scholarly journals Guessing Games on Triangle-Free Graphs

10.37236/4731 ◽  
2016 ◽  
Vol 23 (1) ◽  
Author(s):  
Peter J. Cameron ◽  
Anh N. Dang ◽  
Søren Riis
Keyword(s):  
Directed Graph ◽  
Undirected Graph ◽  
Perfect Graphs ◽  
Directed Edge ◽  
Guessing Games ◽  
Sims Graph

The guessing game introduced by Riis [Electron. J. Combin. 2007] is a variant of the "guessing your own hats" game and can be played on any simple directed graph $G$ on $n$ vertices. For each digraph $G$, it is proved that there exists a unique guessing number $\mathrm{gn}(G)$ associated to the guessing game played on $G$. When we consider the directed edge to be bidirected, in other words, the graph $G$ is undirected, Christofides and Markström [Electron. J. Combin. 2011] introduced a method to bound the value of the guessing number from below using the fractional clique cover number $\kappa_f(G)$. In particular they showed $\mathrm{gn}(G) \geq |V(G)| - \kappa_f(G)$. Moreover, it is pointed out that equality holds in this bound if the underlying undirected graph  $G$ falls into one of the following categories: perfect graphs, cycle graphs or their complement. In this paper, we show that there are triangle-free graphs that have guessing numbers which do not meet the fractional clique cover bound. In particular, the famous triangle-free Higman-Sims graph has guessing number at least $77$ and at most $78$, while the bound given by fractional clique cover is $50$.

Two Streamlined Depth-First Search Algorithms

1986 ◽  
Vol 9 (1) ◽  
pp. 85-94
Author(s):  
Robert Endre Tarjan
Keyword(s):  
Directed Graph ◽  
Graph Algorithms ◽  
Undirected Graph ◽  
Linear Time ◽  
Search Algorithms ◽  
Depth First Search ◽  
Time Graph

Many linear-time graph algorithms using depth-first search have been invented. We propose simplified versions of two such algorithms, for computing a bipolar orientation or st-numbering of an undirected graph and for finding all feedback vertices of a directed graph.

scholarly journals Intrinsic linking and knotting in tournaments

2019 ◽  
Vol 28 (12) ◽  
pp. 1950076
Author(s):  
Thomas Fleming ◽  
Joel Foisy
Keyword(s):  
Directed Graph ◽  
Upper Bound ◽  
Directed Edge ◽  
Undirected Graphs ◽  
Oriented Cycle ◽  
Minimum Number ◽  
The Difference

A directed graph [Formula: see text] is intrinsically linked if every embedding of that graph contains a nonsplit link [Formula: see text], where each component of [Formula: see text] is a consistently oriented cycle in [Formula: see text]. A tournament is a directed graph where each pair of vertices is connected by exactly one directed edge. We consider intrinsic linking and knotting in tournaments, and study the minimum number of vertices required for a tournament to have various intrinsic linking or knotting properties. We produce the following bounds: intrinsically linked ([Formula: see text]), intrinsically knotted ([Formula: see text]), intrinsically 3-linked ([Formula: see text]), intrinsically 4-linked ([Formula: see text]), intrinsically 5-linked ([Formula: see text]), intrinsically [Formula: see text]-linked ([Formula: see text]), intrinsically linked with knotted components ([Formula: see text]), and the disjoint linking property ([Formula: see text]). We also introduce the consistency gap, which measures the difference in the order of a graph required for intrinsic [Formula: see text]-linking in tournaments versus undirected graphs. We conjecture the consistency gap to be nondecreasing in [Formula: see text], and provide an upper bound at each [Formula: see text].

Undirected Graphs Realizable as Graphs of Modular Lattices

1965 ◽  
Vol 17 ◽  
pp. 923-932 ◽  
Author(s):  
Laurence R. Alvarez
Keyword(s):  
Distributive Lattice ◽  
Partial Order ◽  
Directed Graph ◽  
Undirected Graph ◽  
Single Edge ◽  
Undirected Graphs ◽  
Modular Lattices

If (L, ≥) is a lattice or partial order we may think of its Hesse diagram as a directed graph, G, containing the single edge E(c, d) if and only if c covers d in (L, ≥). This graph we shall call the graph of (L, ≥). Strictly speaking it is the basis graph of (L, ≥) with the loops at each vertex removed; see (3, p. 170).We shall say that an undirected graph Gu can be realized as the graph of a (modular) (distributive) lattice if and only if there is some (modular) (distributive) lattice whose graph has Gu as its associated undirected graph.

scholarly journals Skew Spectra of Oriented Graphs

10.37236/270 ◽  
2009 ◽  
Vol 16 (1) ◽  
Author(s):  
Bryan Shader ◽  
Wasin So
Keyword(s):  
Directed Graph ◽  
Adjacency Matrix ◽  
Undirected Graph ◽  
Oriented Graph ◽  
Oriented Graphs ◽  
Underlying Graph ◽  
Adjacency Spectrum ◽  
The Relationship ◽  
Skew Adjacency Matrix

An oriented graph $G^{\sigma}$ is a simple undirected graph $G$ with an orientation $\sigma$, which assigns to each edge a direction so that $G^{\sigma}$ becomes a directed graph. $G$ is called the underlying graph of $G^{\sigma}$, and we denote by $Sp(G)$ the adjacency spectrum of $G$. Skew-adjacency matrix $S( G^{\sigma} )$ of $G^{\sigma}$ is introduced, and its spectrum $Sp_S( G^{\sigma} )$ is called the skew-spectrum of $G^{\sigma}$. The relationship between $Sp_S( G^{\sigma} )$ and $Sp(G)$ is studied. In particular, we prove that (i) $Sp_S( G^{\sigma} ) = {\bf i} Sp(G)$ for some orientation $\sigma$ if and only if $G$ is bipartite, (ii) $Sp_S(G^{\sigma}) = {\bf i} Sp(G)$ for any orientation $\sigma$ if and only if $G$ is a forest, where ${\bf i}=\sqrt{-1}$.

Study on Parameter Transfer Structure of Generalized Modular Based Graph Theory

2012 ◽  
Vol 562-564 ◽  
pp. 1323-1326 ◽  
Author(s):  
Chao Zhou ◽  
Yan Ping Liu
Keyword(s):  
Graph Theory ◽  
Directed Graph ◽  
Mathematical Description ◽  
Theoretical Basis ◽  
Product Structure ◽  
Decomposition Algorithm ◽  
Modular Structure ◽  
Directed Edge ◽  
Transfer Structure ◽  
Transfer Chain

For the purpose of reducing product structure levels and shorting transfer chain of parameter, in this paper the product structure levels are expressed with generalized modular. The concept of directed graph of parameter connection structure for generalized modular is proposed with the use of directed graph theory, generalized modular, sub-modular and part represented by vertex, the driven relations of parameter connection represented by directed edge, and the properties of directed graph of parameter connection structure for generalized modular are gained. The directed graph of parameter connection structure for generalized modular is divided into a number of sub-graphs according to the relations of product-level modular structure. And the horizontal edges of sub-graphs among vertexes are decomposed. Therefore, a standardized relation of parameter connection structure is established by given the decomposition algorithm and the mathematical description of parameters connection that are provide the theoretical basis for parameters connection analysis of variant design.

scholarly journals Hamiltonicity in random directed graphs is born resilient

2020 ◽  
Vol 29 (6) ◽  
pp. 900-942 ◽  
Author(s):  
Richard Montgomery
Keyword(s):  
Directed Graph ◽  
Directed Graphs ◽  
Directed Edge

AbstractLet $\{D_M\}_{M\geq 0}$ be the n-vertex random directed graph process, where $D_0$ is the empty directed graph on n vertices, and subsequent directed graphs in the sequence are obtained by the addition of a new directed edge uniformly at random. For each $$\varepsilon > 0$$ , we show that, almost surely, any directed graph $D_M$ with minimum in- and out-degree at least 1 is not only Hamiltonian (as shown by Frieze), but remains Hamiltonian when edges are removed, as long as at most $1/2-\varepsilon$ of both the in- and out-edges incident to each vertex are removed. We say such a directed graph is $(1/2-\varepsilon)$ -resiliently Hamiltonian. Furthermore, for each $\varepsilon > 0$ , we show that, almost surely, each directed graph $D_M$ in the sequence is not $(1/2+\varepsilon)$ -resiliently Hamiltonian.This improves a result of Ferber, Nenadov, Noever, Peter and Škorić who showed, for each $\varepsilon > 0$ , that the binomial random directed graph $D(n,p)$ is almost surely $(1/2-\varepsilon)$ -resiliently Hamiltonian if $p=\omega(\log^8n/n)$ .

scholarly journals Cliques and colorings in generalized Paley graphs and an approach to synchronization

2015 ◽  
Vol 14 (06) ◽  
pp. 1550088 ◽  
Author(s):  
Csaba Schneider ◽  
Ana C. Silva
Keyword(s):  
Finite Field ◽  
Directed Graph ◽  
Undirected Graph ◽  
Multiplicative Group ◽  
Permutation Groups ◽  
Chromatic Numbers ◽  
Paley Graph ◽  
Paley Graphs

Given a finite field, one can form a directed graph using the field elements as vertices and connecting two vertices if their difference lies in a fixed subgroup of the multiplicative group. If -1 is contained in this fixed subgroup, then we obtain an undirected graph that is referred to as a generalized Paley graph. In this paper, we study generalized Paley graphs whose clique and chromatic numbers coincide and link this theory to the study of the synchronization property in 1-dimensional primitive affine permutation groups.

A Constructive Solution to a Tournament Problem

1971 ◽  
Vol 14 (1) ◽  
pp. 45-48 ◽  
Author(s):  
R. L. Graham ◽  
J. H. Spencer
Keyword(s):  
Directed Graph ◽  
Directed Edge ◽  
Constructive Solution

By a tournament Tn on n vertices, we shall mean a directed graph on n vertices for which every pair of distinct vertices form the endpoints of exactly one directed edge (e.g., see [5]). If x and y are vertices of Tn we say that x dominates y if the edge between x and y is directed from x to y. In 1962, K. Schütte [2] raised the following question: Given k > 0, is there a tournament Tn(k) such that for any set S of k vertices of Tn(k) there is a vertex y which dominates all k elements of S. (Such a tournament will be said to have property Pk.)

scholarly journals The average covering tree value for directed graph games

2019 ◽  
Vol 39 (2) ◽  
pp. 315-333 ◽  
Author(s):  
Anna Khmelnitskaya ◽  
Özer Selçuk ◽  
Dolf Talman
Keyword(s):  
Directed Graph ◽  
Undirected Graph ◽  
Solution Concept ◽  
Transferable Utility ◽  
Communication Structure ◽  
Gravity Center ◽  
Dominance Relations ◽  
Graph Games ◽  
Covering Tree ◽  
Transferable Utility Games

Abstract We introduce a single-valued solution concept, the so-called average covering tree value, for the class of transferable utility games with limited communication structure represented by a directed graph. The solution is the average of the marginal contribution vectors corresponding to all covering trees of the directed graph. The covering trees of a directed graph are those (rooted) trees on the set of players that preserve the dominance relations between the players prescribed by the directed graph. The average covering tree value is component efficient, and under a particular convexity-type condition it is stable. For transferable utility games with complete communication structure the average covering tree value equals to the Shapley value of the game. If the graph is the directed analog of an undirected graph the average covering tree value coincides with the gravity center solution.

Research of Key Nodes of Botnet Based on P2P

2011 ◽  
Vol 88-89 ◽  
pp. 386-390
Author(s):  
Jian Gao ◽  
Kang Feng Zheng ◽  
Yi Xian Yang ◽  
Xin Xin Niu
Keyword(s):  
Directed Graph ◽  
Undirected Graph ◽  
Detection Algorithm ◽  
P2p Network ◽  
P2p Networks ◽  
Cut Vertex ◽  
Peer Network ◽  
Simulation Results ◽  
Peer To Peer Network ◽  
Key Nodes

The paper applies the segmentation of peer-to- peer network to the defense process of P2P-based botnet, in order to cause the greatest damage on the P2P network. A lot of papers have been researching how to find the key nodes in P2P networks. To solve this problem, this paper proposes distributed detection algorithm NEI and centralized detection algorithm COR for detecting cut vertex, NEI algorithm not only apply to detect cut vertex of directed graph but also to the undirected graph. COR algorithm can reduce the additional communication. Then, this paper carries out simulation on P2P botnet, the simulation results show that the maximum damage on the botnet can be achieved by destructing key nodes.

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