Browsing by Author "Díaz Cort, Josep"

Computation of bisection width for random dregular graphs
Díaz Cort, Josep; Serna Iglesias, María José; Wormald, Nick (200307)
External research report
Open AccessIn this paper we describe a randomized greedy algorithm for obtaining bisections of graphs. Analysis of the algorithm's performance on random dregular 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 (201105)
External research report
Open AccessIn 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 (199904)
External research report
Open AccessThis 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 Hcolorings of partial ktrees
Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (200011)
External research report
Open AccessThe problem of counting all Hcolorings of a graph G of n vertices is considered. While the problem is, in general #Pcomplete, we give linear time algorithms that solve the main variants of this problem when the input ... 
Counting list hcolorings and variants
Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (200105)
External research report
Open AccessWe study the counting versions of several variants of the Hcoloring problem. The complexity of the Hcoloring problem is described by a dichotomy theorem that classifies the problem according to the the topology of H ... 
Efficient algorithms for parameterized Hcolorings
Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (200512)
External research report
Open AccessWe 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 preimages of ... 
El problema de l’ordenació no linial òptima és npcomplet
Díaz Cort, Josep (Universitat Politècnica de Barcelona. Centre de Càlcul, 197812)
Article
Open AccessL'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 NPComplet. 
Examples of CFbiinmune and CFlevelable sets in LOGSPACE
Balcázar Navarro, José Luis; Díaz Cort, Josep; Gabarró Vallès, Joaquim (1984)
External research report
Open AccessWe find sets in the class LOGSPACE (online) that do not have good respectively approximations by contextfree languages. For that we introduce the languages CFbiinmune and CFlevelable. We prove the results by defining ... 
Faulty random geometric networks
Díaz Cort, Josep; Petit Silvestre, Jordi; Serna Iglesias, María José (200010)
External research report
Open AccessIn 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 (200105)
External research report
Open AccessWe define a variant of the Hcoloring 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 ... 
Hcolorings of large degree graphs
Díaz Cort, Josep; Nesetril, Jaroslav; Serna Iglesias, María José; Thilikos, Dimitrios (200004)
External research report
Open AccessWe consider the Hcoloring 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 (199807)
External research report
Open AccessThis 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 (199803)
External research report
Open AccessThis 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 (200411)
External research report
Open AccessIn 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 NPcomplete for caterpilars with hair length 2
Álvarez Faura, M. del Carme; Díaz Cort, Josep; Serna Iglesias, María José (199802)
External research report
Open AccessThe 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 NPComplete ... 
Linear and nonlinear systems: a survey
Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (199712)
External research report
Open AccessIn 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 nonlinear ... 
Linear orderings of random geometric graphs (extended abstract)
Díaz Cort, Josep; Penrose, Matthew; Petit Silvestre, Jordi; Serna Iglesias, María José (199904)
External research report
Open AccessIn 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 NPhard on unit disk graphs
Díaz Cort, Josep; Mertzios, George B. (20170518)
Article
Open AccessIn this paper we prove that the MinBisection problem is NPhard on unit disk graphs, thus solving a longstanding open question. 
On RNC approximate counting
Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George (199411)
External research report
Open AccessIn 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