{"title":"多色图兰数 II:鲁兹萨-塞梅雷迪定理的一般化以及关于小群和奇数循环的新结果","authors":"Benedek Kovács, Zoltán Lóránt Nagy","doi":"10.1002/jgt.23147","DOIUrl":null,"url":null,"abstract":"<p>In this paper we continue the study of a natural generalization of Turán's forbidden subgraph problem and the Ruzsa–Szemerédi problem. Let <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <msub>\n <mtext>ex</mtext>\n \n <mi>F</mi>\n </msub>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>n</mi>\n \n <mo>,</mo>\n \n <mi>G</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n </mrow>\n <annotation> ${\\text{ex}}_{F}(n,G)$</annotation>\n </semantics></math> denote the maximum number of edge-disjoint copies of a fixed simple graph <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>F</mi>\n </mrow>\n </mrow>\n <annotation> $F$</annotation>\n </semantics></math> that can be placed on an <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>n</mi>\n </mrow>\n </mrow>\n <annotation> $n$</annotation>\n </semantics></math>-vertex ground set without forming a subgraph <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n </mrow>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> whose edges are from different <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>F</mi>\n </mrow>\n </mrow>\n <annotation> $F$</annotation>\n </semantics></math>-copies. The case when both <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>F</mi>\n </mrow>\n </mrow>\n <annotation> $F$</annotation>\n </semantics></math> and <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n </mrow>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> are triangles essentially gives back the theorem of Ruzsa and Szemerédi. We extend their results to the case when <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>F</mi>\n </mrow>\n </mrow>\n <annotation> $F$</annotation>\n </semantics></math> and <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n </mrow>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> are arbitrary cliques by applying a number theoretic result due to Erdős, Frankl, and Rödl. This extension in turn decides the order of magnitude for a large family of graph pairs, which will be subquadratic, but almost quadratic. Since the linear <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>r</mi>\n </mrow>\n </mrow>\n <annotation> $r$</annotation>\n </semantics></math>-uniform hypergraph Turán problems to determine <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <msubsup>\n <mtext>ex</mtext>\n \n <mi>r</mi>\n \n <mrow>\n <mi>l</mi>\n \n <mi>i</mi>\n \n <mi>n</mi>\n </mrow>\n </msubsup>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>n</mi>\n \n <mo>,</mo>\n \n <mi>G</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n </mrow>\n <annotation> ${\\text{ex}}_{r}^{lin}(n,G)$</annotation>\n </semantics></math> form a class of the multicolor Turán problem, following the identity <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <msubsup>\n <mtext>ex</mtext>\n \n <mi>r</mi>\n \n <mrow>\n <mi>l</mi>\n \n <mi>i</mi>\n \n <mi>n</mi>\n </mrow>\n </msubsup>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>n</mi>\n \n <mo>,</mo>\n \n <mi>G</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n \n <mo>=</mo>\n \n <msub>\n <mtext>ex</mtext>\n \n <msub>\n <mi>K</mi>\n \n <mi>r</mi>\n </msub>\n </msub>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>n</mi>\n \n <mo>,</mo>\n \n <mi>G</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n </mrow>\n <annotation> ${\\text{ex}}_{r}^{lin}(n,G)={\\text{ex}}_{{K}_{r}}(n,G)$</annotation>\n </semantics></math>, our results determine the linear hypergraph Turán numbers of every graph of girth 3 and for every <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>r</mi>\n </mrow>\n </mrow>\n <annotation> $r$</annotation>\n </semantics></math> up to a subpolynomial factor. Furthermore, when <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n </mrow>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> is a triangle, we settle the case <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>F</mi>\n \n <mo>=</mo>\n \n <msub>\n <mi>C</mi>\n \n <mn>5</mn>\n </msub>\n </mrow>\n </mrow>\n <annotation> $F={C}_{5}$</annotation>\n </semantics></math> and give bounds for the cases <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>F</mi>\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 </mrow>\n </mrow>\n <annotation> $F={C}_{2k+1}$</annotation>\n </semantics></math>, <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>k</mi>\n \n <mo>≥</mo>\n \n <mn>3</mn>\n </mrow>\n </mrow>\n <annotation> $k\\ge 3$</annotation>\n </semantics></math> as well.</p>","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"107 3","pages":"629-641"},"PeriodicalIF":0.9000,"publicationDate":"2024-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Multicolor Turán numbers II: A generalization of the Ruzsa–Szemerédi theorem and new results on cliques and odd cycles\",\"authors\":\"Benedek Kovács, Zoltán Lóránt Nagy\",\"doi\":\"10.1002/jgt.23147\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>In this paper we continue the study of a natural generalization of Turán's forbidden subgraph problem and the Ruzsa–Szemerédi problem. Let <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <msub>\\n <mtext>ex</mtext>\\n \\n <mi>F</mi>\\n </msub>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mo>,</mo>\\n \\n <mi>G</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow>\\n </mrow>\\n <annotation> ${\\\\text{ex}}_{F}(n,G)$</annotation>\\n </semantics></math> denote the maximum number of edge-disjoint copies of a fixed simple graph <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>F</mi>\\n </mrow>\\n </mrow>\\n <annotation> $F$</annotation>\\n </semantics></math> that can be placed on an <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>n</mi>\\n </mrow>\\n </mrow>\\n <annotation> $n$</annotation>\\n </semantics></math>-vertex ground set without forming a subgraph <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow>\\n </mrow>\\n <annotation> $G$</annotation>\\n </semantics></math> whose edges are from different <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>F</mi>\\n </mrow>\\n </mrow>\\n <annotation> $F$</annotation>\\n </semantics></math>-copies. The case when both <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>F</mi>\\n </mrow>\\n </mrow>\\n <annotation> $F$</annotation>\\n </semantics></math> and <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow>\\n </mrow>\\n <annotation> $G$</annotation>\\n </semantics></math> are triangles essentially gives back the theorem of Ruzsa and Szemerédi. We extend their results to the case when <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>F</mi>\\n </mrow>\\n </mrow>\\n <annotation> $F$</annotation>\\n </semantics></math> and <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow>\\n </mrow>\\n <annotation> $G$</annotation>\\n </semantics></math> are arbitrary cliques by applying a number theoretic result due to Erdős, Frankl, and Rödl. This extension in turn decides the order of magnitude for a large family of graph pairs, which will be subquadratic, but almost quadratic. Since the linear <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>r</mi>\\n </mrow>\\n </mrow>\\n <annotation> $r$</annotation>\\n </semantics></math>-uniform hypergraph Turán problems to determine <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <msubsup>\\n <mtext>ex</mtext>\\n \\n <mi>r</mi>\\n \\n <mrow>\\n <mi>l</mi>\\n \\n <mi>i</mi>\\n \\n <mi>n</mi>\\n </mrow>\\n </msubsup>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mo>,</mo>\\n \\n <mi>G</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow>\\n </mrow>\\n <annotation> ${\\\\text{ex}}_{r}^{lin}(n,G)$</annotation>\\n </semantics></math> form a class of the multicolor Turán problem, following the identity <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <msubsup>\\n <mtext>ex</mtext>\\n \\n <mi>r</mi>\\n \\n <mrow>\\n <mi>l</mi>\\n \\n <mi>i</mi>\\n \\n <mi>n</mi>\\n </mrow>\\n </msubsup>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mo>,</mo>\\n \\n <mi>G</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mo>=</mo>\\n \\n <msub>\\n <mtext>ex</mtext>\\n \\n <msub>\\n <mi>K</mi>\\n \\n <mi>r</mi>\\n </msub>\\n </msub>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>n</mi>\\n \\n <mo>,</mo>\\n \\n <mi>G</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow>\\n </mrow>\\n <annotation> ${\\\\text{ex}}_{r}^{lin}(n,G)={\\\\text{ex}}_{{K}_{r}}(n,G)$</annotation>\\n </semantics></math>, our results determine the linear hypergraph Turán numbers of every graph of girth 3 and for every <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>r</mi>\\n </mrow>\\n </mrow>\\n <annotation> $r$</annotation>\\n </semantics></math> up to a subpolynomial factor. Furthermore, when <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow>\\n </mrow>\\n <annotation> $G$</annotation>\\n </semantics></math> is a triangle, we settle the case <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>F</mi>\\n \\n <mo>=</mo>\\n \\n <msub>\\n <mi>C</mi>\\n \\n <mn>5</mn>\\n </msub>\\n </mrow>\\n </mrow>\\n <annotation> $F={C}_{5}$</annotation>\\n </semantics></math> and give bounds for the cases <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>F</mi>\\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 </mrow>\\n </mrow>\\n <annotation> $F={C}_{2k+1}$</annotation>\\n </semantics></math>, <span></span><math>\\n <semantics>\\n <mrow>\\n \\n <mrow>\\n <mi>k</mi>\\n \\n <mo>≥</mo>\\n \\n <mn>3</mn>\\n </mrow>\\n </mrow>\\n <annotation> $k\\\\ge 3$</annotation>\\n </semantics></math> as well.</p>\",\"PeriodicalId\":16014,\"journal\":{\"name\":\"Journal of Graph Theory\",\"volume\":\"107 3\",\"pages\":\"629-641\"},\"PeriodicalIF\":0.9000,\"publicationDate\":\"2024-07-14\",\"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.23147\",\"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.23147","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
Multicolor Turán numbers II: A generalization of the Ruzsa–Szemerédi theorem and new results on cliques and odd cycles
In this paper we continue the study of a natural generalization of Turán's forbidden subgraph problem and the Ruzsa–Szemerédi problem. Let denote the maximum number of edge-disjoint copies of a fixed simple graph that can be placed on an -vertex ground set without forming a subgraph whose edges are from different -copies. The case when both and are triangles essentially gives back the theorem of Ruzsa and Szemerédi. We extend their results to the case when and are arbitrary cliques by applying a number theoretic result due to Erdős, Frankl, and Rödl. This extension in turn decides the order of magnitude for a large family of graph pairs, which will be subquadratic, but almost quadratic. Since the linear -uniform hypergraph Turán problems to determine form a class of the multicolor Turán problem, following the identity , our results determine the linear hypergraph Turán numbers of every graph of girth 3 and for every up to a subpolynomial factor. Furthermore, when is a triangle, we settle the case and give bounds for the cases , as well.
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.
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