Iskanje po katalogu digitalne knjižnice

Opis: If S=(a1,a2,...) is a non-decreasing sequence of positive integers, then an S-packing coloring of a graph G is a partition of V (G) into sets X1,X2,... such that for each pair of distinct vertices in the set Xi, the distance between them is larger than ai. If there exists an integer k such that V(G)=X1 U ... U Xk, then the partition is called an S-packing k-coloring. The S-packing chromatic number of G is the smallest k such that G admits an S-packing k-coloring. If ai=i for every i, then the terminology reduces to packing colorings and packing chromatic number. Since the introduction of these generalizations of the chromatic number in 2008 more than fifty papers followed. Here we survey the state of the art on the packing coloring, and ts generalization, the S-packing coloring. We also list several conjecres and open problems.
Ključne besede: packing coloring, packing chromatic number, subcubic graph, S-packing chromatic number, computational complexity
Objavljeno v DKUM: 11.03.2025; Ogledov: 0; Prenosov: 9
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Opis: We propose a new coloring game on a graph, called the independence coloring game, which is played by two players with opposite goals. The result of the game is a proper coloring of vertices of a graph G, and Alice’s goal is that as few colors as possible are used during the game, while Bob wants to maximize the number of colors. The game consists of rounds, and in round i, where i = 1, 2,, … , the players are taking turns in selecting a previously unselected vertex of G and giving it color i (hence, in each round the selected vertices form an independent set). The game ends when all vertices of G are selected (and thus colored), and the total number of rounds during the game when both players are playing optimally with respect to their goals, is called the independence game chromatic number, χig(G), of G. In fact, four different versions of the independence game chromatic number are considered, which depend on who starts a game and who starts next rounds. We prove that the new invariants lie between the chromatic number of a graph and the maximum degree plus 1, and characterize the graphs in which each of the four versions of the game invariant equals 2. We compare the versions of the independence game chromatic number among themselves and with the classical game chromatic number. In addition, we prove that the independence game chromatic number of a tree can be arbitrarily large.
Ključne besede: graph, coloring, coloring game, competition-independence game, game chromatic number, tree
Objavljeno v DKUM: 09.08.2024; Ogledov: 99; Prenosov: 10
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Opis: The square ▫$G^2$▫ of a graph ▫$G$▫ is obtained from ▫$G$▫ by adding edges joining all pairs of nodes at distance 2 in ▫$G$▫. In this note we prove that ▫$chi((C_mBox C_n)^2) le 6$ for $m, n ge 40$▫. This confirms Conjecture 19 stated in [É. Sopena, J. Wu, Coloring the square of the Cartesian product of two cycles, Discrete Math. 310 (2010) 2327-2333].
Ključne besede: matematika, teorija grafov, kromatično število, kartezični produkt, označevanje grafov, kvadrat grafa, mathematics, graph theory, chromatic number, Cartesian product, graph labeling, square if a graph
Objavljeno v DKUM: 10.07.2015; Ogledov: 1460; Prenosov: 85
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Opis: Graphs ▫$S[n,k]$▫ are introduced as the graphs obtained from the Sierpiński graphs ▫$S(n,k)$▫ by contracting edges that lie in no triangle. The family ▫$S[n,k]$▫ is a previously studied class of Sierpiñski gasket graphs ▫$S_n$▫. Several properties of graphs ▫$S[n,k]$▫ are studied in particular, hamiltonicity and chromatic number.
Ključne besede: teorija grafov, kromatično število, Sierpińskijev graf, graph theory, chromatic number, Sierpiński graphs, Sierpiński gasket graphs, hamiltonicity
Objavljeno v DKUM: 10.07.2015; Ogledov: 1212; Prenosov: 55
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Opis: Pakirno kromatično število ▫$chi_{rho}(G)$▫ grafa ▫$G$▫ je najmanjše število ▫$k$▫, tako da lahko množico vozlišč grafa ▫$G$▫ razbijemo v pakiranja s paroma različnimi širinami. Dobljenih je več spodnjih in zgornjih meja za pakirno kromatično število kartezičnega produkta grafov. Dokazano je, da pakirno kromatično število šestkotniške mreže leži med 6 in 8. Optimalne spodnje in zgornje meje so dokazane za subdividirane grafe. Obravnavana so tudi drevesa ter vpeljana monotona barvanja.
Ključne besede: matematika, teorija grafov, pakirno kromatično število, kartezični produkt grafov, šestkotniška mreža, subdividiran graf, drevo, računska zahtevnost, mathematics, graph theory, packing chromatic number, Cartesian product of graphs, hexagonal lattice, subdivision graph, tree, computational complexity
Objavljeno v DKUM: 10.07.2015; Ogledov: 1320; Prenosov: 163
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