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In [3] L.Zapponi studied the arithmetic of plane bipartite trees with prime number of edges. He obtained a lower bound on the degree of tree's definition field. Here we obtain a similar lower bound in the following case. There exists a…

Number Theory · Mathematics 2017-11-10 Yury Kochetkov

We study straight-line drawings of planar graphs with few segments and few slopes. Optimal results are obtained for all trees. Tight bounds are obtained for outerplanar graphs, 2-trees, and planar 3-trees. We prove that every 3-connected…

Combinatorics · Mathematics 2008-09-09 Vida Dujmovic' , David Eppstein , Matthew Suderman , David R. Wood

For a fixed graph $F$, we would like to determine the maximum number of edges in a properly edge-colored graph on $n$ vertices which does not contain a rainbow copy of $F$, that is, a copy of $F$ all of whose edges receive a different…

Combinatorics · Mathematics 2019-01-11 Daniel Johnston , Puck Rombach

An identifying code $C$ of a graph $G$ is a dominating set of $G$ such that any two distinct vertices of $G$ have distinct closed neighbourhoods within $C$. These codes have been widely studied for over two decades. We give an improvement…

Combinatorics · Mathematics 2022-11-14 Florent Foucaud , Tuomo Lehtilä

In this paper, we address the problem of packing large trees in $G_{n,p}$. In particular, we prove the following result. Suppose that $T_1, \dotsc, T_N$ are $n$-vertex trees, each of which has maximum degree at most $(np)^{1/6} / (\log…

Combinatorics · Mathematics 2018-10-03 Asaf Ferber , Wojciech Samotij

We prove that if an $n$-vertex graph $G$ can be drawn in the plane such that each pair of crossing edges is independent and there is a crossing-free edge that connects their endpoints, then $G$ has $O(n)$ edges. Graphs that admit such…

Combinatorics · Mathematics 2016-08-31 Eyal Ackerman , Balázs Keszegh , Mate Vizer

A graph is 1-planar if it can be drawn in the plane such that each edge is crossed at most once. A graph, together with a 1-planar drawing is called 1-plane. Brandenburg et al. showed that there are maximal 1-planar graphs with only…

Combinatorics · Mathematics 2015-09-21 János Barát , Géza Tóth

We consider the recently introduced model of \emph{low ply graph drawing}, in which the ply-disks of the vertices do not have many common overlaps, which results in a good distribution of the vertices in the plane. The \emph{ply-disk} of a…

Data Structures and Algorithms · Computer Science 2016-09-05 Patrizio Angelini , Michael A. Bekos , Till Bruckdorfer , Jaroslav Hančl , Michael Kaufmann , Stephen Kobourov , Antonios Symvonis , Pavel Valtr

The \emph{distance-number} of a graph $G$ is the minimum number of distinct edge-lengths over all straight-line drawings of $G$ in the plane. This definition generalises many well-known concepts in combinatorial geometry. We consider the…

Combinatorics · Mathematics 2008-09-09 Paz Carmi , Vida Dujmović , Pat Morin , David R. Wood

The slope number of a graph $G$ is the smallest number of slopes needed for the segments representing the edges in any straight-line drawing of $G$. It serves as a measure of the visual complexity of a graph drawing. Several bounds on the…

Computational Geometry · Computer Science 2022-10-13 Jonathan Klawitter , Johannes Zink

A fundamental problem in network science is the normalization of the topological or physical distance between vertices, that requires understanding the range of variation of the unnormalized distances. Here we investigate the limits of the…

Discrete Mathematics · Computer Science 2021-02-18 Ramon Ferrer-i-Cancho , Carlos Gómez-Rodríguez , Juan Luis Esteban

Let $T$ be an oriented tree on $n$ vertices with maximum degree at most $e^{o(\sqrt{\log n})}$. If $G$ is a digraph on $n$ vertices with minimum semidegree $\delta^0(G)\geq(\frac12+o(1))n$, then $G$ contains $T$ as a spanning tree, as…

Combinatorics · Mathematics 2024-07-25 Felix Joos , Jonathan Schrodt

A strengthened version of Harborth's well-known conjecture -- known as Kleber's conjecture -- states that every planar graph admits a planar straight-line drawing where every edge has integer length and each vertex is restricted to the…

Computational Geometry · Computer Science 2025-09-05 Henry Förster , Stephen Kobourov , Jacob Miller , Johannes Zink

Let $\mathcal{O}_n$ be the set of ordered labeled trees on ${0,...,n}$. A maximal decreasing subtree of an ordered labeled tree is defined by the maximal ordered subtree from the root with all edges being decreasing. In this paper, we study…

Combinatorics · Mathematics 2022-03-22 Seunghyun Seo , Heesung Shin

Ply number is a recently developed graph drawing metric inspired by studying road networks. Informally, for each vertex v, which is associated with a point in the plane, a disk is drawn centered on v with a radius that is alpha times the…

Computational Geometry · Computer Science 2018-08-13 Michael T. Goodrich , Timothy Johnson

A straight-line drawing $\delta$ of a planar graph $G$ need not be plane, but can be made so by moving some of the vertices. Let shift$(G,\delta)$ denote the minimum number of vertices that need to be moved to turn $\delta$ into a plane…

Computational Geometry · Computer Science 2008-11-06 Xavier Goaoc , Jan Kratochvil , Yoshio Okamoto , Chan-Su Shin , Alexander Wolff

We study the problem of maximizing the number of full degree vertices in a spanning tree $T$ of a graph $G$; that is, the number of vertices whose degree in $T$ equals its degree in $G$. In cubic graphs, this problem is equivalent to…

Combinatorics · Mathematics 2022-11-11 Sarah Acquaviva , Deepak Bal

This paper is a contribution to the problem of counting geometric graphs on point sets. More concretely, we look at the maximum numbers of non-crossing spanning trees and forests. We show that the so-called double chain point configuration…

Combinatorics · Mathematics 2013-10-23 Clemens Huemer , Anna de Mier

We are interested in embedding trees T with maximum degree at most four in a rectangular grid, such that the vertices of T correspond to grid points, while edges of T correspond to non-intersecting straight segments of the grid lines. Such…

Combinatorics · Mathematics 2021-09-08 V. T. F. Luca , F. S. Oliveira , J. L. Szwarcfiter

We study the crossing-minimization problem in a layered graph drawing of planar-embedded rooted trees whose leaves have a given total order on the first layer, which adheres to the embedding of each individual tree. The task is then to…

Discrete Mathematics · Computer Science 2024-02-29 Julia Katheder , Stephen G. Kobourov , Axel Kuckuk , Maximilian Pfister , Johannes Zink