by adminnot | Mar 15, 2011

Speaker: Matthew Ryan

Affiliation: The University of Auckland

Title: Path Independent Choice and the Ranking of Opportunity Sets

Date: Tuesday, 29 Mar 2011

Time: 4:00 pm

Location: Room 6115, Owen Glenn Building

An opportunity set is a non-empty subset of a given set X. A decision-maker, when confronted with an opportunity set, is allowed to choose one element from it.

We assume that the decision-maker has some reflexive and transitive ordering over opportunity sets. Such an ordering is called an “indirect utility ordering” if there

exists a weak order (preference relation) on X such that opportunity set A is weakly preferred to opportunity set B iff the most preferred element(s) from A∪B includes

at least one element of A. Necessary and sufficient conditions for an opportunity set ranking to be an indirect utility ordering are well-known (Kreps, 1979). We give

necessary and sufficient conditions for an ordering of opportunity sets to be consistent with a path independent choice function, or “Plott consistent”. That is, opportunity set A is weakly

preferred to opportunity set B iff the acceptable choice(s) from A∪B include at least one element of A. The proof employs results from the theory of abstract convex geometries.

by adminnot | Mar 4, 2011

Speaker: Arkadii Slinko

Affiliation: The University of Auckland

Title: Hierarchical games

Date: Tuesday, 15 Mar 2011

Time: 4:00 pm

Location: Room 6115, Owen Glenn Building

In many situations, both in human and artificial societies, cooperating agents have different status with respect to the activity and it is not uncommon that certain actions are only allowed to coalitions that satisfy certain criteria, e.g., to sufficiently large coalitions or coalitions which involve players of sufficient seniority. Simmons (1988) formalised this idea in the context of secret sharing schemes by defining the concept of a (disjunctive) hierarchical access structure.

The mathematical concept which describe access structures of secret sharing schemes is that of a simple game. In this paper we aim to start a systematic study of hierarchical games, both disjunctive and conjunctive, and our results show that they deserve such a treatment. We prove the duality between disjunctive and conjunctive hierarchical games. We introduce a canonical representation theorem for both and characterise disjunctive hierarchical games as complete games with a unique shift-maximal losing coalition. We give a short combinatorial proof of the Beimel-Tassa-Weinreb characterisation theorem of weighted disjunctive hierarchical games. By duality we get similar theorems for conjunctive hierarchical games.

This is a joint work with Tatiana Gvozdeva and Ali Hameed.

by adminnot | Feb 21, 2011

Speaker: Nadja Betzler

Affiliation: Technical University of Berlin

Title: Parameterized algorithmics for Kemeny’s voting system

Date: Tuesday, 1 Mar 2011

Time: 4:00 pm

Location: Room 6115, Owen Glenn Building

Kemeny’s voting system is concerned with optimally aggregating a multiset of preference lists into a consensus list. We study the parameterized complexity of the underlying decision problem, called Kemeny Score, with respect to several different parameterizations.This includes a discussion about the relevance and motivation of the parameterizations illustrating the usefulness of a multivariate complexity analysis for voting problems.

We further extend this study by introducing the concept of “partial kernelization”. Based on this, we devise an additional result for the parameter measuring the average distance between pairs of input votes. Moreover, the partial kernelization concept naturally leads to additional parameterizations. Finally, we provide experimental results for computing optimal Kemeny rankings based on some of the previously introduced methods.

by adminnot | Feb 7, 2011

Speaker: John McCabe Dansted

Affiliation: University of Western Australia

Title: Axioms for obligation and robustness with temporal logic

Date: Tuesday, 15 Feb 2011

Time: 4:00 pm

Location: Room 6115, Owen Glenn Building

Deontic logics are used to reason about norms. These norms may include

policies, relating to operation of an automated system, that are

subject to violation. We present a Temporal Logic of Robustness

(RoCTL*) that is intended to verify that a system is Robust to

some number of norm violations. We present sound and complete

axiomatisations of fragments of this logic and briefly discuss the

philosophical background to these axioms, including which axioms may

be relevant in fields other than robust systems. Although every

property that can be expressed in RoCTL* can be expressed in an

existing logic (CTL*), RoCTL* can express some properties much more

succinctly than CTL*.

Everyone welcome!

by adminnot | Jan 28, 2011

This may be of interest to CMSS members.

Special session on **Logics for Games and Social Choice**

CLIMA XII 12th International Workshop on Computational Logic in Multi-Agent Systems

http://centria.di.fct.unl.pt/events/climaXII/sessions.html

Barcelona, Spain, July 17-18, 2011.

Affiliated with IJCAI’11. Submission deadline: April 8.

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