{"title":"折线图的去周期数","authors":"","doi":"10.1016/j.disc.2024.114291","DOIUrl":null,"url":null,"abstract":"<div><div>The decycling number of a graph <em>G</em>, denoted by <span><math><mi>∇</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>, is the number of vertices in a minimum decycling set of <em>G</em>. The line graph of <em>G</em> is denoted by <span><math><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>. In this paper we show that <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>=</mo><mi>β</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>+</mo><mi>μ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>−</mo><mn>1</mn></math></span>, where <span><math><mi>β</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> is the cycle rank of <em>G</em> and <span><math><mi>μ</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> is the path partition number of <em>G</em>. In particular, <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>=</mo><mi>β</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> if and only if <em>G</em> has a Hamilton path, and <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>≤</mo><mfrac><mrow><mn>2</mn><mi>n</mi></mrow><mrow><mn>3</mn></mrow></mfrac><mo>−</mo><mfrac><mrow><mn>2</mn></mrow><mrow><mn>3</mn></mrow></mfrac></math></span> if <em>G</em> is a cubic graph with <em>n</em> vertices, where <span><math><mi>n</mi><mo>≥</mo><mn>10</mn></math></span>. If <span><math><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> is a planar graph, then we prove that <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>≤</mo><mfrac><mrow><mo>|</mo><mi>V</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>|</mo></mrow><mrow><mn>2</mn></mrow></mfrac></math></span>, which means that the conjecture proposed by Albertson and Berman in 1979 that the decycling number of any planar graph <em>H</em> is at most <span><math><mfrac><mrow><mo>|</mo><mi>V</mi><mo>(</mo><mi>H</mi><mo>)</mo><mo>|</mo></mrow><mrow><mn>2</mn></mrow></mfrac></math></span> holds for a planar line graph. If <em>G</em> is a connected graph of order <em>n</em> which is 2-cell embedded on the orientable surface <span><math><msub><mrow><mo>∑</mo></mrow><mrow><mi>g</mi></mrow></msub></math></span> (or the non-orientable surface <span><math><msubsup><mrow><mo>∑</mo></mrow><mrow><mi>k</mi></mrow><mrow><mo>′</mo></mrow></msubsup></math></span>), then we show that <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>≤</mo><mn>2</mn><mi>n</mi><mo>+</mo><mi>l</mi><mo>−</mo><mn>7</mn><mo>+</mo><mn>6</mn><mi>g</mi></math></span> (or <span><math><mn>2</mn><mi>n</mi><mo>+</mo><mi>l</mi><mo>−</mo><mn>7</mn><mo>+</mo><mn>3</mn><mi>k</mi></math></span>) if <em>G</em> has a spanning tree with <em>l</em> leaves. Our bounds are tight for <span><math><mi>l</mi><mo>=</mo><mn>2</mn></math></span>.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":null,"pages":null},"PeriodicalIF":0.7000,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"The decycling number of a line graph\",\"authors\":\"\",\"doi\":\"10.1016/j.disc.2024.114291\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>The decycling number of a graph <em>G</em>, denoted by <span><math><mi>∇</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>, is the number of vertices in a minimum decycling set of <em>G</em>. The line graph of <em>G</em> is denoted by <span><math><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>. In this paper we show that <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>=</mo><mi>β</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>+</mo><mi>μ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>−</mo><mn>1</mn></math></span>, where <span><math><mi>β</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> is the cycle rank of <em>G</em> and <span><math><mi>μ</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> is the path partition number of <em>G</em>. In particular, <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>=</mo><mi>β</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> if and only if <em>G</em> has a Hamilton path, and <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>≤</mo><mfrac><mrow><mn>2</mn><mi>n</mi></mrow><mrow><mn>3</mn></mrow></mfrac><mo>−</mo><mfrac><mrow><mn>2</mn></mrow><mrow><mn>3</mn></mrow></mfrac></math></span> if <em>G</em> is a cubic graph with <em>n</em> vertices, where <span><math><mi>n</mi><mo>≥</mo><mn>10</mn></math></span>. If <span><math><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> is a planar graph, then we prove that <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>≤</mo><mfrac><mrow><mo>|</mo><mi>V</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>|</mo></mrow><mrow><mn>2</mn></mrow></mfrac></math></span>, which means that the conjecture proposed by Albertson and Berman in 1979 that the decycling number of any planar graph <em>H</em> is at most <span><math><mfrac><mrow><mo>|</mo><mi>V</mi><mo>(</mo><mi>H</mi><mo>)</mo><mo>|</mo></mrow><mrow><mn>2</mn></mrow></mfrac></math></span> holds for a planar line graph. If <em>G</em> is a connected graph of order <em>n</em> which is 2-cell embedded on the orientable surface <span><math><msub><mrow><mo>∑</mo></mrow><mrow><mi>g</mi></mrow></msub></math></span> (or the non-orientable surface <span><math><msubsup><mrow><mo>∑</mo></mrow><mrow><mi>k</mi></mrow><mrow><mo>′</mo></mrow></msubsup></math></span>), then we show that <span><math><mi>∇</mi><mo>(</mo><mi>L</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>)</mo><mo>≤</mo><mn>2</mn><mi>n</mi><mo>+</mo><mi>l</mi><mo>−</mo><mn>7</mn><mo>+</mo><mn>6</mn><mi>g</mi></math></span> (or <span><math><mn>2</mn><mi>n</mi><mo>+</mo><mi>l</mi><mo>−</mo><mn>7</mn><mo>+</mo><mn>3</mn><mi>k</mi></math></span>) if <em>G</em> has a spanning tree with <em>l</em> leaves. Our bounds are tight for <span><math><mi>l</mi><mo>=</mo><mn>2</mn></math></span>.</div></div>\",\"PeriodicalId\":50572,\"journal\":{\"name\":\"Discrete Mathematics\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.7000,\"publicationDate\":\"2024-10-22\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Discrete Mathematics\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0012365X24004229\",\"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":"Discrete Mathematics","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0012365X24004229","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
图 G 的去循环数用 ∇(G) 表示,是 G 的最小去循环集合中的顶点数。本文证明了∇(L(G))=β(G)+μ(G)-1,其中β(G)是 G 的循环秩,μ(G)是 G 的路径分割数。尤其是,当且仅当 G 有一条汉密尔顿路径时,∇(L(G))=β(G);当 G 是有 n 个顶点的立方图时,∇(L(G))≤2n3-23,其中 n≥10 。如果 L(G) 是平面图,那么我们证明∇(L(G))≤|V(L(G))|2,这意味着阿尔伯森和伯曼在 1979 年提出的猜想,即任何平面图 H 的去环数最多为|V(H)|2,对于平面线图是成立的。如果 G 是一个阶数为 n 的连通图,并且在可定向曲面 ∑g (或不可定向曲面 ∑k′)上有 2 个单元嵌入,那么我们证明,如果 G 有一棵有 l 个叶子的生成树,∇(L(G))≤2n+l-7+6g(或 2n+l-7+3k)。当 l=2 时,我们的边界是紧密的。
The decycling number of a graph G, denoted by , is the number of vertices in a minimum decycling set of G. The line graph of G is denoted by . In this paper we show that , where is the cycle rank of G and is the path partition number of G. In particular, if and only if G has a Hamilton path, and if G is a cubic graph with n vertices, where . If is a planar graph, then we prove that , which means that the conjecture proposed by Albertson and Berman in 1979 that the decycling number of any planar graph H is at most holds for a planar line graph. If G is a connected graph of order n which is 2-cell embedded on the orientable surface (or the non-orientable surface ), then we show that (or ) if G has a spanning tree with l leaves. Our bounds are tight for .
期刊介绍:
Discrete Mathematics provides a common forum for significant research in many areas of discrete mathematics and combinatorics. Among the fields covered by Discrete Mathematics are graph and hypergraph theory, enumeration, coding theory, block designs, the combinatorics of partially ordered sets, extremal set theory, matroid theory, algebraic combinatorics, discrete geometry, matrices, and discrete probability theory.
Items in the journal include research articles (Contributions or Notes, depending on length) and survey/expository articles (Perspectives). Efforts are made to process the submission of Notes (short articles) quickly. The Perspectives section features expository articles accessible to a broad audience that cast new light or present unifying points of view on well-known or insufficiently-known topics.