Pub Date : 2024-09-18DOI: 10.1016/j.disc.2024.114263
Let denote a finite, simple, connected, and undirected non-bipartite graph with vertex set X and edge set . Fix a vertex , and define , where ∂ denotes the path-length distance in Γ. Observe that the graph is bipartite. We say that Γ supports a uniform structure with respect to x whenever has a uniform structure with respect to x in the sense of Miklavič and Terwilliger [7].
Assume that Γ is a distance-regular graph with classical parameters and diameter . Recall that q is an integer such that . The purpose of this paper is to study when Γ supports a uniform structure with respect to x. We studied the case in [3], and so in this paper we assume . Let denote the Terwilliger algebra of Γ with respect to x. Under an additional assumption that every irreducible T-module with endpoint 1 is thin, we show that if Γ supports a uniform structure with respect to x, then either or , , and .
让Γ=(X,R) 表示具有顶点集 X 和边集 R 的有限、简单、连通和不定向的非双向图。固定一个顶点 x∈X,定义 Rf=R∖{yz|∂(x,y)=∂(x,z)},其中∂表示Γ中的路径长度距离。请注意,图 Γf=(X,Rf) 是双向的。假设 Γ 是一个距离规则图,其经典参数为 (D,q,α,β),直径为 D≥4。回顾一下,q 是一个整数,使得 q∉{-1,0}。我们在 [3] 中研究过 q≤1 的情况,因此本文假设 q≥2 。让 T=T(x) 表示 Γ 关于 x 的泰尔维利格代数。在每个端点为 1 的不可还原 T 模块都是薄的这一额外假设下,我们证明了如果 Γ 支持关于 x 的均匀结构,那么要么 α=0 要么 α=q,β=q2(qD-1)/(q-1),D≡0(mod6)。
{"title":"Distance-regular graphs with classical parameters that support a uniform structure: Case q ≥ 2","authors":"","doi":"10.1016/j.disc.2024.114263","DOIUrl":"10.1016/j.disc.2024.114263","url":null,"abstract":"<div><p>Let <span><math><mi>Γ</mi><mo>=</mo><mo>(</mo><mi>X</mi><mo>,</mo><mi>R</mi><mo>)</mo></math></span> denote a finite, simple, connected, and undirected non-bipartite graph with vertex set <em>X</em> and edge set <span><math><mi>R</mi></math></span>. Fix a vertex <span><math><mi>x</mi><mo>∈</mo><mi>X</mi></math></span>, and define <span><math><msub><mrow><mi>R</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>=</mo><mi>R</mi><mo>∖</mo><mo>{</mo><mi>y</mi><mi>z</mi><mo>|</mo><mo>∂</mo><mo>(</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>)</mo><mo>=</mo><mo>∂</mo><mo>(</mo><mi>x</mi><mo>,</mo><mi>z</mi><mo>)</mo><mo>}</mo></math></span>, where ∂ denotes the path-length distance in Γ. Observe that the graph <span><math><msub><mrow><mi>Γ</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>=</mo><mo>(</mo><mi>X</mi><mo>,</mo><msub><mrow><mi>R</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>)</mo></math></span> is bipartite. We say that Γ supports a uniform structure with respect to <em>x</em> whenever <span><math><msub><mrow><mi>Γ</mi></mrow><mrow><mi>f</mi></mrow></msub></math></span> has a uniform structure with respect to <em>x</em> in the sense of Miklavič and Terwilliger <span><span>[7]</span></span>.</p><p>Assume that Γ is a distance-regular graph with classical parameters <span><math><mo>(</mo><mi>D</mi><mo>,</mo><mi>q</mi><mo>,</mo><mi>α</mi><mo>,</mo><mi>β</mi><mo>)</mo></math></span> and diameter <span><math><mi>D</mi><mo>≥</mo><mn>4</mn></math></span>. Recall that <em>q</em> is an integer such that <span><math><mi>q</mi><mo>∉</mo><mo>{</mo><mo>−</mo><mn>1</mn><mo>,</mo><mn>0</mn><mo>}</mo></math></span>. The purpose of this paper is to study when Γ supports a uniform structure with respect to <em>x</em>. We studied the case <span><math><mi>q</mi><mo>≤</mo><mn>1</mn></math></span> in <span><span>[3]</span></span>, and so in this paper we assume <span><math><mi>q</mi><mo>≥</mo><mn>2</mn></math></span>. Let <span><math><mi>T</mi><mo>=</mo><mi>T</mi><mo>(</mo><mi>x</mi><mo>)</mo></math></span> denote the Terwilliger algebra of Γ with respect to <em>x</em>. Under an additional assumption that every irreducible <em>T</em>-module with endpoint 1 is thin, we show that if Γ supports a uniform structure with respect to <em>x</em>, then either <span><math><mi>α</mi><mo>=</mo><mn>0</mn></math></span> or <span><math><mi>α</mi><mo>=</mo><mi>q</mi></math></span>, <span><math><mi>β</mi><mo>=</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>(</mo><msup><mrow><mi>q</mi></mrow><mrow><mi>D</mi></mrow></msup><mo>−</mo><mn>1</mn><mo>)</mo><mo>/</mo><mo>(</mo><mi>q</mi><mo>−</mo><mn>1</mn><mo>)</mo></math></span>, and <span><math><mi>D</mi><mo>≡</mo><mn>0</mn><mspace></mspace><mo>(</mo><mrow><mi>mod</mi></mrow><mspace></mspace><mn>6</mn><mo>)</mo></math></span>.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0012365X24003947/pdfft?md5=1365ed5c25a5773efbf51cb8def0b01e&pid=1-s2.0-S0012365X24003947-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142238249","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 : 2024-09-16DOI: 10.1016/j.disc.2024.114264
The orthogonal array holds significant importance as a research topic within the realms of combinatorial design theory and experimental design theory, with widespread applications in statistics, computer science, coding theory and cryptography. This paper presents three constructions for asymmetric orthogonal arrays including juxtaposition, generator matrices over Galois fields and mixed difference matrices. Subsequently, many new infinite families of asymmetric orthogonal arrays with strength are obtained. Furthermore, some new infinite families of large sets of orthogonal arrays with mixed levels are also obtained.
{"title":"New results on asymmetric orthogonal arrays with strength t ≥ 3","authors":"","doi":"10.1016/j.disc.2024.114264","DOIUrl":"10.1016/j.disc.2024.114264","url":null,"abstract":"<div><p>The orthogonal array holds significant importance as a research topic within the realms of combinatorial design theory and experimental design theory, with widespread applications in statistics, computer science, coding theory and cryptography. This paper presents three constructions for asymmetric orthogonal arrays including juxtaposition, generator matrices over Galois fields and mixed difference matrices. Subsequently, many new infinite families of asymmetric orthogonal arrays with strength <span><math><mi>t</mi><mo>≥</mo><mn>3</mn></math></span> are obtained. Furthermore, some new infinite families of large sets of orthogonal arrays with mixed levels are also obtained.</p></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142242252","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.2024.114240
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":"","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":null,"pages":null},"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
<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":"","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":null,"pages":null},"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}
Pub Date : 2024-09-12DOI: 10.1016/j.disc.2024.114256
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":"","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":null,"pages":null},"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
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":"","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":null,"pages":null},"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
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":"","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":null,"pages":null},"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
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":"","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":null,"pages":null},"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
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":"","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":null,"pages":null},"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
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":"","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":null,"pages":null},"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}