scholarly journals The Positive Minimum Degree Game on Sparse Graphs

10.37236/1174 ◽  
2012 ◽  
Vol 19 (1) ◽  
Author(s):  
József Balogh ◽  
András Pluhár
Keyword(s):  
Complete Graph ◽  
Special Form ◽  
Minimum Degree ◽  
Sharp Bound ◽  
Sparse Graphs ◽  
Discharging Method ◽  
Graph Game

In this note we investigate a special form of degree games defined by D. Hefetz, M. Krivelevich, M. Stojaković and T. Szabó. Usually the board of a graph game is the edge set of $K_n$, the complete graph on $n$ vertices. Maker and Breaker alternately claim an edge, and Maker wins if his edges form a subgraph with prescribed properties; here a certain minimum degree. In the special form the board is no longer the whole edge set of $K_n$, Maker first selects as few edges of $K_n$ as possible in order to win, and our goal is to compute the necessary size of that board. Solving a question of Hefetz et al., we show, using the discharging method, that the sharp bound is around $10n/7$ for the positive minimum degree game.

scholarly journals A minimum degree condition forcing complete graph immersion

COMBINATORICA ◽  
2014 ◽  
Vol 34 (3) ◽  
pp. 279-298 ◽  
Author(s):  
Matt Devos ◽  
Zdeněk Dvořák ◽  
Jacob Fox ◽  
Jessica McDonald ◽  
Bojan Mohar ◽  
...  
Keyword(s):  
Complete Graph ◽  
Minimum Degree ◽  
Degree Condition

scholarly journals Monochromatic Components in Edge-Coloured Graphs with Large Minimum Degree

10.37236/9039 ◽  
2021 ◽  
Vol 28 (1) ◽  
Author(s):  
Hannah Guggiari ◽  
Alex Scott
Keyword(s):  
Complete Graph ◽  
Minimum Degree ◽  
Connected Component ◽  
Delta G ◽  
Edge Colouring

For every $n\in\mathbb{N}$ and $k\geqslant2$, it is known that every $k$-edge-colouring of the complete graph on $n$ vertices contains a monochromatic connected component of order at least $\frac{n}{k-1}$. For $k\geqslant3$, it is known that the complete graph can be replaced by a graph $G$ with $\delta(G)\geqslant(1-\varepsilon_k)n$ for some constant $\varepsilon_k$. In this paper, we show that the maximum possible value of $\varepsilon_3$ is $\frac16$. This disproves a conjecture of Gyárfas and Sárközy.

Monochromatic paths and cycles in 2-edge-coloured graphs with large minimum degree

2021 ◽  
pp. 1-14
Author(s):  
József Balogh ◽  
Alexandr Kostochka ◽  
Mikhail Lavrov ◽  
Xujun Liu
Keyword(s):  
Complete Graph ◽  
Minimum Degree ◽  
Dense Subgraph ◽  
Degree Condition ◽  
Vertex Graph ◽  
Delta G ◽  
Edge Colouring ◽  
Monochromatic Copy

Abstract A graph G arrows a graph H if in every 2-edge-colouring of G there exists a monochromatic copy of H. Schelp had the idea that if the complete graph $K_n$ arrows a small graph H, then every ‘dense’ subgraph of $K_n$ also arrows H, and he outlined some problems in this direction. Our main result is in this spirit. We prove that for every sufficiently large n, if $n = 3t+r$ where $r \in \{0,1,2\}$ and G is an n-vertex graph with $\delta(G) \ge (3n-1)/4$ , then for every 2-edge-colouring of G, either there are cycles of every length $\{3, 4, 5, \dots, 2t+r\}$ of the same colour, or there are cycles of every even length $\{4, 6, 8, \dots, 2t+2\}$ of the samecolour. Our result is tight in the sense that no longer cycles (of length $>2t+r$ ) can be guaranteed and the minimum degree condition cannot be reduced. It also implies the conjecture of Schelp that for every sufficiently large n, every $(3t-1)$ -vertex graph G with minimum degree larger than $3|V(G)|/4$ arrows the path $P_{2n}$ with 2n vertices. Moreover, it implies for sufficiently large n the conjecture by Benevides, Łuczak, Scott, Skokan and White that for $n=3t+r$ where $r \in \{0,1,2\}$ and every n-vertex graph G with $\delta(G) \ge 3n/4$ , in each 2-edge-colouring of G there exists a monochromatic cycle of length at least $2t+r$ .

Ramsey Problems with Bounded Degree Spread

1993 ◽  
Vol 2 (3) ◽  
pp. 263-269 ◽  
Author(s):  
G. Chen ◽  
R. H. Schelp
Keyword(s):  
Positive Integer ◽  
Complete Graph ◽  
Maximum Degree ◽  
Minimum Degree ◽  
Bipartite Graphs ◽  
Bounded Degree ◽  
Monochromatic Copy

Let k be a positive integer, k ≥ 2. In this paper we study bipartite graphs G such that, for n sufficiently large, each two-coloring of the edges of the complete graph Kn gives a monochromatic copy of G, with some k of its vertices having the maximum degree of these k vertices minus the minimum degree of these k vertices (in the colored Kn) at most k − 2.

scholarly journals Complete graph immersions and minimum degree

2017 ◽  
Vol 88 (1) ◽  
pp. 211-221 ◽  
Author(s):  
Zdeněk Dvořák ◽  
Liana Yepremyan
Keyword(s):  
Complete Graph ◽  
Minimum Degree

scholarly journals Wiener index in graphs with given minimum degree and maximum degree

2021 ◽  
Vol vol. 23 no. 1 (Graph Theory) ◽  
Author(s):  
Peter Dankelmann ◽  
Alex Alochukwu
Keyword(s):  
Graph Theory ◽  
Upper Bound ◽  
Connected Graph ◽  
Maximum Degree ◽  
Minimum Degree ◽  
Large Degree ◽  
Wiener Index ◽  
Sharp Bound

Let $G$ be a connected graph of order $n$.The Wiener index $W(G)$ of $G$ is the sum of the distances between all unordered pairs of vertices of $G$. In this paper we show that the well-known upper bound $\big( \frac{n}{\delta+1}+2\big) {n \choose 2}$ on the Wiener index of a graph of order $n$ and minimum degree $\delta$ [M. Kouider, P. Winkler, Mean distance and minimum degree. J. Graph Theory 25 no. 1 (1997)] can be improved significantly if the graph contains also a vertex of large degree. Specifically, we give the asymptotically sharp bound $W(G) \leq {n-\Delta+\delta \choose 2} \frac{n+2\Delta}{\delta+1}+ 2n(n-1)$ on the Wiener index of a graph $G$ of order $n$, minimum degree $\delta$ and maximum degree $\Delta$. We prove a similar result for triangle-free graphs, and we determine a bound on the Wiener index of $C_4$-free graphs of given order, minimum and maximum degree and show that it is, in some sense, best possible.

scholarly journals On Ryser’s Conjecture for $t$-Intersecting and Degree-Bounded Hypergraphs

10.37236/6448 ◽  
2017 ◽  
Vol 24 (4) ◽  
Author(s):  
Zoltán Király ◽  
Lilla Tóthmérész
Keyword(s):  
Complete Graph ◽  
Maximum Degree ◽  
Sharp Bound ◽  
Famous Conjecture ◽  
Special Cases ◽  
Intersecting Hypergraphs ◽  
Phd Thesis ◽  
Special Case

A famous conjecture (usually called Ryser's conjecture) that appeared in the PhD thesis of his student, J. R. Henderson, states that for an $r$-uniform $r$-partite hypergraph $\mathcal{H}$, the inequality $\tau(\mathcal{H})\le(r-1)\!\cdot\! \nu(\mathcal{H})$ always holds. This conjecture is widely open, except in the case of $r=2$, when it is equivalent to Kőnig's theorem, and in the case of $r=3$, which was proved by Aharoni in 2001.Here we study some special cases of Ryser's conjecture. First of all, the most studied special case is when $\mathcal{H}$ is intersecting. Even for this special case, not too much is known: this conjecture is proved only for $r\le 5$ by Gyárfás and Tuza. For $r>5$ it is also widely open.Generalizing the conjecture for intersecting hypergraphs, we conjecture the following. If an $r$-uniform $r$-partite hypergraph $\mathcal{H}$ is $t$-intersecting (i.e., every two hyperedges meet in at least $t<r$ vertices), then $\tau(\mathcal{H})\le r-t$. We prove this conjecture for the case $t> r/4$.Gyárfás showed that Ryser's conjecture for intersecting hypergraphs is equivalent to saying that the vertices of an $r$-edge-colored complete graph can be covered by $r-1$ monochromatic components.Motivated by this formulation, we examine what fraction of the vertices can be covered by $r-1$ monochromatic components of different colors in an $r$-edge-colored complete graph. We prove a sharp bound for this problem.Finally we prove Ryser's conjecture for the very special case when the maximum degree of the hypergraph is two.

scholarly journals Induced Complete $h$-partite Graphs in Dense Clique-less Graphs

10.37236/1475 ◽  
1999 ◽  
Vol 6 (1) ◽  
Author(s):  
Eldar Fischer
Keyword(s):  
Complete Graph ◽  
Minimum Degree ◽  
Color Class ◽  
Vertex Disjoint

It is proven that for every fixed $h$, $a$ and $b$, a graph with $n$ vertices and minimum degree at least ${h-1 \over h}n$, which contains no copy of $K_b$ (the complete graph with $b$ vertices), contains at least $(1-o(1)){n \over ha}$ vertex disjoint induced copies of the complete $h$-partite graph with $a$ vertices in each color class.

scholarly journals Erdös-Gyárfás Conjecture for Cubic Planar Graphs

10.37236/3252 ◽  
2013 ◽  
Vol 20 (2) ◽  
Author(s):  
Christopher Carl Heckman ◽  
Roi Krakovski
Keyword(s):  
Planar Graphs ◽  
Minimum Degree ◽  
Negative Integer ◽  
Simple Cycle ◽  
Discharging Method ◽  
Computer Based

In 1995, Paul Erdös and András Gyárfás conjectured that for every graph of minimum degree at least 3, there exists a non-negative integer $m$ such that $G$ contains a simple cycle of length $2^m$. In this paper, we prove that the conjecture holds for 3-connected cubic planar graphs. The proof is long, computer-based in parts, and employs the Discharging Method in a novel way.

Sign in / Sign up

Export Citation Format

Share Document