322 research outputs found
The Disjoint Domination Game
We introduce and study a Maker-Breaker type game in which the issue is to
create or avoid two disjoint dominating sets in graphs without isolated
vertices. We prove that the maker has a winning strategy on all connected
graphs if the game is started by the breaker. This implies the same in the
biased game also in the maker-start game. It remains open to
characterize the maker-win graphs in the maker-start non-biased game, and to
analyze the biased game for . For a more restricted
variant of the non-biased game we prove that the maker can win on every graph
without isolated vertices.Comment: 18 page
Adaptive Monte Carlo Search for Conjecture Refutation in Graph Theory
Graph theory is an interdisciplinary field of study that has various
applications in mathematical modeling and computer science. Research in graph
theory depends on the creation of not only theorems but also conjectures.
Conjecture-refuting algorithms attempt to refute conjectures by searching for
counterexamples to those conjectures, often by maximizing certain score
functions on graphs. This study proposes a novel conjecture-refuting algorithm,
referred to as the adaptive Monte Carlo search (AMCS) algorithm, obtained by
modifying the Monte Carlo tree search algorithm. Evaluated based on its success
in finding counterexamples to several graph theory conjectures, AMCS
outperforms existing conjecture-refuting algorithms. The algorithm is further
utilized to refute six open conjectures, two of which were chemical graph
theory conjectures formulated by Liu et al. in 2021 and four of which were
formulated by the AutoGraphiX computer system in 2006. Finally, four of the
open conjectures are strongly refuted by generalizing the counterexamples
obtained by AMCS to produce a family of counterexamples. It is expected that
the algorithm can help researchers test graph-theoretic conjectures more
effectively.Comment: 27 pages, 11 figures, 3 tables; Milo Roucairol pointed out that both
of our papers used an incorrect formula for the harmonic of a graph. The
revised Conjecture 4 was able to be refuted. This paper and the GitHub
repository have been updated accordingl
Protecting a Graph with Mobile Guards
Mobile guards on the vertices of a graph are used to defend it against
attacks on either its vertices or its edges. Various models for this problem
have been proposed. In this survey we describe a number of these models with
particular attention to the case when the attack sequence is infinitely long
and the guards must induce some particular configuration before each attack,
such as a dominating set or a vertex cover. Results from the literature
concerning the number of guards needed to successfully defend a graph in each
of these problems are surveyed.Comment: 29 pages, two figures, surve
Smooth Parametrizations in Dynamics, Analysis, Diophantine and Computational Geometry
Smooth parametrization consists in a subdivision of the mathematical objects
under consideration into simple pieces, and then parametric representation of
each piece, while keeping control of high order derivatives. The main goal of
the present paper is to provide a short overview of some results and open
problems on smooth parametrization and its applications in several apparently
rather separated domains: Smooth Dynamics, Diophantine Geometry, Approximation
Theory, and Computational Geometry.
The structure of the results, open problems, and conjectures in each of these
domains shows in many cases a remarkable similarity, which we try to stress.
Sometimes this similarity can be easily explained, sometimes the reasons remain
somewhat obscure, and it motivates some natural questions discussed in the
paper. We present also some new results, stressing interconnection between
various types and various applications of smooth parametrization
The Disjoint Domination Game
We introduce and study a Maker-Breaker type game in which the issue is to create or avoid two disjoint dominating sets in graphs without isolated vertices. We prove that the maker has a winning strategy on all connected graphs if the game is started by the breaker. This implies the same in the (2:1) biased game also in the maker-start game. It remains open to characterize the maker-win graphs in the maker-start non-biased game, and to analyze the (a:b) biased game for (a:b)≠(2:1). For a more restricted variant of the non-biased game we prove that the maker can win on every graph without isolated vertices. © 2015 Elsevier B.V
Hardness of Non-trivial Generalized Domination Problems Parameterized by Linear Mim-Width
Masteroppgave i informatikkINF399MAMN-INFMAMN-PRO
On Cops and Robbers on and cop-edge critical graphs
Cop Robber game is a two player game played on an undirected graph. In this game cops try to capture a robber moving on the vertices of the graph. The cop number of a graph is the least number of cops needed to guarantee that the robber will be caught. In this paper we presents results concerning games on , that is the graph obtained by connecting the corresponding vertices in and its complement . In particular we show that for planar graphs . Furthermore we investigate the cop-edge critical graphs, i.e. graphs that for any edge in we have either . We show couple examples of cop-edge critical graphs having cop number equal to
Some problems in combinatorial topology of flag complexes
In this work we study simplicial complexes associated to graphs and their homotopical and combinatorial properties. The main focus is on the family of flag complexes, which can be viewed as independence complexes and clique complexes of graphs.
In the first part we study independence complexes of graphs using two cofibre sequences corresponding to vertex and edge removals. We give applications to the connectivity of independence complexes of chordal graphs and to extremal problems in topology and we answer open questions about the homotopy types of those spaces for particular families of graphs. We also study the independence complex as a space
of configurations of particles in the so-called hard-core models on various lattices.
We define, and investigate from an algorithmic perspective, a special family of combinatorially defined homology classes in independence complexes. This enables us to give algorithms as well as NP-hardness results for topological properties of some spaces. As a corollary we prove hardness of computing homology of simplicial complexes in general.
We also view flag complexes as clique complexes of graphs. That leads to the study of various properties of Vietoris-Rips complexes of graphs.
The last result is inspired by a problem in face enumeration. Using methods of extremal graph theory we classify flag triangulations of 3-manifolds with many edges. As a corollary we complete the classification of face vectors of flag simplicial homology 3-spheres
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