Lourdes Cruz, Yuriko Pitones, Enrique Reyes
Let $D=(G,\mathcal{O},w)$ be a weighted oriented graph whose edge ideal is $I(D)$. In this paper, we characterize the unmixed property of $I(D)$ for each one of the following cases: $G$ is an $SCQ$ graph; $G$ is a chordal graph; $G$ is a simplicial graph; $G$ is a perfect graph; $G$ has no $4$- or $5$-cycles; $G$ is a graph without $3$- and $5$-cycles; and ${\rm girth}(G)\geqslant 5$.
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Let $\mathcal{D}$ be a weighted oriented graph and $I(\mathcal{D})$ be its edge ideal. In this paper, we show that all the symbolic and ordinary powers of $I(\mathcal{D})$ coincide when $\mathcal{D}$ is a weighted oriented certain class of tree. Finally, we give necessary and sufficient conditions for the equality of ordinary and symbolic powers of naturally oriented lines.
Let $\mathcal{D}$ be a weighted oriented graph and let $I(\mathcal{D})$ be its edge ideal in a polynomial ring $R$. We give the formula of Castelnuovo-Mumford regularity of $R/I(\mathcal{D})$ when $\mathcal{D}$ is a weighted oriented path or cycle such that edges of $\mathcal{D}$ are oriented in one direction. Additionally, we compute the projective dimension for this class of graphs.
Homological invariants of edge ideals of weighted oriented graphs
该研究确定了固定顶点数加权有向图边理想的深度、维数和正则性三元组，并计算了固定顶点数加权有向树及二部图边理想的贝蒂表大小。
Let $D$ be a weighted oriented graph with the underlying graph $G$ and $I(D), I(G) $ be the edge ideals corresponding to $D$ and $G$ respectively. We show that the regularity of edge ideal of a certain class of weighted oriented graph remains same even after adding certain kind of new edges to it. We also establish the relationship between the regularity of edge ideal of weighted oriented path and cycle with the regularity of edge ideal of their underlying graph when vertices of $V^+$ are sinks.
Let $\mathcal{D}$ be a weighted oriented graph and $I(\mathcal{D})$ be its edge ideal. In this paper, we investigate the Betti numbers of $I(\mathcal{D})$ via upper-Koszul simplicial complexes, Betti splittings and the mapping cone construction. In particular, we provide recursive formulas for the Betti numbers of edge ideals of several classes of weighted oriented graphs. We also identify classes of weighted oriented graphs whose edge ideals have a unique extremal Betti number which allows us to compute the regularity and projective dimension for the identified classes. Furthermore, we charac…
Let $D$ be a weighted oriented graph, whose underlying graph is $G$, and let $I(D)$ be its edge ideal. If $G$ has no $3$-, $5$-, or $7$-cycles, or $G$ is König, we characterize when $I(D)$ is unmixed. If $G$ has no $3$- or $5$-cycles, or $G$ is König, we characterize when $I(D)$ is Cohen--Macaulay. We prove that $I(D)$ is unmixed if and only if $I(D)$ is Cohen--Macaulay when $G$ has girth greater than $7$ or $G$ is König and has no $4$-cycles.
Cohen-Macaulay Weighted Oriented Chordal and Simplicial Graphs
本文将弦图边理想的 Cohen-Macaulay 分类推广到加权有向弦图与单纯图，并证明其 Cohen-Macaulay 性等价于非混合性，从而与基域无关。
Matching powers of monomial ideals and edge ideals of weighted oriented graphs
本文引入单项式理想的匹配幂概念，研究了单项式理想及赋权有向图边理想匹配幂的深度与正则性，并证明了二次单项式理想最后非零幂的多拟阵性及赋权有向森林边理想具有线性分解的条件。
We consider bicolored maps, i.e. graphs which are drawn on surfaces, and construct a bijection between (i) oriented maps with arbitary face structure, and (ii) (weighted) non-oriented maps with exactly one face. Above, each non-oriented map is counted with a multiplicity which is based on the concept of the orientability generating series and the measure of orientability of a map. This bijection has the remarkable property of preserving the underlying bicolored graph. Our bijection shows equivalence between two explicit formulas for the top-degree of Jack characters, i.e. (suitably normalized)…
In this paper we study irreducible representations and symbolic Rees algebras of monomial ideals. Then we examine edge ideals associated to vertex-weighted oriented graphs. These are digraphs having no oriented cycles of length two with weights on the vertices. For a monomial ideal with no embedded primes we classify the normality of its symbolic Rees algebra in terms of its primary components. If the primary components of a monomial ideal are normal, we present a simple procedure to compute its symbolic Rees algebra using Hilbert bases, and give necessary and sufficient conditions for the equ…
Cohen-Macaulay oriented graphs with large girth
该研究针对底图围长不小于5的带权有向图，完成了Cohen-Macaulay类型的分类工作。
We characterize unmixed and Cohen-Macaulay edge-weighted edge ideals of very well-covered graphs. We also provide examples of oriented graphs which have unmixed and non-Cohen-Macaulay vertex-weighted edge ideals, while the edge ideal of their underlying graph is Cohen-Macaulay. This disproves a conjecture posed by Pitones, Reyes and Toledo.
Ornaments and Difference Distance Magic Oriented Graphs
通过引入装饰概念，研究加权和构造差距离幻定向图的方法，给出s-节点装饰的构造结果，并列出开放问题。
In this work, we establish an analogue result of the Erdös-Stone theorem of weighted digraphs using Regularity Lemma of digraphs. We give a stability result of oriented graphs and digraphs with forbidden blow-up transitive triangle and show that almost all oriented graphs and almost all digraphs with forbidden blow-up transitive triangle are almost bipartite respectively.
List-antimagic labeling of vertex-weighted graphs
本文证明了任意不含孤立点或孤立边分量的n顶点图是⌊4n/3⌋-加权列表反幻影的，且任意不含孤立点分量的n顶点图存在一个方向使其成为⌊2n/3⌋-有向反幻影的。
Symbolic powers: Simis and weighted monomial ideals
本文利用交换代数与组合学比较单项式理想的符号幂与普通幂，研究 Simis 理想和加权单项式理想，并给出加权有向图边理想对偶在次数 2 上为 Simis 的组合分类。
A strongly connected digraph is called a cactoid-type if each of its blocks is a digraph consisting of finitely many oriented cycles sharing a common directed path. In this article, we find the formula for the determinant of the distance matrix for weighted cactoid-type digraphs and find its inverse, whenever it exists. We also compute the determinant of the distance matrix for a class of unweighted and undirected graphs consisting of finitely many cycles, sharing a common path.
Forests whose matching powers are linear
本文分类了边理想的某个匹配幂具有线性分解性质的赋权有向森林。
We consider the random Markov matrix obtained by assigning i.i.d. non-negative weights to each edge of the complete oriented graph. In this study, the weights have unbounded first moment and belong to the domain of attraction of an alpha-stable law. We prove that as the dimension tends to infinity, the empirical measure of the singular values tends to a probability measure which depends only on alpha, characterized as the expected value of the spectral measure at the root of a weighted random tree. The latter is a generalized two-stage version of the Poisson weighted infinite tree (PWIT) intro…
Feedback Arc Sets and Feedback Arc Set Decompositions in Weighted and Unweighted Oriented Graphs
研究有向图中反馈弧集分解数及其在加权有向图中的界，提出针对不同度数和圈长条件下的反馈弧集分解数的结论。
Enumeration of tree-type diagrams assembled from oriented chains of edges
该研究针对离散Erdős-Rényi随机矩阵模型累积量展开中的树型图计数问题，利用改进的Prüfer码得到有向边链组装树型图的数量及加权求和的显式表达式，并推广至非规则链的情况。
The typical structure of oriented graphs and digraphs with forbidden blow-up of transitive tournaments
研究禁止转置竞赛 tournaments 的吹胀体的有向图和有向图的典型结构，证明几乎所有此类图是 r 分支的，扩展了 Kuhn 等人的结果，验证了 Cherlin 的猜想。
Let $G$ be a simple graph with an orientation $σ$, which assigns to each edge a direction so that $G^σ$ becomes a directed graph. $G$ is said to be the underlying graph of the directed graph $G^σ$. In this paper, we define a weighted skew adjacency matrix with Randć weight, the skew Randić matrix ${\bf R_S}(G^σ)$, of $G^σ$ as the real skew symmetric matrix $[(r_s)_{ij}]$ where $(r_s)_{ij} = (d_id_j)^{-\frac{1}{2}}$ and $(r_s)_{ji} = -(d_id_j)^{-\frac{1}{2}}$ if $v_i \rightarrow v_j$ is an arc of $G^σ$, otherwise $(r_s)_{ij} = (r_s)_{ji} = 0$. We derive some properties of the skew Randić energy…
The typical structure of oriented graphs and digraphs with forbidden blow-up of transitive tournaments
研究禁止传递竞赛图爆破的有向图与有向图的典型结构，证明几乎所有此类图都具有特定r-划分，并给出计数渐近公式。
We give a simple combinatorial proof of a formula that extends a result by Grigorchuk (rediscovered by Cohen) relating cogrowth and spectral radius of random walks. Our main result is an explicit equation determining the number of `bumps' on paths in a graph: in a $d$-regular (not necessarily transitive) non-oriented graph let the series $G(t)$ count all paths between two fixed points weighted by their length $t^{length}$, and $F(u,t)$ count the same paths, weighted as $u^{number of bumps}t^{length}$. Then one has $$F(1-u,t)/(1-u^2t^2) = G(t/(1+u(d-u)t^2))/(1+u(d-u)t^2).$$ We then derive the c…
For each $n \ge 1$, let $\mathrm{d}^n=(d^{n}(i),1 \le i \le n)$ be a sequence of positive integers with even sum $\sum_{i=1}^n d^n(i) \ge 2n$. Let $(G_n,T_n,Γ_n)$ be uniformly distributed over the set of simple graphs $G_n$ with degree sequence $\mathrm{d}^n$, endowed with a spanning tree $T_n$ and rooted along an oriented edge $Γ_n$ of $G_n$ which is not an edge of $T_n$. Under a finite variance assumption on degrees in $G_n$, we show that, after rescaling, $T_n$ converges in distribution to the Brownian continuum random tree as $n \to \infty$. Our main tool is a new version of Pitman's addit…
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