Ara es mostren els items 1-20 de 27

  • A differential approach for bounding the index of graphs under perturbations 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2011-03)
    Report de recerca
    Accés obert
  • A differential approach for bounding the index of graphs under perturbations 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2011-09-02)
    Article
    Accés obert
    This paper presents bounds for the variation of the spectral radius (G) of a graph G after some perturbations or local vertex/edge modifications of G. The perturbations considered here are the connection of a new vertex ...
  • 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
    Accés obert
    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
    Accés restringit per política de l'editorial
    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 ...
  • Aprenentatge de càlcul 

    Aguiló Gost, Francisco de Asis L.; Barguilla Navarrete, Jorge; Garriga Valle, Ernest; Miralles de la Asunción, Alicia (Edicions UPC, 2002)
    Llibre
    Accés restringit a la comunitat UPC
    Conté: 1. Successions, continuïtat i derivació. 2. Integració i sèries.
  • Characterizing (l,m)-walk-regularity 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2009-05)
    Article
    Accés obert
    A graph $\G$ with diameter $D$ and $d+1$ distinct eigenvalues is said to be {\it $(\ell,m)$-walk-regular}, for some integers $\ell\in[0,d]$ and $m\in[0,D]$, $\ell\ge m$, if the number of walks of length $i\in [0,\ell]$ ...
  • Combinatorial vs. algebraic characterizations of pseudo-distance-regularity around a set 

    Cámara Vallejo, Marc; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2009-06)
    Report de recerca
    Accés obert
    Given a simple connected graph $\Gamma$ and a subset of its vertices $C$, the pseudo-distance-regularity around $C$ generalizes, for not necessarily regular graphs, the notion of completely regular code. Up to now, most ...
  • Contribució a la teoria espectral de grafs problemes mètrics i distància-regularitat 

    Garriga Valle, Ernest (Universitat Politècnica de Catalunya, 1997-12-12)
    Tesi
    Accés obert
  • 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 (Iniciativa Digital Politècnica, 2011)
    Text en actes de congrés
    Accés obert
    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 ...
  • Edge distance-regular graphs 

    Cámara Vallejo, Marc; Dalfó Simó, Cristina; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2011)
    Article
    Accés obert
    Edge-distance-regularity is a concept recently introduced by the authors which is similar to that of distance-regularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ...
  • Edge-distance-regular graphs 

    Cámara Vallejo, Marc; Dalfó Simó, Cristina; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2011-03-11)
    Report de recerca
    Accés obert
    Edge-distance-regularity is a concept recently introduced by the authors which is similar to that of distance-regularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ...
  • Edge-distance-regular graphs 

    Cámara Vallejo, Marc; Dalfó Simó, Cristina; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2011)
    Article
    Accés restringit per política de l'editorial
    Edge-distance-regularity is a concept recently introduced by the authors which is similar to that of distance-regularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ...
  • Moments in graphs 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2013)
    Article
    Accés obert
    Let G be a connected graph with vertex set V and a weight function that assigns a nonnegative number to each of its vertices. Then, the -moment of G at vertex u is de ned to be M G(u) = P v2V (v) dist(u; v), where ...
  • Number of walks and degree powers in a graph 

    Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2006-04)
    Article
    Accés obert
    This letter deals with the relationship between the total number of k-walks in a graph, and the sum of the k-th powers of its vertex degrees. In particular, it is shown that the sum of all k-walks is upper bounded by the ...
  • On Almost Distance-Regular Graphs 

    Dalfó Simó, Cristina; Van Dam, Edwin; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest; Gorissen, Bram (2010-03-12)
    Report de recerca
    Accés obert
  • On almost distance-regular graphs 

    Dalfó Simó, Cristina; Van Dam, Edwin; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest; Gorissen, Bram (2010)
    Article
    Accés restringit per política de l'editorial
    Distance-regular graphs are a key concept in Algebraic Combinatorics and have given rise to several generalizations, such as association schemes. Motivated by spectral and other algebraic characterizations of distance-regular ...
  • On k-Walk-Regular Graphs 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2008-08)
    Article
    Accés obert
    Considering a connected graph $G$ with diameter $D$, we say that it is \emph{$k$-walk-regular}, for a given integer $k$ $(0\leq k \leq D)$, if the number of walks of length $\ell$ between vertices $u$ and $v$ only depends ...
  • On t-cliques in k-walk-regular graphs 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (Université de Bourdeaux, 2009)
    Text en actes de congrés
    Accés obert
  • On t-cliques in k-walk-regular graphs 

    Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2009-08)
    Article
    Accés restringit per política de l'editorial
    A graph is walk-regular if the number of cycles of length rooted at a given vertex is a constant through all the vertices. For a walk-regular graph G with d+1 different eigenvalues and spectrally maximum diameter D = ...
  • On the algebraic theory of pseudo-distance-regulariry around a set 

    Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (Elsevier, 1999-09)
    Article
    Accés restringit per política de l'editorial
    Let C be a connected graph with vertex set V, adjacency matrix A, positive eigenvector and corresponding eigenvalue 0. A natural generalization of distance-regularity around a vertex subset C V , which makes sense ...