Nicolas Maudet

New Results on Equilibria in Strategic Candidacy

We consider a voting setting where candidates have preferences about the outcome of the election and are free to join or leave the election. The corresponding candidacy game, where candidates choose strategically to participate or not, has been studied in very few papers, mainly by Dutta et al. [5,6], who showed that no non-dictatorial voting procedure satisfying unanimity is candidacy-strategyproof, or equivalently, is such that the joint action where all candidates enter the election is always a pure strategy Nash equilibrium. They also showed that for voting trees, there are candidacy games with no pure strategy equilibria. However, no results were known about other voting rules. Here we prove several such results. Some are positive (a pure strategy Nash equilibrium is guaranteed for Copeland and the uncovered set, whichever is the number of candidates, and for all Condorcet-consistent rules, for 4 candidates). Some are negative, namely for plurality and maximin.

Rewriting Rules for the Computation of Goal-Oriented Changes in an Argumentation System

When several agents are engaged in an argumentation process, they are faced with the problem of deciding how to contribute to the current state of the debate in order to satisfy their own goal, ie. to make an argument under a given semantics accepted or not. In this paper, we study the minimal changes or target sets on the current state of the debate that are required to achieve such a goal, where changes are the addition and/or deletion of attacks among arguments. We study some properties of these target sets, and propose a Maude specification of rewriting rules which allow to compute all the target sets for some types of goals.

Multi-attribute auctions with different types of attributes: Enacting properties in multi-attribute auctions

Abstract Multi-attribute auctions allow agents to sell and purchase goods and services taking into account more attributes than just price (e.g. service time, tolerances, qualities, etc.). In this paper we analyze attributes involved during the auction process and propose to classify them between verifiable attributes, unverifiable attributes and auctioneer provided attributes. According to this classification we present VMA2, a new Vickrey-based reverse multi-attribute auction mechanism, which takes into account the different types of attributes involved in the auction and allows the auction customization in order to suit the auctioneer needs. On the one hand, the use of auctioneer provided attributes enables the inclusion of different auction concepts, such as social welfare, trust or robustness whilst, on the other hand, the use of verifiable attributes guarantee truthful bidding. The paper exemplifies the behavior of VMA2 describing how an egalitarian allocation can be achieved. The mechanism is then tested in a simulated manufacturing environment and compared with other existing auction allocation methods.

Empirical Evaluation of Strategies for Multiparty Argumentative Debates

Debating agents have often different areas of expertise and conflicting opinions on the subjects under discussion. They are faced with the problem of deciding how to contribute to the current state of the debate in order to satisfy their personal goals. We focus on target sets, that specify minimal changes on the current state of the debate allowing agents to satisfy their goals, where changes are the addition and/or deletion of attacks among arguments. In this paper, we experimentally test a number of strategies based on target sets, and we evaluate them with respect to different criteria, as the length of the debate, the happiness of the agents, and the rationality of the result.

Aggregating CP-nets with Unfeasible Outcomes

We consider settings where a collection of agents express preferences over a set of candidates with a combinatorial structure via the use of CP-nets, and we need to exploit the information contained in the CP-nets to choose one of the candidates. Moreover, there is a set of constraints which defines the unfeasible candidates, which cannot be the result of the preference aggregation. We propose a method to achieve this which is based on voting, and considers one variable at a time in a sequence. This method has been studied in the literature to aggregate non-constrained CP-nets. Here we generalise it to work with constrained CP-nets, and we study its properties. The constraints are used to leave in the variable domains only the admissible values. This allows the voting steps to return only feasible values. We find conditions of coherence between the preference expressed in the CP nets and the constraints, in order to guarantee that the classical sequential aggregation method always returns a feasible candidate. Even when such conditions are not met, but the constraints defining the unfeasible candidates have a tree structure (or a structure with bounded tree-width), and the collection of CP-nets is O-legal (that is, the dependency graphs of the CP-nets are compatible), we show that our more general voting procedure can be used, and that it is polynomial in the number of features describing the candidates and in the number of voters.

DESIGNING PROTOCOLS FOR ABDUCTIVE HYPOTHESIS REFINEMENT IN DYNAMIC MULTIAGENT ENVIRONMENTS

This paper studies multiagent systems where each agent has access to local observations of a dynamic environment and needs to build from this partial information an hypothesis on the state of the system. Each agent ensures that its hypothesis is consistent with its observations, and communicates with other agents to refine this hypothesis by confronting them to their own views. However, these communications are restricted by temporal and topological constraints, and can only be bilateral. We first study in this paper an abstract model of this problem, identifying conditions under which satisfying states can (or will) be reached. We rely in particular on a compositional consistency relation. We then detail a case study involving agents able to reason abductively (with Theorist), and study how demanding are the conditions required in this context. Different bilateral protocols are finally introduced and formally studied, to account for both compositional and noncompositional settings.