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Spectral upper bounds for the Grundy number of a graph 图形格兰迪数的谱系上限
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-16 DOI: 10.1016/j.disc.2024.114326
Thiago Assis, Gabriel Coutinho, Emanuel Juliano
The Grundy number of a graph is the minimum number of colors needed to properly color the graph using the first-fit greedy algorithm regardless of the initial vertex ordering. Computing the Grundy number of a graph is an NP-Hard problem. There is a characterization in terms of induced subgraphs: a graph has a Grundy number at least k if and only if it contains a k-atom. In this paper, using properties of the matching polynomial, we determine the smallest possible largest eigenvalue of a k-atom. With this result, we present an upper bound for the Grundy number of a graph in terms of the largest eigenvalue of its adjacency matrix. We also present another upper bound using the largest eigenvalue and the size of the graph. Our bounds are asymptotically tight for some infinite families of graphs and provide improvements on the known bounds for the Grundy number of sparse random graphs.
图形的格兰迪数是指在不考虑初始顶点排序的情况下,使用第一拟合贪婪算法为图形正确着色所需的最少颜色数。计算图形的格兰迪数是一个 NP-Hard(近乎困难)问题。从诱导子图的角度来看,有这样一个特征:当且仅当一个图包含一个 k 原子时,该图的格兰迪数至少为 k。在本文中,我们利用匹配多项式的特性,确定了 k 原子的最小最大特征值。有了这一结果,我们根据图的邻接矩阵的最大特征值提出了图的格兰迪数上限。我们还利用最大特征值和图的大小提出了另一个上限。对于某些无限图族,我们的上界是渐近紧密的,并且改进了稀疏随机图的格兰迪数的已知上界。
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引用次数: 0
Transitive (q − 1)-fold packings of PGn(q) PGn(q) 的传递 (q - 1)- 倍堆积
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-16 DOI: 10.1016/j.disc.2024.114330
Daniel R. Hawtin
A t-fold packing of a projective space PGn(q) is a collection P of line-spreads such that each line of PGn(q) occurs in precisely t spreads in P. A t-fold packing P is transitive if a subgroup of PΓLn+1(q) preserves and acts transitively on P. We give a construction for a transitive (q1)-fold packing of PGn(q), where q=2k, for any odd positive integers n and k, such that n3. This generalises a construction of Baker from 1976 for the case q=2.
如果 PΓLn+1(q)的一个子群保存并在 P 上起传递作用,那么一个 t 折叠包装 P 就是传递性的。我们给出了一个 PGn(q)的传递性 (q-1)-fold 包装的构造,其中 q=2k, 对于任何奇数正整数 n 和 k,使得 n⩾3 。这概括了贝克 1976 年针对 q=2 情况的构造。
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引用次数: 0
Truncated theta series related to the Jacobi Triple Product identity 与雅可比三乘积特性相关的截断θ级数
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-14 DOI: 10.1016/j.disc.2024.114319
Cristina Ballantine , Brooke Feigon
The work of Andrews and Merca on the truncated Euler's pentagonal number theorem led to a resurgence in research on truncated theta series identities. In particular, Yee proved a truncated version of the Jacobi Triple Product (JTP) identity. Recently, Merca conjectured a stronger form of the truncated JTP identity. In this article we prove the first three cases of the conjecture and several related truncated identities. We prove combinatorially an identity related to the JTP identity which in particular cases reduces to identities conjectured by Merca and proved analytically by Krattenthaler, Merca and Radu. Moreover, we introduce a new combinatorial interpretation for the number of distinct 5-regular partitions of n.
安德鲁斯(Andrews)和梅尔卡(Merca)在截断欧拉五边形数定理方面的工作,导致了截断θ级数特性研究的复苏。其中,Yee 证明了雅可比三乘积(JTP)特性的截断版本。最近,Merca 猜想出了截断 JTP 特性的更强形式。在本文中,我们证明了猜想的前三种情况和几个相关的截断标识。我们通过组合证明了一个与 JTP 特性相关的特性,在特定情况下,它还原了由梅尔卡猜想并由克拉滕塔勒、梅尔卡和拉杜分析证明的特性。此外,我们还为 n 的不同 5-regular 分割数引入了一种新的组合解释。
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引用次数: 0
The e−positivity of some new classes of graphs 几类新图的电子正向性
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-13 DOI: 10.1016/j.disc.2024.114322
Stefan Mitrović, Tanja Stojadinović
We introduce two classes of graphs - suns and dumbbells, both with few variations and explore their chromatic symmetric function and its e-positivity. We also give many connections of these two classes with other classes of connected graphs.
我们介绍了两类图--太阳图和哑铃图,它们都有很少的变化,并探讨了它们的色度对称函数及其 e 正性。我们还给出了这两类图与其他连通图的许多联系。
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引用次数: 0
Explicit enumeration formulas for m-regular simple stacks 多规则简单堆栈的显式枚举公式
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-13 DOI: 10.1016/j.disc.2024.114317
Qianghui Guo , Yinglie Jin , Lisa Hui Sun , Hang Yang , Jie Yang
Combinatorial enumeration of various RNA secondary structures and protein contact maps is of significant interest for both combinatorialists and computational biologists. Numerous results have been obtained, most of which are in terms of generating functions, recurrences or asymptotic formulas, few are of explicit formulas. This paper is mainly concerned with finding explicit enumeration formulas related to m-regular simple stacks, a classic combinatorial model for RNA secondary structures. By using the theories of noncrossing matching and Dyck path, we obtain explicit enumeration formulas for m-regular simple stacks with statistics on arcs, hairpins, components and visible vertices. The results can reduce to some classic formulas like Schmitt and Waterman's closed form formula for the number of RNA secondary structures. Furthermore, we study the enumeration of enhanced m-regular simple stacks, stimulated by the study of protein contact maps, in which the upper bound of the degrees of the two terminal vertices is relaxed to two, explicit formulas are obtained.
对各种 RNA 二级结构和蛋白质接触图进行组合枚举,是组合学家和计算生物学家的重要兴趣所在。目前已经取得了许多成果,其中大部分是生成函数、递推公式或渐近公式,很少有明确的公式。本文主要研究与 m-regular 简单堆积相关的显式枚举公式,m-regular 简单堆积是 RNA 二级结构的经典组合模型。通过使用非交叉匹配和戴克路径理论,我们得到了m-正则简单堆积的显式枚举公式,并对弧线、发夹、分量和可见顶点进行了统计。这些结果可以还原为一些经典公式,如施密特和沃特曼关于 RNA 二级结构数的封闭式公式。此外,我们还研究了增强型 m-regular 简单堆栈的枚举,这是受蛋白质接触图研究的启发,其中两个末端顶点的度数上限被放宽为两个,从而得到了明确的公式。
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引用次数: 0
On the minimum length of linear codes of dimension 5 关于维数为 5 的线性编码的最小长度
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-13 DOI: 10.1016/j.disc.2024.114324
E.J. Cheon , S.J. Kim , W. Kuranaka , T. Maruta
A fundamental problem in coding theory is to find the exact value nq(k,d), the minimum length n for which an [n,k,d]q code exists for given q,k and d. The code of length nq(k,d) is called length optimal. Finding length optimal codes presents the most interesting problem in optimal linear codes, because length optimal codes are simultaneously distance optimal and dimension optimal. In this article, we focus on finding 5-dimensional length optimal codes. We prove the nonexistence of 5-dimensional Griesmer code, and it is proved nq(5,d)=gq(5,d)+1 for 3q44q3aq+1d3q44q3q with 1a23q+1 and 2q42q32q2q+1d2q42q32q2 with q5.
编码理论中的一个基本问题是找到精确值 nq(k,d),即给定 q、k 和 d 时存在 [n,k,d]q 码的最小长度 n。寻找长度最优编码是最优线性编码中最有趣的问题,因为长度最优编码同时是距离最优编码和维数最优编码。在本文中,我们重点研究寻找 5 维长度最优编码。我们证明了五维格里斯梅尔码的不存在性,并证明了对于 1≤a≤⌊23q+1⌋ 的 3q4-4q3-aq+1≤d≤3q4-4q3-q 和 q≥5 的 2q4-2q3-2q2-q+1≤d≤2q4-2q3-2q2 ,nq(5,d)=gq(5,d)+1。
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引用次数: 0
On the edge-chromatic number of 2-complexes 关于 2-复合物的边色数
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-12 DOI: 10.1016/j.disc.2024.114309
Jan Kurkofka , Emily Nevinson
We propose an open question that seeks to generalise the Four Colour Theorem from two to three dimensions. As an appetiser, we show that 12 instead of four colours are both sufficient and necessary to colour every 2-complex that embeds in a prescribed 3-manifold. However, our example of a 2-complex that requires 12 colours is not simplicial.
我们提出了一个开放性问题,旨在将四色定理从二维推广到三维。作为开胃菜,我们展示了 12 种颜色而不是 4 种颜色对嵌入规定的三维曲面的每个二元复数的着色既充分又必要。然而,我们举例说明的需要 12 种颜色的二元复合物并不简单。
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引用次数: 0
Symmetric functions in noncommuting variables in superspace 超空间非交换变量中的对称函数
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-12 DOI: 10.1016/j.disc.2024.114320
Diego Arcis , Camilo González , Sebastián Márquez
In 2004, Rosas and Sagan developed the theory of symmetric functions in noncommuting variables, achieving results analogous to classical symmetric functions. On the other hand, the same year, Desrosiers, Lapointe and Mathieu introduced the theory of symmetric functions in superspace, involving both commuting and anticommuting variables, extending the classic theory. Here, we introduce symmetric functions in noncommuting variables in superspace. We extend the classical symmetric functions in noncommuting variables to superspace: monomial, power sum, elementary and complete homogeneous functions. These functions generalize both those studied by Rosas and Sagan and those studied by Desrosiers, Lapointe, and Mathieu. Additionally, we define Schur–type functions in noncommuting variables in superspace.
2004 年,罗萨斯和萨根发展了非交换变量中的对称函数理论,取得了与经典对称函数类似的结果。另一方面,同年,Desrosiers、Lapointe 和 Mathieu 引入了超空间对称函数理论,涉及交换变量和反交换变量,扩展了经典理论。在此,我们介绍超空间中非交换变量的对称函数。我们将经典的非交换变量对称函数扩展到超空间:单项式函数、幂和函数、初等函数和完全同调函数。这些函数既概括了罗萨斯和萨根研究的函数,也概括了德斯罗西耶、拉普安特和马修研究的函数。此外,我们还定义了超空间非交换变量中的舒尔型函数。
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引用次数: 0
Projective geometries, Q-polynomial structures, and quantum groups 投影几何、Q-多项式结构和量子群
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-12 DOI: 10.1016/j.disc.2024.114321
Paul Terwilliger
In 2023 we obtained a Q-polynomial structure for the projective geometry LN(q). In the present paper, we display a more general Q-polynomial structure for LN(q). Our new Q-polynomial structure is defined using a free parameter φ that takes any positive real value. For φ=1 we recover the original Q-polynomial structure. We interpret the new Q-polynomial structure using the quantum group Uq1/2(sl2) in the equitable presentation. We use the new Q-polynomial structure to obtain analogs of the four split decompositions that appear in the theory of Q-polynomial distance-regular graphs.
2023 年,我们获得了投影几何 LN(q) 的 Q 多项式结构。在本文中,我们为 LN(q) 展示了一种更通用的 Q 多项式结构。我们的新 Q 多项式结构使用自由参数 φ 定义,该参数可取任意正实值。当 φ=1 时,我们将恢复原来的 Q 多项式结构。我们用衡平表示法中的量子群 Uq1/2(sl2)来解释新的 Q 多项式结构。我们利用新的 Q 多项式结构得到了 Q 多项式距离规则图理论中出现的四种分裂分解的类似物。
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引用次数: 0
A note on the lacking polynomial of the complete bipartite graph 关于完整二方图缺多项式的说明
IF 0.7 3区 数学 Q2 MATHEMATICS Pub Date : 2024-11-12 DOI: 10.1016/j.disc.2024.114323
Amal Alofi, Mark Dukes
The lacking polynomial is a graph polynomial introduced by Chan, Marckert, and Selig in 2013 that is closely related to the Tutte polynomial of a graph. It arose by way of a generalization of the Abelian sandpile model and is essentially the generating function of the level statistic on the set of recurrent configurations, called stochastically recurrent states, for that model. In this note we consider the lacking polynomial of the complete bipartite graph. We classify the stochastically recurrent states of the stochastic sandpile model on the complete bipartite graphs K2,n and Km,2 where the sink is always an element of the set counted by the first index. We use these characterizations to give explicit formulae for the lacking polynomials of these graphs. Log-concavity of the sequence of coefficients of these two lacking polynomials is proven, and we conjecture log-concavity holds for this general class of graphs.
缺乏多项式是由 Chan、Marckert 和 Selig 于 2013 年提出的一种图多项式,与图的 Tutte 多项式密切相关。它是通过对阿贝尔沙堆模型进行广义化而产生的,本质上是该模型中被称为随机循环状态的循环配置集合上的水平统计量的生成函数。在本说明中,我们考虑了完整双方形图的缺省多项式。我们将随机沙堆模型的随机循环状态归类于完整双方形图 K2,n 和 Km,2,其中水槽总是第一个索引所计集合的元素。我们利用这些特征给出了这些图的缺省多项式的明确公式。我们证明了这两个缺省多项式系数序列的对数凹性,并推测对数凹性在这一类图中也成立。
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引用次数: 0
期刊
Discrete Mathematics
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