Ara es mostren els items 15-34 de 37

    • 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 ...
    • Fixed-parameter algorithms for the (k,r)-center in planar graphs and map graphs 

      Demaine, Erik D.; Fomin, Fedor V.; Hajiaghayi, Mohammad Taghi; Thilikos Touloupas, Dimitrios (2003-09)
      Report de recerca
      Accés obert
      The (k,r)-center problem} asks whether an input graph G has atr most k vertices (called centers) such that every vertex of $ is within distance at most r from some center. In this paper we prove that the (k,r)-center ...
    • (H,C,K)-colorings: fast, easy, and hard cases 

      Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2001-05)
      Report de recerca
      Accés obert
      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 ...
    • Monotonicity and inert fugitive search games 

      Stamatiou, Yannis; Thilikos Touloupas, Dimitrios (1999-10)
      Report de recerca
      Accés obert
      In general, graph search can be described in terms of a sequence of searchers' moves on a graph, able to capture a fugitive resorting on its vertices/edges. Several variations of graph search have been introduced, ...
    • New upper bounds on the decomposability of planar graphs and fixed parameter algorithms 

      Fomin, Fedor V.; Thilikos Touloupas, Dimitrios (2002-08)
      Report de recerca
      Accés obert
      It is known that a planar graph on n vertices has branch-width/tree-width bounded by alphasqrt{n}. In many algorithmic applications it is useful to have a small bound on the constant alpha. We give a ...
    • On graph powers for leaf-labeled trees 

      Nishimura, Naomi; Prabhakar, Ragde; Thilikos Touloupas, Dimitrios (2000-07)
      Report de recerca
      Accés obert
      We extend the well-studied concept of a graph power to that of a k-leaf power G of a tree T: G is formed by creating a node for each leaf in the tree and an edge between a pair of nodes if and only if the associated ...
    • On the existence of Nash equilibria in strategic search games 

      Álvarez Faura, M. del Carme; Duch Brown, Amalia; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2011)
      Text en actes de congrés
      Accés obert
      We consider a general multi-agent framework in which a set of n agents are roaming a network where m valuable and sharable goods (resources, services, information ....) are hidden in m different vertices of the network. ...
    • On the monotonicity of games generated by symmetric submodular functions 

      Fomin, Fedor V.; Thilikos Touloupas, Dimitrios (2001-02)
      Report de recerca
      Accés obert
      Submodular functions have appeared to be a key tool for proving the monotonicity of several graph searching games. In this paper we provide a general game theoretic framework able to unify old and new monotonicity ...
    • Outerplanar obstructions for the vertex feedback set 

      Rué Perna, Juan José; Thilikos Touloupas, Dimitrios; Stavropoulos, Konstantinos (2012-07-02)
      Article
      Accés obert
      For k = 1, let Fk be the class of graphs that contains k vertices meeting all its cycles. The minor-obstruction set for Fk is the set obs(Fk) containing all minor-minimal graphs that do not belong to Fk. We denote by Yk ...
    • Problems and conjectures on parameterized H-coloring 

      Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2002-03)
      Report de recerca
      Accés obert
    • Recent results on parameterized H-coloring 

      Díaz Cort, Josep; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios (2002-03)
      Report de recerca
      Accés obert
      We survey recent results on the complexity of several versions of the H-coloring and the list-H-coloring problems that are amenable to parameterization.
    • Smaller kernels for hitting set problems of constant arity 

      Nishimura, Naomi; Ragde, Prabhakar; Thilikos Touloupas, Dimitrios (2004-05)
      Report de recerca
      Accés obert
      We demonstrate a kernel of size O(k^2) for 3-HITTING SET when all subsets in the collection to be hit are of size at most three), giving a partial answer to an open question of Niedermeier by improving on the O(k^3) ...
    • Structure and enumeration of K4-minor-free links and link diagrams 

      Rué Perna, Juan José; Thilikos Touloupas, Dimitrios; Velona, Vasiliki (2018-07-01)
      Article
      Accés obert
      We study the class L of link-types that admit a K4-minor-free diagram, i.e., they can be projected on the plane so that the resulting graph does not contain any subdivision of K4. We prove that L is the closure of a subclass ...