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41.
42.
On colour-preserving automorphisms of Cayley graphs
Klavdija Kutnar, Ademir Hujdurović, Edward Dobson, Dave Witte Morris, Joy Morris, 2016, published scientific conference contribution abstract

Keywords: Cayley graph, automorphism, group, colouring
Published in RUP: 08.08.2016; Views: 2566; Downloads: 87
URL Link to full text

43.
Symmetry of graphs via even/odd automorphisms
Dragan Marušič, Klavdija Kutnar, 2016, published scientific conference contribution abstract (invited lecture)

Keywords: vertex-transitive, graph, odd automorphism, automorphism group
Published in RUP: 08.08.2016; Views: 2085; Downloads: 26
URL Link to full text

44.
On the split structure of lifted groups
Aleksander Malnič, Rok Požar, 2016, original scientific article

Abstract: Let ▫$\wp \colon \tilde{X} \to X$▫ be a regular covering projection of connected graphs with the group of covering transformations ▫$\rm{CT}_\wp$▫ being abelian. Assuming that a group of automorphisms ▫$G \le \rm{Aut} X$▫ lifts along $\wp$ to a group ▫$\tilde{G} \le \rm{Aut} \tilde{X}$▫, the problem whether the corresponding exact sequence ▫$\rm{id} \to \rm{CT}_\wp \to \tilde{G} \to G \to \rm{id}$▫ splits is analyzed in detail in terms of a Cayley voltage assignment that reconstructs the projection up to equivalence. In the above combinatorial setting the extension is given only implicitly: neither ▫$\tilde{G}$▫ nor the action ▫$G\to \rm{Aut} \rm{CT}_\wp$▫ nor a 2-cocycle ▫$G \times G \to \rm{CT}_\wp$▫, are given. Explicitly constructing the cover ▫$\tilde{X}$▫ together with ▫$\rm{CT}_\wp$▫ and ▫$\tilde{G}$▫ as permutation groups on ▫$\tilde{X}$▫ is time and space consuming whenever ▫$\rm{CT}_\wp$▫ is large; thus, using the implemented algorithms (for instance, HasComplement in Magma) is far from optimal. Instead, we show that the minimal required information about the action and the 2-cocycle can be effectively decoded directly from voltages (without explicitly constructing the cover and the lifted group); one could then use the standard method by reducing the problem to solving a linear system of equations over the integers. However, along these lines we here take a slightly different approach which even does not require any knowledge of cohomology. Time and space complexity are formally analyzed whenever ▫$\rm{CT}_\wp$▫ is elementary abelian.
Keywords: algorithm, abelian cover, Cayley voltages, covering projection, graph, group extension, group presentation, lifting automorphisms, linear systems over the integers, semidirect product
Published in RUP: 15.10.2015; Views: 2673; Downloads: 157
.pdf Full text (422,56 KB)

45.
Half-arc-transitive group actions with a small number of alternets
Klavdija Kutnar, 2015, published scientific conference contribution abstract

Keywords: automorphism group, half-arc-tranistive graph, alternet
Published in RUP: 15.10.2015; Views: 2313; Downloads: 28
URL Link to full text

46.
On the full automorphism group in vertex-transitive graphs
Dragan Marušič, 2015, published scientific conference contribution abstract

Keywords: odd automorphism, automorphism group, graph
Published in RUP: 15.10.2015; Views: 2266; Downloads: 35
URL Link to full text

47.
48.
Distance-regular Cayley graphs on dihedral groups
Štefko Miklavič, Primož Potočnik, 2005, original scientific article

Abstract: The main result of this article is a classification of distance-regular Cayley graphs on dihedral groups. There exist four obvious families of such graphs, which are called trivial. These are: complete graphs, complete bipartite graphs, complete bipartite graphs with the edges of a 1-factor removed, and cycles. It is proved that every non-trivial distance-regular Cayley graph on a dihedral group is bipartite, non-antipodal, has diameter 3 and arises either from a cyclic di#erence set, or possibly (if any such exists) from a dihedral difference set satisfying some additional conditions. Finally, all distance-transitive Cayley graphs on dihedral groups are determined. It transpires that a Cayley graph on a dihedral group is distance-transitive if and only if it is trivial, or isomorphic to the incidence or to the non-incidence graph of a projective space ▫$\mathrm{PG}_{d-1} (d,q)$▫, ▫$d \ge 2$▫, or the unique pair of complementary symmetric designs on 11 vertices.
Keywords: mathematics, grah theory, distance-regular graph, distance-transitive graph, Cayley graph, dihedral group, dihedrant, difference set
Published in RUP: 10.07.2015; Views: 2454; Downloads: 89
URL Link to full text

49.
On overgroups of regular abelian p-groups
Edward Dobson, 2009, original scientific article

Abstract: Let ▫$G$▫ be a transitive group of odd prime-power degree whose Sylow ▫$p$▫-subgroup ▫$P$▫ is abelian od rank ▫$t$▫. Weshow that if ▫$p > 2^{t-1}$▫, then ▫$G$▫ has a normal subgroup that is a direct product of ▫$t$▫ permutation groups of smaller degree that are either cyclic or doubly-transitive simple groups. As a consequence, we determine the full automorphism group of a Cayley diagraph of an abelian group with rank two such that the Sylow ▫$p$▫-subgroup of the full automorphism group is abelian.
Keywords: group theory, graph theory, Cayley graph, abelian group, regular group, p-group
Published in RUP: 15.10.2013; Views: 3133; Downloads: 157
URL Link to full text

50.
Arc-transitive cycle decompositions of tetravalent graphs
Štefko Miklavič, Primož Potočnik, Steve Wilson, 2008, original scientific article

Abstract: A cycle decomposition of a graph ▫$\Gamma$▫ is a set ▫$\mathcal{C}$▫ of cycles of ▫$\Gamma$▫ such that every edge of ▫$\Gamma$▫ belongs to exactly one cycle in ▫$\mathcal{C}$▫. Such a decomposition is called arc-transitive if the group of automorphisms of ▫$\Gamma$▫ that preserve setwise acts transitively on the arcs of ▫$\Gamma$▫. In this paper, we study arc-transitive cycle decompositions of tetravalent graphs. In particular, we are interested in determining and enumerating arc-transitive cycle decompositions admitted by a given arc-transitive tetravalent graph. Among other results we show that a connected tetravalent arc-transitive graph is either 2-arc-transitive, or is isomorphic to the medial graph of a reflexible map, or admits exactly one cycle structure.
Keywords: mathematics, graph theory, cycle decomposition, automorphism group, consistent cycle, medial maps
Published in RUP: 15.10.2013; Views: 3531; Downloads: 85
URL Link to full text

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