Browsing by Author "Spirakis, Paul George"

Now showing items 1-10 of 10

    • Approximating the permanent is in RNC 

      Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (1995-04)
      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 give a RNC almost uniform generator for perfect matchings in ...

    • Chromatic number in random scaled sector graphs 

      Díaz Cort, Josep; Sanwalani, Vishal; Serna Iglesias, María José; Spirakis, Paul George (2004-04)
      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 ...

    • Efficient parallel algorithms for some tree layout problems 

      Díaz Cort, Josep; Gibbons, Alan M.; Pantziou, Grammati; Serna Iglesias, María José; Spirakis, Paul George; Torán Romero, Jacobo (1992)
      Research report
      Open Access
      The minimum cut and minimum sum linear arrangement problems usually occur in solving wiring problems and have a lot in common with job sequencing questions. Both problems are NP-complete for general graphs and P for trees. ...

    • 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)
      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)
      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 ...

    • Linear and non-linear systems: a survey 

      Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (1997-12)
      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 ...

    • On RNC approximate counting 

      Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (1994-11)
      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

    • On the expected depth of boolean circuits 

      Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George; Torán Romero, Jacobo (1994-02)
      Research report
      Open Access
      In this paper we analyze the expected depth of a circuit randomly generated from a uniform model. We show that the expected depth of such circuits is polylogarithmic in the number of gates. This result allows us to place ...

    • Sampling matchings in parallel 

      Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (1998-03)
      Research report
      Open Access
      We present a parallel algorithm to sample matchings from an almost uniform distribution on the set of matchings of all sizes in a graph. The technique used is based on the definition of a genetic system that converges ...

    • Some remarks on the approximability of graph layout problems 

      Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (1994-03)
      Research report
      Open Access
      In this paper we look at several well known layout problems. We show that MINCUT layout and Topological bandwidth cannot be approximated unless P=NP, whereas the Maximum linear arrangement problem can be approximated within ...