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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
Spanning Bipartite Quadrangulations of Triangulations of the Projective Plane 投影平面三角剖分的跨二元四分法
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-04-08 DOI: 10.1137/23m1566960
Kenta Noguchi
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1250-1268, June 2024.
Abstract. We completely characterize the triangulations of the projective plane that admit a spanning bipartite quadrangulation subgraph. This is an affirmative answer to a question by Kündgen and Ramamurthi [J. Combin. Theory Ser. B, 85 (2002), pp. 307–337] for the projective planar case.
SIAM 离散数学杂志》,第 38 卷第 2 期,第 1250-1268 页,2024 年 6 月。 摘要。我们完全描述了射影平面中包含跨两方四面体子图的三角剖分。这是对 Kündgen 和 Ramamurthi [J. Combin. Theory Ser. B, 85 (2002), pp.
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引用次数: 0
The Rainbow Saturation Number Is Linear 彩虹饱和度数值是线性的
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-04-08 DOI: 10.1137/23m1566881
Natalie Behague, Tom Johnston, Shoham Letzter, Natasha Morrison, Shannon Ogden
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1239-1249, June 2024.
Abstract. Given a graph [math], we say that an edge-colored graph [math] is [math]-rainbow saturated if it does not contain a rainbow copy of [math], but the addition of any nonedge in any color creates a rainbow copy of [math]. The rainbow saturation number [math] is the minimum number of edges among all [math]-rainbow saturated edge-colored graphs on [math] vertices. We prove that for any nonempty graph [math], the rainbow saturation number is linear in [math], thus proving a conjecture of Girão, Lewis, and Popielarz. In addition, we give an improved upper bound on the rainbow saturation number of the complete graph, disproving a second conjecture of Girão, Lewis, and Popielarz.
SIAM 离散数学杂志》第 38 卷第 2 期第 1239-1249 页,2024 年 6 月。 摘要。给定一个图[math],如果一个边色图[math]不包含[math]的彩虹副本,但添加任何颜色的非边都会产生[math]的彩虹副本,我们就说这个边色图[math]是[math]-彩虹饱和的。彩虹饱和数[math]是[math]顶点上所有[math]-彩虹饱和边色图中最少的边数。我们证明了对于任何非空图 [math],彩虹饱和度数在 [math] 中是线性的,从而证明了 Girão、Lewis 和 Popielarz 的猜想。此外,我们还给出了完整图的彩虹饱和数的改进上界,推翻了吉朗、刘易斯和波皮拉尔兹的第二个猜想。
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引用次数: 0
On the Gap Between Hereditary Discrepancy and the Determinant Lower Bound 论遗传差异与决定因素下限之间的差距
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-04-05 DOI: 10.1137/23m1566790
Lily Li, Aleksandar Nikolov
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1222-1238, June 2024.
Abstract. The determinant lower bound of Lovász, Spencer, and Vesztergombi [European J. Combin., 7 (1986), pp. 151–160] is a general way to prove lower bounds on the hereditary discrepancy of a set system. In their paper, Lovász, Spencer, and Vesztergombi asked if hereditary discrepancy can also be bounded from above by a function of the determinant lower bound. This was answered in the negative by Hoffman, and the largest known multiplicative gap between the two quantities for a set system of [math] subsets of a universe of size [math] is on the order of [math]. On the other hand, building upon work of Matoušek [Proc. Amer. Math. Soc., 141 (2013), pp. 451–460], Jiang and Reis [in Proceedings of the Symposium on Simplicity in Algorithms (SOSA), SIAM, Philadelphia, 2022, pp. 308–313] showed that this gap is always bounded up to constants by [math]. This is tight when [math] is polynomial in [math] but leaves open the case of large [math]. We show that the bound of Jiang and Reis is tight for nearly the entire range of [math]. Our proof amplifies the discrepancy lower bounds of a set system derived from the discrete Haar basis via Kronecker products.
SIAM 离散数学杂志》第 38 卷第 2 期第 1222-1238 页,2024 年 6 月。 摘要。Lovász、Spencer 和 Vesztergombi 的行列式下界 [European J. Combin., 7 (1986), pp.在他们的论文中,Lovász、Spencer 和 Vesztergombi 询问遗传差异是否也可以通过行列式下界的函数从上而下地限定。霍夫曼对此的回答是否定的,对于大小为[math]的宇宙的[math]子集的集合系统,这两个量之间已知的最大乘法差距是[math]数量级。另一方面,在马图塞克 [Proc. Amer. Math. Soc., 141 (2013), pp. 451-460] 的工作基础上,蒋和雷斯 [in Proceedings of the Symposium on Simplicity in Algorithms (SOSA), SIAM, Philadelphia, 2022, pp.当 [math] 是 [math] 的多项式时,这个界限很窄,但当 [math] 较大时,这个界限就很宽了。我们证明,几乎在 [math] 的整个范围内,Jiang 和 Reis 的约束都很紧。我们的证明扩大了通过克朗内克积从离散哈尔基导出的集合系统的差异下界。
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引用次数: 0
Maximum Matchings and Popularity 最大匹配度和人气
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-04-04 DOI: 10.1137/22m1523248
Telikepalli Kavitha
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1202-1221, June 2024.
Abstract. Let [math] be a bipartite graph where every node has a strict ranking of its neighbors. For any node, its preferences over neighbors extend naturally to preferences over matchings. A maximum matching [math] in [math] is a popular max-matching if there is no maximum matching more popular than [math]. In other words, for any maximum matching [math], the number of nodes that prefer [math] to [math] is at least the number of nodes that prefer [math] to [math]. It is known that popular max-matchings always exist in [math] and one such matching can be efficiently computed. In this paper we are in the weighted setting, i.e., there is a cost function [math], and our goal is to find a min-cost popular max-matching. We prove that such a matching can be computed in polynomial time by showing a compact extended formulation for the popular max-matching polytope. By contrast, it is known that the popular matching polytope has near-exponential extension complexity and finding a min-cost popular matching is NP-hard. We also consider Pareto-optimality. Though it is easy to find a Pareto-optimal matching/max-matching, we show that it is NP-hard to find a min-cost Pareto-optimal matching/max-matching.
SIAM 离散数学杂志》,第 38 卷第 2 期,第 1202-1221 页,2024 年 6 月。 摘要设 [math] 是一个双方图,其中每个节点都对其邻居有严格的排序。对于任何一个节点,它对邻居的偏好自然扩展为对匹配的偏好。如果没有比[math]更受欢迎的最大匹配,那么[math]中的最大匹配[math]就是受欢迎的最大匹配。换句话说,对于任何最大匹配[math],喜欢[math]而不喜欢[math]的节点数至少是喜欢[math]而不喜欢[math]的节点数。众所周知,[math] 中总是存在流行的最大匹配,而且可以高效地计算出这样的匹配。本文采用加权设置,即存在一个成本函数 [math],我们的目标是找到一个成本最小的流行最大匹配。我们通过展示流行最大匹配多面体的紧凑扩展公式,证明这种匹配可以在多项式时间内计算出来。相比之下,众所周知,流行匹配多面体具有接近指数的扩展复杂度,而找到最小成本的流行匹配是 NP 难的。我们还考虑了帕累托最优性。虽然找到帕累托最优匹配/最大匹配很容易,但我们证明找到最小成本的帕累托最优匹配/最大匹配是 NP 难的。
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引用次数: 0
Circuit Decompositions of Binary Matroids 二元矩阵的电路分解
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-04-01 DOI: 10.1137/23m1587439
Bryce Frederickson, Lukas Michel
SIAM Journal on Discrete Mathematics, Volume 38, Issue 2, Page 1193-1201, June 2024.
Abstract. Given a simple Eulerian binary matroid [math], what is the minimum number of disjoint circuits necessary to decompose [math]? We prove that [math] many circuits suffice if [math] is the complete binary matroid, for certain values of [math], and that [math] many circuits suffice for general [math]. We also determine the asymptotic behavior of the minimum number of circuits in an odd-cover of [math].
SIAM 离散数学杂志》第 38 卷第 2 期第 1193-1201 页,2024 年 6 月。 摘要。给定一个简单的欧拉二元矩阵[math],分解[math]所需的互不相交的电路的最小数目是多少?我们证明,如果[math]是完整的二元矩阵,在[math]的特定值下,[math]许多电路就足够了,而对于一般的[math],[math]许多电路就足够了。我们还确定了[math]奇数覆盖中最小电路数的渐近行为。
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引用次数: 0
期刊
SIAM Journal on Discrete Mathematics
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