2. Articole
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Item MAXIMUM NONTRIVIAL CONVEX COVER NUMBER OF JOIN AND CORONA OF GRAPHS(2021) Buzatu, RaduLet G be a connected graph. We say that a set S ⊆ X(G) is convex in G if, for any two vertices x, y ∈ S, all vertices of every shortest path between x and y are in S. If 3 ≤ |S| ≤ |X(G)| − 1, then S is a nontrivial set. The greatest p ≥ 2 for which there is a cover of G by p nontrivial and convex sets is the maximum nontrivial convex cover number of G. In this paper, we determine the maximum nontrivial convex cover number of join and corona of graphs.Item MAXIMUM NONTRIVIAL CONVEX COVER NUMBER OF JOIN AND CORONA OF GRAPHS(Institutul de Matematică şi Informatică al AŞM, 2021) Buzatu, RaduLet G be a connected graph. We say that a set S ⊆ X(G) is convex in G if, for any two vertices x, y ∈ S, all vertices of every shortest path between x and y are in S. If 3 ≤ |S| ≤ |X(G)| − 1, then S is a nontrivial set. The greatest p ≥ 2 for which there is a cover of G by p nontrivial and convex sets is the maximum nontrivial convex cover number of G. In this paper, we determine the maximum nontrivial convex cover number of join and corona of graphsItem ON THE COMPUTATIONAL COMPLEXITY OF OPTIMIZATION CONVEX COVERING PROBLEMS OF GRAPHS(Institutul de Matematică şi Informatică al AŞM, 2020) Buzatu, RaduIn this paper we present further studies of convex covers and convex partitions of graphs. Let G be a finite simple graph. A set of vertices S of G is convex if all vertices lying on a shortest path between any pair of vertices of S are in S . If 3 ≤ | S | ≤ | X | − 1, then S is a nontrivial set. We prove that determining the minimum number of convex sets and the minimum number of nontrivial convex sets, which cover or partition a graph, is in general NP-hard. We also prove that it is NP-hard to determine the maximum number of nontrivial convex sets, which cover or partition a graph.