Ryan Porter

Simple search methods for finding a Nash equilibrium

We present two simple search methods for computing a sample Nash equilibrium in a normal-form game: one for 2- player games and one for n-player games. We test these algorithms on many classes of games, and show that they perform well against the state of the art- the Lemke-Howson algorithm for 2-player games, and Simplicial Subdivision and Govindan-Wilson for n-player games.

Mechanism design for online real-time scheduling

For the problem of online real-time scheduling of jobs on a single processor, previous work presents matching upper and lower bounds on the competitive ratio that can be achieved by a deterministic algorithm. However, these results only apply to the non-strategic setting in which the jobs are released directly to the algorithm. Motivated by emerging areas such as grid computing, we instead consider this problem in an economic setting, in which each job is released to a separate, self-interested agent. The agent can then delay releasing the job to the algorithm, inflate its length, and declare an arbitrary value and deadline for the job, while the center determines not only the schedule, but the payment of each agent. For the resulting mechanism design problem (in which we also slightly strengthen an assumption from the non-strategic setting), we present a mechanism that addresses each incentive issue, while only increasing the competitive ratio by one. We then show a matching lower bound for deterministic mechanisms that never pay the agents.

On cheating in sealed-bid auctions

Motivated by the rise of online auctions and their relative lack of security, this paper analyzes two forms of cheating in sealed-bid auctions. The first type of cheating we consider occurs when the seller spies on the bids of a second-price auction and then inserts a fake bid in order to increase the payment of the winning bidder. In the second type, a bidder cheats in a first-price auction by examining the competing bids before deciding on his own bid. In both cases, we derive equilibrium strategies when bidders are aware of the possibility of cheating. These results provide insights into sealed-bid auctions even in the absence of cheating, including some counterintuitive results on the effects of overbidding in a first-price auction.footnotetext[1]This work was supported in part by DARPA grant F30602-00-2-0598.

Fault tolerant mechanism design

We introduce the notion of fault tolerant mechanism design, which extends the standard game theoretic framework of mechanism design to allow for uncertainty about execution. Specifically, we define the problem of task allocation in which the private information of the agents is not only their costs of attempting the tasks but also their probabilities of failure. For several different instances of this setting we present both, positive results in the form of mechanisms that are incentive compatible, individually rational, and efficient, and negative results in the form of impossibility theorems.

Designing efficient online trading systems

In many online domains, agents share goods or services that are both cheap to provide and valuable to receive. Examples include ratings in a recommender system, forwarding a message to node closer to its destination in a mobile ad-hoc network, and uploading a file in a P2P system. Existing systems in these domains often rely on agents to voluntarily provide goods. Despite the low cost of doing so, many agents instead choose to free-ride, leading to a loss in social efficiency. We present an initial step towards addressing this problem in the context of an abstract, extremely simplified model, where we identify more efficient mechanisms, including one that is provably optimal. Of course, we are not the first to consider this problem, or to offer a solution (see, e.g., [1] for recommender systems, [3] for ad-hoc networks, and [2] and [4] for P2P systems).

Conference report: the fourth ACM conference on electronic commerce

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