Now showing items 21-40 of 61

  • 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.
  • 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 ...
  • Génesis y evolución de la informática teórica 

    Díaz Cort, Josep (1984)
    External research report
    Open Access
  • (H,C,K)-colorings: fast, easy, and hard cases 

    Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2001-05)
    External research report
    Open Access
    We define a variant of the H-coloring problem by fixing the number of preimages of a subset C of the vertices of H, thus allowing parameterization. We provide sufficient conditions to guarantee that the problem can be ...
  • H-colorings of large degree graphs 

    Díaz Cort, Josep; Nesetril, Jaroslav; Serna Iglesias, María José; Thilikos, Dimitrios (2000-04)
    External research report
    Open Access
    We consider the H-coloring problem on graphs with vertices of large degree. We prove that for H an odd cycle, the problem belongs to P. We also study the phase transition of the problem, for an infinite family of ...
  • Heuristics for the MinLA problem: an empirical and theoretical analysis 

    Díaz Cort, Josep; Petit Silvestre, Jordi; Serna Iglesias, María José; Spirakis, Paul George (1998-07)
    External research report
    Open Access
    This paper considers the development and the analysis of Local Search heuristics to approximate the Minimum Linear Arrangement problem. First of all, we present a new heuristic that we call SS+SA based on the combination ...
  • Heuristics for the MinLA problem: some theoretical and empirical considerations 

    Díaz Cort, Josep; Petit Silvestre, Jordi; Spirakis, Paul George; Serna Iglesias, María José (1998-03)
    External research report
    Open Access
    This paper deals with some aspects on finding good solutions for the Minimum Linear Arrangement problem (MinLA). We consider some random type of sparse graphs, for which it is possible to obtain trivial constant ...
  • High level communication functionalities for wireless sensor networks 

    Álvarez Faura, M. del Carme; Díaz Cort, Josep; Petit Silvestre, Jordi; Rolim, José; Serna Iglesias, María José (2004-11)
    External research report
    Open Access
    In this work we propose a way to establish a reliable and efficient high level communication system in a randomly deployed network of sensors equipped with directional antennas. This high level communication system will ...
  • Intervalizing colored graphs is NP-complete for caterpilars with hair length 2 

    Álvarez Faura, M. del Carme; Díaz Cort, Josep; Serna Iglesias, María José (1998-02)
    External research report
    Open Access
    The problem of Intervalizing Colored Graphs has received a lot of attention due to their use as a model for DNA physical mapping with ambiguous data. If k is the number of colors, the problem is known to be NP-Complete ...
  • Linear and non-linear systems: a survey 

    Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (1997-12)
    External research report
    Open Access
    In this paper we present the research that has been done with Linear Dynamical Systems to generate almost uniformly elements from a given set, and thus approximate some hard counting problems. We also indicate how non-linear ...
  • Linear orderings of random geometric graphs (extended abstract) 

    Díaz Cort, Josep; Penrose, Matthew; Petit Silvestre, Jordi; Serna Iglesias, María José (1999-04)
    External research report
    Open Access
    In random geometric graphs, vertices are randomly distributed on [0,1]^2 and pairs of vertices are connected by edges whenever they are sufficiently close together. Layout problems seek a linear ordering of the vertices ...
  • Minimum bisection is NP-hard on unit disk graphs 

    Díaz Cort, Josep; Mertzios, George B. (2017-05-18)
    Article
    Open Access
    In this paper we prove that the Min-Bisection problem is NP-hard on unit disk graphs, thus solving a longstanding open question.
  • On RNC approximate counting 

    Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (1994-11)
    External research report
    Open Access
    In this work we look into the parallelization (in the NC sense) of the Markov Chain approach to almost random generation (as described by Sinclair (1993)). We prove that for several problems rapid mixing is