{"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":0,"journal":{"name":"","volume":null,"pages":null},"PeriodicalIF":0.0,"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\":0,\"journal\":{\"name\":\"\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.0,\"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\":\"\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23100\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"","FirstCategoryId":"100","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23100","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","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.