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The median of a graph $G$ with weighted vertices is the set of all vertices $x$ minimizing the sum of weighted distances from $x$ to the vertices of $G$. For any integer $p\ge 2$, we characterize the graphs in which, with respect to any…

Combinatorics · Mathematics 2023-11-06 Laurine Bénéteau , Jérémie Chalopin , Victor Chepoi , Yann Vaxès

In this paper, we introduce some reduction processes on graphs which preserve the regularity of related edge ideals. As a consequence, an alternative proof for the theorem of R. Fr\"oberg on linearity of resolution of edge ideal of graphs…

Commutative Algebra · Mathematics 2015-07-28 Marcel Morales , Ali Akbar Yazdan Pour , Rashid Zaare-Nahandi

We consider a class of graphs $G$ such that the height of the edge ideal $I(G)$ is half of the number $\sharp V(G)$ of the vertices. We give Cohen-Macaulay criteria for such graphs.

Commutative Algebra · Mathematics 2009-09-25 Marilena Crupi , Giancarlo Rinaldo , Naoki Terai

The notion of a contractible transformation on a graph was introduced by Ivashchenko as a means to study molecular spaces arising from digital topology and computer image analysis, and more recently has been applied to topological data…

Let $G$ be a finite simple graph. We give a lower bound for the Castelnuovo-Mumford regularity of the toric ideal $I_G$ associated to $G$ in terms of the sizes and number of induced complete bipartite graphs in $G$. When $G$ is a chordal…

Commutative Algebra · Mathematics 2016-05-24 Jennifer Biermann , Augustine O'Keefe , Adam Van Tuyl

We consider the family of graphs whose vertex set is Z^k where two vertices are connected by an edge when their l\infty-distance is 1. We prove the optimal vertex isoperimetric inequality for this family of graphs. That is, given a positive…

Combinatorics · Mathematics 2012-02-21 Ellen Veomett , A. J. Radcliffe

Fr\"oberg's classical theorem about edge ideals with $2$-linear resolution can be regarded as a classification of graphs whose edge ideals have linearity defect zero. Extending his theorem, we classify all graphs whose edge ideals have…

Commutative Algebra · Mathematics 2016-01-19 Hop D. Nguyen , Thanh Vu

Denote the Laplacian of a graph $G$ by $L(G)$ and its second smallest Laplacian eigenvalue by $\lambda_2(G)$. If $G$ is a graph on $n\ge 2$ vertices, then it is shown that the second smallest eigenvalue of $L(G) + \frac{1}{n}…

Combinatorics · Mathematics 2024-07-03 B. Afshari

We study the problem of extracting a selective connector for a given set of query vertices $Q \subseteq V$ in a graph $G = (V,E)$. A selective connector is a subgraph of $G$ which exhibits some cohesiveness property, and contains the query…

Social and Information Networks · Computer Science 2017-09-06 Natali Ruchansky , Francesco Bonchi , David Garcia-Soriano , Francesco Gullo , Nicolas Kourtellis

Reliability evaluation and fault tolerance of an interconnection network of some parallel and distributed systems are discussed separately under various link-faulty hypotheses in terms of different $\mathcal{P}$-conditional…

Combinatorics · Mathematics 2022-03-25 Mingzu Zhang , Zhaoxia Tian , Lianzhu Zhang

Let $G$ be a graph with $n$ vertices and $m$ edges. The energy $E$ of the graph $G$ is defined as the sum of the moduli of the adjacency eigenvalues $\lambda_{1} \geq \lambda_{2} \geq \ldots \geq \lambda_{n}$ of $G$: $$…

Combinatorics · Mathematics 2014-09-04 Felix Goldberg

Let $I_G$ be the toric ideal of a graph $G$. We characterize in graph theoretical terms the primitive, the minimal, the indispensable and the fundamental binomials of the toric ideal $I_G$.

Commutative Algebra · Mathematics 2010-02-11 Enrique Reyes , Christos Tatakis , Apostolos Thoma

For any finite abelian group $G$ and any subset $S\seq G$, we determine the connectivity of the addition Cayley graph induced by $S$ on $G$. Moreover, we show that if this graph is not complete, then it possesses a minimum vertex cut of a…

Combinatorics · Mathematics 2007-10-08 David J. Grynkiewicz , Oriol Serra , Vsevolod Lev

Let $G$ be a finite simple graph and $I(G)$ denote the corresponding edge ideal in a polynomial ring over a field $\mathbb{K}$. In this paper, we obtain upper bounds for the Castelnuovo-Mumford regularity of symbolic powers of certain…

Commutative Algebra · Mathematics 2021-08-20 Arvind Kumar , S Selvaraja

We study the minimal homogeneous generating sets of the Eulerian ideal associated with a simple graph and its maximal generating degree. We show that the Eulerian ideal is a lattice ideal and use this to give a characterization of binomials…

Commutative Algebra · Mathematics 2024-05-24 Jorge Neves , Gonçalo Varejão

The Brualdi-Solheid problem asks which graph achieves the extremal (maximum or minimum) spectral radius for a given class of graphs. This paper addresses the Brualdi-Solheid problem for \( \mathcal{G}_{n,\beta} \), the family of graphs with…

Combinatorics · Mathematics 2026-01-27 Jiaqi Liu , Zhenzhen Lou , Vilmar Trevisan

A graph $G$ is called collapsible if for every even subset $R\subseteq V(G)$, there is a spanning connected subgraph $H$ of $G$ such that $R$ is the set of vertices of odd degree in $H$. A graph is the reduction of $G$ if it is obtained…

Combinatorics · Mathematics 2016-01-08 Wei-Guo Chen , Zhi-Hong Chen , Mei Lu

Let I be a toric ideal. We say I is robust if its universal Groebner basis is a minimal generating set. We show that any robust toric ideal arising from a graph G is also minimally generated by its Graver basis. We then completely…

In the past decades, many scholars concerned which edge-extremal problems have spectral analogues? Recently, Wang, Kang and Xue showed an interesting result on $F$-free graphs [J. Combin. Theory Ser. B 159 (2023) 20--41]. In this paper, we…

Combinatorics · Mathematics 2025-03-14 Zhenzhen Lou , Changxiang He

Let R = K[x_1; : : : ; x_n] be a polynomial ring over a field K, and I := I_C_n be an edge ideal of n-cycle graph C_n. In the present paper, we compute the last column of the Lyubeznik table of R/I.

Commutative Algebra · Mathematics 2019-11-18 Parvaneh Nadi , Farhad Rahmati , Majid Eghbali
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