{"title":"稀疏图形多副本的拉姆齐数","authors":"Aurelio Sulser, Miloš Trujić","doi":"10.1002/jgt.23100","DOIUrl":null,"url":null,"abstract":"<p>For a graph <span></span><math>\n \n <mrow>\n <mi>H</mi>\n </mrow></math> and an integer <span></span><math>\n \n <mrow>\n <mi>n</mi>\n </mrow></math>, we let <span></span><math>\n \n <mrow>\n <mi>n</mi>\n \n <mi>H</mi>\n </mrow></math> denote the disjoint union of <span></span><math>\n \n <mrow>\n <mi>n</mi>\n </mrow></math> copies of <span></span><math>\n \n <mrow>\n <mi>H</mi>\n </mrow></math>. In 1975, Burr, Erdős and Spencer initiated the study of Ramsey numbers for <span></span><math>\n \n <mrow>\n <mi>n</mi>\n \n <mi>H</mi>\n </mrow></math>, one of few instances for which Ramsey numbers are now known precisely. They showed that there is a constant <span></span><math>\n \n <mrow>\n <mi>c</mi>\n \n <mo>=</mo>\n \n <mi>c</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>H</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow></math> such that <span></span><math>\n \n <mrow>\n <mi>r</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>n</mi>\n \n <mi>H</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n \n <mo>=</mo>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mn>2</mn>\n \n <mo>∣</mo>\n \n <mi>H</mi>\n \n <mo>∣</mo>\n \n <mo>−</mo>\n \n <mi>α</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>H</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n \n <mi>n</mi>\n \n <mo>+</mo>\n \n <mi>c</mi>\n </mrow></math>, provided <span></span><math>\n \n <mrow>\n <mi>n</mi>\n </mrow></math> is sufficiently large. Subsequently, Burr gave an implicit way of computing <span></span><math>\n \n <mrow>\n <mi>c</mi>\n </mrow></math> and noted that this long-term behaviour occurs when <span></span><math>\n \n <mrow>\n <mi>n</mi>\n </mrow></math> is triply exponential in <span></span><math>\n \n <mrow>\n <mo>∣</mo>\n \n <mi>H</mi>\n \n <mo>∣</mo>\n </mrow></math>. Very recently, Bucić and Sudakov revived the problem and established an essentially tight bound on <span></span><math>\n \n <mrow>\n <mi>n</mi>\n </mrow></math> by showing <span></span><math>\n \n <mrow>\n <mi>r</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>n</mi>\n \n <mi>H</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n </mrow></math> follows this behaviour already when the number of copies is just a single exponential. We provide significantly stronger bounds on <span></span><math>\n \n <mrow>\n <mi>n</mi>\n </mrow></math> in case <span></span><math>\n \n <mrow>\n <mi>H</mi>\n </mrow></math> is a sparse graph, most notably of bounded maximum degree. These are relatable to the current state-of-the-art bounds on <span></span><math>\n \n <mrow>\n <mi>r</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>H</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow></math> and (in a way) tight. Our methods rely on a beautiful classic proof of Graham, Rödl and Ruciński, with an emphasis on developing an efficient absorbing method for bounded degree graphs.</p>","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"106 4","pages":"843-870"},"PeriodicalIF":0.9000,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jgt.23100","citationCount":"0","resultStr":"{\"title\":\"Ramsey numbers for multiple copies of sparse graphs\",\"authors\":\"Aurelio Sulser, Miloš Trujić\",\"doi\":\"10.1002/jgt.23100\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>For a graph <span></span><math>\\n \\n <mrow>\\n <mi>H</mi>\\n </mrow></math> and an integer <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n </mrow></math>, we let <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mi>H</mi>\\n </mrow></math> denote the disjoint union of <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n </mrow></math> copies of <span></span><math>\\n \\n <mrow>\\n <mi>H</mi>\\n </mrow></math>. In 1975, Burr, Erdős and Spencer initiated the study of Ramsey numbers for <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mi>H</mi>\\n </mrow></math>, one of few instances for which Ramsey numbers are now known precisely. They showed that there is a constant <span></span><math>\\n \\n <mrow>\\n <mi>c</mi>\\n \\n <mo>=</mo>\\n \\n <mi>c</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>H</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow></math> such that <span></span><math>\\n \\n <mrow>\\n <mi>r</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mi>H</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mo>=</mo>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mn>2</mn>\\n \\n <mo>∣</mo>\\n \\n <mi>H</mi>\\n \\n <mo>∣</mo>\\n \\n <mo>−</mo>\\n \\n <mi>α</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>H</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mi>n</mi>\\n \\n <mo>+</mo>\\n \\n <mi>c</mi>\\n </mrow></math>, provided <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n </mrow></math> is sufficiently large. Subsequently, Burr gave an implicit way of computing <span></span><math>\\n \\n <mrow>\\n <mi>c</mi>\\n </mrow></math> and noted that this long-term behaviour occurs when <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n </mrow></math> is triply exponential in <span></span><math>\\n \\n <mrow>\\n <mo>∣</mo>\\n \\n <mi>H</mi>\\n \\n <mo>∣</mo>\\n </mrow></math>. Very recently, Bucić and Sudakov revived the problem and established an essentially tight bound on <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n </mrow></math> by showing <span></span><math>\\n \\n <mrow>\\n <mi>r</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mi>H</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow></math> follows this behaviour already when the number of copies is just a single exponential. We provide significantly stronger bounds on <span></span><math>\\n \\n <mrow>\\n <mi>n</mi>\\n </mrow></math> in case <span></span><math>\\n \\n <mrow>\\n <mi>H</mi>\\n </mrow></math> is a sparse graph, most notably of bounded maximum degree. These are relatable to the current state-of-the-art bounds on <span></span><math>\\n \\n <mrow>\\n <mi>r</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>H</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow></math> and (in a way) tight. Our methods rely on a beautiful classic proof of Graham, Rödl and Ruciński, with an emphasis on developing an efficient absorbing method for bounded degree graphs.</p>\",\"PeriodicalId\":16014,\"journal\":{\"name\":\"Journal of Graph Theory\",\"volume\":\"106 4\",\"pages\":\"843-870\"},\"PeriodicalIF\":0.9000,\"publicationDate\":\"2024-04-11\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jgt.23100\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Graph Theory\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23100\",\"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.23100","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
Ramsey numbers for multiple copies of sparse graphs
For a graph and an integer , we let denote the disjoint union of copies of . In 1975, Burr, Erdős and Spencer initiated the study of Ramsey numbers for , one of few instances for which Ramsey numbers are now known precisely. They showed that there is a constant such that , provided is sufficiently large. Subsequently, Burr gave an implicit way of computing and noted that this long-term behaviour occurs when is triply exponential in . Very recently, Bucić and Sudakov revived the problem and established an essentially tight bound on by showing follows this behaviour already when the number of copies is just a single exponential. We provide significantly stronger bounds on in case is a sparse graph, most notably of bounded maximum degree. These are relatable to the current state-of-the-art bounds on and (in a way) tight. Our methods rely on a beautiful classic proof of Graham, Rödl and Ruciński, with an emphasis on developing an efficient absorbing method for bounded degree graphs.
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 .