{"title":"在具有大最小半度的图中计算定向树","authors":"Felix Joos, Jonathan Schrodt","doi":"10.1016/j.jctb.2024.05.004","DOIUrl":null,"url":null,"abstract":"<div><p>Let <em>T</em> be an oriented tree on <em>n</em> vertices with maximum degree at most <span><math><msup><mrow><mi>e</mi></mrow><mrow><mi>o</mi><mo>(</mo><msqrt><mrow><mi>log</mi><mo></mo><mi>n</mi></mrow></msqrt><mo>)</mo></mrow></msup></math></span>. If <em>G</em> is a digraph on <em>n</em> vertices with minimum semidegree <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>0</mn></mrow></msup><mo>(</mo><mi>G</mi><mo>)</mo><mo>≥</mo><mo>(</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>2</mn></mrow></mfrac><mo>+</mo><mi>o</mi><mo>(</mo><mn>1</mn><mo>)</mo><mo>)</mo><mi>n</mi></math></span>, then <em>G</em> contains <em>T</em> as a spanning tree, as recently shown by Kathapurkar and Montgomery (in fact, they only require maximum degree <span><math><mi>o</mi><mo>(</mo><mi>n</mi><mo>/</mo><mi>log</mi><mo></mo><mi>n</mi><mo>)</mo></math></span>). This generalizes the corresponding result by Komlós, Sárközy and Szemerédi for graphs. We investigate the natural question how many copies of <em>T</em> the digraph <em>G</em> contains. Our main result states that every such <em>G</em> contains at least <span><math><mo>|</mo><mrow><mi>Aut</mi><mi>(</mi><mi>T</mi><mi>)</mi></mrow><mspace></mspace><msup><mrow><mo>|</mo></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><msup><mrow><mo>(</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>2</mn></mrow></mfrac><mo>−</mo><mi>o</mi><mo>(</mo><mn>1</mn><mo>)</mo><mo>)</mo></mrow><mrow><mi>n</mi></mrow></msup><mi>n</mi><mo>!</mo></math></span> copies of <em>T</em>, which is optimal. This implies the analogous result in the undirected case.</p></div>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":16.4000,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0095895624000431/pdfft?md5=7f84c56186e46b0ae787c373b4164785&pid=1-s2.0-S0095895624000431-main.pdf","citationCount":"0","resultStr":"{\"title\":\"Counting oriented trees in digraphs with large minimum semidegree\",\"authors\":\"Felix Joos, Jonathan Schrodt\",\"doi\":\"10.1016/j.jctb.2024.05.004\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>Let <em>T</em> be an oriented tree on <em>n</em> vertices with maximum degree at most <span><math><msup><mrow><mi>e</mi></mrow><mrow><mi>o</mi><mo>(</mo><msqrt><mrow><mi>log</mi><mo></mo><mi>n</mi></mrow></msqrt><mo>)</mo></mrow></msup></math></span>. If <em>G</em> is a digraph on <em>n</em> vertices with minimum semidegree <span><math><msup><mrow><mi>δ</mi></mrow><mrow><mn>0</mn></mrow></msup><mo>(</mo><mi>G</mi><mo>)</mo><mo>≥</mo><mo>(</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>2</mn></mrow></mfrac><mo>+</mo><mi>o</mi><mo>(</mo><mn>1</mn><mo>)</mo><mo>)</mo><mi>n</mi></math></span>, then <em>G</em> contains <em>T</em> as a spanning tree, as recently shown by Kathapurkar and Montgomery (in fact, they only require maximum degree <span><math><mi>o</mi><mo>(</mo><mi>n</mi><mo>/</mo><mi>log</mi><mo></mo><mi>n</mi><mo>)</mo></math></span>). This generalizes the corresponding result by Komlós, Sárközy and Szemerédi for graphs. We investigate the natural question how many copies of <em>T</em> the digraph <em>G</em> contains. Our main result states that every such <em>G</em> contains at least <span><math><mo>|</mo><mrow><mi>Aut</mi><mi>(</mi><mi>T</mi><mi>)</mi></mrow><mspace></mspace><msup><mrow><mo>|</mo></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><msup><mrow><mo>(</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>2</mn></mrow></mfrac><mo>−</mo><mi>o</mi><mo>(</mo><mn>1</mn><mo>)</mo><mo>)</mo></mrow><mrow><mi>n</mi></mrow></msup><mi>n</mi><mo>!</mo></math></span> copies of <em>T</em>, which is optimal. This implies the analogous result in the undirected case.</p></div>\",\"PeriodicalId\":1,\"journal\":{\"name\":\"Accounts of Chemical Research\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":16.4000,\"publicationDate\":\"2024-05-29\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://www.sciencedirect.com/science/article/pii/S0095895624000431/pdfft?md5=7f84c56186e46b0ae787c373b4164785&pid=1-s2.0-S0095895624000431-main.pdf\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Accounts of Chemical Research\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0095895624000431\",\"RegionNum\":1,\"RegionCategory\":\"化学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"CHEMISTRY, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Accounts of Chemical Research","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0095895624000431","RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
摘要
设 T 是 n 个顶点上的定向树,其最大度最多为 eo(logn)。如果 G 是 n 个顶点上的数图,最小半度 δ0(G)≥(12+o(1))n,那么 G 包含作为生成树的 T,正如 Kathapurkar 和 Montgomery 最近证明的那样(事实上,他们只要求最大度为 o(n/logn))。这推广了 Komlós、Sárközy 和 Szemerédi 对图的相应结果。我们研究了数图 G 包含多少份 T 的自然问题。我们的主要结果表明,每个这样的 G 至少包含 T 的 |Aut(T)|-1(12-o(1))nn!这意味着无向情况下的类似结果。
Counting oriented trees in digraphs with large minimum semidegree
Let T be an oriented tree on n vertices with maximum degree at most . If G is a digraph on n vertices with minimum semidegree , then G contains T as a spanning tree, as recently shown by Kathapurkar and Montgomery (in fact, they only require maximum degree ). This generalizes the corresponding result by Komlós, Sárközy and Szemerédi for graphs. We investigate the natural question how many copies of T the digraph G contains. Our main result states that every such G contains at least copies of T, which is optimal. This implies the analogous result in the undirected case.
期刊介绍:
Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance.
Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.