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The orientation completion problem for a class of oriented graphs asks whether a given partially oriented graph can be completed to an oriented graph in the class by orienting the unoriented edges of the partially oriented graph.…

Combinatorics · Mathematics 2022-11-07 Kevin Hsu , Jing Huang

A graph is locally chordal if each of its small-radius balls is chordal. In an earlier work [AKK25], the authors and Kobler proved that locally chordal graphs can be characterized by having chordal local covers, by forbidding short cycles…

Combinatorics · Mathematics 2025-12-23 Tara Abrishami , Paul Knappe

Let $G$ be a simple graph on $n$ vertices and $J_G$ denote the binomial edge ideal of $G$ in the polynomial ring $S = \mathbb{K}[x_1, \ldots, x_n, y_1, \ldots, y_n].$ In this article, we compute the second graded Betti numbers of $J_G$, and…

Commutative Algebra · Mathematics 2020-10-22 A. V. Jayanthan , Arvind Kumar , Rajib Sarkar

Let $(G, \Lambda)$ be a self-similar $k$-graph with a possibly infinite vertex set $\Lambda^0$. We associate a universal C*-algebra $\mathcal{O}_{G,\Lambda}$ to $(G,\Lambda)$. The main purpose of this paper is to investigate the ideal…

Operator Algebras · Mathematics 2019-06-26 Hui Li , Dilian Yang

A graph $G$ is said to be $1$-perfectly orientable if it has an orientation such that for every vertex $v\in V(G)$, the out-neighborhood of $v$ in $D$ is a clique in $G$. In $1982$, Skrien posed the problem of characterizing the class of…

Combinatorics · Mathematics 2016-04-20 Boštjan Brešar , Tatiana Romina Hartinger , Tim Kos , Martin Milanič

In this paper we prove the conjectured upper bound for Castelnuovo-Mumford regularity of binomial edge ideals posed in [23], in the case of chordal graphs. Indeed, we show that the regularity of any chordal graph G is bounded above by the…

Commutative Algebra · Mathematics 2018-10-09 M. Rouzbahani Malayeri , S. Saeedi Madani , D. Kiani

Let $G$ be a finite connected simple graph and $I_{G}$ the toric ideal of the edge ring $K[G]$ of $G$. In the present paper, we study finite graphs $G$ with the property that $I_{G}$ is generated by quadratic binomials and $I_{G}$ possesses…

Commutative Algebra · Mathematics 2014-05-15 Takayuki Hibi , Kenta Nishiyama , Hidefumi Ohsugi , Akihiro Shikama

Let $G$ be a simple graph on the vertex set $\{1,\ldots,n\}$ with $m$ edges. An algebraic object attached to $G$ is the ideal $P_{G}$ generated by diagonal 2-minors of an $n \times n$ matrix of variables. In this paper we prove that if $G$…

Commutative Algebra · Mathematics 2016-07-26 Anargyros Katsabekis

We consider the problem of designing succinct navigational oracles, i.e., succinct data structures supporting basic navigational queries such as degree, adjacency, and neighborhood efficiently for intersection graphs on a circle, which…

Data Structures and Algorithms · Computer Science 2020-10-12 Hüseyin Acan , Sankardeep Chakraborty , Seungbum Jo , Kei Nakashima , Kunihiko Sadakane , Srinivasa Rao Satti

The undirected power graph (or simply power graph) of a group $G$, denoted by $P(G)$, is a graph whose vertices are the elements of the group $G$, in which two vertices $u$ and $v$ are connected by an edge between if and only if either…

Combinatorics · Mathematics 2023-05-09 Pallabi Manna , Peter J. Cameron , Ranjit Mehatari

For all integers $4 \leq r \leq d$, we show that there exists a finite simple graph $G= G_{r,d}$ with toric ideal $I_G \subset R$ such that $R/I_G$ has (Castelnuovo-Mumford) regularity $r$ and $h$-polynomial of degree $d$. To achieve this…

Commutative Algebra · Mathematics 2020-03-17 Giuseppe Favacchio , Graham Keiper , Adam Van Tuyl

A classical enumerative result states that, given a graph $G$ and a vertex $u$, the number of connected subgraphs of $G$ is equal to the number of orientations of $G$ such that every vertex can reach $u$ by a directed path. We show that…

Combinatorics · Mathematics 2026-05-18 Oliver Bernardi , Jonathan J. Fang

Let $R$ be a commutative ring with non-zero identity. We describe all $C_3$- and $C_4$-free intersection graph of non-trivial ideals of $R$ as well as $C_n$-free intersection graph when $R$ is a reduced ring. Also, we shall describe all…

Commutative Algebra · Mathematics 2014-01-28 Ali Azimi , Ahmad Erfanian , Mohammad Farrokhi Derakhshandeh Ghouchan , Nesa Hoseini

In this paper we investigate results of the form "every graph $G$ has a cycle $C$ such that the induced subgraph of $G$ on $V(G)\setminus V(C)$ has small maximum degree." Such results haven't been studied before, but are motivated by the…

Combinatorics · Mathematics 2016-07-26 Alexey Pokrovskiy

The $G$-graph $\Gamma(G,S)$ is a graph from the group $G$ generated by $S\subseteq G$, where the vertices are the right cosets of the cyclic subgroups $\langle s \rangle, s\in S$ with $k$-edges between two distinct cosets if there is an…

Combinatorics · Mathematics 2016-09-05 Lord Clifford Kavi

We classify modules and rings with some specific properties of their intersection graphs. In particular, we describe rings with infinite intersection graphs containing maximal left ideals of finite degree. This answers a question raised in…

Rings and Algebras · Mathematics 2017-07-26 Jerzy Matczuk , Marta Nowakowska , Edmund R. Puczyłowski

Homomorphically full graphs are those for which every homomorphic image is isomorphic to a subgraph. We extend the definition of homomorphically full to oriented graphs in two different ways. For the first of these, we show that…

Discrete Mathematics · Computer Science 2024-02-14 Thomas Bellitto , Christopher Duffy , Gary MacGillivray

A central question in liaison theory asks whether every Cohen-Macaulay, graded ideal of a standard graded K-algebra belongs to the same G-liaison class of a complete intersection. In this paper we answer this question positively for toric…

Algebraic Geometry · Mathematics 2017-12-14 Alexandru Constantinescu , Elisa Gorla

We introduce a new subclass of chordal graphs that generalizes split graphs, which we call well-partitioned chordal graphs. Split graphs are graphs that admit a partition of the vertex set into cliques that can be arranged in a star…

Combinatorics · Mathematics 2020-02-26 Jungho Ahn , Lars Jaffke , O-joung Kwon , Paloma T. Lima

Let R be monomial sub-algebra of $k[x_1,...,x_N]$ generated by square free monomials of degree two. This paper addresses the following question: when is R a complete intersection? For such a k-algebra we can associate a graph G whose…

Commutative Algebra · Mathematics 2007-05-23 Mordechai Katzman