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Let $G_1$ and $G_2$ be two graphs on disjoint sets of $n_1$ and $n_2$ vertices, respectively. The corona of graphs $G_1$ and $G_2$, denoted by $G_1\circ G_2$, is the graph formed from one copy of $G_1$ and $n_1$ copies of $G_2$ where the…

Combinatorics · Mathematics 2015-03-27 Jia-Bao Liu , Xiang-Feng Pan , Fu-Tao Hu

Effective resistances are ubiquitous in graph algorithms and network analysis. In this work, we study sublinear time algorithms to approximate the effective resistance of an adjacent pair $s$ and $t$. We consider the classical adjacency…

Data Structures and Algorithms · Computer Science 2023-07-06 Dongrun Cai , Xue Chen , Pan Peng

A graph $G=(V,E)$ is said to be odd (or even, resp.) if $d_G(v)$ is odd (or even, resp.) for any $v\in V$. Trivially, the order of an odd graph must be even. In this paper, we show that every 4-edge connected graph of even order has a…

Combinatorics · Mathematics 2025-03-25 Jingyu Zheng , Baoyindureng Wu

The goal of graph inference is to design algorithms for learning properties of a hidden graph using queries to an oracle that returns information about the graph. Graph reconstruction, verification, and property testing are all types of…

Data Structures and Algorithms · Computer Science 2025-02-26 Huck Bennett , Mitchell Black , Amir Nayyeri , Evelyn Warton

With applications in distribution systems and communication networks, the minimum stretch spanning tree problem is to find a spanning tree T of a graph G such that the maximum distance in T between two adjacent vertices is minimized. The…

Combinatorics · Mathematics 2017-12-12 Lan Lin , Yixun Lin

We study planar straight-line drawings of graphs that minimize the ratio between the length of the longest and the shortest edge. We answer a question of Lazard et al. [Theor. Comput. Sci. 770 (2019), 88--94] and, for any given constant…

Computational Geometry · Computer Science 2020-08-21 Václav Blažej , Jiří Fiala , Giuseppe Liotta

Metric graphs are ubiquitous in science and engineering. For example, many data are drawn from hidden spaces that are graph-like, such as the cosmic web. A metric graph offers one of the simplest yet still meaningful ways to represent the…

Computational Geometry · Computer Science 2017-12-05 Tamal K. Dey , Dayu Shi , Yusu Wang

A graph $G$ is called a cactus if each block of $G$ is either an edge or a cycle. Denote by $Cact(n;t)$ the set of connected cacti possessing $n$ vertices and $t$ cycles. In this paper, we show that there are some errors in [J. Du, G. Su,…

Combinatorics · Mathematics 2015-05-21 Jia-Bao Liu , Wen-Rui Wang , Yong-Ming Zhang , Xiang-Feng Pan

Let G be an undirected graph on n vertices and let S(G) be the set of all real symmetric n x n matrices whose nonzero off-diagonal entries occur in exactly the positions corresponding to the edges of G. The inverse inertia problem for G…

Combinatorics · Mathematics 2007-11-21 Wayne Barrett , H. Tracy Hall , Raphael Loewy

The \emph{resistance matrix} of a simple connected graph $G$ is denoted by $R$, and is defined by $R =(r_{ij})$, where $r_{ij}$ is the resistance distance between the vertices $i$ and $j$ of $G$. In this paper, we consider the resistance…

Combinatorics · Mathematics 2018-04-05 Fouzul Atik , Ravindra B Bapat , M. Rajesh Kannan

We investigate the problem of reconstructing a set $P\subseteq \mathbb{R}$ of distinct points, where the only information available about $P$ consists of the distances between some of the pairs of points. More precisely, we examine which…

Combinatorics · Mathematics 2025-02-24 Richard Montgomery , Rajko Nenadov , Julien Portier , Tibor Szabó

We study two popular ways to sketch the shortest path distances of an input graph. The first is distance preservers, which are sparse subgraphs that agree with the distances of the original graph on a given set of demand pairs. Prior work…

Data Structures and Algorithms · Computer Science 2021-08-17 Greg Bodwin , Virginia Vassilevska Williams

In a directed graph $G$ with non-correlated edge lengths and costs, the \emph{network design problem with bounded distances} asks for a cost-minimal spanning subgraph subject to a length bound for all node pairs. We give a bi-criteria…

Data Structures and Algorithms · Computer Science 2014-09-24 Markus Chimani , Joachim Spoerhase

A set D of vertices of a graph G with vertex set V is irredundant if each non-isolated vertex of G[D] has a neighbour in V-D that is not adjacent to any other vertex in D. The upper irredundance number IR(G) is the largest cardinality of an…

Combinatorics · Mathematics 2021-04-26 C. M. Mynhardt , A. Roux

Let $G$ be a finite plane multigraph and $G'$ its dual. Each edge $e$ of $G$ is interpreted as a resistor of resistance $R_e$, and the dual edge $e'$ is assigned the dual resistance $R_{e'}:=1/R_e$. Then the equivalent resistance $r_e$ over…

Combinatorics · Mathematics 2018-05-04 Martina Furrer , Norbert Hungerbühler , Simon Jantschgi

The central graph $C(G)$ of a graph $G$ is the graph obtained by inserting a new vertex into each edge of $G$ exactly once and joining all the non-adjacent vertices in $G$. Let $G_1$ and $G_2$ be two vertex disjoint graphs. The central…

Combinatorics · Mathematics 2024-04-10 Haritha T , Chithra A

Given a graph on n vertices with m edges, each of unit resistance, how small can the average resistance between pairs of vertices be? There are two very plausible extremal constructions -- graphs like a star, and graphs which are close to…

Combinatorics · Mathematics 2022-06-17 J. Robert Johnson , Mark Walters

A random geometric digraph $G_n$ is constructed by taking $\{X_1,X_2,... X_n\}$ in $\mathbb{R}^2$ independently at random with a common bounded density function. Each vertex $X_i$ is assigned at random a sector $S_i$ of central angle…

Combinatorics · Mathematics 2019-09-18 Yilun Shang

Rotation distances measure the differences in structure between rooted ordered binary trees. The one-dimensional skeleta of associahedra are rotation graphs, where two vertices representing trees are connected by an edge if they differ by a…

Data Structures and Algorithms · Computer Science 2020-06-29 Sean Cleary , Haris Nadeem

In an oriented graph $\overrightarrow{G}$, the inversion of a subset $X$ of vertices is the operation that reverses the orientation of all arcs with both end-vertices in $X$. The inversion graph of a graph $G$, denoted by $\mathcal{I}(G)$,…

Combinatorics · Mathematics 2026-05-27 Yichen Wang , Haozhe Wang , Yuxuan Yang , Mei Lu