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A Precise Condition for Independent Transversals in Bipartite Covers 二方覆盖中独立横截面的精确条件
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-05-06 DOI: 10.1137/23m1600384
Stijn Cambie, Penny Haxell, Ross J. Kang, Ronen Wdowinski
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1451-1461, June 2024.
Abstract. Given a bipartite graph [math] in which any vertex in [math] (resp., [math]) has degree at most [math] (resp., [math]), suppose there is a partition of [math] that is a refinement of the bipartition [math] such that the parts in [math] (resp., [math]) have size at least [math] (resp., [math]). We prove that the condition [math] is sufficient for the existence of an independent set of vertices of [math] that is simultaneously transversal to the partition and show, moreover, that this condition is sharp. This result is a bipartite refinement of two well-known results on independent transversals, one due to the second author and the other due to Szabó and Tardos.
SIAM 离散数学杂志》第 38 卷第 2 期第 1451-1461 页,2024 年 6 月。 摘要。给定一个双分部图[math],其中[math](或[math])中的任何顶点的度最多为[math](或[math]),假设[math]有一个分部,它是双分部[math]的细化,使得[math](或[math])中各部分的大小至少为[math](或[math])。我们证明,[math] 这个条件足以使 [math] 中存在一个独立的顶点集,而这个顶点集同时又是横切于这个分部的,此外,我们还证明了这个条件是尖锐的。这一结果是对关于独立横切的两个著名结果的双向细化,一个由第二位作者提出,另一个由 Szabó 和 Tardos 提出。
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引用次数: 0
A Menger-Type Theorem for Two Induced Paths 两条诱导路径的门格尔定理
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-05-03 DOI: 10.1137/23m1573082
Sandra Albrechtsen, Tony Huynh, Raphael W. Jacobs, Paul Knappe, Paul Wollan
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1438-1450, June 2024.
Abstract. We give an approximate Menger-type theorem for the case when a graph [math] contains two [math] paths [math] and [math] such that [math] is an induced subgraph of [math]. More generally, we prove that there exists a function [math], such that for every graph [math] and [math], either there exist two [math] paths [math] and [math] such that the distance between [math] and [math] is at least [math], or there exists [math] such that the ball of radius [math] centered at [math] intersects every [math] path.
SIAM 离散数学杂志》第 38 卷第 2 期第 1438-1450 页,2024 年 6 月。摘要。当一个图[math]包含两条[math]路径[math]和[math],且[math]是[math]的诱导子图时,我们给出了一个近似门格尔定理。更广义地说,我们证明存在一个函数[math],使得对于每一个图[math]和[math],要么存在两条[math]路径[math]和[math],使得[math]和[math]之间的距离至少为[math],要么存在[math],使得以[math]为中心的半径为[math]的球与每一条[math]路径相交。
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引用次数: 0
Hypergraph Horn Functions 超图角函数
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-05-02 DOI: 10.1137/23m1569162
Kristóf Bérczi, Endre Boros, Kazuhisa Makino
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1417-1437, June 2024.
Abstract. Horn functions form a subclass of Boolean functions possessing interesting structural and computational properties. These functions play a fundamental role in algebra, artificial intelligence, combinatorics, computer science, database theory, and logic. In the present paper, we introduce the subclass of hypergraph Horn functions that generalizes matroids and equivalence relations. We provide multiple characterizations of hypergraph Horn functions in terms of implicate-duality and the closure operator, which are, respectively, regarded as generalizations of matroid duality and the Mac Lane–Steinitz exchange property of matroid closure. We also study algorithmic issues on hypergraph Horn functions and show that the recognition problem (i.e., deciding if a given definite Horn CNF represents a hypergraph Horn function) and key realization (i.e., deciding if a given hypergraph is realized as a key set by a hypergraph Horn function) can be done in polynomial time, while implicate sets can be generated with polynomial delay.
SIAM 离散数学杂志》第 38 卷第 2 期第 1417-1437 页,2024 年 6 月。 摘要。霍恩函数是布尔函数的一个子类,具有有趣的结构和计算性质。这些函数在代数、人工智能、组合学、计算机科学、数据库理论和逻辑学中发挥着基础性作用。在本文中,我们介绍了超图霍恩函数的子类,它概括了矩阵和等价关系。我们从蕴涵对偶性和闭合算子的角度提供了超图霍恩函数的多种特征,它们分别被视为矩阵对偶性和矩阵闭合的 Mac Lane-Steinitz 交换属性的广义化。我们还研究了超图 Horn 函数的算法问题,并证明识别问题(即判定给定的定 Horn CNF 是否代表一个超图 Horn 函数)和键实现(即判定给定的超图是否被一个超图 Horn 函数实现为一个键集)可以在多项式时间内完成,而蕴含集可以在多项式延迟内生成。
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引用次数: 0
Sárközy’s Theorem in Various Finite Field Settings 各种有限域设置中的萨尔科齐定理
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-04-29 DOI: 10.1137/23m1563256
Anqi Li, Lisa Sauermann
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1409-1416, June 2024.
Abstract. In this paper, we strengthen a result by Green about an analogue of Sárközy’s theorem in the setting of polynomial rings [math]. In the integer setting, for a given polynomial [math] with constant term zero, (a generalization of) Sárközy’s theorem gives an upper bound on the maximum size of a subset [math] that does not contain distinct [math] satisfying [math] for some [math]. Green proved an analogous result with much stronger bounds in the setting of subsets [math] of the polynomial ring [math], but this result required the additional condition that the number of roots of the polynomial [math] be coprime to [math]. We generalize Green’s result, removing this condition. As an application, we also obtain a version of Sárközy’s theorem with similar strong bounds for subsets [math] for [math] for a fixed prime [math] and large [math].
SIAM 离散数学杂志》第 38 卷第 2 期第 1409-1416 页,2024 年 6 月。摘要在本文中,我们强化了格林关于多项式环[math]中的萨科齐定理的一个结果。在整数环境中,对于给定的常数项为零的多项式[math],萨尔柯兹定理的(广义)给出了对于某些[math]不包含满足[math]的不同[math]的子集[math]的最大大小的上界。格林在多项式环[math]的子集[math]中证明了一个类似的结果,并给出了更强的约束,但这个结果需要一个附加条件,即多项式[math]的根数与[math]共素。我们对格林的结果进行了归纳,去掉了这个条件。作为应用,我们还得到了萨科齐定理的一个版本,它对固定素数[math]和大[math]的[math]子集[math]具有类似的强约束。
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引用次数: 0
Random Necklaces Require Fewer Cuts 随机项链所需的剪裁更少
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-04-26 DOI: 10.1137/22m1506699
Noga Alon, Dor Elboim, János Pach, Gábor Tardos
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1381-1408, June 2024.
Abstract. It is known that any open necklace with beads of [math] types, in which the number of beads of each type is divisible by [math], can be partitioned by at most [math] cuts into intervals that can be distributed into [math] collections, each containing the same number of beads of each type. This is tight for all values of [math] and [math]. Here, we consider the case of random necklaces, where the number of beads of each type is [math]. Then the minimum number of cuts required for a “fair” partition with the above property is a random variable [math]. We prove that for fixed [math] and large [math], this random variable is at least [math] with high probability. For [math], fixed [math], and large [math], we determine the asymptotic behavior of the probability that [math] for all values of [math]. We show that this probability is polynomially small when [math], is bounded away from zero when [math], and decays like [math] when [math]. We also show that for large [math], [math] is at most [math] with high probability and that for large [math] and large ratio [math], [math] is [math] with high probability.
SIAM 离散数学杂志》,第 38 卷第 2 期,第 1381-1408 页,2024 年 6 月。摘要已知任何有[math]类型珠子的开放项链,其中每种类型珠子的数量都能被[math]整除,可以用至多[math]个切割分割成[math]集合的区间,每个区间包含每种类型相同数量的珠子。这对所有 [math] 和 [math] 值都是严密的。在这里,我们考虑随机项链的情况,即每种类型的珠子数量为 [math]。那么,具有上述性质的 "公平 "分割所需的最小切割次数就是一个随机变量 [math]。我们证明,对于固定的[math]和较大的[math],这个随机变量至少是[math],而且概率很高。对于[math]、固定[math]和大[math],我们确定了[math]在所有[math]值下的概率渐近行为。我们证明,当[math]时,这个概率是多项式小概率;当[math]时,这个概率离零有界;当[math]时,这个概率像[math]一样衰减。我们还证明,对于较大的 [math],[math] 最有可能是 [math],而对于较大的 [math]和较大比率的 [math],[math] 极有可能是 [math]。
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引用次数: 0
On the Chromatic Number of Random Regular Hypergraphs 论随机正则超图的色度数
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-04-24 DOI: 10.1137/22m1544476
Patrick Bennett, Alan Frieze
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1369-1380, June 2024.
Abstract. We estimate the likely values of the chromatic and independence numbers of the random [math]-uniform [math]-regular hypergraph on [math] vertices for fixed [math], large fixed [math], and [math].
SIAM 离散数学杂志》第 38 卷第 2 期第 1369-1380 页,2024 年 6 月。摘要。我们估计了固定[数学]、大固定[数学]和[数学]顶点上随机[数学]-均匀[数学]-规则超图的色度数和独立性数的可能值。
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引用次数: 0
Tropicalizing the Graph Profile of Some Almost-Stars 将一些近似恒星的图谱热带化
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-04-22 DOI: 10.1137/23m1594947
Maria Dascălu, Annie Raymond
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1351-1368, June 2024.
Abstract. Many important problems in extremal combinatorics can be stated as certifying polynomial inequalities in graph homomorphism numbers, and in particular, many ask to certify pure binomial inequalities. For a fixed collection of graphs [math], the tropicalization of the graph profile of [math] essentially records all valid pure binomial inequalities involving graph homomorphism numbers for graphs in [math]. Building upon ideas and techniques described by Blekherman and Raymond in 2022, we compute the tropicalization of the graph profile for the graph containing a single vertex as well as stars where one edge is subdivided. This allows pure binomial inequalities in homomorphism numbers (or densities) for these graphs to be verified through an explicit linear program where the number of variables is equal to the number of edges in the biggest graph involved.
SIAM 离散数学杂志》第 38 卷第 2 期第 1351-1368 页,2024 年 6 月。 摘要。极值组合学中的许多重要问题可以说是图同态数的多项式不等式证明,特别是许多问题要求证明纯二项式不等式。对于一个固定的图集合[math],[math]图轮廓的热带化本质上记录了[math]中所有涉及图同态数的有效纯二项式不等式。基于布莱克曼和雷蒙德在 2022 年描述的想法和技术,我们计算了包含单个顶点的图以及一条边被细分的星图的图轮廓的热带化。这样,这些图的同态数(或密度)的纯二项式不等式就可以通过一个显式线性程序来验证,其中变量的数量等于所涉及的最大图中的边的数量。
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引用次数: 0
An Algorithmic Framework for Locally Constrained Homomorphisms 局部受限同态的算法框架
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-04-18 DOI: 10.1137/22m1513290
Laurent Bulteau, Konrad K. Dabrowski, Noleen Köhler, Sebastian Ordyniak, Daniël Paulusma
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1315-1350, June 2024.
Abstract. A homomorphism [math] from a guest graph [math] to a host graph [math] is locally bijective, injective, or surjective if for every [math], the restriction of [math] to the neighbourhood of [math] is bijective, injective, or surjective, respectively. We prove a number of new FPT (fixed-parameter tractable), W[1]-hard, and paraNP-complete results for the corresponding decision problems LBHom, LIHom, and LSHom by considering a hierarchy of parameters of the guest graph [math]. In this way we strengthen several existing results. For our FPT results, we develop a new algorithmic framework that involves a general ILP (integer linear program) model. We also use our framework to prove FPT results for the Role Assignment problem, which originates from social network theory and is closely related to locally surjective homomorphisms.
SIAM 离散数学杂志》,第 38 卷第 2 期,第 1315-1350 页,2024 年 6 月。 摘要如果对于每一个[math],[math]对[math]邻域的限制分别是双射、注入或射出的,那么从客图[math]到主图[math]的同态[math]就是局部双射、注入或射出的。通过考虑客体图 [math] 的参数层次,我们证明了相应决策问题 LBHom、LIHom 和 LSHom 的一系列新的 FPT(固定参数可处理)、W[1]-困难和 paraNP-完备结果。通过这种方法,我们加强了几个已有的结果。对于我们的 FPT 结果,我们开发了一个新的算法框架,涉及一般的 ILP(整数线性规划)模型。我们还利用我们的框架证明了角色分配问题的 FPT 结果,该问题源于社交网络理论,与局部投射同构密切相关。
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引用次数: 0
Discursive Voter Models on the Supercritical Scale-Free Network 超临界无标度网络上的议论性选民模型
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-04-16 DOI: 10.1137/22m1544373
John Fernley
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1285-1314, June 2024.
Abstract. The voter model is a classical interacting particle system, modeling how global consensus is formed by local imitation. We analyze the time to consensus for a particular family of voter models when the underlying structure is a scale-free inhomogeneous random graph in the high edge–density regime, where this graph features a giant component. In this regime, we verify that the polynomial orders of consensus agree with those of their mean-field approximation in [A. Moinet, A. Barrat, and R. Pastor-Satorras, Phys. Rev. E, 98 (2018), 022303]. This “discursive” family of models has a symmetrized interaction to better model discussions and is indexed by a temperature parameter that, for certain parameters of the power law tail of the network’s degree distribution, is seen to produce two distinct phases of consensus speed. Our proofs rely on the well-known duality to coalescing random walks and a novel bound on the mixing time of these walks using the known fast mixing of the Erdős–Rényi giant subgraph. Unlike in the subcritical case [J. Fernley and M. Ortgiese, Random Structures Algorithms, 62 (2023), pp. 376–429], which requires tail exponent of the limiting degree distribution [math] as well as low edge density, in the giant component case, we also address the “ultrasmall world” power law exponents [math].
SIAM 离散数学杂志》第 38 卷第 2 期第 1285-1314 页,2024 年 6 月。 摘要投票者模型是一个经典的相互作用粒子系统,它模拟了全球共识是如何通过局部模仿形成的。我们分析了当底层结构是一个无标度的非均质随机图时,在高边沿密度系统中,一个特定的投票者模型族达成共识的时间。在这种情况下,我们验证了共识的多项式阶数与平均场近似 [A. Moinet, A. Barrat] 中的多项式阶数一致。Moinet, A. Barrat, and R. Pastor-Satorras, Phys. Rev. E, 98 (2018), 022303]。这个 "辨证 "模型系列有一个对称的相互作用,以更好地模拟讨论,并以一个温度参数为指标,对于网络度分布幂律尾的某些参数,可以看到共识速度会产生两个不同的阶段。我们的证明依赖于众所周知的凝聚随机游走的对偶性,以及利用已知的厄尔多斯-雷尼巨型子图的快速混合对这些游走的混合时间的新约束。与亚临界情况不同 [J. Fernley 和 M. Ort.Fernley 和 M. Ortgiese,Random Structures Algorithms,62 (2023),pp. 376-429]需要极限度分布的尾指数[数学]以及低边缘密度,而在巨型分量情况下,我们还解决了 "超小世界 "幂律指数[数学]。
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引用次数: 0
Rainbow Even Cycles 彩虹均匀周期
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-04-09 DOI: 10.1137/23m1564808
Zichao Dong, Zijian Xu
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1269-1284, June 2024.
Abstract. We prove that every family of (not necessarily distinct) even cycles [math] on some fixed [math]-vertex set has a rainbow even cycle (that is, a set of edges from distinct [math]’s, forming an even cycle). This resolves an open problem of Aharoni, Briggs, Holzman and Jiang. Moreover, the result is best possible for every positive integer [math].
SIAM 离散数学杂志》,第 38 卷第 2 期,第 1269-1284 页,2024 年 6 月。 摘要。我们证明在某个固定的[math]顶点集合上的每个(不一定不同的)偶数循环[math]族都有一个彩虹偶数循环(即来自不同[math]的边的集合,形成一个偶数循环)。这解决了阿哈罗尼、布里格斯、霍尔兹曼和江的一个未决问题。此外,对于每一个正整数[math],这个结果都是最可能的。
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引用次数: 0
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SIAM Journal on Discrete Mathematics
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