Ara es mostren els items 1-20 de 31

  • 1.5-Approximation for treewidth of graphs excluding a graph with one crossing as a minor 

    Demaine, Erik D.; Hajiaghayi, Mohammad Taghi; Thilikos Touloupas, Dimitrios (2002-05)
    Report de recerca
    Accés obert
    We give polynomial-time constant-factor approximation algorithms for the treewidth and branchwidth of any H-minor-free graph for a given graph H with crossing number at most 1. The approximation factors are 1.5 for ...
  • A Constructive linear time algorithm for small cutwidth 

    Thilikos Touloupas, Dimitrios; Serna Iglesias, María José; Bodlaender, Hans L. (2000-09)
    Report de recerca
    Accés obert
    The cutwidth of a graph G is defined to be the smallest integer k such that the vertices of G can be arranged in a linear layout [v(1),...,v(n)] in such a way that for every i=1,...,n-1, there are at most k edges with the ...
  • A list of parameterized problems in bioinformatics 

    Félix Ávila, Liliana; García Chacón, Alina; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2006-05)
    Report de recerca
    Accés obert
    In this report we present a list of problems that originated in bionformatics. Our aim is to collect information on such problems that have been analyzed from the point of view of Parameterized Complexity. For every problem ...
  • A note on the subgraphs of the (2×\infty)-grid 

    Díaz Cort, Josep; Kaminski, Marcin; Thilikos Touloupas, Dimitrios (2010-02)
    Article
    Accés restringit per política de l'editorial
    We give a linear-time algorithm checking whether a graph is a subgraph of the (2×k)-grid for some value of k. Our algorithm is based on a detailed characterization of the structure of such graphs.
  • A polynomial time algorithm for the cutwidth of bounded degree graphs with small treewidth 

    Thilikos Touloupas, Dimitrios; Serna Iglesias, María José; Bodlaender, Hans L. (2001-02)
    Report de recerca
    Accés obert
    The cutwidth of a graph G is defined to be the smallest integer k such that the vertices of G can be arranged in a vertex ordering [v(1),...,v(n)] in a way that, for every i=1,...,n-1, there are at most k ...
  • A Simple and fast approach for solving problems on planar graphs 

    Fomin, Fedor V.; Thilikos Touloupas, Dimitrios (2003-12)
    Report de recerca
    Accés obert
    It is well known that the celebrated Lipton-Tarjan planar separation theorem, in a combination with a divide-and-conquer strategy leads to many complexity results for planar graph problems. For example, by using this ...
  • Bidimensional parameters and local treewidth 

    Demaine, Erik D.; Fomin, Fedor V.; Hajiaghayi, Mohammad Taghi; Thilikos Touloupas, Dimitrios (2003-10)
    Report de recerca
    Accés obert
    For several graph theoretic parameters such as vertex cover and dominating set, it is known that if their values are bounded by k then the treewidth of the graph is bounded by some function of k. This fact is used as the ...
  • Connected and internal graph searching 

    Barrière Figueroa, Eulalia; Fraigniaud, Pierre; Santoro, Nicola; Thilikos Touloupas, Dimitrios (2002-07)
    Report de recerca
    Accés obert
    This paper is concerned with the graph searching game. The search number es(G) of a graph G is the smallest number of searchers required to clear G. A search strategy is monotone (m) if no recontamination ever occurs. It ...
  • Connected graph searching 

    Barrière Figueroa, Eulalia; Flocchini, Paola; Fomin, Fedor V.; Fraigniaud, Pierre; Nisse, Nicolas; Santoro, Nicola; Thilikos Touloupas, Dimitrios (2010-09-26)
    Report de recerca
    Accés obert
    In graph searching game the opponents are a set of searchers and a fugitive in a graph. The searchers try to capture the fugitive by applying some sequence moves that include placement, removal, or sliding of a searcher ...
  • Constructive linear time algorithms for branchwidth 

    Thilikos Touloupas, Dimitrios; Bodlaender, Hans L. (2000-10)
    Report de recerca
    Accés obert
    We prove that, for any fixed k, one can construct a linear time algorithm that checks if a graph has branchwidth at most k and, if so, outputs a branch decomposition of minimum width.
  • Counting H-colorings of Partial k-trees 

    Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2000-11)
    Report de recerca
    Accés obert
    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)
    Report de recerca
    Accés obert
    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 ...
  • Derivation of algorithms for cutwidth and related graph layout problems 

    Bodlaender, Hans; Michael, Fellows; Thilikos Touloupas, Dimitrios (2002-07)
    Report de recerca
    Accés obert
    In this paper, we investigate algorithms for some related graph parameters. Each of these asks for a linear ordering of the vertices of the graph (or can be formulated as such), and there are constructive linear time ...
  • Dominating sets and local treewidth 

    Thilikos Touloupas, Dimitrios; Fomin, Fedor V. (2003-09)
    Report de recerca
    Accés obert
    It is known that the treewidth of a planar graph with a dominating set of size d is O(sqrt{d}) and this fact is used as the basis for several fixed parameter algorithms on planar graphs. An interesting question ...
  • Dominating sets in planar graphs: branch-width and exponential speed-up 

    Fomin, Fedor V.; Thilikos Touloupas, Dimitrios (2002-12)
    Report de recerca
    Accés obert
    Graph minors theory, developed by Robertson & Seymour, provides a list of powerful theoretical results and tools. However, the wide spread opinion in Graph Algorithms community about this theory is that it is mainly of ...
  • Efficient algorithms for parameterized H-colorings 

    Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2005-12)
    Report de recerca
    Accés obert
    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 ...
  • Exponential speedup of fixed parameter algorithms on K_{3,3}-minor-free or K_{5}-minor-free graphs 

    Hajiaghayi, Mohammad Taghi; Demaine, Erik D.; Thilikos Touloupas, Dimitrios (2002-03)
    Report de recerca
    Accés obert
    We present a fixed parameter algorithm that constructively solves the k-dominating set problem on graphs excluding one of the K_{5} or K_3,3 as a minor in time O(3^{6sqrt{34 k}}n^{O(1)}). In fact, we present our ...
  • Fast approximation schemes for K_{3,3}-minor-free or K_{5}-minor-free graphs 

    Hajiaghayi, Mohammad Taghi; Nishimura, Naomi; Ragde, Prabhakar; Thilikos Touloupas, Dimitrios (2002-05)
    Report de recerca
    Accés obert
    As the class of graphs of bounded treewidth is of limited size, we need to solve NP-hard problems for wider classes of graphs than this class. Eppstein introduced a new concept which can be considered as a generalization ...
  • Fast fixed-parameter tractable algorithms for (nontrivial) generalizations of vertex cover 

    Nishimura, Naomi; Ragde, Prabhakar; Thilikos Touloupas, Dimitrios (2001-09)
    Report de recerca
    Accés obert
    Our goal in this paper is the development of fast algorithms for recognizing general classes of graphs. We seek algorithms whose complexity can be expressed as a linear function of the graph size plus an exponential function ...
  • Finding smallest supertrees under minor containment 

    Nishimura, Naomi; Prabhakar, Ragde; Thilikos Touloupas, Dimitrios (1999-10)
    Report de recerca
    Accés obert
    The diversity of application areas relying on tree-structured data results in a wide interest in algorithms which determine differences or similarities among trees. One way of measuring the similarity between trees ...