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Type of publication:Inproceedings
Entered by:
TitleTraveling Salesman Problems in Temporal Graphs
Bibtex cite IDRACTI-RU1-2014-25
Booktitle 39th International Symposium on Mathematical Foundations of Computer Science (MFCS)
Series Lecture Notes in Computer Science
Year published 2014
Publisher Springer Berlin Heidelberg
Location Budapest, Hungary
Note To appear
URL http://www.inf.u-szeged.hu/mfcs2014/?page_id=142
Keywords traveling salesman problem,temporal graph,approximation algorithm,inapproximability,hardness result,dynamic network,TSP with costs one and two,temporal matching,exploration
Abstract
In this work, we introduce the notion of time to some well-known combinatorial optimization problems. In particular, we study problems defined on temporal graphs. A temporal graph D=(V,A) may be viewed as a time-sequence G_1,G_2,...,G_l of static graphs over the same (static) set of nodes V. Each G_t = D(t) = (V,A(t)) is called the instance of D at time t and l is called the lifetime of D. Our main focus is on analogues of traveling salesman problems in temporal graphs. A sequence of time-labeled edges (e.g. a tour) is called temporal if its labels are strictly increasing. We begin by considering the problem of exploring the nodes of a temporal graph as soon as possible. In contrast to the positive results known for the static case, we prove that, it cannot be approximated within cn, for some constant c > 0, in general temporal graphs and within (2 − \varepsilon), for every constant \varepsilon > 0, in the special case in which D(t) is connected for all 1 <= t <= l, both unless P = NP. We then study the temporal analogue of TSP(1,2), abbreviated TTSP(1,2), where, for all 1 <= t <= l, D(t) is a complete weighted graph with edge-costs from 1,2 and the cost of an edge may vary from instance to instance. The goal is to find a minimum cost temporal TSP tour. We give several polynomial-time approximation algorithms for TTSP(1,2). Our best approximation is (1.7 + \varepsilon) for the generic TTSP(1,2) and (13/8 + \varepsilon) for its interesting special case in which the lifetime of the temporal graph is restricted to n. In the way, we also introduce temporal versions of Maximum Matching, Path Packing, Max-TSP, and Minimum Cycle Cover, for which we obtain polynomial-time approximation algorithms and hardness results.
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 MS-mfcs14.pdf (main file) MS-mfcs14-full.pdf

Publication ID1051