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arXiv 2102.04909cs.GT
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两个世界中最好的公平份额分配

Best-of-Both-Worlds Fair-Share Allocations

Moshe Babaioff, Tomer Ezra, Uriel Feige

摘要:

我们考虑了当代理商对商品享有平等的权利并且没有转让时,在具有附加价值的$n$代理商之间公平分配不可分割物品的问题。两个世界最佳(BoBW)公平机制旨在为所有代理提供事前保证(例如获得预期中的比例份额)和事后保证。之前的BoBW结果集中在基于“最多一个项目”范式的事后保证上,例如最多一个项目(EF1)。在这项工作中,我们试图给每个代理一个高价值的事后,具体来说,他的最大最小份额(MMS)的一个恒定的分数。最多一个项目的范例不能给出这样的保证,并且不难给出先前BoBW机制仅向代理提供其MMS的$\frac{1}{n}$部分的示例。我们的主要结果是一个确定性的多项式时间算法,计算分配,是事前成比例的,事后,每个分配给每个代理至少他的比例份额一个项目,更重要的是,至少有一半的MMS。此外,这最后一项事后保证甚至适用于本文介绍的要求更高的份额概念,我们称之为截断比例份额(TPS)。我们的保证几乎是最好的可能,在这个意义上,我们不能保证代理人超过他们的比例份额事前,也不能保证代理人超过他们的TPS的$\frac{n}{2n-1}$分数事后。

英文摘要:

We consider the problem of fair allocation of indivisible items among $n$ agents with additive valuations, when agents have equal entitlements to the goods, and there are no transfers. Best-of-Both-Worlds (BoBW) fairness mechanisms aim to give all agents both an ex-ante guarantee (such as getting the proportional share in expectation) and an ex-post guarantee. Prior BoBW results have focused on ex-post guarantees that are based on the "up to one item" paradigm, such as envy-free up to one item (EF1). In this work we attempt to give every agent a high value ex-post, and specifically, a constant fraction of his maximin share (MMS). The up to one item paradigm fails to give such a guarantee, and it is not difficult to present examples in which previous BoBW mechanisms give agents only a $\frac{1}{n}$ fraction of their MMS. Our main result is a deterministic polynomial time algorithm that computes a distribution over allocations that is ex-ante proportional, and ex-post, every allocation gives every agent at least his proportional share up to one item, and more importantly, at least half of his MMS. Moreover, this last ex-post guarantee holds even with respect to a more demanding notion of a share, introduced in this paper, that we refer to as the truncated proportional share (TPS). Our guarantees are nearly best possible, in the sense that one cannot guarantee agents more than their proportional share ex-ante, and one cannot guarantee agents more than a $\frac{n}{2n-1}$ fraction of their TPS ex-post.

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