arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2103.16340cs.DS
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秘书模型中的日程安排

Scheduling in the Secretary Model

Susanne Albers, Maximilian Janke

摘要:

本文研究了秘书模型中的最小制造时间问题。形式上,由其处理时间指定的作业以均匀随机顺序呈现。在线算法必须将每个作业永久地、可重复地分配给m台并行且相同的机器中的一台,使得处理所有作业所需的预期时间(即完工时间)最小化。我们给出了两个确定性算法。首先,半在线策略LightLoad的直接适应提供了一个非常简单的算法,保留了1.75的竞争比。一个新的和复杂的算法是1.535竞争。这些竞争比率不仅是在预期中获得的,而且实际上,除了一小部分工作订单之外,所有工作订单都是如此。经典的在线最大完工时间最小化只考虑最坏情况的订单。这里,对于确定性算法,不可能有低于1.885的竞争比,而对于随机化算法,不可能有低于1.581的竞争比。到目前为止,最好的随机算法是1.916-竞争。我们的研究结果表明,经典的最坏情况订单是相当罕见的,悲观的许多应用程序。与更强的确定性重排序模型相比,它们还展示了随机化的力量。我们补充我们的结果,提供第一个下界。在几乎所有可能的工作订单上获得的竞争比必须至少为1.257。这意味着一般模型中确定性算法和随机算法的下限均为1.043。

英文摘要:

This paper studies Makespan Minimization in the secretary model. Formally, jobs, specified by their processing times, are presented in a uniformly random order. An online algorithm has to assign each job permanently and irrevocably to one of m parallel and identical machines such that the expected time it takes to process them all, the makespan, is minimized. We give two deterministic algorithms. First, a straightforward adaptation of the semi-online strategy LightLoad provides a very simple algorithm retaining its competitive ratio of 1.75. A new and sophisticated algorithm is 1.535-competitive. These competitive ratios are not only obtained in expectation but, in fact, for all but a very tiny fraction of job orders. Classically, online makespan minimization only considers the worst-case order. Here, no competitive ratio below 1.885 for deterministic algorithms and 1.581 using randomization is possible. The best randomized algorithm so far is 1.916-competitive. Our results show that classical worst-case orders are quite rare and pessimistic for many applications. They also demonstrate the power of randomization when compared to much stronger deterministic reordering models. We complement our results by providing first lower bounds. A competitive ratio obtained on nearly all possible job orders must be at least 1.257. This implies a lower bound of 1.043 for both deterministic and randomized algorithms in the general model.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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