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PRODID:-//University of Liverpool Computer Science Seminar System//v2//EN
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DTSTAMP:20260915T193553Z
UID:Seminar-dept-308@lxserverM.csc.liv.ac.uk
ORGANIZER:CN=Lutz Oettershagen:MAILTO:Lutz.Oettershagen@liverpool.ac.uk
DTSTART:20130122T160000
DTEND:20130122T170000
SUMMARY:School Seminar Series
DESCRIPTION:Dr. Dimitris Fotakis: Approximate Strategyproof Mechanisms for Facility Location Games\n\nWe consider k-Facility Location games, where n strategic agents report their locations in a metric space, and a mechanism maps them to k facilities. The agents seek to minimize their connection cost, namely the distance of their true location to the nearest facility, and may misreport their location. We are interested in (deterministic or randomized) mechanisms that are strategyproof, i.e., ensure that no agent can benefit from misreporting her location, do not resort to monetary transfers, and achieve a good approximation ratio to either the total connection cost or the maximum connection cost of the agents.\n\n\n\nWe present an elegant characterization of deterministic strategyproof mechanisms with a bounded approximation ratio for 2-Facility Location on the line. In particular, we show that for instances with n \geq 5 agents, any such mechanism either admits a unique dictator, or places the facilities at the leftmost and the rightmost location of the instance. As a corollary, we obtain that the best approximation ratio achievable by deterministic strategyproof mechanisms for the problem of locating 2 facilities on the line to minimize the total connection cost is precisely n-2.\n\n\n\nBuilding on the techniques used for the characterization, we also show that:\n\n\n\n-- For every k \geq 3, there do not exist any deterministic anonymous strategyproof mechanisms with a bounded approximation ratio for k-Facility Location on the line, even for simple instances with k+1 agents.\n\n\n\n-- There do not exist any deterministic strategyproof mechanisms with a bounded approximation ratio for 2-Facility Location on general metric spaces, which is true even for simple instances with 3 agents located in a star.\n\n\n\nOn the positive side, we present a randomized mechanism for locating k facilities on the line that achieves an approximation ratio of 2 for the objective of maximum cost.\n\nhttps://www.csc.liv.ac.uk/research/seminars/abstract.php?id=308
LOCATION:Ashton Lecture Theatre
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