn>\n </mrow>\n <annotation> $k\\ge 5$</annotation>\n </semantics></math>. In this paper, we give a complete answer for any <span></span><math>\n <semantics>\n <mrow>\n <mi>k</mi>\n \n <mo>≥</mo>\n \n <mn>5</mn>\n </mrow>\n <annotation> $k\\ge 5$</annotation>\n </semantics></math>. We show that if <span></span><math>\n <semantics>\n <mrow>\n <mi>k</mi>\n \n <mo>≥</mo>\n \n <mn>5</mn>\n </mrow>\n <annotation> $k\\ge 5$</annotation>\n </semantics></math> and <span></span><math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> is an <span></span><math>\n <semantics>\n <mrow>\n <mi>n</mi>\n </mrow>\n <annotation> $n$</annotation>\n </semantics></math>-vertex <span></span><math>\n <semantics>\n <mrow>\n <msub>\n <mi>C</mi>\n \n <mrow>\n <mn>2</mn>\n \n <mi>k</mi>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n </msub>\n </mrow>\n <annotation> ${C}_{2k+1}$</annotation>\n </semantics></math>-free graph with <span></span><math>\n <semantics>\n <mrow>\n <mi>δ</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo>≥</mo>\n \n <mfrac>\n <mi>n</mi>\n \n <mn>6</mn>\n </mfrac>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n <annotation> $\\delta (G)\\ge \\frac{n}{6}+1$</annotation>\n </semantics></math>, then <span></span><math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> is bipartite, and the bound <span></span><math>\n <semantics>\n <mrow>\n <mfrac>\n <mi>n</mi>\n \n <mn>6</mn>\n </mfrac>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n <annotation> $\\frac{n}{6}+1$</annotation>\n </semantics></math> is tight.</p>","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"106 2","pages":"307-321"},"PeriodicalIF":0.9000,"publicationDate":"2024-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Minimum degree stability of \\n \\n \\n \\n C\\n \\n 2\\n k\\n +\\n 1\\n \\n \\n \\n ${C}_{2k+1}$\\n -free graphs\",\"authors\":\"Xiaoli Yuan,&nbsp;Yuejian Peng\",\"doi\":\"10.1002/jgt.23086\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>We consider the minimum degree stability of graphs forbidding odd cycles: What is the tight bound on the minimum degree to guarantee that the structure of a <span></span><math>\\n <semantics>\\n <mrow>\\n <msub>\\n <mi>C</mi>\\n \\n <mrow>\\n <mn>2</mn>\\n \\n <mi>k</mi>\\n \\n <mo>+</mo>\\n \\n <mn>1</mn>\\n </mrow>\\n </msub>\\n </mrow>\\n <annotation> ${C}_{2k+1}$</annotation>\\n </semantics></math>-free graph inherits from the extremal graph (a balanced complete bipartite graph)? Andrásfai, Erdős, and Sós showed that if a <span></span><math>\\n <semantics>\\n <mrow>\\n <mo>{</mo>\\n \\n <msub>\\n <mi>C</mi>\\n \\n <mn>3</mn>\\n </msub>\\n \\n <mo>,</mo>\\n \\n <msub>\\n <mi>C</mi>\\n \\n <mn>5</mn>\\n </msub>\\n \\n <mo>,</mo>\\n \\n <mtext>…</mtext>\\n \\n <mo>,</mo>\\n \\n <msub>\\n <mi>C</mi>\\n \\n <mrow>\\n <mn>2</mn>\\n \\n <mi>k</mi>\\n \\n <mo>+</mo>\\n \\n <mn>1</mn>\\n </mrow>\\n </msub>\\n \\n <mo>}</mo>\\n </mrow>\\n <annotation> $\\\\{{C}_{3},{C}_{5},\\\\ldots ,{C}_{2k+1}\\\\}$</annotation>\\n </semantics></math>-free graph on <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>n</mi>\\n </mrow>\\n <annotation> $n$</annotation>\\n </semantics></math> vertices has minimum degree greater than <span></span><math>\\n <semantics>\\n <mrow>\\n <mfrac>\\n <mn>2</mn>\\n \\n <mrow>\\n <mn>2</mn>\\n \\n <mi>k</mi>\\n \\n <mo>+</mo>\\n \\n <mn>3</mn>\\n </mrow>\\n </mfrac>\\n \\n <mi>n</mi>\\n </mrow>\\n <annotation> $\\\\frac{2}{2k+3}n$</annotation>\\n </semantics></math>, then it is bipartite. Häggkvist showed that for <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>k</mi>\\n \\n <mo>∈</mo>\\n \\n <mrow>\\n <mo>{</mo>\\n \\n <mrow>\\n <mn>1</mn>\\n \\n <mo>,</mo>\\n \\n <mn>2</mn>\\n \\n <mo>,</mo>\\n \\n <mn>3</mn>\\n \\n <mo>,</mo>\\n \\n <mn>4</mn>\\n </mrow>\\n \\n <mo>}</mo>\\n </mrow>\\n </mrow>\\n <annotation> $k\\\\in \\\\{1,2,3,4\\\\}$</annotation>\\n </semantics></math>, if a <span></span><math>\\n <semantics>\\n <mrow>\\n <msub>\\n <mi>C</mi>\\n \\n <mrow>\\n <mn>2</mn>\\n \\n <mi>k</mi>\\n \\n <mo>+</mo>\\n \\n <mn>1</mn>\\n </mrow>\\n </msub>\\n </mrow>\\n <annotation> ${C}_{2k+1}$</annotation>\\n </semantics></math>-free graph on <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>n</mi>\\n </mrow>\\n <annotation> $n$</annotation>\\n </semantics></math> vertices has minimum degree greater than <span></span><math>\\n <semantics>\\n <mrow>\\n <mfrac>\\n <mn>2</mn>\\n \\n <mrow>\\n <mn>2</mn>\\n \\n <mi>k</mi>\\n \\n <mo>+</mo>\\n \\n <mn>3</mn>\\n </mrow>\\n </mfrac>\\n \\n <mi>n</mi>\\n </mrow>\\n <annotation> $\\\\frac{2}{2k+3}n$</annotation>\\n </semantics></math>, then it is bipartite. Häggkvist also pointed out that this result cannot be extended to <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>k</mi>\\n \\n <mo>≥</mo>\\n \\n <mn>5</mn>\\n </mrow>\\n <annotation> $k\\\\ge 5$</annotation>\\n </semantics></math>. In this paper, we give a complete answer for any <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>k</mi>\\n \\n <mo>≥</mo>\\n \\n <mn>5</mn>\\n </mrow>\\n <annotation> $k\\\\ge 5$</annotation>\\n </semantics></math>. We show that if <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>k</mi>\\n \\n <mo>≥</mo>\\n \\n <mn>5</mn>\\n </mrow>\\n <annotation> $k\\\\ge 5$</annotation>\\n </semantics></math> and <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>G</mi>\\n </mrow>\\n <annotation> $G$</annotation>\\n </semantics></math> is an <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>n</mi>\\n </mrow>\\n <annotation> $n$</annotation>\\n </semantics></math>-vertex <span></span><math>\\n <semantics>\\n <mrow>\\n <msub>\\n <mi>C</mi>\\n \\n <mrow>\\n <mn>2</mn>\\n \\n <mi>k</mi>\\n \\n <mo>+</mo>\\n \\n <mn>1</mn>\\n </mrow>\\n </msub>\\n </mrow>\\n <annotation> ${C}_{2k+1}$</annotation>\\n </semantics></math>-free graph with <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>δ</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>G</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mo>≥</mo>\\n \\n <mfrac>\\n <mi>n</mi>\\n \\n <mn>6</mn>\\n </mfrac>\\n \\n <mo>+</mo>\\n \\n <mn>1</mn>\\n </mrow>\\n <annotation> $\\\\delta (G)\\\\ge \\\\frac{n}{6}+1$</annotation>\\n </semantics></math>, then <span></span><math>\\n <semantics>\\n <mrow>\\n <mi>G</mi>\\n </mrow>\\n <annotation> $G$</annotation>\\n </semantics></math> is bipartite, and the bound <span></span><math>\\n <semantics>\\n <mrow>\\n <mfrac>\\n <mi>n</mi>\\n \\n <mn>6</mn>\\n </mfrac>\\n \\n <mo>+</mo>\\n \\n <mn>1</mn>\\n </mrow>\\n <annotation> $\\\\frac{n}{6}+1$</annotation>\\n </semantics></math> is tight.</p>\",\"PeriodicalId\":16014,\"journal\":{\"name\":\"Journal of Graph Theory\",\"volume\":\"106 2\",\"pages\":\"307-321\"},\"PeriodicalIF\":0.9000,\"publicationDate\":\"2024-02-11\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Graph Theory\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23086\",\"RegionNum\":3,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Graph Theory","FirstCategoryId":"100","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23086","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0

摘要

我们考虑的是禁止奇数循环的图的最小度稳定性:要保证不含 C2k+1${C}_{2k+1}$ 的图的结构继承于极值图(平衡的完整二叉图),最小度数的严格约束是什么?Andrásfai、Erdős 和 Sós 发现,如果 n$n$ 个顶点上的{C3,C5,...,C2k+1}${{C}_{3},{C}_{5},\ldots ,{C}_{2k+1}\}$ 无顶图的最小度大于 22k+3n$/frac{2}{2k+3}n$,那么它是双向图。Häggkvist 证明了对于 k∈{1,2,3,4}$k\in \{1,2,3,4/}$,如果 n$n$ 个顶点上的无 C2k+1${C}_{2k+1}$ 图的最小度大于 22k+3n$/frac{2}{2k+3}n$,那么它是双方形的。海格奎斯特还指出,这一结果无法扩展到 k≥5$k\ge 5$。在本文中,我们给出了任意 k≥5$k\ge 5$ 的完整答案。我们证明,如果 k≥5$k\ge 5$ 并且 G$G$ 是一个 n$n$-vertex C2k+1${C}_{2k+1}$-free graph,δ(G)≥n6+1$\delta (G)\ge \frac{n}{6}+1$,那么 G$G$ 是双分部图,并且约束 n6+1$\frac{n}{6}+1$ 是紧密的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Minimum degree stability of C 2 k + 1 ${C}_{2k+1}$ -free graphs

We consider the minimum degree stability of graphs forbidding odd cycles: What is the tight bound on the minimum degree to guarantee that the structure of a C 2 k + 1 ${C}_{2k+1}$ -free graph inherits from the extremal graph (a balanced complete bipartite graph)? Andrásfai, Erdős, and Sós showed that if a { C 3 , C 5 , , C 2 k + 1 } $\{{C}_{3},{C}_{5},\ldots ,{C}_{2k+1}\}$ -free graph on n $n$ vertices has minimum degree greater than 2 2 k + 3 n $\frac{2}{2k+3}n$ , then it is bipartite. Häggkvist showed that for k { 1 , 2 , 3 , 4 } $k\in \{1,2,3,4\}$ , if a C 2 k + 1 ${C}_{2k+1}$ -free graph on n $n$ vertices has minimum degree greater than 2 2 k + 3 n $\frac{2}{2k+3}n$ , then it is bipartite. Häggkvist also pointed out that this result cannot be extended to k 5 $k\ge 5$ . In this paper, we give a complete answer for any k 5 $k\ge 5$ . We show that if k 5 $k\ge 5$ and G $G$ is an n $n$ -vertex C 2 k + 1 ${C}_{2k+1}$ -free graph with δ ( G ) n 6 + 1 $\delta (G)\ge \frac{n}{6}+1$ , then G $G$ is bipartite, and the bound n 6 + 1 $\frac{n}{6}+1$ is tight.

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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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