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1.
2-local 3/4-competitive algorithm for multicoloring hexagonal graphs
Petra Šparl, Janez Žerovnik, 2005, original scientific article

Abstract: An important optimization problem in the design of cellular networks is to assign sets of frequencies to transmitters to avoid unacceptable interference.A cellular network is generally modeled as a subgraph of the infinite triangular lattice. Frequency assignment problem can be abstracted asa multicoloring problem on a weighted hexagonal graph, where the weights represent the number of calls to be assigned at vertices. In this paper we present a distributed algorithm for multicoloring hexagonal graphs using only the local clique numbers ▫$omega_1(v)$▫ and ▫$omega_2(v)$▫ at each vertex v of the given hexagonal graph, which can be computed from local information available at thevertex. We prove the algorithm uses no more than ▫$4omega(G)/3$▫ colors for any hexagonal graph G, without explicitly computing the global clique number ▫$omega(G)$▫. We also prove that our algorithm is 2-local, i.e., the computation at a vertex v ▫$in$▫ G uses only information about the demands of vertices whose graph distance from v is less than or equal to 2.
Keywords: mathematics, graph theory, graph colouring, 2-local distributed algorithm, cellular networks, frequency planning
Published: 01.06.2012; Views: 1398; Downloads: 66
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2.
3.
Simpler multicoloring of triangle-free hexagonal graphs
Ignasi Sau Walls, Petra Šparl, Janez Žerovnik, 2012, published scientific conference contribution

Abstract: Preslikavo ▫$f colon V(G)to 2^{{1,.,n}}$▫, za katero velja ▫$|f(v)| ge p(v)$▫ za vsako točko ▫$v in V(G)$▫ in ▫$f(v) cap f(u) = emptyset$▫ za poljubni sosedi ▫$u$▫ in ▫$v$▫ grafa ▫$G$▫, imenujemo dobro ▫$n-[p]$▫barvanje grafa ▫$G$▫. Najmanjše naravno število, za katero obstaja dobro ▫$n-[p]$▫barvanje grafa ▫$G$▫, ▫$chi_p(G)$▫, imenujemo uteženo kromatično število grafa ▫$G$▫. Iskanje uteženega kromatičnega števila za inducirane podgrafe trikotniške mreže (imenovane heksagonalni grafi) ima aplikacije v celičnih mrežah. Uteženo kromatično število grafa ▫$G$▫, ▫$omega_p(G)$▫, je enako maksimalni uteži klike grafa ▫$G$▫, kjer utež klike predstavlja vsoto uteži njenih točk. McDiarmid in Reed (2000) sta postavila domnevo, da za poljuben heksagonalen graf brez trikotnikov velja ▫$chi_p(G) le (9/8)omega_p(G) + C$▫. V članku je podan algoritem, ki poda dobro ▫$7-[3]$▫barvanje poljubnega heksagonalnega grafa brez trikotnikov, ki aplicira neenakost ▫$chi_p(G) le (7/6)omega_p(G) + C$▫. Naš rezultat podaja krajšo alternativo induktivnega dokaza Haveta (2001) in izboljša kratek dokaz Sudepa in Vishwanathana (2005), ki sta dokazala obstoj ▫$14-[6]$▫barvanja. (Omeniti je potrebno, da v sklopu našega dokaza uporabimo izrek o štirih barvah.) Vsi koraki algoritma so linearni glede na ▫$|V(G)|$▫, razen 4-barvanje ravninskega grafa. Novi pristop lahko v prihodnje pripomore k dokazovanju domneve McDiarmida in Reeda (2000).
Keywords: matematika, teorija grafov, aproksimacijski algoritem, barvanje grafov, dodeljevanje frekvenc, celične mreže, mathematics, graph algorithm, graph theory, approximation algorithm, graph coloring, frequency planning, cellular networks
Published: 10.07.2015; Views: 513; Downloads: 55
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4.
2-local distributed algorithms for generalized coloring of hexagonal graphs
Petra Šparl, Janez Žerovnik, 2005, published scientific conference contribution

Abstract: A 2-local distributed approximation algorithm for multicoloring of a triangle-free hexagonal graph which uses at most ▫$lceil frac{5omega(G)}{4} rceil + 3$▫ colors is presented.
Keywords: matematika, teorija grafov, barvanje grafov, aproksimacijski algoritem, frekvenčni načrt, ▫$k$▫-lokalen porazdeljen algoritem, mathematics, graph theory, approximation algorithms, graph coloring, frequency planning, ▫$k$▫-local distributed algorithm
Published: 10.07.2015; Views: 593; Downloads: 66
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