Allocating indivisible items between agents in a fair manner is a fundamental problem that has attracted a lot of interests in the last decades due to the wide range of its applications. There are several common criteria for defining what a fair allocation is, including: max-min share, proportional share, min-max share, envy-freeness, CEEI. In this paper, we introduce a new notion of fairness, called Nash-product share, which can be determined through computing an allocation of maximum Nash-product welfare, assuming that all agents have the same additive utilities. An allocation satisfies this fairness criterion is called a Nashproduct fair allocation. We first show that computing the Nash-product share of every agent is NP-hard, even with two agents only. In addition, we prove that the problem of testing the existence of a Nash-product fair allocation is an NP-hard problem when the number of agents is part of the input. Finally, since a Nash-product fair allocation does not always exist, we investigate the problem that, given a problem instance, asks for the largest value c for which there is an allocation such that every agent receives a subset of items of values of at least c times her Nash-product share. For the case where the number of agents is constant, we present a polynomial-time approximation scheme (PTAS).
I. GIỚI THIỆUFair allocation is a fundamental problem which is of interest in both computer science and economics due to the wide range of its applications (see a book chapter by Bouveret [8] and Lang and Rothe [15]). This problem concerns with allocating a finite set of goods (that may also be called items or objects) among a group of agents having different preferences over the subsets of goods. We will assume that the preferences of agents are presented by additive (or linear) utility functions. Our goal is to find an allocation that satisfies a certain notion of fairness. Among others, maxmin share, proportional share, and envy-freeness are the three notions that have been studied intensively in the literature. The max-min share of an agent is defined as the bundle that the agent can guarantee for herself when partitioning the items into bundles but choosing last. In a proportionally fair allocation between n agents, each agent receives a bundle of value at least 1/ n of the whole. An allocation is said to be envy-free if no agent wants to exchange her bundle of goods with that of any other agent. These three fairness criteria have attractive theoretical and practical properties (see the references cited above and the references therein). In [7], it was shown that envy-freeness is the strongest among the above fairness notions and implies proportional fairness, which implies max-min fairnessthe weakest one. On the other hand, as argued in the literature (see, for example, [14,16,17]), an allocation satisfying any of the these fairness notions is not guaranteed to exist in general. Furthermore, checking the existence of an envyfree (proportional fair) allocation is NP-complete (see [7]) even in th...