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Thesis Defense: Fionn Mc Inerney "Domination and Identification Games in Graphs"

08/07/2019   :   14h00
Inria Sophia Antipolis, Euler violet
Publication : 08/07/2019
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In this thesis, 2-player games on graphs and their algorithmic and structural aspects are studied. First, we investigate two dynamic dominating set games: the eternal domination game and its generalization, the spy game. In these two games, a team of guards pursue a fast attacker or spy in a graph with the objective of staying close to him eternally and one wants to calculate the eternal domination number (guard number in the spy game) which is the minimum number of guards needed to do this. Secondly, the metric dimension of digraphs and a sequential version of the metric dimension of graphs are then studied. These two problems are those of finding a minimum subset of vertices that uniquely identify all the vertices of the graph by their distances from the vertices in the subset. In particular, in the latter, one can probe a certain number of vertices per turn which return their distances to a hidden target and the goal is to minimize the number of turns in order to ensure locating the target. These games and problems are studied in particular graph classes and their computational complexities are also studied.
Precisely, the NP-hardness of the spy game and the guard numbers of paths and cycles are first presented. Then, results for the spy game on trees and grids are presented. Notably, we show an equivalence between the fractional variant and the ``integral" version of the spy game in trees which allowed us to use Linear Programming to come up with what we believe to be the first exact algorithm using the fractional variant of a game to solve the ``integral" version. Asymptotic bounds on the eternal domination number of strong grids are then presented. This is followed by results on the NP-completeness of the Localization game under different conditions (and a variant of it) and the game in trees. Notably, we show that the problem is NP-complete in trees, but despite this, we come up with a polynomial-time (+1)-approximation algorithm in trees. We consider such an approximation to be rare as we are not aware of any other such approximation in games on graphs. Lastly, results on the metric dimension of oriented graphs are presented. In particular, the orientations which maximize the metric dimension are investigated for graphs of bounded degree, tori, and grids.