Now showing items 1-20 of 23

  • A new approach to the spectral excess theorem for distance-regular graphs 

    Fiol Mora, Miquel Àngel; Gago Álvarez, Silvia; Garriga Valle, Ernest (2009-04-01)
    Article
    Open Access
    The Spectral Excess Theorem provides a quasi-spectral characterization for a (regular) graph $\Gamma$ with $d+1$ different eigenvalues to be distance-regular graph, in terms of the mean (d-1)-excess of its vertices.\ The ...
  • A simple proof of the spectral excess theorem for distance-regular graphs 

    Fiol Mora, Miquel Àngel; Gago Álvarez, Silvia; Garriga Valle, Ernest (Elsevier, 2010-04-15)
    Article
    Restricted access - publisher's policy
    The spectral excess theorem provides a quasi-spectral characterization for a (regular) graph Γ with d+1 distinct eigenvalues to be distance-regular graph, in terms of the excess (number of vertices at distance d) of each ...
  • Betweenness Centrality in Graphs 

    Gago Álvarez, Silvia; Coronicová Hurajová, Jana; Madaras, Tomas (CRC Press Taylor & Francis Group, 2014-10-27)
    Part of book or chapter of book
    Restricted access - publisher's policy
    The first book devoted exclusively to quantitative graph theory, Quantitative Graph Theory: Mathematical Foundations and Applications presents and demonstrates existing and novel methods for analyzing graphs quantitatively. ...
  • Betweenness-selfcentric graphs 

    Gago Álvarez, Silvia; Hurajová, Jana; Madaras, Tomas (2012-04-11)
    External research report
    Open Access
    The betweenness centrality of a vertex of a graph is the portion of shortest paths between all pairs of vertices passing through that vertex. In this paper, we study properties and constructions of graphs whose vertices ...
  • Boundary value problems for Schrödinger operators on a path 

    Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos; Gago Álvarez, Silvia (2012-05-25)
    External research report
    Open Access
    In this work, we concentrate on determining explicit expressions, via suitable orthogonal polynomials on the line, for the Green function associated with any regular boundary value problem on a weighted path, whose weights ...
  • Boundary value problems for Schrödinger operators on a Path Associated to Orthogonal Polynomials 

    Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos; Gago Álvarez, Silvia (Springer, 2013)
    Part of book or chapter of book
    Restricted access - publisher's policy
    In this work, we concentrate on determining explicit expressions, via suitable orthogonal polynomials on the line, for the Green function associated with any regular boundary value problem on a weighted path, whose weights ...
  • Bounded expansion in models of webgraphs 

    Gago Álvarez, Silvia; Schlatter, Dirk (2007-10-02)
    Article
    Open Access
    We study the bounded expansion of several models of web graphs. We show that various deterministic graph models for large complex networks have constant bounded expansion.We study two random models of webgraphs, showing ...
  • Design of highly synchronizable and robust networks 

    Estrada Roger, Ernesto; Gago Álvarez, Silvia; Caporossi, Gilles (2010-11)
    Article
    Restricted access - publisher's policy
    In this paper, the design of highly synchronizable, sparse and robust dynamical networks is addressed. Better synchronizability means faster synchronization of the oscillators, sparsity means a low ratio of links per ...
  • Eigenvalue distribution in scale free graphs 

    Gago Álvarez, Silvia (2007-08-16)
    Article
    Open Access
    Scale free graphs can be found very often as models of real networks and are characterized by a power law degree distribution, that is, for a constant $\gamma\geq 1$ the number of vertices of degree $d$ is proportional ...
  • Green matrices of weighted graphs with pendant vertices 

    Gago Álvarez, Silvia (2014)
    Lecture
    Open Access
  • Green operators of networks with a new vertex 

    Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos; Gago Álvarez, Silvia; Mitjana Riera, Margarida (Elsevier, 2016-02)
    Article
    Open Access
    Any elliptic operator defines an automorphism on the orthogonal subspace to the eigenfunctions associated with the lowest eigenvalue, whose inverse is the orthogonal Green operator. In this study, we show that elliptic ...
  • Green's function of a weighted $n$-cycle 

    Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos; Gago Álvarez, Silvia; Jiménez Jiménez, María José; Mitjana Riera, Margarida (2016)
    Conference report
    Open Access
  • Group inverse of the laplacian of connections of networks 

    Gago Álvarez, Silvia (2018-03-25)
    External research report
    Restricted access - publisher's policy
    In previous works the group inverse of a network obtained by some perturbations, as the deletion of a vertex, the addition of a new vertex, contraction of an edge, etc. is obtained in terms of the group inverse of the ...
  • Jacobi matrices and boundary value problems in distance-regular graphs 

    Bendito Pérez, Enrique; Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos; Gago Álvarez, Silvia (2012-01-25)
    External research report
    Open Access
    In this work we analyze regular boundary value problems on a distance-regular graph associated with SchrÄodinger operators. These problems include the cases in which the boundary has two or one vertices. Moreover, we obtain ...
  • Kirchhoff index of a non-complete wheel 

    Gago Álvarez, Silvia (2016)
    Article
    Open Access
    In this work, we compute analitycally the Kirchhoff index and effective resistances of a weighted non–complete wheel that has been obtained by adding a vertex to a weighted cycle and some edges conveniently chosen. To this ...
  • Matriz Laplaciana de grafos ponderados con vértices independientes 

    Gago Álvarez, Silvia (Editorial Universidad de Almería, 2015)
    Conference report
    Open Access
  • Notes on betweenness centrality of a graph 

    Gago Álvarez, Silvia; Hurajová, Jana; Madaras, Tomas (2009-05-19)
    External research report
    Open Access
    The betweenness centrality of a vertex of a graph is the portion of shortest paths between all pairs of vertices passing through that vertex. We study selected general properties of this invariant and its relations to ...
  • On decay centrality in graphs 

    Coronicová Hurajová, Jana; Gago Álvarez, Silvia; Madaras, Tomas (2018-08-06)
    Article
    Open Access
    The decay centrality of a vertex v in a graph G with respect to a parameter d¿(0,1) is a polynomial in d such that for fixed k the coefficient of dk is equal to the number of vertices of G at distance k from v. This invariant ...
  • On golden spectral graphs 

    Estrada Roger, Ernesto; Gago Álvarez, Silvia (2009-03-26)
    External research report
    Open Access
    The concept of golden spectral graphs is introduced and some of their general properties reported. Golden spectral graphs are those having a golden proportion for the spectral ratios defined on the basis of the spectral ...
  • The betweenness centrality of a graph 

    Gago Álvarez, Silvia (2007-05-10)
    Article
    Open Access
    A measure of the centrality of a vertex of a graph is the portion of shortest paths crossing through it between other vertices of the graph. This is called betweenness centrality and here we study some of its general ...