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On signed arc total domination in digraphs

Asgharsharghi L., Khodkar A., Sheikholeslami S. M.

Opuscula Mathematica

2018

Vol. 38, no. 6

779--794

Let D = (V, A) be a finite simple digraph and N(uv) = {u'v' ≠ uv | u = u' or v = v'} be the open neighbourhood of uv in D. A function ƒ : A → { — 1, +1} is said to be a signed arc total dominating function (SATDF) of D if [formula] holds for every arc uv ∈ A. The signed arc total domination number [formula] is defined as [formula]. In this paper we initiate the study of the signed arc total domination in digraphs and present some lower bounds for this parameter.

Trees whose 2-domination subdivision number is 2

Atapour M., Sheikholeslami S. M., Khodkar A.

Opuscula Mathematica

2012

Vol. 32, no. 3

423-437

A set S of vertices in a graph G = (V,E) is a 2-dominating set if every vertex of V \ S is adjacent to at least two vertices of S. The 2-domination number of a graph G, denoted by γ2(G), is the minimum size of a 2-dominating set of G. The 2-domination subdivision number sdγ2 (G) is the minimum number of edges that must be subdivided (each edge in G can be subdivided at most once) in order to increase the 2-domination number. The authors have recently proved that for any tree T of order at least 3, 1 ≤ sdγ2 (T ) ≤ 2. In this paper we provide a constructive characterization of the trees whose 2-domination subdivision number is 2.