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1.
Guarded subgraphs and the domination game
Boštjan Brešar, Sandi Klavžar, Gašper Košmrlj, Douglas F. Rall, 2015, original scientific article

Abstract: V članku vpeljemo koncept zaščitenega podgrafa. Množica le-teh po definicji leži med množico konveksnih in 2-izometričnih podgrafov, hkrati pa ni primerljiva z množico izometričnimih podgrafov. Dokažemo nekatere metrične lastnosti zaščitenih podgrafov ter koncept uporabimo v dominacijski igri, v kateri dva igralca, Dominator in Zavlačevalka, izmenično izbirata vozlišča grafa, tako da vsako izbrano vozlišče poveča množico dominiranih vozlišč. Dominatorjev cilj je končati igro, tj. dominirati celoten graf, čim hitreje, medtem ko je Zavlačevalkin cilj odigrati čim več potez. Igralno dominacijsko število je število potez v igri, ko Dominator začne in oba igralca igrata optimalno. Kot glavni rezultat članka dokažemo, da igralno dominacijsko število grafa ni nikoli manjše, kot igralno dominacijsko število njegovega zaščitenega podgrafa. Predstavljenih je tudi več aplikacij tega rezultata.
Keywords: dominacijska igra, igralno dominacijsko številko, konveksni podgraf, (2-)izometrični podgraf
Published in DKUM: 10.07.2017; Views: 1022; Downloads: 149
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2.
How long can one bluff in the domination game?
Boštjan Brešar, Paul Dorbec, Sandi Klavžar, Gašper Košmrlj, 2017, original scientific article

Abstract: The domination game is played on an arbitrary graph ▫$G$▫ by two players, Dominator and Staller. The game is called Game 1 when Dominator starts it, and Game 2 otherwise. In this paper bluff graphs are introduced as the graphs in which every vertex is an optimal start vertex in Game 1 as well as in Game 2. It is proved that every minus graph (a graph in which Game 2 finishes faster than Game 1) is a bluff graph. A non-trivial infinite family of minus (and hence bluff) graphs is established. Minus graphs with game domination number equal to 3 are characterized. Double bluff graphs are also introduced and it is proved that Kneser graphs ▫$K(n,2)$▫, za ▫$n \ge 6$▫, are double bluff. The domination game is also studied on generalized Petersen graphs and on Hamming graphs. Several generalized Petersen graphs that are bluff graphs but not vertex-transitive are found. It is proved that Hamming graphs are not double bluff.
Keywords: domination game, game domination number, bluff graphs, minus graphs, generalized Petersen graphs, Kneser graphs, Cartesian product of graphs, Hamming graphs
Published in DKUM: 09.05.2017; Views: 983; Downloads: 420
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3.
Domination game critical graphs
Csilla Bujtás, Sandi Klavžar, Gašper Košmrlj, original scientific article

Abstract: The domination game is played on a graph ▫$G$▫ by two players who alternately take turns by choosing a vertex such that in each turn at least one previously undominated vertex is dominated. The game is over when each vertex becomes dominated. One of the players, namely Dominator, wants to finish the game as soon as possible, while the other one wants to delay the end. The number of turns when Dominator starts the game on ▫$G$▫ and both players play optimally is the graph invariant ▫$\gamma_g(G)$▫, named the game domination number. Here we study the ▫$\gamma_g$▫-critical graphs which are critical with respect to vertex predomination. Besides proving some general properties, we characterize ▫$\gamma_g$▫-critical graphs with ▫$\gamma_g =2$▫ and with ▫$\gamma_g =3$▫, moreover for each ▫$n$▫ we identify the (infinite) class of all ▫$\gamma_g$▫-critical ones among the ▫$n$▫th powers ▫$C_N^n$▫ of cycles. Along the way we determine ▫$\gamma_g(C_N^n)$▫ for all ▫$n$▫ and ▫$N$▫. Results of a computer search for ▫$\gamma_g$▫-critical trees are presented and several problems and research directions are also listed.
Keywords: domination game, domination game critical graphs, powers of cycles, trees
Published in DKUM: 31.03.2017; Views: 1000; Downloads: 375
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4.
Domination game: extremal families of graphs for 3/5-conjectures
Boštjan Brešar, Sandi Klavžar, Gašper Košmrlj, Douglas F. Rall, 2013, original scientific article

Abstract: Igralca, Dominator in Zavlačevalka, izmenoma izbirata vozlišča grafa ▫$G$▫, takoda vsako izbrano vozlišče poveča množico do sedaj dominiranih vozlišč. Cilj Dominatorja je končati igro čim hitreje, medtem ko je Zavlačevalkin cilj ravno nasprotno. Igralno dominacijsko število ▫$gamma_g(G)$▫ je skupno število izbranih vozlišč v igri, ko Dominator naredi prvo potezo in oba igralca igrata optimalno. Postavljena je bila domneva [W.B. Kinnersley, D.B. West, R. Zemani, Extremal problems for game domination number, Manuscript, 2012], da velja ▫$gamma_g(G) leq frac{3|V(G)|}{5}$▫ za poljuben graf ▫$G$▫ brez izoliranih vozlišč. V posebnem je domneva odprta tudi, ko je ▫$G$▫ gozd. V tem članku predstavimo konstrukcije, ki nam dajo velike družine dreves, ki dosežejo domnevno mejo ▫$3/5$▫. Leplenje dreves iz nekaterih izmed teh družin napoljuben graf nam da konstrukcijo grafov ▫$G$▫, ki imajo igralno dominacijsko število enako ▫$3|V(G)|/5$▫. Z računalnikom smo poiskali vsa ekstremna drevesa znajveč 20 vozlišči. V posebnem, na 20 vozliščih obstaja natanko deset dreves ▫$T$▫, za katere velja ▫$gamma_g(T) = 12$▫, in vsa pripadajo skonstruiranim družinam.
Keywords: matematika, teorija grafov, dominacijska igra, igralno dominacijsko številko, 3/5-domneva, računalniško iskanje, mathematics, graph theory, domination game, game domination number, 3/5-conjecture, computer search
Published in DKUM: 10.07.2015; Views: 1117; Downloads: 90
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