Browsing by Author "Hajiaghayi, Mohammad Taghi"
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1.5Approximation for treewidth of graphs excluding a graph with one crossing as a minor
Demaine, Erik D.; Hajiaghayi, Mohammad Taghi; Thilikos Touloupas, Dimitrios (200205)
External research report
Open AccessWe give polynomialtime constantfactor approximation algorithms for the treewidth and branchwidth of any Hminorfree graph for a given graph H with crossing number at most 1. The approximation factors are 1.5 for ... 
Bidimensional parameters and local treewidth
Demaine, Erik D.; Fomin, Fedor V.; Hajiaghayi, Mohammad Taghi; Thilikos Touloupas, Dimitrios (200310)
External research report
Open AccessFor 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 ... 
Exponential speedup of fixed parameter algorithms on K_{3,3}minorfree or K_{5}minorfree graphs
Hajiaghayi, Mohammad Taghi; Demaine, Erik D.; Thilikos Touloupas, Dimitrios (200203)
External research report
Open AccessWe present a fixed parameter algorithm that constructively solves the kdominating 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}minorfree or K_{5}minorfree graphs
Hajiaghayi, Mohammad Taghi; Nishimura, Naomi; Ragde, Prabhakar; Thilikos Touloupas, Dimitrios (200205)
External research report
Open AccessAs the class of graphs of bounded treewidth is of limited size, we need to solve NPhard problems for wider classes of graphs than this class. Eppstein introduced a new concept which can be considered as a generalization ... 
Fixedparameter algorithms for the (k,r)center in planar graphs and map graphs
Demaine, Erik D.; Fomin, Fedor V.; Hajiaghayi, Mohammad Taghi; Thilikos Touloupas, Dimitrios (200309)
External research report
Open AccessThe (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 ...