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A Property on Monochromatic Copies of Graphs Containing a Triangle 包含三角形的图形单色副本的性质
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-12 DOI: 10.1137/23m1564894
Hao Chen, Jie Ma
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 316-326, March 2024.
Abstract. A graph [math] is called common and, respectively, strongly common if the number of monochromatic copies of [math] in a 2-edge-coloring [math] of a large clique is asymptotically minimized by the random coloring with an equal proportion of each color and, respectively, by the random coloring with the same proportion of each color as in [math]. A well-known theorem of Jagger, Št’ovíček, and Thomason states that every graph containing a [math] is not common. Here we prove an analogous result that every graph containing a [math] and with at least four edges is not strongly common.
SIAM 离散数学杂志》,第 38 卷第 1 期,第 316-326 页,2024 年 3 月。 摘要。如果在一个大的簇的 2 边着色[math]中,[math]的单色副本数被每种颜色比例相等的随机着色和每种颜色比例与[math]相同的随机着色渐近地最小化,则图[math]分别称为普通图和强普通图。贾格尔、什特奥维切克和托马森的一个著名定理指出,每个包含一个[math]的图都是不常见的。在这里,我们证明了一个类似的结果,即每个包含一个[math]且至少有四条边的图都不是强公共图。
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引用次数: 0
Geometric Network Creation Games 几何网络创建游戏
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-11 DOI: 10.1137/20m1376662
Davide Bilò, Tobias Friedrich, Pascal Lenzner, Anna Melnichenko
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 277-315, March 2024.
Abstract. Network creation games are a well-known approach for explaining and analyzing the structure, quality, and dynamics of real-world networks that evolved via the interaction of selfish agents without a central authority. In these games selfish agents corresponding to nodes in a network strategically buy incident edges to improve their centrality. However, past research on these games only considered the creation of networks with unit-weight edges. In practice, e.g., when constructing a fiber-optic network, the choice of which nodes to connect and also the induced price for a link crucially depend on the distance between the involved nodes, and such settings can be modeled via edge-weighted graphs. We incorporate arbitrary edge weights by generalizing the well-known model by Fabrikant et al. [Proceedings of PODC ’03, ACM, 2003, pp. 347–351] to edge-weighted host graphs and focus on the geometric setting where the weights are induced by the distances in some metric space. In stark contrast to the state of the art for the unit-weight version, where the price of anarchy is conjectured to be constant and where resolving this is a major open problem, we prove a tight nonconstant bound on the price of anarchy for the metric version and a slightly weaker upper bound for the nonmetric case. Moreover, we analyze the existence of equilibria, the computational hardness, and the game dynamics for several natural metrics. The model we propose can be seen as the game-theoretic analogue of the classical network design problem. Thus, low-cost equilibria of our game correspond to decentralized and stable approximations of the optimum network design.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 277-315 页,2024 年 3 月。 摘要网络创建博弈是一种著名的解释和分析现实世界网络结构、质量和动态的方法。在这些博弈中,与网络中节点相对应的自私代理会策略性地购买附带边来提高自己的中心地位。然而,过去对这些博弈的研究只考虑了创建具有单位权重边的网络。在实践中,例如在构建光纤网络时,选择连接哪些节点以及链接的诱导价格在很大程度上取决于相关节点之间的距离,而这种情况可以通过边权重图来建模。我们将 Fabrikant 等人的著名模型[PODC'03 论文集,ACM,2003 年,第 347-351 页]推广到边缘加权主机图,并将重点放在几何设置上,即权重是由某个度量空间中的距离引起的。在单位权重版本中,无政府状态的价格被猜测为常数,而解决这个问题是一个重大的未决难题。与此形成鲜明对比的是,我们证明了公度量版本中无政府状态价格的严格非常数约束,以及非公度量情况下稍弱的上界。此外,我们还分析了几个自然度量的均衡存在性、计算难度和博弈动态。我们提出的模型可以看作是经典网络设计问题的博弈论类似物。因此,我们博弈的低成本均衡点对应于最优网络设计的分散和稳定近似值。
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引用次数: 0
The Treewidth and Pathwidth of Graph Unions 图元的树宽和路径宽
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-10 DOI: 10.1137/22m1524047
Bogdan Alecu, Vadim V. Lozin, Daniel A. Quiroz, Roman Rabinovich, Igor Razgon, Viktor Zamaraev
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 261-276, March 2024.
Abstract. Given two [math]-vertex graphs [math] and [math] of bounded treewidth, is there an [math]-vertex graph [math] of bounded treewidth having subgraphs isomorphic to [math] and [math]? Our main result is a negative answer to this question, in a strong sense: we show that the answer is no even if [math] is a binary tree and [math] is a ternary tree. We also provide an extensive study of cases where such “gluing” is possible. In particular, we prove that if [math] has treewidth [math] and [math] has pathwidth [math], then there is an [math]-vertex graph of treewidth at most [math] containing both [math] and [math] as subgraphs.
SIAM 离散数学杂志》,第 38 卷第 1 期,第 261-276 页,2024 年 3 月。 摘要。给定两个有界树宽的[math]顶点图[math]和[math],是否存在一个有界树宽的[math]顶点图[math],其子图与[math]和[math]同构?我们的主要结果从强意义上否定了这个问题:我们证明,即使 [math] 是二叉树,[math] 是三叉树,答案也是否定的。我们还对这种 "粘合 "可能发生的情况进行了广泛研究。特别是,我们证明了如果[math]的树宽是[math],而[math]的路径宽是[math],那么就存在一个树宽至多为[math]的[math]顶点图,它同时包含[math]和[math]这两个子图。
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引用次数: 0
On Ramsey Size-Linear Graphs and Related Questions 论拉姆齐大小线性图及相关问题
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-09 DOI: 10.1137/22m1481713
Domagoj Bradač, Lior Gishboliner, Benny Sudakov
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 225-242, March 2024.
Abstract. In this paper we prove several results on Ramsey numbers [math] for a fixed graph [math] and a large graph [math], in particular for [math]. These results extend earlier work of Erdős, Faudree, Rousseau, and Schelp and of Balister, Schelp, and Simonovits on so-called Ramsey size-linear graphs. Among other results, we show that if [math] is a subdivision of [math] with at least six vertices, then [math] for every graph [math]. We also conjecture that if [math] is a connected graph with [math], then [math]. The case [math] was proved by Erdős, Faudree, Rousseau, and Schelp. We prove the case [math].
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 225-242 页,2024 年 3 月。 摘要在本文中,我们证明了关于固定图[math]和大图[math]的拉姆齐数[math],特别是[math]的拉姆齐数[math]的几个结果。这些结果扩展了 Erdős、Faudree、Rousseau 和 Schelp 以及 Balister、Schelp 和 Simonovits 早期关于所谓拉姆齐大小线性图的工作。在其他结果中,我们证明了如果 [math] 是至少有六个顶点的 [math] 的细分图,那么 [math] 对于每个图 [math]。我们还猜想,如果[math]是[math]的连通图,那么[math]。Erdős, Faudree, Rousseau 和 Schelp 证明了 [math] 的情况。我们证明了 [math] 的情况。
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引用次数: 0
Highly Connected Subgraphs with Large Chromatic Number 色度数大的高连接子图
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-09 DOI: 10.1137/22m150040x
Tung H. Nguyen
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 243-260, March 2024.
Abstract. For integers [math] and [math], let [math] be the least integer [math] such that every graph with chromatic number at least [math] contains a [math]-connected subgraph with chromatic number at least [math]. Refining the recent result of Girão and Narayanan [Bull. Lond. Math. Soc., 54 (2022), pp. 868–875] that [math] for all [math], we prove that [math] for all [math] and [math]. This sharpens earlier results of Alon et al. [J. Graph Theory, 11 (1987), pp. 367–371], of Chudnovsky [J. Combin. Theory Ser. B, 103 (2013), pp. 567–586], and of Penev, Thomassé, and Trotignon [SIAM J. Discrete Math., 30 (2016), pp. 592–619]. Our result implies that [math] for all [math], making a step closer towards a conjecture of Thomassen [J. Graph Theory, 7 (1983), pp. 261–271] that [math], which was originally a result with a false proof and was the starting point of this research area.
SIAM 离散数学杂志》第 38 卷第 1 期第 243-260 页,2024 年 3 月。 摘要。对于整数[math]和[math],设[math]是最小整数[math],使得每个色度数至少为[math]的图都包含一个色度数至少为[math]的[math]连接子图。在完善吉朗和纳拉亚南[Bull. Lond. Math. Soc., 54 (2022), pp. 868-875]关于[math]为所有[math]的最新结果的基础上,我们证明[math]为所有[math]和[math]。这使 Alon 等人 [J. Graph Theory, 11 (1987), pp. 367-371]、Chudnovsky [J. Combin. Theory Ser. B, 103 (2013), pp.我们的结果意味着[math]适用于所有[math],从而向托马森[J. Graph Theory, 7 (1983), pp. 261-271]的猜想[math]又迈近了一步,这个猜想原本是一个假证明的结果,是这一研究领域的起点。
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引用次数: 0
Stochastic Probing with Increasing Precision 精度不断提高的随机探测
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-08 DOI: 10.1137/22m149466x
Martin Hoefer, Kevin Schewior, Daniel Schmand
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 148-169, March 2024.
Abstract. We consider a selection problem with stochastic probing. There is a set of items whose values are drawn from independent distributions. The distributions are known in advance. Each item can be tested repeatedly. Each test reduces the uncertainty about the realization of its value. We study a testing model, where the first test reveals whether the realized value is smaller or larger than the [math]-quantile of the underlying distribution of some constant [math]. Subsequent tests allow us to further narrow down the interval in which the realization is located. There is a limited number of possible tests, and our goal is to design near-optimal testing strategies that allow us to maximize the expected value of the chosen item. We study both identical and nonidentical distributions and develop polynomial-time algorithms with constant approximation factors in both scenarios.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 148-169 页,2024 年 3 月。 摘要。我们考虑一个随机探测的选择问题。有一组项目,其值从独立的分布中抽取。这些分布是事先已知的。每个项目都可以重复测试。每次测试都会减少其值实现的不确定性。我们研究一个测试模型,其中第一次测试揭示了实现值是小于还是大于某个常数[math]的基础分布的[math]-四分位数。随后的测试允许我们进一步缩小实现值所在的区间。可能的测试数量有限,我们的目标是设计接近最优的测试策略,使我们能够最大化所选项目的期望值。我们研究了相同分布和非相同分布,并开发了在这两种情况下都具有恒定近似因子的多项式时间算法。
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引用次数: 0
Modules in Robinson Spaces 罗宾逊空间中的模块
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-08 DOI: 10.1137/22m1494348
Mikhael Carmona, Victor Chepoi, Guyslain Naves, Pascal Préa
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 190-224, March 2024.
Abstract. A Robinson space is a dissimilarity space [math] (i.e., a set [math] of size [math] and a dissimilarity [math] on [math]) for which there exists a total order [math] on [math] such that [math] implies that [math]. Recognizing if a dissimilarity space is Robinson has numerous applications in seriation and classification. An mmodule of [math] (generalizing the notion of a module in graph theory) is a subset [math] of [math] which is not distinguishable from the outside of [math]; i.e., the distance from any point of [math] to all points of [math] is the same. If [math] is any point of [math], then [math], and the maximal-by-inclusion mmodules of [math] not containing [math] define a partition of [math], called the copoint partition. In this paper, we investigate the structure of mmodules in Robinson spaces and use it and the copoint partition to design a simple and practical divide-and-conquer algorithm for recognition of Robinson spaces in optimal [math] time.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 190-224 页,2024 年 3 月。 摘要。罗宾逊空间是一个相似性空间[math](即大小为[math]的集合[math]和[math]上的相似性[math]),对于它,[math]上存在一个总阶[math],使得[math]意味着[math]。识别异或空间是否为鲁滨逊空间在序列化和分类中有着广泛的应用。[math]的模块(概括图论中模块的概念)是[math]的子集[math],它与[math]的外部无法区分;也就是说,从[math]的任意一点到[math]的所有点的距离是相同的。如果[math]是[math]的任意一点,那么[math]和不包含[math]的[math]最大包含模块定义了[math]的一个分区,称为共点分区。在本文中,我们研究了罗宾逊空间中的模块结构,并利用它和共点分割设计了一种简单实用的分而治之算法,用于在最优[math]时间内识别罗宾逊空间。
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引用次数: 0
Exchange Distance of Basis Pairs in Split Matroids 分裂 Matroids 中基对的交换距离
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-08 DOI: 10.1137/23m1565115
Kristóf Bérczi, Tamás Schwarcz
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 132-147, March 2024.
Abstract. The basis exchange axiom has been a driving force in the development of matroid theory. However, the axiom gives only a local characterization of the relation of bases, which is a major stumbling block to further progress, and providing a global understanding of the structure of matroid bases is a fundamental goal in matroid optimization. While studying the structure of symmetric exchanges, Gabow proposed the problem that any pair of bases admits a sequence of symmetric exchanges. A different extension of the exchange axiom was proposed by White, who investigated the equivalence of compatible basis sequences. These conjectures suggest that the family of bases of a matroid possesses much stronger structural properties than we are aware of. In the present paper, we study the distance of basis pairs of a matroid in terms of symmetric exchanges. In particular, we give a polynomial-time algorithm that determines a shortest possible exchange sequence that transforms a basis pair into another for split matroids, a class that was motivated by the study of matroid polytopes from a tropical geometry point of view. As a corollary, we verify the above-mentioned long-standing conjectures for this large class. As paving matroids form a subclass of split matroids, our result settles the conjectures for paving matroids as well.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 132-147 页,2024 年 3 月。 摘要。基交换公理一直是矩阵理论发展的推动力。然而,该公理只给出了基关系的局部表征,这是进一步发展的主要绊脚石,而提供对 matroid 基结构的全局理解是 matroid 优化的基本目标。在研究对称交换结构时,Gabow 提出了这样一个问题:任何一对基都允许一个对称交换序列。怀特对交换公理提出了不同的扩展,他研究了兼容基序列的等价性。这些猜想表明,矩阵的基群具有比我们所知道的更强的结构性质。在本文中,我们从对称交换的角度研究了 matroid 的基对距离。特别是,我们给出了一种多项式时间算法,它可以确定一个最短的交换序列,将分裂矩阵的基对转换成另一个基对。作为推论,我们为这一大类验证了上述长期存在的猜想。由于铺垫矩阵构成了分裂矩阵的一个子类,我们的结果也解决了铺垫矩阵的猜想。
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引用次数: 0
On Weighted Graph Separation Problems and Flow Augmentation 论加权图分离问题和流量增强
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-08 DOI: 10.1137/22m153118x
Eun Jung Kim, Tomáš Masařík, Marcin Pilipczuk, Roohani Sharma, Magnus Wahlström
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 170-189, March 2024.
Abstract. One of the first applications of the recently introduced technique of flow augmentation [Kim et al., STOC 2022] is a fixed-parameter algorithm for the weighted version of Directed Feedback Vertex Set, a landmark problem in parameterized complexity. In this article, we explore the applicability of flow augmentation to other weighted graph separation problems parameterized by the size of the cutset. We show the following: In weighted undirected graphs, Multicut is fixed-parameter tractable (FPT) in both the edge- and the vertex-deletion version. The weighted version of Group Feedback Vertex Set is FPT, even with oracle access to group operations. The weighted version of Directed Subset Feedback Vertex Set is FPT. Our study reveals Directed Symmetric Multicut as the next important graph separation problem whose parameterized complexity remains unknown, even in the unweighted setting.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 170-189 页,2024 年 3 月。 摘要最近引入的流增强技术[Kim 等人,STOC 2022]的首批应用之一是加权版定向反馈顶点集的固定参数算法,这是参数化复杂度的一个标志性问题。在本文中,我们探讨了流量增强对其他以切集大小为参数的加权图分离问题的适用性。我们展示了以下内容:在加权无向图中,Multicut 在边和顶点删除版本中都是固定参数可处理(FPT)的。群反馈顶点集的加权版本是 FPT,甚至可以用甲骨文访问群操作。有向子集反馈顶点集合的加权版本是 FPT。我们的研究揭示了有向对称多重图是下一个重要的图分离问题,它的参数化复杂度仍是未知的,即使在无权设置中也是如此。
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引用次数: 0
On a Conjecture of Feige for Discrete Log-Concave Distributions 关于离散对数凹分布的费格猜想
IF 0.8 3区 数学 Q2 MATHEMATICS Pub Date : 2024-01-05 DOI: 10.1137/22m1539514
Abdulmajeed Alqasem, Heshan Aravinda, Arnaud Marsiglietti, James Melbourne
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 93-102, March 2024.
Abstract. A remarkable conjecture of Feige [SIAM J. Comput., 35 (2006), pp. 964–984] asserts that for any collection of [math] independent nonnegative random variables [math], each with expectation at most 1, [math], where [math]. In this paper, we investigate this conjecture for the class of discrete log-concave probability distributions, and we prove a strengthened version. More specifically, we show that the conjectured bound [math] holds when [math]’s are independent discrete log-concave with arbitrary expectation.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 93-102 页,2024 年 3 月。 摘要。费格的一个惊人猜想 [SIAM J. Comput., 35 (2006), pp.在本文中,我们针对离散对数凹概率分布类研究了这一猜想,并证明了它的加强版。更具体地说,我们证明了当[math]的独立离散对数凹具有任意期望时,猜想的约束[math]成立。
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引用次数: 0
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SIAM Journal on Discrete Mathematics
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