Speaker: |
Apurva Mudgal Indian Institute of Technology, Ropar Department of Computer Science and Engineering Nangal Roa |

Date: |
Monday, 28 Jun 2010 (all day) |

Venue: |
A-212 (STCS Seminar Room) |

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We give an $O(\\log3 n)$-factor algorithm which runs in polynomial time. The key idea is to plan travel in a ``majority-rule'' map, which eliminates uncertainty and permits a link to the $\\frac{1}{2}$-Group Steiner (not Group Steiner) problem. The approximation factor is not far from optimal: we prove a $c\\log^{2-\\epsilon} n$ lower bound, assuming $NP \\not\\subseteq ZTIME(n^{polylog(n)})$, for the grid graphs commonly used in practice. We also extend the algorithm to polygonal maps by discretizing the problem using novel geometric techniques.