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1
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Strongly multiplicative graphs

100%
Beineke L., Hegde S.
Discussiones Mathematicae Graph Theory
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2001
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tom 21
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nr 1
63-75
EN
A graph with p vertices is said to be strongly multiplicative if its vertices can be labelled 1,2,...,p so that the values on the edges, obtained as the product of the labels of their end vertices, are all distinct. In this paper, we study structural properties of strongly multiplicative graphs. We show that all graphs in some classes, including all trees, are strongly multiplicative, and consider the question of the maximum number of edges in a strongly multiplicative graph of a given order.
2
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An upper bound for maximum number of edges in a strongly multiplicative graph

100%
Adiga C., Smitha M.
Discussiones Mathematicae Graph Theory
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2006
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tom 26
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nr 2
225-229
EN
In this note we give an upper bound for λ(n), the maximum number of edges in a strongly multiplicative graph of order n, which is sharper than the upper bounds given by Beineke and Hegde [3] and Adiga, Ramaswamy and Somashekara [2], for n ≥ 28.
3
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Difference labelling of cacti

80%
Sonntag M.
Discussiones Mathematicae Graph Theory
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2003
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tom 23
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nr 1
55-65
EN
A graph G is a difference graph iff there exists S ⊂ IN⁺ such that G is isomorphic to the graph DG(S) = (V,E), where V = S and E = {{i,j}:i,j ∈ V ∧ |i-j| ∈ V}. It is known that trees, cycles, complete graphs, the complete bipartite graphs $K_{n,n}$ and $K_{n,n-1}$, pyramids and n-sided prisms (n ≥ 4) are difference graphs (cf. [4]). Giving a special labelling algorithm, we prove that cacti with a girth of at least 6 are difference graphs, too.
4
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Cyclic decompositions of complete graphs into spanning trees

80%
Froncek D.
Discussiones Mathematicae Graph Theory
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2004
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tom 24
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nr 2
345-353
EN
We examine decompositions of complete graphs with an even number of vertices, $K_{2n}$, into n isomorphic spanning trees. While methods of such decompositions into symmetric trees have been known, we develop here a more general method based on a new type of vertex labelling, called flexible q-labelling. This labelling is a generalization of labellings introduced by Rosa and Eldergill.
5
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Difference labelling of digraphs

80%
Sonntag M.
Discussiones Mathematicae Graph Theory
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2004
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tom 24
|
nr 3
509-527
EN
A digraph G is a difference digraph iff there exists an S ⊂ N⁺ such that G is isomorphic to the digraph DD(S) = (V,A), where V = S and A = {(i,j):i,j ∈ V ∧ i-j ∈ V}.For some classes of digraphs, e.g. alternating trees, oriented cycles, tournaments etc., it is known, under which conditions these digraphs are difference digraphs (cf. [5]). We generalize the so-called source-join (a construction principle to obtain a new difference digraph from two given ones (cf. [5])) and construct a difference labelling for the source-join of an even number of difference digraphs. As an application we obtain a sufficient condition guaranteeing that certain (non-alternating) trees are difference digraphs.
6
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Total edge irregularity strength of trees

70%
Ivančo J., Jendrol' S.
Discussiones Mathematicae Graph Theory
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2006
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tom 26
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nr 3
449-456
EN
A total edge-irregular k-labelling ξ:V(G)∪ E(G) → {1,2,...,k} of a graph G is a labelling of vertices and edges of G in such a way that for any different edges e and f their weights wt(e) and wt(f) are distinct. The weight wt(e) of an edge e = xy is the sum of the labels of vertices x and y and the label of the edge e. The minimum k for which a graph G has a total edge-irregular k-labelling is called the total edge irregularity strength of G, tes(G). In this paper we prove that for every tree T of maximum degree Δ on p vertices tes(T) = max{⎡(p+1)/3⎤,⎡(Δ+1)/2⎤}.
7
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On constant-weight TSP-tours

41%
Jones S., Kayll P., Mohar B., Wallis W.
Discussiones Mathematicae Graph Theory
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2003
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tom 23
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nr 2
287-307
EN
Is it possible to label the edges of Kₙ with distinct integer weights so that every Hamilton cycle has the same total weight? We give a local condition characterizing the labellings that witness this question's perhaps surprising affirmative answer. More generally, we address the question that arises when "Hamilton cycle" is replaced by "k-factor" for nonnegative integers k. Such edge-labellings are in correspondence with certain vertex-labellings, and the link allows us to determine (up to a constant factor) the growth rate of the maximum edge-label in a "most efficient" injective metric trivial-TSP labelling.
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