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キーワード:
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要旨:
We consider the problem of Online Facility Location, where demands arrive
online and must be irrevocably assigned to an open facility upon arrival. The
objective is to minimize the sum of facility and assignment costs. We prove
that the competitive ratio for Online Facility Location is $\Theta(\frac{\log
n}{\log\log n})$. On the negative side, we show that no randomized algorithm
can achieve a competitive ratio better than $O(\frac{\log n}{\log\log n})$
against an oblivious adversary even if the demands lie on a line segment. On
the positive side, we present a deterministic algorithm achieving a competitive
ratio of $O(\frac{\log n}{\log\log n})$. The analysis is based on a
hierarchical decomposition of the optimal facility locations such that each
component either is relatively well-separated or has a relatively large
diameter, and a potential function argument which distinguishes between the two
kinds of components.
