This edition of IWONT is dedicated to Professor Miquel Àngel Fiol on the occasion of his 60th birthday

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  • Proceedings of the 3rd International Workshop on Optimal Networks Topologies IWONT 2010 

    Brunat Blay, Josep M.; Fàbrega, Josep (Fàbrega Canudas); Širáň, Josef (2011-02)
    Comunicació de congrés
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  • The beginnings 

    Yebra, J. L. A. (2011)
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    The simple title tells many things. Of course, it could tell almost nothing since a well-known motto says that ‘everything must have a beginning’. However, another motto is more appropriate here: ‘A journey of a thousand ...
  • Infinite families of 3-numerical semigroups with arithmetic-like links 

    Aguiló-Gost, Francesc (2011)
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    Let S = a, b,N be a numerical semigroup generated by a, b,N ∈ N with 1 < a < b < N and gcd(a, b,N) = 1. The conductor of S, denoted by c(S) or c(a, b,N), is the minimum element of S such that c(S) + m ∈ S for all m ∈ N ...
  • On identifying codes in partial linear spaces 

    Araujo-Pardo, Gabriela; Montejano, Luis; Camino, Balbuena; Valenzuela, Juan Carlos (2011)
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    Let (P,L, I) be a partial linear space and X ⊆ P ∪ L. Let us denote by (X)I = x∈X{y : yIx} and by [X] = (X)I ∪ X. With this terminology a partial linear space (P,L, I) is said to admit a (1,≤ k)-identifying code if the ...
  • Subdivisions in a bipartite graph 

    Balbuena Martínez, Maria Camino Teófila; Cera, Martín; García-Vázquez, Pedro; Valenzuela, Juan Carlos (2011)
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    Given a bipartite graph G with m and n vertices, respectively,in its vertices classes, and given two integers s, t such that 2 ≤ s ≤ t, 0 ≤ m−s ≤ n−t, and m+n ≤ 2s+t−1, we prove that if G has at least mn−(2(m−s)+n−t) edges ...
  • On the λ'-optimality of s-geodetic digraphs 

    Balbuena Martínez, Maria Camino Teófila; García-Vázquez, Pedro (2011)
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    For a strongly connected digraph D the restricted arc-connectivity λ'(D) is defined as the minimum cardinality of an arc-cut over all arc-cuts S satisfying that D − S has a non trivial strong component D1 such that D − V ...
  • On the connectivity and restricted edge-connectivity of 3-arc graphs 

    Balbuena Martínez, Maria Camino Teófila; García-Vázquez, Pedro (2011)
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    A 3−arc of a graph G is a 4-tuple (y, a, b, x) of vertices such that both (y, a, b) and (a, b, x) are paths of length two in G. Let ←→G denote the symmetric digraph of a graph G. The 3-arc graph X(G) of a given graph G is ...
  • Edge-superconnectivity of semiregular cages with odd girth 

    Balbuena Martínez, Maria Camino Teófila; Salas, Julián; González-Moreno, Diego (2011)
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    A graph is said to be edge-superconnected if each minimum edge-cut consists of all the edges incident with some vertex of minimum degree. A graph G is said to be a {d, d + 1}- semiregular graph if all its vertices have ...
  • M-Matrix Inverse problem for distance-regular graphs 

    Bendito Pérez, Enrique; Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos; Mitjana Riera, Margarida (2011)
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    We analyze when the Moore–Penrose inverse of the combinatorial Laplacian of a distance–regular graph is a M–matrix;that is, it has non–positive off–diagonal elements or, equivalently when the Moore-Penrose inverse of the ...
  • Graphs with equal domination and 2-domination numbers 

    Hansberg, Adriana (2011)
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    For a graph G a subset D of the vertex set of G is a k-dominating set if every vertex not in D has at least k neighbors in D. The k-domination number γk(G) is the minimum cardinality among the k-dominating sets of G. Note ...
  • Spectral behavior of some graph and digraph compositions 

    Boulet, Romain (2011)
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    Let G be a graph of order n the vertices of which are labeled from 1 to n and let $G_1$, · · · ,$G_n$ be n graphs. The graph composition G[$G_1$, · · · ,$G_n$] is the graph obtained by replacing the vertex i of G by the ...
  • On the existence of combinatorial configurations 

    Bras Amorós, Maria; Stokes, Klara (2011)
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    A (v, b, r, k) combinatorial configuration can be defined as a connected, (r, k)-biregular bipartite graph with v vertices on one side and b vertices on the other and with no cycle of length 4. Combinatorial configurations ...
  • Symmetric L-graphs 

    Camarero, Cristóbal; Martínez, Carmen; Beivide Palacio, Julio Ramón (2011)
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    In this paper we characterize symmetric L-graphs, which are either Kronecker products of two cycles or Gaussian graphs. Vertex symmetric networks have the property that the communication load is uniformly distributed on ...
  • On the vulnerability of some families of graphs 

    Moreno Casablanca, Rocío; Díanez, Ana R.; García-Vázquez, Pedro (2011)
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    The toughness of a noncomplete graph G is defined as τ (G) = min{|S|/ω(G − S)}, where the minimum is taken over all cutsets S of vertices of G and ω(G − S) denotes the number of components of the resultant graph G − S by ...
  • On the diameter of random planar graphs 

    Chapuy, Guillaume; Fraser, Simon; Fusy, Eric; Giménez, Omer; Noy Serrano, Marc (2011)
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    We show that the diameter D(Gn) of a random labelled connected planar graph with n vertices is asymptotically almost surely of order $n^{1/4}$, in the sense that there exists a constant c > 0 such that $P(D(G_n) \in{} ...
  • Radially Moore graphs of radius three and large odd degree 

    López, Nacho; Gómez Martí, José (2011)
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    Extremal graphs which are close related to Moore graphs have been defined in different ways. Radially Moore graphs are one of these examples of extremal graphs. Although it is proved that radially Moore graphs exist for ...
  • Application layer multicast algorithm 

    Machado Sánchez, Sergio; Ozón Górriz, Francisco Javier (2011)
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    This paper presents a multicast algorithm, called MSM-s, for point-to-multipoint transmissions. The algorithm, which has complexity O(n2) in respect of the number n of nodes, is easy to implement and can actually be applied ...
  • On the k-restricted edge-connectivity of matched sum graphs 

    Marcote Ordax, Francisco Javier (2011)
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    A matched sum graph $G_1$M$G_2$ of two graphs $G_1$ and $G_2$ of the same order n is obtained by adding to the union (or sum) of $G_1$ and $G_2$ a set M of n independent edges which join vertices in V ($G_1$) to vertices ...
  • An overview of the degree/diameter problem for directed, undirected and mixed graphs 

    Miller, Mirka (2011)
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    A well-known fundamental problem in extremal graph theory is the degree/diameter problem, which is to determine the largest (in terms of the number of vertices) graphs or digraphs or mixed graphs of given maximum degree, ...
  • Large graphs of diameter two and given degree 

    Širáň, Jozef; Siagiová, Jana; Ždímalová, Mária (2011)
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    Let r(d, 2), C(d, 2), and AC(d, 2) be the largest order of a regular graph, a Cayley graph, and a Cayley graph of an Abelian group, respectively, of diameter 2 and degree d. The best currently known lower bounds on these ...
  • Fiedler’s Clustering on m-dimensional Lattice Graphs 

    Trajanovski, Stojan; Mieghem, Piet Van (2011)
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    We consider the partitioning of m-dimensional lattice graphs using Fiedler’s approach [1], that requires the determination of the eigenvector belonging to the second smallest eigenvalue of the Laplacian. We examine the ...
  • Large digraphs of given diameter and degree from coverings 

    Ždímalová, Mária; Staneková, Lubica (2011)
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    We show that a construction of Comellas and Fiol for large vertex-transitive digraphs of given degree and diameter from small digraphs preserves the properties of being a Cayley digraph and being a regular covering.
  • Dual concepts of almost distance-regularity and the spectral excess theorem 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest; Dam, Edwin R. van (2011)
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    Generally speaking, ‘almost distance-regular’ graphs are graphs that share some, but not necessarily all, regularity properties that characterize distance-regular graphs. In this paper we first propose two dual concepts ...
  • Large Edge-non-vulnerable Graphs 

    Delorme, Charles (2011)
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    In this paper we study the graphs such that the deletion of any edge does not increase the diameter. We give some upper bounds for the order of such a graph with given maximum degree and diameter. On the other hand ...
  • A mathematical model for dynamic memory networks 

    Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Serra Albó, Oriol; Andrés Yebra, José Luis (2011)
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    The aim of this paper is to bring together the work done several years ago by M.A. Fiol and the other authors to formulate a quite general mathematical model for a kind of permutation networks known as dynamic memories. A ...
  • Algebraic characterizations of bipartite distance-regular graphs 

    Fiol Mora, Miquel Àngel (2011)
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    Bipartite graphs are combinatorial objects bearing some interesting symmetries. Thus, their spectra—eigenvalues of its adjacency matrix—are symmetric about zero, as the corresponding eigenvectors come into pairs. Moreover, ...
  • Topology of Cayley graphs applied to inverse additive problems 

    Hamidoune, Yahya Ould (2011)
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    We present the basic isopermetric structure theory, obtaining some new simplified proofs. Let 1 ≤ r ≤ k be integers. As an application, we obtain simple descriptions for the subsets S of an abelian group with |kS| ≤ ...