32 research outputs found

    Metric dimension of directed graphs

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    A metric basis for a digraph G(V, A) is a set WβŠ‚V such that for each pair of vertices u and v of V, there is a vertex w∈W such that the length of a shortest directed path from w to u is different from the length of a shortest directed path from w to v in G; that is d(w, u)β‰ d(w, v). A minimum metric basis is a metric basis of minimum cardinality. The cardinality of a minimum metric basis of G is called the metric dimension and is denoted by Ξ² (G). In this paper, we prove that the metric dimension problem is NP-complete for directed graphs by a reduction from 3-SAT. The technique adopted is due to Khuller et al. [Landmarks in graphs, Discrete Appl. Math. 70(3) (1996), pp. 217–229]. We also solve the metric dimension problem for De Bruijn and Kautz graphs in polynomial time

    Rupture Degree Of Interconnection Networks

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    A well-designed interconnection network makes efficient use of scarce communication resources and is used in systems ranging from large supercomputers to small embedded systems on a chip. This paper deals with certain measures of vulnerability in interconnection networks. Let G be a non-complete connected graph and for S βŠ† V(G), let Ο‰(G – S) and m(G – S) denote the number of components and the order of the largest component in G – S respectively. The Vertex-Integrity of G is defined as I(G) = min {β”‚S β”‚ + m(G – S) : S βŠ† V(G)}. A set S βŠ† V(G) is called an I-set of G if I(G) = β”‚Sβ”‚+ m(G – S). The rupture degree of G is defined by r(G) = max {Ο‰ ( G – S) – β”‚S β”‚ – m(G – S) : S βŠ‚ V(G), Ο‰ ( G – S) β‰₯ 2}. A set S βŠ‚ V(G) is called an R-set of G if r(G) = Ο‰ ( G – S) – β”‚Sβ”‚ – m(G – S). In this paper, we compute the rupture degree of split graphs, regular caterpillars and a class of meshes. We also study the relationship between an I-set and an R-set and also find an upper bound for the rupture degree of Hamiltonian graphs and a lower bound for the rupture degree of a complete binary tree

    On Induced Matching Partitions of Certain Interconnection Networks

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    Abstract – The induced matching partition number of a graph G, denoted by imp(G), is the minimum integer k such that V(G) has a k-partition (V1, V2 … Vk) such that, for each i, 1 ≀ i ≀ k, G[Vi], the subgraph of G induced by Vi, is a 1-regular graph. The induced matching k-partition problem is NP-complete even for k = 2. In this paper we investigate the induced matching partition problem for butterfly networks. We identify hypercubes, cube-connected cycles, grids of order m x n, where at least one of m and n is even, as graphs for which imp(G) = 2. In the sequel we prove that imp(G) does not exist for grids of order m x n where m and n are both odd and Mesh of trees MT(n), n β‰₯ 2

    Minimum Tree Spanner Problem for Butterfly and Benes Networks

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    The minimum tree spanner problem requires selecting a spanning tree of a fixed interconnection network that minimizes the cost of transmission between each pair of processors over the tree edges. In [8] we developed a technique to solve this problem for all parallel architectures including hypercube, CCC, wrapped butterfly, torus, star graphs which are classified under Cayley graphs. We introduced a new class of graphs called Diametrically Uniform Graphs and we provided a simple, efficient parallel algorithm to decide whether or not a parallel architecture is diametrically uniform. In this paper we consider the class of Butterfly and Benes networks, which are diametrically uniform and we solve the minimum tree spanner problem for this class
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