Now showing items 21-40 of 72

  • A Survey on graph layout problems 

    Díaz Cort, Josep; Petit Silvestre, Jordi; Serna Iglesias, María José (2000-10)
    External research report
    Open Access
    In this paper we survey results on several graph layout problems from an algorithmic point of view. Graph layout problems are a particular class of combinatorial optimization problems whose goal is to find a linear layout ...
  • Bisection of random cubic graphs 

    Díaz Cort, Josep; Do, Norman; Serna Iglesias, María José; Wormald, Nick (2002-05)
    External research report
    Open Access
    In this paper we present two randomized algorithms to compute the bisection width of random cubic graphs with n vertices, giving an asymptotic upper bound for the bisection width respectively of 0.174039n and 0.174501n. ...
  • Bounds on the bisection width for random d-regular graphs 

    Díaz Cort, Josep; Serna Iglesias, María José; Wormald, Nick (2004-04)
    External research report
    Open Access
    In this paper we provide an explicit way to compute asymptotically almost sure upper bounds on the bisection width of random d-regular graphs, for any value of d. The upper bounds are obtained from the analysis of the ...
  • Bounds on the max and min bisection of random cubic and 4-regular graphs 

    Díaz Cort, Josep; Do, Norman; Serna Iglesias, María José; Wormald, Nick (2002-12)
    External research report
    Open Access
    In this paper we present simple randomized algorithms to bisect cubic and 4-regular graphs. These algorithms produce bisections of size asymptotically at most 0.17404n for typical random cubic n-vertex graphs, and ...
  • Chromatic number in random scaled sector graphs 

    Díaz Cort, Josep; Sanwalani, Vishal; Serna Iglesias, María José; Spirakis, Paul George (2004-04)
    External research report
    Open Access
    In this paper, we introduce a new model of random graph that we call random sector graph. This model aims to provide a tool for studying communication problems in networks of sensors using laser communication such as ...
  • Communication tree problems 

    Álvarez Faura, M. del Carme; Cases Muñoz, Rafel; Díaz Cort, Josep; Petit Silvestre, Jordi; Serna Iglesias, María José (2001-03)
    External research report
    Open Access
    In this paper, we consider random communication requirements and several cost measures for a particular model of tree routing on a complete network. First we show that a random tree does not give any approximation. Then ...
  • Complejidad de problemas combinatorios 

    Díaz Cort, Josep (Universitat Politècnica de Barcelona. Centre de Càlcul, 1978-03)
    Article
    Open Access
    Un gran número de problemas entre los que se encuentran problemas tan conocidos como el del viajante de comercio, o el problema isoperimétrico, se muéstran como equivalentes en el sentido de que si uno de ellos admite una ...
  • Complexity issues on bounded restrictive H-coloring 

    Serna Iglesias, María José; Díaz Cort, Josep; Thilikos Touloupas, Dimitrios (2004-04)
    External research report
    Open Access
    We consider the restriction of the H-coloring problem where we are looking for homomorphisms were the number of preimages of certain vertices of H is bounded by some fixed constant. We consider the decision and the ...
  • Complexity of metric dimension on planar graphs 

    Díaz Cort, Josep; Pottonen, Ollie; Serna Iglesias, María José; van Leeuwen, Erik Jan (2017-04-03)
    Article
    Open Access
    The metric dimension of a graph G is the size of a smallest subset L ¿ V (G) such that for any x, y ¿ V (G) with x =/ y there is a z ¿ L such that the graph distance between x and z differs from the graph distance between ...
  • Computation of bisection width for random d-regular graphs 

    Díaz Cort, Josep; Serna Iglesias, María José; Wormald, Nick (2003-07)
    External research report
    Open Access
    In this paper we describe a randomized greedy algorithm for obtaining bisections of graphs. Analysis of the algorithm's performance on random d-regular graphs yields asymptotically almost sure upper bounds on the bisection ...
  • Continuous monitoring in the dynamic sensor field model 

    Álvarez Faura, M. del Carme; Díaz Cort, Josep; Dieter Wilhelm, Mitsche; Serna Iglesias, María José (2011-05)
    External research report
    Open Access
    In this work we consider the problem of continuously monitoring a collection of data sets produced by sensors placed on moving or static targets. We propose a modification of the static sensor field model (SSSF) [2] to ...
  • Convergence theorems for some layout measures on random lattice and random geometric graphs 

    Díaz Cort, Josep; Penrose, Matthew; Petit Silvestre, Jordi; Serna Iglesias, María José (1999-04)
    External research report
    Open Access
    This work deals with convergence theorems and bounds on the cost of several layout measures for lattice graphs, random lattice graphs and sparse random geometric graphs. For full square lattices, we give optimal layouts ...
  • Counting H-colorings of partial k-trees 

    Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2000-11)
    External research report
    Open Access
    The problem of counting all H-colorings of a graph G of n vertices is considered. While the problem is, in general #P-complete, we give linear time algorithms that solve the main variants of this problem when the input ...
  • Counting list h-colorings and variants 

    Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2001-05)
    External research report
    Open Access
    We study the counting versions of several variants of the H-coloring problem. The complexity of the H-coloring problem is described by a dichotomy theorem that classifies the problem according to the the topology of H ...
  • Efficient algorithms for parameterized H-colorings 

    Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2005-12)
    External research report
    Open Access
    We study the fixed parameter tractability of the restrictive $H$-coloring and the restrictive list $H$-coloring problems, introduced in~cite{DST01b}. The parameterizations are defined by fixing the number of pre-images of ...
  • El problema de l’ordenació no linial òptima és np-complet 

    Díaz Cort, Josep (Universitat Politècnica de Barcelona. Centre de Càlcul, 1978-12)
    Article
    Open Access
    L'article descriu la reducció del Problema de Tall màxim Simple al Problema de l'Ordenació no Lineal Òptima, la qual cosa implica la pertinença d'aquest últim a la classe NP-Complet.
  • ESQUEMES ALGORÍSMICS (Examen 1r quadrim.) 

    Díaz Cort, Josep (Universitat Politècnica de Catalunya, 1999-01-08)
    Exam
    Restricted access to the UPC academic community
  • ESQUEMES ALGORÍSMICS (Examen 2n quadrim.) 

    Díaz Cort, Josep (Universitat Politècnica de Catalunya, 2001-06-30)
    Exam
    Restricted access to the UPC academic community
  • Examples of CF-bi-inmune and CF-levelable sets in LOGSPACE 

    Balcázar Navarro, José Luis; Díaz Cort, Josep; Gabarró Vallès, Joaquim (1984)
    External research report
    Open Access
    We find sets in the class LOGSPACE (on-line) that do not have good respectively approximations by context-free languages. For that we introduce the languages CF-bi-inmune and CF-levelable. We prove the results by defining ...
  • Faulty random geometric networks 

    Díaz Cort, Josep; Petit Silvestre, Jordi; Serna Iglesias, María José (2000-10)
    External research report
    Open Access
    In this paper we analyze the computational power of random geometric networks in the presence of random (edge or node) faults considering several important network parameters. We first analyze how to emulate an original ...