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Rank-Metric Lattices Rank-Metric晶格
4区 数学 Q2 MATHEMATICS Pub Date : 2023-01-13 DOI: 10.37236/11373
Giuseppe Cotardo, Alberto Ravagnani
We introduce the class of rank-metric geometric lattices and initiate the study of their structural properties. Rank-metric lattices can be seen as the $q$-analogues of higher-weight Dowling lattices, defined by Dowling himself in 1971. We fully characterize the supersolvable rank-metric lattices and compute their characteristic polynomials. We then concentrate on small rank-metric lattices whose characteristic polynomial we cannot compute, and provide a formula for them under a polynomiality assumption on their Whitney numbers of the first kind. The proof relies on computational results and on the theory of vector rank-metric codes, which we review in this paper from the perspective of rank-metric lattices. More precisely, we introduce the notion of lattice-rank weights of a rank-metric code and investigate their properties as combinatorial invariants and as code distinguishers for inequivalent codes.
介绍了秩-度量几何格类,并对其结构性质进行了初步研究。秩-度量格可以看作是高权重的道林格的$q$-类似物,道林格是由道林自己在1971年定义的。我们充分刻画了超可解秩度量格,并计算了它们的特征多项式。然后,我们重点研究了无法计算其特征多项式的小秩度量格,并在第一类惠特尼数的多项式假设下给出了它们的公式。该证明依赖于计算结果和向量秩-度量码理论,本文从秩-度量格的角度对其进行了回顾。更准确地说,我们引入了秩-度量码的格-秩权重的概念,并研究了它们作为组合不变量和不等价码的码区分符的性质。
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引用次数: 0
Extremal Independent Set Reconfiguration 极值独立集重构
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2023-01-05 DOI: 10.48550/arXiv.2301.02020
N. Bousquet, Bastien Durain, Théo Pierron, St'ephan Thomass'e
The independent set reconfiguration problem asks whether one can transform one given independent set of a graph into another, by changing vertices one by one in such a way the intermediate sets remain independent. Extremal problems on independent sets are widely studied: for example, it is well known that an $n$-vertex graph has at most $3^{n/3}$ maximum independent sets (and this is tight). This paper investigates the asymptotic behavior of maximum possible length of a shortest reconfiguration sequence for independent sets of size $k$ among all $n$-vertex graphs. We give a tight bound for $k=2$. We also provide a subquadratic upper bound (using the hypergraph removal lemma) as well as an almost tight construction for $k=3$. We generalize our results for larger values of $k$ by proving an $n^{2lfloor k/3 rfloor}$ lower bound.
独立集重构问题是指是否可以将图中一个给定的独立集转换为另一个给定的独立集,通过逐个改变中间集的顶点,使中间集保持独立。独立集上的极值问题被广泛研究:例如,众所周知,一个$n$顶点的图最多有$3^{n/3}$个最大独立集(这是紧的)。本文研究了在所有$n$顶点图中对于大小为$k$的独立集的最短重构序列的最大可能长度的渐近性。我们给出了k=2的紧界。我们还提供了次二次上界(使用超图去除引理)以及$k=3$的几乎紧构造。我们通过证明$n^{2lfloor k/3 rfloor}$的下界,将结果推广到更大的$k$值。
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引用次数: 0
Rowmotion on 321-Avoiding Permutations 关于321-避免排列的动议
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-21 DOI: 10.37236/11792
Ben Adenbaum, S. Elizalde
We give a natural definition of rowmotion for $321$-avoiding permutations, by translating, through bijections involving Dyck paths and the Lalanne--Kreweras involution, the analogous notion for antichains of the positive root poset of type $A$. We prove that some permutation statistics, such as the number of fixed points, are homomesic under rowmotion, meaning that they have a constant average over its orbits. Our setting also provides a more natural description of the celebrated Armstrong--Stump--Thomas equivariant bijection between antichains and non-crossing matchings in types $A$ and $B$, by showing that it is equivalent to the Robinson--Schensted--Knuth correspondence on $321$-avoiding permutations permutations.
通过引入Dyck路径的双射和Lalanne—Kreweras对合,我们给出了$321$-避免置换的行运动的一个自然定义,这与类型$ a $的正根序集的反链的类似概念是等价的。我们证明了一些排列统计量,如不动点的数目,在行运动下是同调的,这意味着它们在其轨道上有一个常数平均值。我们的设置也提供了一个更自然的描述著名的Armstrong- Stump- Thomas等变双射之间的反链和非交叉匹配类型$ a $和$B$,通过表明它是等价于$321$-避免排列排列的Robinson- Schensted- Knuth对应。
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引用次数: 3
A Linear Hypergraph Extension of Turán's Theorem Turán定理的线性超图推广
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-16 DOI: 10.37236/10525
Guorong Gao, A. Chang
An $r$-uniform hypergraph is linear if every two edges intersect in at most one vertex. Given a family of $r$-uniform hypergraphs $mathcal{F}$, the linear Turán number ex$_r^{lin}(n,mathcal{F})$ is the maximum number of edges of a linear $r$-uniform hypergraph on $n$ vertices that does not contain any member of $mathcal{F}$ as a subgraph. Let $K_l$ be a complete graph with $l$ vertices and $rgeq 2$. The $r$-expansion of $K_l$ is the $r$-graph $K_l^+$ obtained from $K_l$ by enlarging each edge of $K_l$ with $r-2$ new vertices disjoint from $V(K_l)$ such that distinct edges of $K_l$ are enlarged by distinct vertices. When $lgeq r geq 3$ and $n$ is sufficiently large, we prove the following extension of Turán's Theorem $$ex_{r}^{lin}left(n, K_{l+1}^{+}right)leq |TD_r(n,l)|,$$ with equality achieved only by the Turán design $TD_r(n,l)$, where the Turán design $TD_r(n,l)$ is an almost balanced $l$-partite $r$-graph such that each pair of vertices from distinct parts are contained in one edge exactly. Moreover, some results on linear Turán number of general configurations are also presented.
a $r$-均匀超图是线性的,如果每两条边相交于至多一个顶点。给定一个家庭 $r$-均匀超图 $mathcal{F}$,线性Turán数ex$_r^{lin}(n,mathcal{F})$ 一条线的最大边数是线性的吗 $r$-均匀超图 $n$ 不包含任何成员的顶点 $mathcal{F}$ 作为子图。让 $K_l$ 是与的完备图 $l$ 顶点和 $rgeq 2$. The $r$-膨胀 $K_l$ 是? $r$-图 $K_l^+$ 获得自 $K_l$ 通过扩大的每条边 $K_l$ 有 $r-2$ 新的顶点从 $V(K_l)$ 这样的明显的边缘 $K_l$ 被不同的顶点放大。什么时候 $lgeq r geq 3$ 和 $n$ 是足够大的,我们证明Turán定理的以下推广 $$ex_{r}^{lin}left(n, K_{l+1}^{+}right)leq |TD_r(n,l)|,$$ 只有Turán设计才能实现平等 $TD_r(n,l)$,其中Turán设计 $TD_r(n,l)$ 几乎是平衡的 $l$-分 $r$-图,使得来自不同部分的每对顶点都精确地包含在一条边中。此外,还给出了一般构型的线性Turán数的一些结果。
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引用次数: 0
A Combinatorial Characterization of Extremal Generalized Hexagons 极值广义六边形的组合表征
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-16 DOI: 10.37236/9245
B. Bruyn
A finite generalized $2d$-gon of order $(s,t)$ with $d in { 2,3,4 }$ and $s not= 1$ is called extremal if $t$ attains its maximal possible value $s^{e_d}$, where $e_2=e_4=2$ and $e_3=3$. The problem of finding combinatorial conditions that are both necessary and sufficient for a finite generalized $2d$-gon of order $(s,t)$ to be extremal has so far only be solved for the generalized quadrangles. In this paper, we obtain a solution for the generalized hexagons. We also obtain a related combinatorial characterization for extremal regular near hexagons.
当$t$达到最大可能值$s^{e_d}$时,当$t$达到最大可能值$s^{e_d}$时,称为$2d$- $ $(s,t)$,其中$e_2=e_4=2$和$e_3=3$。对于阶$(s,t)$的有限广义$2d$-gon求极值的充分必要组合条件的问题,迄今为止只解决了广义四边形的问题。本文得到了广义六边形的一个解。我们还得到了极值正则近六边形的相关组合表征。
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引用次数: 1
Density of Balanced 3-Partite Graphs without 3-Cycles or 4-Cycles 无3环或4环的平衡3部图的密度
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-16 DOI: 10.37236/10958
Zequn Lv, Mei Lu, Chunqiu Fang
Let $C_k$ be a cycle of order $k$, where $kge 3$. Let ex$(n, n, n, {C_{3}, C_{4}})$ be the maximum number of edges in a balanced $3$-partite graph whose vertex set consists of three parts, each has $n$ vertices that has no subgraph isomorphic to $C_3$ or $C_4$. We construct dense balanced 3-partite graphs without 3-cycles or 4-cycles and show that ex$(n, n, n, {C_{3}, C_{4}})ge (frac{6sqrt{2}-8}{(sqrt{2}-1)^{3/2}}+o(1))n^{3/2}$.
设$C_k$为顺序的一个循环$k$,其中$kge 3$。设ex $(n, n, n, {C_{3}, C_{4}})$为平衡的$3$部图的最大边数,该图的顶点集由三个部分组成,每个部分都有$n$个顶点,并且没有同$C_3$或$C_4$同构的子图。我们构造了没有3环和4环的稠密平衡3部图,并证明了ex $(n, n, n, {C_{3}, C_{4}})ge (frac{6sqrt{2}-8}{(sqrt{2}-1)^{3/2}}+o(1))n^{3/2}$。
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引用次数: 1
Weighted Modulo Orientations of Graphs and Signed Graphs 图与符号图的加权模取向
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-16 DOI: 10.37236/10740
Jianbing Liu, Miaomiao Han, H. Lai
Given a graph $G$ and an odd prime $p$, for a mapping $f: E(G) to {mathbb Z}_psetminus{0}$ and a ${mathbb Z}_p$-boundary $b$ of $G$, an orientation $tau$ is called an $(f,b;p)$-orientation if the net out $f$-flow is the same as $b(v)$ in ${mathbb Z}_p$ at each vertex $vin V(G)$ under orientation $D$. This concept was introduced by Esperet et al. (2018), generalizing mod $p$-orientations and closely related to Tutte's nowhere zero 3-flow conjecture. They proved that $(6p^2 - 14p + 8)$-edge-connected graphs have all possible $(f,b;p)$-orientations. In this paper, the framework of such orientations is extended to signed graph through additive bases. We also study the $(f,b;p)$-orientation problem for some (signed) graphs families including complete graphs, chordal graphs, series-parallel graphs and bipartite graphs, indicating that much lower edge-connectivity bound still guarantees the existence of such orientations for those graph families.
给定一个图$G$和一个奇数素数$p$,对于映射$f: E(G) 到$G$的{mathbb Z}_psetminus{0}$和$G$的${mathbb Z}_p$-边界$b$,如果净流出$f$流与${mathbb Z}_p$中的$b(v)$在v (G)$中的每个顶点$v $在取向$D$下的$b(f,b;p)$-取向$tau$称为$(f,b;p)$-取向。这个概念是由Esperet et al.(2018)引入的,它推广了mod $p$-取向,与Tutte的nowhere zero 3-flow猜想密切相关。他们证明了$(6p^2 - 14p + 8)$-边连通图具有所有可能的$(f,b;p)$-方向。本文通过加性基将这种定向的框架扩展到签名图。我们还研究了一些(有符号)图族的$(f,b;p)$取向问题,这些图族包括完全图、弦图、序列-平行图和二部图,表明了更低的边连通界仍然保证了这些图族的这种取向的存在。
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引用次数: 0
Splitting Matchings and the Ryser-Brualdi-Stein Conjecture for Multisets 多集的分裂匹配和Ryser-Brualdi-Stein猜想
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-06 DOI: 10.37236/11714
Michael Anastos, David Fabian, Alp Müyesser, T. Szab'o
We study multigraphs whose edge-sets are the union of three perfect matchings, $M_1$, $M_2$, and $M_3$. Given such a graph $G$ and any $a_1,a_2,a_3in mathbb{N}$ with $a_1+a_2+a_3leq n-2$, we show there exists a matching $M$ of $G$ with $|Mcap M_i|=a_i$ for each $iin {1,2,3}$. The bound $n-2$ in the theorem is best possible in general.We conjecture however that if $G$ is bipartite, the same result holds with $n-2$ replaced by $n-1$. We give a construction that shows such a result would be tight. We also make a conjecture generalising the Ryser-Brualdi-Stein conjecture with colour multiplicities.
我们研究了边集为三个完美匹配$M_1$, $M_2$, $M_3$的并集的多图。给定这样的图$G$和任何$a_1,a_2,a_3in mathbb{N}$与$a_1+a_2+a_3leq n-2$,我们显示对于每个$iin {1,2,3}$存在$G$与$|Mcap M_i|=a_i$的匹配$M$。这个定理的界$n-2$一般来说是最好的。然而,我们推测,如果$G$是二部的,那么将$n-2$替换为$n-1$时,同样的结果成立。我们给出了一个构造,表明这样的结果是紧的。我们还提出了一个用颜色多重性推广Ryser-Brualdi-Stein猜想的猜想。
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引用次数: 0
On Infinite, Cubic, Vertex-Transitive Graphs with Applications to Totally Disconnected, Locally Compact Groups 无限三次顶点传递图及其在完全不连通局部紧群上的应用
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-02 DOI: 10.37236/10709
Arnbjörg Soffía Árnadóttir, Waltraud Lederle, R. G. Möller
We study groups acting vertex-transitively and non-discretely on connected, cubic graphs (regular graphs of degree 3). Using ideas from Tutte's fundamental papers in 1947 and 1959, it is shown that if the action is edge-transitive, then the graph has to be a tree. When the action is not edge-transitive Tutte's ideas are still useful and can, amongst other things, be used to fully classify the possible two-ended graphs. Results about cubic graphs are then applied to Willis' scale function from the theory of totally disconnected, locally compact groups. Some of the results in this paper have most likely been known to experts but most of them are not stated explicitly with proofs in the literature.
我们研究了在连通的三次图(3次正则图)上作用于顶点传递和非离散的群。使用Tutte在1947年和1959年的基础论文中的思想,证明了如果作用是边传递的,那么图必须是树。当动作不是边传递时,Tutte的思想仍然是有用的,并且可以用于对可能的两端图进行完全分类。然后将关于三次图的结果应用于完全不连通的局部紧群理论中的Willis尺度函数。本文中的一些结果很可能已经为专家所知,但大多数结果都没有在文献中明确说明和证明。
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引用次数: 0
Congruences for Consecutive Coefficients of Gaussian Polynomials with Crank Statistics 用曲柄统计量研究高斯多项式连续系数的同余性
IF 0.7 4区 数学 Q2 MATHEMATICS Pub Date : 2022-12-02 DOI: 10.37236/10493
Dennis Eichhorn, Lydia Engle, Brandt Kronholm
In this paper, we establish infinite families of congruences in consecutive arithmetic progressions modulo any odd prime $ell$ for the function $pbig(n,m,Nbig)$, which enumerates the partitions of $n$ into at most $m$ parts with no part larger than $N$. We also treat the function $pbig(n,m,(a,b]big)$, which bounds the largest part above and below, and obtain similar infinite families of congruences. For $m leq 4$ and $ell = 3$, simple combinatorial statistics called "cranks" witness these congruences. We prove this analytically for $m=4$, and then both analytically and combinatorially for $m = 3$. Our combinatorial proof relies upon explicit dissections of convex lattice polygons.   For $m leq 4$ and $ell = 3$, simple combinatorial statistics called ``cranks"  witness these congruences.  We prove this analytically for $m=4$, and then both analytically and combinatorially for $m = 3$.  Our combinatorial proof relies upon explicit dissections of convex lattice polygons. 
本文对函数$pbig(n,m,Nbig)$建立了取任意奇素数$ell$为模的连续等差数列的无穷同余族,它列举了$n$的划分为不大于$N$的最多$m$个部分。我们还处理了函数$pbig(n,m,(a,b]big)$,它的上下界是最大的部分,并得到了类似的无穷同余族。对于$m leq 4$和$ell = 3$,被称为“曲柄”的简单组合统计证明了这些同余。我们对$m=4$进行了解析证明,然后对$m = 3$进行了解析和组合证明。我们的组合证明依赖于凸点阵多边形的显式解剖。对于$m leq 4$和$ell = 3$,被称为“曲柄”的简单组合统计证明了这些一致性。我们对$m=4$进行了解析证明,然后对$m = 3$进行了解析和组合证明。我们的组合证明依赖于凸点阵多边形的显式解剖。
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引用次数: 0
期刊
Electronic Journal of Combinatorics
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