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A finite group is called $\psi$-divisible iff $\psi(H)|\psi(G)$ for any subgroup $H$ of a finite group $G$. Here, $\psi(G)$ is the sum of element orders of $G$. For now, the only known examples of such groups are the cyclic ones of…

Group Theory · Mathematics 2022-03-02 Mihai-Silviu Lazorec

A point visibility graph is a graph induced by a set of points in the plane, where every vertex corresponds to a point, and two vertices are adjacent whenever the two corresponding points are visible from each other, that is, the open…

Computational Geometry · Computer Science 2019-02-05 Jean Cardinal , Udo Hoffmann

The problem of extending partial geometric graph representations such as plane graphs has received considerable attention in recent years. In particular, given a graph $G$, a connected subgraph $H$ of $G$ and a drawing $\mathcal{H}$ of $H$,…

Computational Geometry · Computer Science 2020-07-13 Eduard Eiben , Robert Ganian , Thekla Hamm , Fabian Klute , Martin Nöllenburg

The general position problem for graphs asks for the largest number of vertices in a subset $S \subseteq V(G)$ of a graph $G$ such that for any $u,v \in S$ and any shortest $u,v$-path $P$ we have $S \cap V(P) = \{ u,v\} $, whereas the…

Combinatorics · Mathematics 2025-07-23 Ethan Shallcross , James Tuite , Aoise Evans , Aditi Krishnakumar , Sumaiyah Boshar

Algorithmic extension problems of partial graph representations such as planar graph drawings or geometric intersection representations are of growing interest in topological graph theory and graph drawing. In such an extension problem, we…

Data Structures and Algorithms · Computer Science 2020-04-28 Eduard Eiben , Robert Ganian , Thekla Hamm , Fabian Klute , Martin Nöllenburg

If $x\in V(G)$, then $S\subseteq V(G)\setminus\{x\}$ is an $x$-visibility set if for any $y\in S$ there exists a shortest $x,y$-path avoiding $S$. The $x$-visibility number $v_x(G)$ is the maximum cardinality of an $x$-visibility set, and…

Discrete Mathematics · Computer Science 2025-10-23 Dhanya Roy , Gabriele Di Stefano , Sandi Klavžar , Aparna Lakshmanan S

As set systems, hypergraphs are omnipresent and have various representations ranging from Euler and Venn diagrams to contact representations. In a geometric representation of a hypergraph $H=(V,E)$, each vertex $v\in V$ is associated with a…

Computational Geometry · Computer Science 2023-08-21 Daniel Bertschinger , Nicolas El Maalouly , Linda Kleist , Tillmann Miltzow , Simon Weber

An \emph{obstacle representation} of a graph consists of a set of polygonal obstacles and a distinct point for each vertex such that two points see each other if and only if the corresponding vertices are adjacent. Obstacle representations…

Computational Geometry · Computer Science 2013-06-14 Alexander Koch , Marcus Krug , Ignaz Rutter

We consider undirected simple finite graphs. The sets of vertices and edges of a graph $G$ are denoted by $V(G)$ and $E(G)$, respectively. For a graph $G$, we denote by $\delta(G)$ and $\eta(G)$ the least degree of a vertex of $G$ and the…

Combinatorics · Mathematics 2013-07-05 N. N. Davtyan , R. R. Kamalian

A graph $G=(V,E)$ is representable if there exists a word $W$ over the alphabet $V$ such that letters $x$ and $y$ alternate in $W$ if and only if $(x,y)\in E$ for each $x\neq y$. If $W$ is $k$-uniform (each letter of $W$ occurs exactly $k$…

Combinatorics · Mathematics 2008-10-03 Magnus Mar Halldorsson , Sergey Kitaev , Artem Pyatkin

An ortho-polygon visibility representation of an $n$-vertex embedded graph $G$ (OPVR of $G$) is an embedding-preserving drawing of $G$ that maps every vertex to a distinct orthogonal polygon and each edge to a vertical or horizontal…

Computational Geometry · Computer Science 2017-05-17 Emilio Di Giacomo , Walter Didimo , William S. Evans , Giuseppe Liotta , Henk Meijer , Fabrizio Montecchiani , Stephen K. Wismath

Let $G$ and $H$ be two simple graphs. A bijection $\phi:V(G)\rightarrow V(H)$ is called an isomorphism between $G$ and $H$ if $(\phi v_i)(\phi v_j)\in E(H)$ $\Leftrightarrow$ $v_i v_j\in E(G)$, $\forall v_i,v_j \in V(G)$. In the case that…

Combinatorics · Mathematics 2017-10-27 Wenxue Du

Graph embedding is a central problem in social network analysis and many other applications, aiming to learn the vector representation for each node. While most existing approaches need to specify the neighborhood and the dependence form to…

Machine Learning · Computer Science 2018-06-06 Shupeng Gui , Xiangliang Zhang , Shuang Qiu , Mingrui Wu , Jieping Ye , Ji Liu

A visibility representation of a graph $G$ is an assignment of the vertices of $G$ to geometric objects such that vertices are adjacent if and only if their corresponding objects are "visible" each other, that is, there is an uninterrupted…

Combinatorics · Mathematics 2016-09-06 Eric Peterson , Paul S. Wenger

For any graph G = (V, E) and proportion $p\in(0,1]$, a set $S\subseteq V$ is a p-dominating set if $\frac{|N[S]|}{|V|}\geq p$. The $p$-domination number $\gamma_{p}(G)$ equals the minimum cardinality of a $p$-dominating set in G. For a…

Combinatorics · Mathematics 2022-01-12 L. Philo Nithya , Joseph Varghese Kureethara

A temporal graph $\mathcal{G}=(G,\lambda)$ can be represented by an underlying graph $G=(V,E)$ together with a function $\lambda$ that assigns to each edge $e\in E$ the set of time steps during which $e$ is present. The reachability graph…

Computational Complexity · Computer Science 2025-03-21 Thomas Erlebach , Othon Michail , Nils Morawietz

Vertex splitting is a graph operation that replaces a vertex $v$ with two nonadjacent new vertices and makes each neighbor of $v$ adjacent with one or both of the introduced vertices. Vertex splitting has been used in contexts from circuit…

Computational Complexity · Computer Science 2024-01-30 Alexander Firbas , Manuel Sorge

Let $G=(V,E)$ be a graph and $P\subseteq V$ a set of points. Two points are mutually visible if there is a shortest path between them without further points. $P$ is a mutual-visibility set if its points are pairwise mutually visible. The…

Combinatorics · Mathematics 2021-07-16 Gabriele Di Stefano

Simple drawings of graphs are those in which each pair of edges share at most one point, either a common endpoint or a proper crossing. In this paper we study the problem of extending a simple drawing $D(G)$ of a graph $G$ by inserting a…

Computational Geometry · Computer Science 2019-08-27 Alan Arroyo , Martin Derka , Irene Parada

Interval graphs are intersection graphs of closed intervals. A generalization of recognition called partial representation extension was introduced recently. The input gives an interval graph with a partial representation specifying some…

Combinatorics · Mathematics 2016-02-22 Pavel Klavík , Maria Saumell