Safe sets, network majority on weighted trees

Let G=(V,E) be a graph and let w:V→ℝ>0 be a positive weight function on the vertices of G. For every subset X of V, let w(X):=∑v∈Gw(v). A non‐empty subset S⊆V(G) is a weighted safe set if, for every component C of the subgraph induced by S and every component D of G∖S, we have w(C)≥w(D) whenever...

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Bibliographic Details
Published in:Networks Vol. 71; no. 1; pp. 81 - 92
Main Authors: Bapat, Ravindra B., Fujita, Shinya, Legay, Sylvain, Manoussakis, Yannis, Matsui, Yasuko, Sakuma, Tadashi, Tuza, Zsolt
Format: Journal Article
Language:English
Published: New York Wiley Subscription Services, Inc 01.01.2018
Wiley
Subjects:
approximation algorithm
centroid
Computer Science
Data Structures and Algorithms
Minimum weight
network majority
NP‐completeness
safe set
Set theory
Trees
Trees (mathematics)
weighted tree
Weighting functions
ISSN:0028-3045, 1097-0037
Online Access:Get full text
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Summary:Let G=(V,E) be a graph and let w:V→ℝ>0 be a positive weight function on the vertices of G. For every subset X of V, let w(X):=∑v∈Gw(v). A non‐empty subset S⊆V(G) is a weighted safe set if, for every component C of the subgraph induced by S and every component D of G∖S, we have w(C)≥w(D) whenever there is an edge between C and D. If the subgraph G[S] induced by a weighted safe set S is connected, then the set S is called a weighted connected safe set. In this article, we show that the problem of computing the minimum weight of a safe set is NP‐hard for trees, even if the underlying tree is restricted to be a star, but it is polynomially solvable for paths. We also give an O(nlog⁡n) time 2‐approximation algorithm for finding a weighted connected safe set with minimum weight in a weighted tree. Then, as a generalization of the concept of a minimum safe set, we define the concept of a parameterized infinite family of proper central subgraphs on weighted trees, whose polar ends are the vertex set of the tree and the centroid points. We show that each of these central subgraphs includes a centroid point.
Bibliography:.
An extended abstract of this paper appears in the proceedings of the 10th edition of the Jornadas de Matematica Discreta y Algoritmica (10th JMDA)
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ISSN:0028-3045
1097-0037
DOI:10.1002/net.21794