Pub Date : 2024-09-12DOI: 10.1016/j.disc.2024.114240
Chao Liu, Dabin Zheng , Wei Lu, Xiaoqiang Wang
The study of the generalized Hamming weight of linear codes is a significant research topic in coding theory as it conveys the structural information of the codes and determines their performance in various applications. However, determining the generalized Hamming weights of linear codes, especially the weight hierarchy, is generally challenging. In this paper, we investigate the generalized Hamming weights of a class of linear code over , which is constructed from defining sets. These defining sets are either special simplicial complexes or their complements in . We determine the complete weight hierarchies of these codes by analyzing the maximum or minimum intersection of certain simplicial complexes and all r-dimensional subspaces of , where .
线性编码的广义汉明权重传递了编码的结构信息,决定了编码在各种应用中的性能,因此研究线性编码的广义汉明权重是编码理论中的一个重要研究课题。然而,确定线性编码的广义汉明权重,尤其是权重层次结构,通常具有挑战性。本文研究了一类 Fq 上线性编码 C 的广义汉明权重,该编码由定义集构建。这些定义集要么是特殊的单纯复数,要么是它们在 Fqm 中的补集。我们通过分析某些单纯复数与 Fqm 的所有 r 维子空间的最大或最小交集(其中 1≤r≤dimFq(C) ),确定这些代码的完整权重等级。
{"title":"The weight hierarchies of linear codes from simplicial complexes","authors":"Chao Liu, Dabin Zheng , Wei Lu, Xiaoqiang Wang","doi":"10.1016/j.disc.2024.114240","DOIUrl":"10.1016/j.disc.2024.114240","url":null,"abstract":"<div><p>The study of the generalized Hamming weight of linear codes is a significant research topic in coding theory as it conveys the structural information of the codes and determines their performance in various applications. However, determining the generalized Hamming weights of linear codes, especially the weight hierarchy, is generally challenging. In this paper, we investigate the generalized Hamming weights of a class of linear code <span><math><mi>C</mi></math></span> over <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub></math></span>, which is constructed from defining sets. These defining sets are either special simplicial complexes or their complements in <span><math><msubsup><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow><mrow><mi>m</mi></mrow></msubsup></math></span>. We determine the complete weight hierarchies of these codes by analyzing the maximum or minimum intersection of certain simplicial complexes and all <em>r</em>-dimensional subspaces of <span><math><msubsup><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow><mrow><mi>m</mi></mrow></msubsup></math></span>, where <span><math><mn>1</mn><mo>≤</mo><mi>r</mi><mo>≤</mo><msub><mrow><mi>dim</mi></mrow><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub></mrow></msub><mo>(</mo><mi>C</mi><mo>)</mo></math></span>.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 1","pages":"Article 114240"},"PeriodicalIF":0.7,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0012365X24003716/pdfft?md5=b31c93fc7520c0f919446480a13b7f62&pid=1-s2.0-S0012365X24003716-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142173918","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-12DOI: 10.1016/j.disc.2024.114260
Jin-Hui Fang, Ying Cheng
<div><p>Let <span><math><mi>N</mi></math></span> be the set of all positive integers. For a set <em>A</em> of positive integers, let <span><math><mi>A</mi><mo>∼</mo><mi>N</mi></math></span> denote that <em>A</em> contains all but finitely many positive integers. For an integer <span><math><mi>h</mi><mo>⩾</mo><mn>2</mn></math></span>, define <span><math><mi>h</mi><mi>A</mi><mo>=</mo><mo>{</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><mo>⋯</mo><mo>+</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>:</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>⋯</mo><mo>,</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>∈</mo><mi>A</mi><mo>}</mo></math></span> and <span><math><mi>h</mi><mo>×</mo><mi>A</mi><mo>=</mo><mo>{</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><mo>⋯</mo><mo>+</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>:</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>⋯</mo><mo>,</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>∈</mo><mi>A</mi><mo>,</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>≠</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>j</mi></mrow></msub></math></span> for <span><math><mi>i</mi><mo>≠</mo><mi>j</mi><mo>}</mo></math></span>. In 2023, Chen and Yu [Discrete Math. 346 (2023), Paper No. 113388.] proved that, there exists a set <em>B</em> of positive integers such that: <span><math><msub><mrow><mi>lim</mi></mrow><mrow><mi>x</mi><mo>→</mo><mo>∞</mo></mrow></msub><mo></mo><mi>B</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>/</mo><mi>x</mi><mo>=</mo><mn>1</mn><mo>/</mo><mn>2</mn></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mi>B</mi><mo>)</mo><mo>∼</mo><mi>N</mi></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mo>×</mo><mi>B</mi><mo>)</mo><mo>≁</mo><mi>N</mi></math></span>, and <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mo>×</mo><mi>B</mi><mo>)</mo><mo>⋃</mo><mo>(</mo><mn>3</mn><mo>×</mo><mi>B</mi><mo>)</mo><mo>∼</mo><mi>N</mi></math></span>. In this paper, we construct a <em>somewhat dense</em> set <em>B</em> satisfying the above properties. That is, there exists a set <em>B</em> of positive integers such that: <span><math><msub><mrow><mrow><mi>lim</mi></mrow><mspace></mspace><mrow><mi>inf</mi></mrow></mrow><mrow><mi>x</mi><mo>→</mo><mo>∞</mo></mrow></msub><mspace></mspace><mi>B</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>/</mo><mi>x</mi><mo>=</mo><mn>1</mn><mo>/</mo><mn>2</mn></math></span>, <span><math><msub><mrow><mrow><mi>lim</mi></mrow><mspace></mspace><mrow><mi>sup</mi></mrow></mrow><mrow><mi>x</mi><mo>→</mo><mo>∞</mo></mrow></msub><mspace></mspace><mi>B</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>/</mo><mi>x</mi><mo>=</mo><mn>1</mn></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mi>B</mi><mo>)</mo><mo>∼</mo><mi>N</mi></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><m
设 N 是所有正整数的集合。对于一个正整数集合 A,让 A∼N 表示 A 包含所有但不超过有限个的正整数。对于整数 h⩾2,定义 hA={a1+⋯+ah:a1,⋯,ah∈A} 和 h×A={a1+⋯+ah:a1,⋯,ah∈A,ai≠aj for i≠j} 。2023 年,Chen 和 Yu [Discrete Math. 346 (2023),Paper No. 113388.] 证明,存在一个正整数集合 B,使得:limx→∞B(x)/x=1/2,B⋃(2B)∼N,B⋃(2×B)≁N,且 B⋃(2×B)⋃(3×B)∼N。在本文中,我们将构造一个满足上述性质的略密集 B。也就是说,存在一个正整数集合 B,使得:liminfx→∞B(x)/x=1/2,limsupx→∞B(x)/x=1,B⋃(2B)∼N,B⋃(2×B)≁N,且 B⋃(2×B)⋃(3×B)∼N。
{"title":"On the restricted order of asymptotic bases","authors":"Jin-Hui Fang, Ying Cheng","doi":"10.1016/j.disc.2024.114260","DOIUrl":"10.1016/j.disc.2024.114260","url":null,"abstract":"<div><p>Let <span><math><mi>N</mi></math></span> be the set of all positive integers. For a set <em>A</em> of positive integers, let <span><math><mi>A</mi><mo>∼</mo><mi>N</mi></math></span> denote that <em>A</em> contains all but finitely many positive integers. For an integer <span><math><mi>h</mi><mo>⩾</mo><mn>2</mn></math></span>, define <span><math><mi>h</mi><mi>A</mi><mo>=</mo><mo>{</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><mo>⋯</mo><mo>+</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>:</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>⋯</mo><mo>,</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>∈</mo><mi>A</mi><mo>}</mo></math></span> and <span><math><mi>h</mi><mo>×</mo><mi>A</mi><mo>=</mo><mo>{</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><mo>⋯</mo><mo>+</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>:</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>⋯</mo><mo>,</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>∈</mo><mi>A</mi><mo>,</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>≠</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>j</mi></mrow></msub></math></span> for <span><math><mi>i</mi><mo>≠</mo><mi>j</mi><mo>}</mo></math></span>. In 2023, Chen and Yu [Discrete Math. 346 (2023), Paper No. 113388.] proved that, there exists a set <em>B</em> of positive integers such that: <span><math><msub><mrow><mi>lim</mi></mrow><mrow><mi>x</mi><mo>→</mo><mo>∞</mo></mrow></msub><mo></mo><mi>B</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>/</mo><mi>x</mi><mo>=</mo><mn>1</mn><mo>/</mo><mn>2</mn></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mi>B</mi><mo>)</mo><mo>∼</mo><mi>N</mi></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mo>×</mo><mi>B</mi><mo>)</mo><mo>≁</mo><mi>N</mi></math></span>, and <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mo>×</mo><mi>B</mi><mo>)</mo><mo>⋃</mo><mo>(</mo><mn>3</mn><mo>×</mo><mi>B</mi><mo>)</mo><mo>∼</mo><mi>N</mi></math></span>. In this paper, we construct a <em>somewhat dense</em> set <em>B</em> satisfying the above properties. That is, there exists a set <em>B</em> of positive integers such that: <span><math><msub><mrow><mrow><mi>lim</mi></mrow><mspace></mspace><mrow><mi>inf</mi></mrow></mrow><mrow><mi>x</mi><mo>→</mo><mo>∞</mo></mrow></msub><mspace></mspace><mi>B</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>/</mo><mi>x</mi><mo>=</mo><mn>1</mn><mo>/</mo><mn>2</mn></math></span>, <span><math><msub><mrow><mrow><mi>lim</mi></mrow><mspace></mspace><mrow><mi>sup</mi></mrow></mrow><mrow><mi>x</mi><mo>→</mo><mo>∞</mo></mrow></msub><mspace></mspace><mi>B</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>/</mo><mi>x</mi><mo>=</mo><mn>1</mn></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><mn>2</mn><mi>B</mi><mo>)</mo><mo>∼</mo><mi>N</mi></math></span>, <span><math><mi>B</mi><mo>⋃</mo><mo>(</mo><m","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 1","pages":"Article 114260"},"PeriodicalIF":0.7,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0012365X24003911/pdfft?md5=aacfc54f27829de05568c6d3ed5aa0a2&pid=1-s2.0-S0012365X24003911-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142173812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We correct an error in Theorem 13 in our published article Barik et al. [1].
我们纠正了已发表文章 Barik 等人 [1] 中定理 13 中的一个错误。
{"title":"Corrigendum to “Singular graphs and the reciprocal eigenvalue property” [Discrete Math. 347 (2024) 114003]","authors":"Sasmita Barik , Debabrota Mondal , Sukanta Pati , Kuldeep Sarma","doi":"10.1016/j.disc.2024.114198","DOIUrl":"10.1016/j.disc.2024.114198","url":null,"abstract":"<div><div>We correct an error in <span><span>Theorem 13</span></span> in our published article Barik et al. <span><span>[1]</span></span>.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 1","pages":"Article 114198"},"PeriodicalIF":0.7,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-12DOI: 10.1016/j.disc.2024.114256
Ezgi Kantarcı Oğuz
We define oriented posets with corresponding rank matrices, where linking two posets by an edge corresponds to matrix multiplication. In particular, linking chains via this method gives us fence posets, and taking traces gives us circular fence posets. As an application, we give a combinatorial model for q-deformed Markov numbers. We also resolve a conjecture of Leclere and Morier-Genoud and give several identities between circular rank polynomials.
{"title":"Oriented posets, rank matrices and q-deformed Markov numbers","authors":"Ezgi Kantarcı Oğuz","doi":"10.1016/j.disc.2024.114256","DOIUrl":"10.1016/j.disc.2024.114256","url":null,"abstract":"<div><p>We define <em>oriented posets</em> with corresponding <em>rank matrices</em>, where linking two posets by an edge corresponds to matrix multiplication. In particular, linking chains via this method gives us fence posets, and taking traces gives us circular fence posets. As an application, we give a combinatorial model for <em>q</em>-deformed Markov numbers. We also resolve a conjecture of Leclere and Morier-Genoud and give several identities between circular rank polynomials.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 2","pages":"Article 114256"},"PeriodicalIF":0.7,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142172371","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-11DOI: 10.1016/j.disc.2024.114250
Cheng Yeaw Ku , Kok Bin Wong
Let be the set of non-negative integers, and let denote the set of all weak compositions of n with k parts, i.e., . For any element , denote its ith-coordinate by , i.e., . A family is said to be t-intersecting if for all . In this paper, we consider the diversity and other intersecting theorems for weak compositions.
设 N0 为非负整数集合,P(n,k) 表示 n 的所有 k 部分的弱合成集合,即 P(n,k)={(x1,x2,...,xk)∈N0k:x1+x2+⋯+xk=n}。对于任何元素 u=(u1,u2,...,uk)∈P(n,k),用 u(i) 表示其 ith 坐标,即 u(i)=ui 。对于所有 u,v∈A,如果|{i:u(i)=v(i)}|≥t,则称一个族 A⊆P(n,k)为 t 交族。在本文中,我们将考虑弱组合的多样性和其他相交定理。
{"title":"Diversity and intersecting theorems for weak compositions","authors":"Cheng Yeaw Ku , Kok Bin Wong","doi":"10.1016/j.disc.2024.114250","DOIUrl":"10.1016/j.disc.2024.114250","url":null,"abstract":"<div><p>Let <span><math><msub><mrow><mi>N</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> be the set of non-negative integers, and let <span><math><mi>P</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>)</mo></math></span> denote the set of all weak compositions of <em>n</em> with <em>k</em> parts, i.e., <span><math><mi>P</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>)</mo><mo>=</mo><mo>{</mo><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>x</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>)</mo><mo>∈</mo><msubsup><mrow><mi>N</mi></mrow><mrow><mn>0</mn></mrow><mrow><mi>k</mi></mrow></msubsup><mspace></mspace><mo>:</mo><mspace></mspace><msub><mrow><mi>x</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><mo>⋯</mo><mo>+</mo><msub><mrow><mi>x</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>=</mo><mi>n</mi><mo>}</mo></math></span>. For any element <span><math><mi>u</mi><mo>=</mo><mo>(</mo><msub><mrow><mi>u</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><msub><mrow><mi>u</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>u</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>)</mo><mo>∈</mo><mi>P</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>)</mo></math></span>, denote its <em>i</em>th-coordinate by <span><math><mi>u</mi><mo>(</mo><mi>i</mi><mo>)</mo></math></span>, i.e., <span><math><mi>u</mi><mo>(</mo><mi>i</mi><mo>)</mo><mo>=</mo><msub><mrow><mi>u</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span>. A family <span><math><mi>A</mi><mo>⊆</mo><mi>P</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>)</mo></math></span> is said to be <em>t</em>-intersecting if <span><math><mo>|</mo><mo>{</mo><mi>i</mi><mspace></mspace><mo>:</mo><mspace></mspace><mi>u</mi><mo>(</mo><mi>i</mi><mo>)</mo><mo>=</mo><mi>v</mi><mo>(</mo><mi>i</mi><mo>)</mo><mo>}</mo><mo>|</mo><mo>≥</mo><mi>t</mi></math></span> for all <span><math><mi>u</mi><mo>,</mo><mi>v</mi><mo>∈</mo><mi>A</mi></math></span>. In this paper, we consider the diversity and other intersecting theorems for weak compositions.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 2","pages":"Article 114250"},"PeriodicalIF":0.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-11DOI: 10.1016/j.disc.2024.114239
Jack H. Koolen , Chenhui Lv , Jongyook Park , Qianqian Yang
Let Γ be a distance-regular graph with classical parameters and . It is known that Γ is Q-polynomial with respect to , where is the second largest eigenvalue of Γ. And it was shown that for a distance-regular graph Γ with classical parameters , and , if is large enough compared to b and Γ is thin, then the intersection number of Γ is bounded above by a function of b. In this paper, we obtain a similar result without the assumption that the graph Γ is thin.
{"title":"Bounding the intersection number c2 of a distance-regular graph with classical parameters (D,b,α,β) in terms of b","authors":"Jack H. Koolen , Chenhui Lv , Jongyook Park , Qianqian Yang","doi":"10.1016/j.disc.2024.114239","DOIUrl":"10.1016/j.disc.2024.114239","url":null,"abstract":"<div><p>Let Γ be a distance-regular graph with classical parameters <span><math><mo>(</mo><mi>D</mi><mo>,</mo><mi>b</mi><mo>,</mo><mi>α</mi><mo>,</mo><mi>β</mi><mo>)</mo></math></span> and <span><math><mi>b</mi><mo>≥</mo><mn>1</mn></math></span>. It is known that Γ is <em>Q</em>-polynomial with respect to <span><math><msub><mrow><mi>θ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>, where <span><math><msub><mrow><mi>θ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>=</mo><mfrac><mrow><msub><mrow><mi>b</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow><mrow><mi>b</mi></mrow></mfrac><mo>−</mo><mn>1</mn></math></span> is the second largest eigenvalue of Γ. And it was shown that for a distance-regular graph Γ with classical parameters <span><math><mo>(</mo><mi>D</mi><mo>,</mo><mi>b</mi><mo>,</mo><mi>α</mi><mo>,</mo><mi>β</mi><mo>)</mo></math></span>, <span><math><mi>D</mi><mo>≥</mo><mn>5</mn></math></span> and <span><math><mi>b</mi><mo>≥</mo><mn>1</mn></math></span>, if <span><math><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> is large enough compared to <em>b</em> and Γ is thin, then the intersection number <span><math><msub><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> of Γ is bounded above by a function of <em>b</em>. In this paper, we obtain a similar result without the assumption that the graph Γ is thin.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 2","pages":"Article 114239"},"PeriodicalIF":0.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-11DOI: 10.1016/j.disc.2024.114238
Myungho Choi, Hojin Chu, Suh-Ryung Kim
The Friendship Theorem states that if in a party any pair of persons has precisely one common friend, then there is always a person who is everybody's friend and the theorem has been proved by Paul Erdős, Alfréd Rényi, and Vera T. Sós in 1966. “What would happen if instead any pair of persons likes precisely one person?” While a friendship relation is symmetric, a liking relation may not be symmetric. Therefore to represent a liking relation we should use a directed graph. We call this digraph a “liking digraph”. It is easy to check that a symmetric liking digraph becomes a friendship graph if each directed cycle of length two is replaced with an edge. In this paper, we provide a digraph formulation of the Friendship Theorem which characterizes the liking digraphs. We also establish a sufficient and necessary condition for the existence of liking digraphs.
{"title":"A digraph version of the Friendship Theorem","authors":"Myungho Choi, Hojin Chu, Suh-Ryung Kim","doi":"10.1016/j.disc.2024.114238","DOIUrl":"10.1016/j.disc.2024.114238","url":null,"abstract":"<div><p>The Friendship Theorem states that if in a party any pair of persons has precisely one common friend, then there is always a person who is everybody's friend and the theorem has been proved by Paul Erdős, Alfréd Rényi, and Vera T. Sós in 1966. “What would happen if instead any pair of persons likes precisely one person?” While a friendship relation is symmetric, a liking relation may not be symmetric. Therefore to represent a liking relation we should use a directed graph. We call this digraph a “liking digraph”. It is easy to check that a symmetric liking digraph becomes a friendship graph if each directed cycle of length two is replaced with an edge. In this paper, we provide a digraph formulation of the Friendship Theorem which characterizes the liking digraphs. We also establish a sufficient and necessary condition for the existence of liking digraphs.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 1","pages":"Article 114238"},"PeriodicalIF":0.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0012365X24003698/pdfft?md5=368b7d4c1379f8549152a904b901804b&pid=1-s2.0-S0012365X24003698-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167394","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-11DOI: 10.1016/j.disc.2024.114249
Xiaocong He , Yongtao Li , Lihua Feng
The Turán number of a graph H is the maximum number of edges in an n-vertex graph which does not contain H as a subgraph. The Turán number of regular polyhedrons was widely studied in a series of works due to Simonovits. In this paper, we shall present the exact Turán number of the prism , which is defined as the Cartesian product of an odd cycle and an edge . Applying a deep theorem of Simonovits and a stability result of Yuan (2022) [55], we shall determine the exact value of for every and sufficiently large n, and we also characterize the extremal graphs. Moreover, in the case of , motivated by a recent result of Xiao et al. (2022) [49], we will determine the exact value of for every n instead of for sufficiently large n.
图 H 的图兰数 ex(n,H) 是 n 个顶点图中不包含 H 作为子图的最大边数。西蒙诺维茨在一系列著作中对正多面体的图兰数进行了广泛研究。在本文中,我们将提出棱 C2k+1□ 的精确图兰数,它被定义为奇数循环 C2k+1 与边 K2 的笛卡尔积。应用 Simonovits 的深层定理和 Yuan (2022) 的稳定性结果[55],我们将确定每 k≥1 且 n 足够大时 ex(n,C2k+1□) 的精确值,并描述极值图的特征。此外,在 k=1 的情况下,受肖等人(2022)的最新结果[49]的启发,我们将确定每个 n 而不是足够大的 n 的 ex(n,C3□) 的精确值。
{"title":"Extremal graphs for the odd prism","authors":"Xiaocong He , Yongtao Li , Lihua Feng","doi":"10.1016/j.disc.2024.114249","DOIUrl":"10.1016/j.disc.2024.114249","url":null,"abstract":"<div><p>The Turán number <span><math><mrow><mi>ex</mi></mrow><mo>(</mo><mi>n</mi><mo>,</mo><mi>H</mi><mo>)</mo></math></span> of a graph <em>H</em> is the maximum number of edges in an <em>n</em>-vertex graph which does not contain <em>H</em> as a subgraph. The Turán number of regular polyhedrons was widely studied in a series of works due to Simonovits. In this paper, we shall present the exact Turán number of the prism <span><math><msubsup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow><mrow><mo>□</mo></mrow></msubsup></math></span>, which is defined as the Cartesian product of an odd cycle <span><math><msub><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub></math></span> and an edge <span><math><msub><mrow><mi>K</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>. Applying a deep theorem of Simonovits and a stability result of Yuan (2022) <span><span>[55]</span></span>, we shall determine the exact value of <span><math><mrow><mi>ex</mi></mrow><mo>(</mo><mi>n</mi><mo>,</mo><msubsup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow><mrow><mo>□</mo></mrow></msubsup><mo>)</mo></math></span> for every <span><math><mi>k</mi><mo>≥</mo><mn>1</mn></math></span> and sufficiently large <em>n</em>, and we also characterize the extremal graphs. Moreover, in the case of <span><math><mi>k</mi><mo>=</mo><mn>1</mn></math></span>, motivated by a recent result of Xiao et al. (2022) <span><span>[49]</span></span>, we will determine the exact value of <span><math><mrow><mi>ex</mi></mrow><mo>(</mo><mi>n</mi><mo>,</mo><msubsup><mrow><mi>C</mi></mrow><mrow><mn>3</mn></mrow><mrow><mo>□</mo></mrow></msubsup><mo>)</mo></math></span> for every <em>n</em> instead of for sufficiently large <em>n</em>.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 1","pages":"Article 114249"},"PeriodicalIF":0.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0012365X24003807/pdfft?md5=e2bc8fb4249126377f15948ed27aebbf&pid=1-s2.0-S0012365X24003807-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-11DOI: 10.1016/j.disc.2024.114259
István Estélyi , Ján Karabáš , Alexander Mednykh , Roman Nedela
In the present paper we investigate the faithfulness of certain linear representations of groups of automorphisms of a graph X in the group of symmetries of the Jacobian of X. As a consequence we show that if a 3-edge-connected graph X admits a nonabelian semiregular group of automorphisms, then the Jacobian of X cannot be cyclic. In particular, Cayley graphs of degree at least three arising from nonabelian groups have non-cyclic Jacobians. While the size of the Jacobian of X is well-understood – it is equal to the number of spanning trees of X – the combinatorial interpretation of the rank of Jacobian of a graph is unknown. Our paper presents a contribution in this direction.
在本文中,我们研究了图 X 的自变量群的某些线性表示在 X 的雅各布对称群中的忠实性。结果表明,如果一个三边连接的图 X 接受一个非阿贝尔半圆自变量群,那么 X 的雅各布不可能是循环的。特别是,由非阿贝尔群产生的阶数至少为 3 的 Cayley 图具有非循环雅各布。虽然 X 的雅各布的大小很好理解--它等于 X 的生成树的数量,但对图的雅各布秩的组合解释还不清楚。我们的论文在这方面做出了贡献。
{"title":"The Jacobian of a graph and graph automorphisms","authors":"István Estélyi , Ján Karabáš , Alexander Mednykh , Roman Nedela","doi":"10.1016/j.disc.2024.114259","DOIUrl":"10.1016/j.disc.2024.114259","url":null,"abstract":"<div><p>In the present paper we investigate the faithfulness of certain linear representations of groups of automorphisms of a graph <em>X</em> in the group of symmetries of the Jacobian of <em>X</em>. As a consequence we show that if a 3-edge-connected graph <em>X</em> admits a nonabelian semiregular group of automorphisms, then the Jacobian of <em>X</em> cannot be cyclic. In particular, Cayley graphs of degree at least three arising from nonabelian groups have non-cyclic Jacobians. While the size of the Jacobian of <em>X</em> is well-understood – it is equal to the number of spanning trees of <em>X</em> – the combinatorial interpretation of the rank of Jacobian of a graph is unknown. Our paper presents a contribution in this direction.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 2","pages":"Article 114259"},"PeriodicalIF":0.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Graph burning is a discrete-time process that models the spread of influence in a network. Vertices are either burning or unburned, and in each round, a burning vertex causes all of its neighbours to become burning before a new fire source is chosen to become burning. We introduce a variation of this process that incorporates an adversarial game played on a nested, growing sequence of graphs. Two players, Arsonist and Builder, play in turns: Builder adds a certain number of new unburned vertices and edges incident to these to create a larger graph, then every vertex neighbouring a burning vertex becomes burning, and finally Arsonist ‘burns’ a new fire source. This process repeats forever. Arsonist is said to win if the limiting fraction of burning vertices tends to 1, while Builder is said to win if this fraction is bounded away from 1.
The central question of this paper is determining if, given that Builder adds vertices at turn n, either Arsonist or Builder has a winning strategy. In the case that is asymptotically polynomial, we give threshold results for which player has a winning strategy.
{"title":"Adversarial graph burning densities","authors":"Karen Gunderson , William Kellough , J.D. Nir , Hritik Punj","doi":"10.1016/j.disc.2024.114253","DOIUrl":"10.1016/j.disc.2024.114253","url":null,"abstract":"<div><p>Graph burning is a discrete-time process that models the spread of influence in a network. Vertices are either <em>burning</em> or <em>unburned</em>, and in each round, a burning vertex causes all of its neighbours to become burning before a new <em>fire source</em> is chosen to become burning. We introduce a variation of this process that incorporates an adversarial game played on a nested, growing sequence of graphs. Two players, Arsonist and Builder, play in turns: Builder adds a certain number of new unburned vertices and edges incident to these to create a larger graph, then every vertex neighbouring a burning vertex becomes burning, and finally Arsonist ‘burns’ a new fire source. This process repeats forever. Arsonist is said to win if the limiting fraction of burning vertices tends to 1, while Builder is said to win if this fraction is bounded away from 1.</p><p>The central question of this paper is determining if, given that Builder adds <span><math><mi>f</mi><mo>(</mo><mi>n</mi><mo>)</mo></math></span> vertices at turn <em>n</em>, either Arsonist or Builder has a winning strategy. In the case that <span><math><mi>f</mi><mo>(</mo><mi>n</mi><mo>)</mo></math></span> is asymptotically polynomial, we give threshold results for which player has a winning strategy.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 1","pages":"Article 114253"},"PeriodicalIF":0.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0012365X24003844/pdfft?md5=844834b3c93d41373d6c5d8d83ccf0aa&pid=1-s2.0-S0012365X24003844-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142167395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}