81. Divergence zero quaternionic vector fields and Hamming graphsJasna Prezelj, Fabio Vlacci, 2020, izvirni znanstveni članek Opis: We give a possible extension of the definition of quaternionic power series, partial derivatives and vector fields in the case of two (and then several) non commutative (quaternionic) variables. In this setting we also investigate the problem of describing zero functions which are not null functions in the formal sense. A connection between an analytic condition and a graph theoretic property of a subgraph of a Hamming graph is shown, namely the condition that polynomial vector field has formal divergence zero is equivalent to connectedness of subgraphs of Hamming graphs ▫$H(d, 2)$▫. We prove that monomials in variables ▫$z$▫ and ▫$w$▫ are always linearly independent as functions only in bidegrees ▫$(p, 0)$▫, ▫$(p, 1)$▫, ▫$(0, q)$▫, ▫$(1, q)$▫ and ▫$(2, 2)$▫.
Ključne besede: quaternionic power series, bidegree full functions, Hamming graph, linearly independent quaternionic monomials
Objavljeno v RUP: 03.01.2022; Ogledov: 1721; Prenosov: 17
 Celotno besedilo (354,73 KB) |
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84. Total positivity of Toeplitz matrices of recursive hypersequencesTomislav Došlić, Ivica Martinjak, Riste Škrekovski, 2019, izvirni znanstveni članek Ključne besede: total positivity, totally positive matrix, Toeplitz matrix, Hankel matrix, hyperfibonacci sequence, log-concavity
Objavljeno v RUP: 03.01.2022; Ogledov: 1455; Prenosov: 32
Celotno besedilo (254,44 KB) |
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86. Splittable and unsplittable graphs and configurationsNino Bašić, Jan Grošelj, Branko Grünbaum, Tomaž Pisanski, 2019, izvirni znanstveni članek Opis: We prove that there exist infinitely many splittable and also infinitely many unsplittable cyclic ▫$(n_3)$▫ configurations. We also present a complete study of trivalent cyclic Haar graphs on at most 60 vertices with respect to splittability. Finally, we show that all cyclic flag-transitive configurations with the exception of the Fano plane and the Möbius-Kantor configuration are splittable.
Ključne besede: configuration of points and lines, unsplittable configuration, unsplittable graph, independent set, Levi graph, Grünbaum graph, splitting type, cyclic Haar graph
Objavljeno v RUP: 03.01.2022; Ogledov: 1686; Prenosov: 20
Celotno besedilo (355,79 KB) |
87. Linking rings structures and semisymmetric graphs : combinatorial constructionsPrimož Potočnik, Steve Wilson, 2018, izvirni znanstveni članek Ključne besede: graphs, automorphism group, symmetry, locally arc-transitive graphs, symmetric graphs, cycle structure, linking ring structure
Objavljeno v RUP: 03.01.2022; Ogledov: 1620; Prenosov: 19
Celotno besedilo (397,55 KB) |
88. Combinatorial configurations, quasiline arrangements, and systems of curves on surfacesJürgen Bokowski, Jurij Kovič, Tomaž Pisanski, Arjana Žitnik, 2018, izvirni znanstveni članek Ključne besede: pseudoline arrangement, quasiline arrangement, projective plane, incidence structure, combinatorial configuration, topological configuration, geometric configuration, sweep, wiring diagram, allowable sequence of permutations, maps on surfaces
Objavljeno v RUP: 03.01.2022; Ogledov: 1528; Prenosov: 24
Celotno besedilo (3,66 MB) |
89. Semiregular automorphisms in vertex-transitive graphs with a solvable group of automorphismsDragan Marušič, 2017, izvirni znanstveni članek Opis: It has been conjectured that automorphism groups of vertex-transitive (di)graphs, and more generally 2-closures of transitive permutation groups, must necessarily possess a fixed-point-free element of prime order, and thus a non-identity element with all orbits of the same length, in other words, a semiregular element. The known affirmative answers for graphs with primitive and quasiprimitive groups of automorphisms suggest that solvable groups need to be considered if one is to hope for a complete solution of this conjecture. It is the purpose of this paper to present an overview of known results and suggest possible further lines of research towards a complete solution of the problem.
Ključne besede: solvable group, semiregular automorphism, fixed-point-free automorphism, polycirculant conjecture
Objavljeno v RUP: 03.01.2022; Ogledov: 1497; Prenosov: 19
Celotno besedilo (235,26 KB) |
90. A note on acyclic number of planar graphsMirko Petruševski, Riste Škrekovski, 2017, izvirni znanstveni članek Opis: The acyclic number ▫$a(G)$▫ of a graph ▫$G$▫ is the maximum order of an induced forest in ▫$G$▫. The purpose of this short paper is to propose a conjecture that ▫$a(G)\geq \left( 1-\frac{3}{2g}\right)n$▫ holds for every planar graph ▫$G$▫ of girth ▫$g$▫ and order ▫$n$▫, which captures three known conjectures on the topic. In support of this conjecture, we prove a weaker result that ▫$a(G)\geq \left( 1-\frac{3}{g} \right)n$▫ holds. In addition, we give a construction showing that the constant ▫$\frac{3}{2}$▫ from the conjecture cannot be decreased.
Ključne besede: induced forest, acyclic number, planar graph, girth
Objavljeno v RUP: 03.01.2022; Ogledov: 1567; Prenosov: 17
Celotno besedilo (227,50 KB) |
