Light spanners and approximate TSP in weighted graphs with forbidden minors

  • Authors:
  • Michelangelo Grigni;Papa Sissokho

  • Affiliations:
  • Emory University, Atlanta GA;Emory University, Atlanta GA

  • Venue:
  • SODA '02 Proceedings of the thirteenth annual ACM-SIAM symposium on Discrete algorithms
  • Year:
  • 2002

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Abstract

Given an edge weighted graph G with n vertices and no Kτ-minor and a small positive constant ε, we show that a simple greedy algorithm [1] finds a spanning subgraph approximating all shortest-path distances within a factor of 1 + ε, and with total edge weight at most O((τ√logτ · logn)/ε) times the weight of a minimum spanning tree. This result implies a quasi-polynomial time approximation scheme (QPTAS) for the traveling salesman problem (TSP) in such graphs, with running time nO((τ4√logτ·log n·log log n)/ε2).Our analysis shows that a graph with detour gap number [5] Ω(τ√logτ · log n) has a Kτ-minor. We also show that this dependence on n is nearly tight, by exhibiting graphs with no K6-minor (apex graphs) and detour gap number Ω((log n)/log log n).As a step towards eliminating the log n factors the first paragraph, we propose a generalized detour gap number, now depending on ε, and we show that it remains bounded for apex graphs and some similar graph families.