Multi-item Vickrey-Dutch auctions

Descending price auctions are adopted for goods that must be sold quickly and in private values environments, for instance in flower, fish, and tobacco auctions. In this paper, we introduce ex post efficient descending auctions for two environments: multiple non-identical items and buyers with unit-demand valuations; and multiple identical items and buyers with non-increasing marginal values. Our auctions are designed using the notion of universal competitive equilibrium (UCE) prices and they terminate with UCE prices, from which the Vickrey payments can be determined. For the unit-demand setting, our auction maintains linear and anonymous prices. For the homogeneous items setting, our auction maintains a single price and adopts Ausubel's notion of "clinching" to compute the final payments dynamically. The auctions support truthful bidding in an ex post Nash equilibrium and terminate with an ex post efficient allocation. In simulation, we illustrate the speed and elicitation advantages of these auctions over their ascending price counterparts.

Simplicity-Expressiveness Tradeoffs in Mechanism Design

A fundamental result in mechanism design theory, the so-called revelation principle, asserts that for many questions concerning the existence of mechanisms with a given outcome one can restrict attention to truthful direct revelation-mechanisms. In practice, however, many mechanism use a restricted message space. This motivates the study of the tradeoffs involved in choosing simplified mechanisms, which can sometimes bring benefits in precluding bad or promoting good equilibria, and other times impose costs on welfare and revenue. We study the simplicity-expressiveness tradeoff in two representative settings, sponsored search auctions and combinatorial auctions, each being a canonical example for complete information and incomplete information analysis, respectively. We observe that the amount of information available to the agents plays an important role for the tradeoff between simplicity and expressiveness

An Iterative Generalized Vickrey Auction: Strategy-Proofness without Complete Revelation

The generalized Vickrey auction (GVA) is a strategy-proof combinatorial auction, in which truthful bidding is the optimal strategy for an agent. In this paper we address a fundamental problem with the GVA, which is that it requires agents to compute and reveal their values for all combinations of items. This can be very difficult for bounded-rational agents with limited or costly computation. We propose an experimental design for an iterative combinatorial auction. We have a theoretical proof that the the auction implements the outcome of the Vickrey auction in special cases, and initial experimental results support our conjecture that the auction implements the outcome of the Vickrey auction in all cases. The auction has better information properties than the sealedbid GVA: in each round agents must only bid for the set of bundles that maximize their utility given current ask prices, which does not require agents to compute their exact values for every bundle.Engineering and Applied Science

Online Mechanisms

Online mechanisms extend the methods of mechanism design to dynamic environments with multiple agents and private information. Decisions must be made as information about types is revealed online and without knowledge of the future in the sense of online algorithms. We first consider single-valued preference domains and characterize the space of decision policies that can be truthfully implemented in a dominant strategy equilibrium. Working in a model-free environment we present truthful auctions for domains with expiring items and limited-supply items. Turning to a more general preference domain, and assuming the existence of a probabilistic model for agent types, we define a dynamic Vickrey-Clarke-Groves mechanism that is efficient and Bayes-Nash incentive compatible. We close with some thoughts about future research directions in this area.Engineering and Applied Science

Challenge Problem: Agent-Mediated Decentralized Information Mechanisms

Pervasive computing, driven by faster, cheaper and smaller devices, and wireless networking technology, promises to make people perpetual users of a massive and decentralized computational system. Pervasive computing blurs the boundary between the physical and the virtual. Information, always cheap to duplicate, now becomes cheap to generate everywhere. At once both the opportunities, such as for data mining and collaborative ltering, and the dangers, such as for privacy abuse, are clear. As a challenge to the agent community this paper proposes the development of agent-mediated, decentralized informationprocessing mechanisms, that enshrine the principles of information property rights and provides economic incentives to support efficient information sharing.We discuss the complementary roles of markets, informationdegradation and aggregation, and reputation, within such a mechanism, and propose a straw-man model.Engineering and Applied Science