Exploració per autor "Thilikos Touloupas, Dimitrios"

Ara es mostren els items 8-27 de 37

    • Bidimensional parameters and local treewidth 

      Demaine, Erik D.; Fomin, Fedor V.; Hajiaghayi, Mohammad Taghi; Thilikos Touloupas, Dimitrios (2003-10)
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      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 ...

    • Complexity issues on bounded restrictive H-coloring 

      Serna Iglesias, María José; Díaz Cort, Josep; Thilikos Touloupas, Dimitrios (2004-04)
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      We consider the restriction of the H-coloring problem where we are looking for homomorphisms were the number of preimages of certain vertices of H is bounded by some fixed constant. We consider the decision and the ...

    • Connected and internal graph searching 

      Barrière Figueroa, Eulalia; Fraigniaud, Pierre; Santoro, Nicola; Thilikos Touloupas, Dimitrios (2002-07)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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)
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      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 ...