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Eigenpolytope Universality and Graphical Designs 特征多面体普遍性和图形设计
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-03-05 DOI: 10.1137/22m1528768
Catherine Babecki, David Shiroma
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 947-964, March 2024.
Abstract. We show that the eigenpolytopes of graphs are universal in the sense that every polytope, up to affine equivalence, appears as the eigenpolytope of some positively weighted graph. We next extend the theory of graphical designs, which are quadrature rules for graphs, to positively weighted graphs. Through Gale duality for polytopes, we show a bijection between graphical designs and the faces of eigenpolytopes. This bijection proves the existence of graphical designs with positive quadrature weights and upper bounds the size of a minimal graphical design. Connecting this bijection with the universality of eigenpolytopes, we establish three complexity results: It is strongly NP-complete to determine if there is a graphical design smaller than the mentioned upper bound, it is NP-hard to find a smallest graphical design, and it is #P-complete to count the number of minimal graphical designs.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 947-964 页,2024 年 3 月。 摘要我们证明了图的特征多面体是普适的,即每个多面体(直到仿射等价)都是某个正向加权图的特征多面体。接下来,我们将图形设计理论(即图形的正交规则)扩展到正加权图形。通过多面体的盖尔对偶性,我们展示了图形设计与特征多面体的面之间的双射关系。这个偏射证明了具有正二次权重的图形设计的存在,并给出了最小图形设计的大小上限。将这一偏射与特征多面体的普遍性联系起来,我们建立了三个复杂性结果:确定是否存在小于上述上限的图形设计是强 NP-完全的,找到最小图形设计是 NP-困难的,计算最小图形设计的数量是 #P- 完全的。
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引用次数: 0
Robust Factorizations and Colorings of Tensor Graphs 张量图的稳健因式分解和着色
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-28 DOI: 10.1137/23m1552474
Joshua Brakensiek, Sami Davies
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 883-916, March 2024.
Abstract. Since the seminal result of Karger, Motwani, and Sudan, algorithms for approximate 3-coloring have primarily centered around rounding the solution to a Semidefinite Program. However, it is likely that important combinatorial or algebraic insights are needed in order to break the [math] threshold. One way to develop new understanding in graph coloring is to study special subclasses of graphs. For instance, Blum studied the 3-coloring of random graphs, and Arora and Ge studied the 3-coloring of graphs with low threshold-rank. In this work, we study graphs that arise from a tensor product, which appear to be novel instances of the 3-coloring problem. We consider graphs of the form [math] with [math] and [math], where [math] is any edge set such that no vertex has more than an [math]-fraction of its edges in [math]. We show that one can construct [math] with [math] that is close to [math]. For arbitrary [math], [math] satisfies [math]. Additionally, when [math] is a mild expander, we provide a 3-coloring for [math] in polynomial time. These results partially generalize an exact tensor factorization algorithm of Imrich. On the other hand, without any assumptions on [math], we show that it is NP-hard to 3-color [math].
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 883-916 页,2024 年 3 月。 摘要。自从 Karger、Motwani 和 Sudan 的开创性成果问世以来,近似 3-着色的算法主要围绕半定式程序解的四舍五入展开。然而,要突破[数学]门槛,很可能需要重要的组合或代数见解。发展对图形着色新理解的一种方法是研究特殊的图形子类。例如,Blum 研究了随机图的 3 着色,Arora 和 Ge 研究了低阈值等级图的 3 着色。在这项工作中,我们研究的是由张量乘积产生的图,这似乎是 3 着色问题的新实例。我们考虑[math]与[math]和[math]的[math]形式的图,其中[math]是任意边集,使得没有顶点在[math]中的边超过[math]的分数。我们证明,我们可以用[math]构造出接近[math]的[math]。对于任意 [math],[math] 满足 [math]。此外,当 [math] 是一个温和的扩展器时,我们可以在多项式时间内为 [math] 提供一个 3 色。这些结果部分推广了伊姆里奇的精确张量因式分解算法。另一方面,在不对[math]做任何假设的情况下,我们证明了对[math]进行 3 着色是 NP 难的。
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引用次数: 0
Rainbow Spanning Trees in Randomly Colored [math] 随机彩色彩虹生成树[数学]
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-27 DOI: 10.1137/22m1537497
Deepak Bal, Alan Frieze, Paweł Prałat
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 867-882, March 2024.
Abstract. Given a graph [math] on [math] vertices and an assignment of colors to its edges, a set of edges [math] is said to be rainbow if edges from [math] have pairwise different colors assigned to them. In this paper, we investigate rainbow spanning trees in randomly colored random [math] graphs.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 867-882 页,2024 年 3 月。 摘要。给定[math]顶点上的图[math]及其边的颜色赋值,如果[math]中的边有成对的不同颜色赋值,则称一组边[math]为彩虹边。本文研究了随机颜色随机 [math] 图中的彩虹生成树。
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引用次数: 0
Pathwidth Versus Cocircumference 路径宽度与头围
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-26 DOI: 10.1137/23m158663x
Marcin Briański, Gwenaël Joret, Michał T. Seweryn
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 857-866, March 2024.
Abstract. The circumference of a graph [math] with at least one cycle is the length of a longest cycle in [math]. A classic result of Birmelé [J. Graph Theory, 43 (2003), pp. 24–25] states that the treewidth of [math] is at most its circumference minus 1. In case [math] is 2-connected, this upper bound also holds for the pathwidth of [math]; in fact, even the treedepth of [math] is upper bounded by its circumference (Briański et al. [Treedepth vs circumference, Combinatorica, 43 (2023), pp. 659–664]). In this paper, we study whether similar bounds hold when replacing the circumference of [math] by its cocircumference, defined as the largest size of a bond in [math], an inclusionwise minimal set of edges [math] such that [math] has more components than [math]. In matroidal terms, the cocircumference of [math] is the circumference of the bond matroid of [math]. Our first result is the following “dual” version of Birmelé’s theorem: The treewidth of a graph [math] is at most its cocircumference. Our second and main result is an upper bound of [math] on the pathwidth of a 2-connected graph [math] with cocircumference [math]. Contrary to circumference, no such bound holds for the treedepth of [math]. Our two upper bounds are best possible up to a constant factor.
SIAM 离散数学杂志》,第 38 卷第 1 期,第 857-866 页,2024 年 3 月。 摘要。至少有一个循环的图[math]的周长是[math]中最长循环的长度。Birmelé [J. Graph Theory, 43 (2003), pp. 24-25] 的一个经典结果指出,[math] 的树宽最多为周长减 1。如果[math]是 2 连接的,那么[math]的路径宽度也有这个上界;事实上,甚至[math]的树深也有其周长的上界(Briański 等人 [Treedepth vs circumference, Combinatorica, 43 (2023), pp. 659-664])。在本文中,我们将研究当用[math]的cocircumference 代替[math]的周长时,类似的边界是否成立。cocircumference 的定义是[math]中一个结合点的最大尺寸,它是边[math]的包容最小集,使得[math]的成分多于[math]。用母陀螺术语来说,[math] 的cocircumference 就是[math] 的bond matroid 的周长。我们的第一个结果是以下伯梅莱定理的 "对偶 "版本:一个图[math]的树宽最多是它的cocircumference。我们的第二个也是主要的结果是[math]关于具有圆周率[math]的 2 连接图[math]的路径宽度的上界[math]。与圆周率相反,[math] 的树深度不存在这样的上界。我们的两个上界在一个常数因子以内都是最好的。
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引用次数: 0
Cops and Robbers on [math]-Free Graphs 无[数学]图形上的警察与强盗
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-26 DOI: 10.1137/23m1549912
Maria Chudnovsky, Sergey Norin, Paul D. Seymour, Jérémie Turcotte
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 845-856, March 2024.
Abstract. We prove that every connected [math]-free graph has cop number at most two, solving a conjecture of Sivaraman. In order to do so, we first prove that every connected [math]-free graph [math] with independence number at least three contains a three-vertex induced path with vertices [math] in order, such that every neighbor of [math] is also adjacent to one of [math].
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 845-856 页,2024 年 3 月。 摘要。我们证明了每一个连通的无[数学]图的 cop 数最多只有两个,从而解决了 Sivaraman 的一个猜想。为此,我们首先证明,每一个独立数至少为三的连通无[math]图[math]都包含一条顶点[math]按顺序排列的三顶点诱导路径,使得[math]的每一个邻接点都与[math]的一个邻接点相邻。
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引用次数: 0
Strong Cocomparability Graphs and Slash-Free Orderings of Matrices 矩阵的强可比性图和无斜线排序
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-12 DOI: 10.1137/22m153238x
Pavol Hell, Jing Huang, Jephian C.-H. Lin
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 828-844, March 2024.
Abstract. We introduce the class of strong cocomparability graphs, as the class of reflexive graphs whose adjacency matrix can be rearranged by a simultaneous row and column permutation to avoid the submatrix with rows 01,10, which we call Slash. We provide an ordering characterization, a forbidden structure characterization, and a polynomial-time certifying recognition algorithm for the class. These results complete the picture in which in addition to, or instead of, the [math] matrix one forbids the [math] matrix (which has rows 11,10). It is well known that in these two cases one obtains the class of interval graphs and the class of strongly chordal graphs, respectively. By complementation, we obtain the class of strong comparability graphs, whose adjacency matrix can be rearranged by a simultaneous row and column permutation to avoid the two-by-two identity submatrix. Thus our results give characterizations and algorithms for this class of irreflexive graphs as well. In other words, our results may be interpreted as solving the following problem: given a symmetric 0,1-matrix with 0-diagonal, can the rows and columns of be simultaneously permuted to avoid the two-by-two identity submatrix?
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 828-844 页,2024 年 3 月。 摘要我们介绍了强可比较性图类,即其邻接矩阵可以通过同时行列排列来避免01,10行的子矩阵的反折图类,我们称之为Slash。我们提供了该类图的排序特征、禁止结构特征和多项式时间认证识别算法。这些结果完善了除了[math]矩阵之外或代替[math]矩阵的[math]矩阵(有 11,10 行)的情况。众所周知,在这两种情况下,我们可以分别得到区间图类和强弦图类。通过互补,我们得到了强可比性图类,其邻接矩阵可以通过同时进行行列排列来重新排列,从而避免出现二乘二的同一性子矩阵。因此,我们的结果也给出了这类不可反图的特征和算法。换句话说,我们的结果可以解释为解决了以下问题:给定一个对角线为 0 的对称 0,1 矩阵,能否同时对其行和列进行排列以避免出现二乘二的同一性子矩阵?
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引用次数: 0
Stable Approximation Algorithms for the Dynamic Broadcast Range-Assignment Problem 动态广播范围分配问题的稳定近似算法
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-09 DOI: 10.1137/23m1545975
Mark de Berg, Arpan Sadhukhan, Frits Spieksma
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 790-827, March 2024.
Abstract. Let [math] be a set of points in [math], where each point [math] has an associated transmission range, denoted [math]. The range assignment [math] induces a directed communication graph [math] on [math], which contains an edge [math] iff [math]. In the broadcast range-assignment problem, the goal is to assign the ranges such that [math] contains an arborescence rooted at a designated root node and the cost [math] of the assignment is minimized. We study the dynamic version of this problem. In particular, we study trade-offs between the stability of the solution—the number of ranges that are modified when a point is inserted into or deleted from [math]—and its approximation ratio. To this end we study [math]-stable algorithms, which are algorithms that modify the range of at most [math] points when they update the solution. We also introduce the concept of a stable approximation scheme, or SAS for short. A SAS is an update algorithm [math] that, for any given fixed parameter [math], is [math]-stable and that maintains a solution with approximation ratio [math], where the stability parameter [math] only depends on [math] and not on the size of [math]. We study such trade-offs in three settings. (1) For the problem in [math], we present a SAS with [math]. Furthermore, we prove that this is tight in the worst case: any SAS for the problem must have [math]. We also present 1-, 2-, and 3-stable algorithms with constant approximation ratio. (2) For the problem in [math] (that is, when the underlying space is a circle) we prove that no SAS exists. This is in spite of the fact that, for the static problem in [math], we prove that an optimal solution can always be obtained by cutting the circle at an appropriate point and solving the resulting problem in [math]. (3) For the problem in [math], we also prove that no SAS exists, and we present a [math]-stable [math]-approximation algorithm. Most results generalize to the setting where, for any given constant [math], the range-assignment cost is [math].
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 790-827 页,2024 年 3 月。 摘要。设[math]是[math]中的一组点,其中每个点[math]都有一个相关的传输范围,记为[math]。范围分配[math]在[math]上引起一个有向通信图[math],如果[math]包含一条边[math]。在广播范围分配问题中,我们的目标是分配范围,使[math]包含一个以指定根节点为根的树状图,且分配的代价[math]最小。我们研究这个问题的动态版本。特别是,我们研究了解的稳定性--当[math]中插入或删除一个点时修改的范围数--与其近似率之间的权衡。为此,我们研究了[math]稳定算法,即在更新解时最多只修改[math]个点的范围的算法。我们还引入了稳定近似方案(简称 SAS)的概念。SAS 是一种更新算法[math],对于任何给定的固定参数[math],它都是[math]稳定的,并且能保持一个近似率为[math]的解,其中稳定参数[math]只取决于[math],而不取决于[math]的大小。我们在三种情况下研究这种权衡。(1) 对于[math]中的问题,我们提出了一个具有[math]的 SAS。此外,我们还证明,在最坏的情况下这是紧密的:问题的任何 SAS 都必须有 [math]。我们还提出了具有恒定近似率的 1-、2- 和 3-稳定算法。(2) 对于 [math] 中的问题(即当底层空间是圆时),我们证明不存在任何 SAS。尽管对于[math]中的静态问题,我们证明了总是可以通过在适当的点上切割圆并求解[math]中的问题来获得最优解。(3) 对于[math]中的问题,我们也证明不存在 SAS,并提出了一种[math]稳定的[math]逼近算法。对于任何给定常数[math],范围分配成本为[math],大多数结果都可以推广到这种情况。
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引用次数: 0
Bernoulli Factories for Flow-Based Polytopes 基于流的多面体的伯努利工厂
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-06 DOI: 10.1137/23m1558343
Rad Niazadeh, Renato Paes Leme, Jon Schneider
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 726-742, March 2024.
Abstract. We construct explicit combinatorial Bernoulli factories for the following class of flow-based polytopes: integral 0/1-polytopes defined by a set of network flow constraints. This generalizes the results of Niazadeh et al. (who constructed an explicit factory for the specific case of bipartite perfect matchings) and provides novel exact sampling procedures for sampling paths, circulations, and [math]-flows. In the process, we uncover new connections to algebraic combinatorics.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 726-742 页,2024 年 3 月。 摘要。我们为以下一类基于流的多面体构建了显式组合伯努利工厂:由一组网络流约束定义的积分 0/1 多面体。这推广了 Niazadeh 等人的研究成果(他们为双方格完全匹配的特定情况构建了一个显式工厂),并为路径、循环和 [math] 流的采样提供了新的精确采样程序。在此过程中,我们发现了代数组合学的新联系。
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引用次数: 0
Fractionally Subadditive Maximization under an Incremental Knapsack Constraint with Applications to Incremental Flows 增量包约束条件下的分数次增量最大化及其在增量流量中的应用
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-06 DOI: 10.1137/23m1569265
Yann Disser, Max Klimm, Annette Lutz, David Weckbecker
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 764-789, March 2024.
Abstract. We consider the problem of maximizing a fractionally subadditive function under an increasing knapsack constraint. An incremental solution to this problem is given by an order in which to include the elements of the ground set, and the competitive ratio of an incremental solution is defined by the worst ratio over all capacities relative to an optimum solution of the corresponding capacity. We present an algorithm that finds an incremental solution of competitive ratio at most [math], under the assumption that the values of singleton sets are in the range [math], and we give a lower bound of [math] on the attainable competitive ratio. In addition, we establish that our framework captures potential-based flows between two vertices, and we give a lower bound of [math] and an upper bound of [math] for the incremental maximization of classical flows with capacities in [math] which is tight for the unit capacity case.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 764-789 页,2024 年 3 月。 摘要。我们考虑的问题是,在一个递增的包约束条件下,最大化一个分数次正函数。该问题的增量解由包含地面集元素的顺序给出,增量解的竞争率由所有容量相对于相应容量最优解的最差比率定义。我们提出了一种算法,在假设单子集的值在[math]范围内的情况下,它能找到竞争比最多为[math]的增量解,我们还给出了可达到的竞争比的下限[math]。此外,我们还确定了我们的框架可以捕捉到两个顶点之间基于势的流量,并给出了容量在 [math] 范围内的经典流量增量最大化的 [math] 下限和 [math] 上限,这对于单位容量情况来说是严密的。
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引用次数: 0
Global Rigidity of Line Constrained Frameworks 线性约束框架的全局刚性
IF 0.8 3区 数学 Q2 Mathematics Pub Date : 2024-02-06 DOI: 10.1137/22m151707x
James Cruickshank, Fatemeh Mohammadi, Harshit J. Motwani, Anthony Nixon, Shin-ichi Tanigawa
SIAM Journal on Discrete Mathematics, Volume 38, Issue 1, Page 743-763, March 2024.
Abstract. We consider the global rigidity problem for bar-joint frameworks where each vertex is constrained to lie on a particular line in [math]. In our setting, we allow multiple vertices to be constrained to the same line. We give a combinatorial characterization of generic rigidity in this setting for arbitrary line sets. Further, under a mild assumption on the given set of lines, we give a complete combinatorial characterization of graphs that are generically globally rigid. This gives a [math]-dimensional extension of the well-known combinatorial characterization of two-dimensional global rigidity. In particular, our results imply that global rigidity is a generic property in this setting.
SIAM 离散数学杂志》,第 38 卷,第 1 期,第 743-763 页,2024 年 3 月。 摘要。我们在[math]中考虑了条形连接框架的全局刚度问题,其中每个顶点都被约束在特定的直线上。在我们的设置中,我们允许多个顶点被约束在同一条直线上。在这种情况下,我们给出了任意线集一般刚性的组合特征。此外,在给定线集的温和假设下,我们给出了一般全局刚性图的完整组合特征。这给出了著名的二维全局刚性组合特征的[数学]维扩展。特别是,我们的结果意味着全局刚性是这种情况下的一个通用属性。
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引用次数: 0
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SIAM Journal on Discrete Mathematics
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