论文标题

在线多商品设施位置问题

The Online Multi-Commodity Facility Location Problem

论文作者

Castenow, Jannik, Feldkord, Björn, Knollmann, Till, Malatyali, Manuel, der Heide, Friedhelm Meyer auf

论文摘要

我们认为自然扩展到公制的无竞争设施位置问题(FLP),其中要求从有限的商品套装中要求不同的商品。 Ravi和Sinha(Soda'04)将该模型作为多商品设施位置问题(MFLP)引入,并认为这是一个离线优化问题。该模型本身与FLP相似:即,请求位于有限度量空间的点,算法的任务是构建设施并将请求分配给设施,同时最大程度地减少所有分配距离的施工成本和SUM。此外,请求和设施是异质的;他们要求或提供$ S $的多种商品。必须将请求与一套共同提供其要求的商品的设施连接。与FLP相比,算法不仅必须决定是否以及在何处放置设施,还必须在每种设施提供哪些商品。 据我们所知,我们是第一个在其在线变体中研究问题的人,其中要求,其立场和商品事先不知道,而是随着时间的流逝而揭示的。我们提出了有关竞争比率的结果。一方面,我们表明,异质性通过为$ω(\ sqrt {| s |}+\ frac {\ frac {\ log n} {\ log log \ log \ log n})的任何随机在线算法而开发竞争比的下限来影响竞争比率。在这里,$ n $是请求的数量。另一方面,我们建立了确定性的$ o(\ sqrt {| s |} \ cdot \ log n)$ - 竞争性算法和一个随机的$ o(\ sqrt {| s |} \ cdot \ cdot \ frac \ frac {\ log n}此外,我们表明,当考虑设施的施工成本的更特殊的成本功能时,根据功能,确定性算法给出的竞争比率会降低。

We consider a natural extension to the metric uncapacitated Facility Location Problem (FLP) in which requests ask for different commodities out of a finite set $S$ of commodities. Ravi and Sinha (SODA'04) introduced the model as the Multi-Commodity Facility Location Problem (MFLP) and considered it an offline optimization problem. The model itself is similar to the FLP: i.e., requests are located at points of a finite metric space and the task of an algorithm is to construct facilities and assign requests to facilities while minimizing the construction cost and the sum over all assignment distances. In addition, requests and facilities are heterogeneous; they request or offer multiple commodities out of $S$. A request has to be connected to a set of facilities jointly offering the commodities demanded by it. In comparison to the FLP, an algorithm has to decide not only if and where to place facilities, but also which commodities to offer at each. To the best of our knowledge we are the first to study the problem in its online variant in which requests, their positions and their commodities are not known beforehand but revealed over time. We present results regarding the competitive ratio. On the one hand, we show that heterogeneity influences the competitive ratio by developing a lower bound on the competitive ratio for any randomized online algorithm of $Ω(\sqrt{|S|}+\frac{\log n}{\log\log n})$ that already holds for simple line metrics. Here, $n$ is the number of requests. On the other side, we establish a deterministic $O(\sqrt{|S|}\cdot\log n)$-competitive algorithm and a randomized $O(\sqrt{|S|}\cdot\frac{\log n}{\log\log n})$-competitive algorithm. Further, we show that when considering a more special class of cost functions for the construction cost of a facility, the competitive ratio decreases given by our deterministic algorithm depending on the function.

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