Relating the annihilation number and the total domination number of a tree

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Abstract

A set S of vertices in a graph G is a total dominating set if every vertex of G is adjacent to some vertex in S. The total domination number γt(G) is the minimum cardinality of a total dominating set in G. The annihilation number a(G) is the largest integer k such that the sum of the first k terms of the non-decreasing degree sequence of G is at most the number of edges in G. In this paper, we investigate relationships between the annihilation number and the total domination number of a graph. Let T be a tree of order n2. We show that γt(T)a(T)+1, and we characterize the extremal trees achieving equality in this bound.

Keywords

Total domination
Total domination number
Annihilation number

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