Programme available – CMSS summer workshop
The website for the CMSS summer workshop has been updated with the programme and information about the workshop location, including maps.
Computer Science Seminar: Arkadii Slinko
Speaker: Arkadii Slinko
Affiliation: Department of Mathematics
Title: Approximation Algorithms for Fully Proportional Representation by Clustering Voters
Date: Wednesday, 9 Dec 2015
Time: 12:00 pm
Location: 303-561
Charles Dodgson (Lewis Carroll) asserted that “a representation system should find the coalitions in the election that would have formed if the voters had the necessary time and information … and allow each of the coalitions to elect their representative using some single-winner voting method.”
Both the Chamberlin-Courant and Monroe voting rules do exactly that. Given the preferences of voters, they select committees whose members represent the voters so that voters’ satisfaction with their assigned representatives is maximised. These rules suffer from a common disadvantage, being computationally intractable to compute the winning committee exactly when the numbers get large. As both of these rules, explicitly or implicitly, partition voters, they can be seen as clustering of voters so that the voters in each group share the same representative.This suggest studying approximation algorithms for these voting rules by means of cluster analysis, which is the subject of this paper. We develop several such algorithms and experimentally analyse their performance.
Joint work with Piotr Faliszewski and Nimrod Talmon.
Everyone welcome!
CMSS Seminar: Mark C. Wilson
Speaker: Mark Wilson
Affiliation: Computer Science Department
Title: Predicting FPP elections
Date: Tuesday, 6 Oct 2015
Time: 5:00 pm
Location: CAG15/114-G15 (Commerce A)
In this informal talk I will discuss some basic issues involved predicting elections in countries using the First Past The Post (single-winner plurality in districts) electoral system. A variety of methods have been tried with varying success. Part of the reason for this talk is to clarify for myself what “success” means. The talk will focus on standard methods involving models of “swing”, which often underlie more complicated models. I will make some predictions for the Canada 2015 election.
Everyone welcome!
CMSS Seminar: Samin Aref
Speaker: Samin Aref
Affiliation: Department of Computer Science
Title: Measuring Partial Balance in Signed Networks
Date: Tuesday, 29 Sep 2015
Time: 5:00 pm
Location: CAG15/114-G15 (Commerce A)
Is the enemy of an enemy necessarily a friend, or is a friend of a friend a friend? If not, to what extent does this tend to hold? Such questions were formulated in terms of signed (social) networks and necessary and sufficient conditions for a network to be “balanced” were obtained around 1960. Since then the idea that signed networks tend over time to become more balanced has been widely used in several application areas, such as international relations. However investigation of this hypothesis has been complicated by the lack of a standard measure of partial balance, since complete balance is almost never achieved in practice.
We formalise the concept of a measure of partial balance, compare several known measures on real-world and synthetic datasets, as well as investigating their axiomatic properties. We use both well-known datasets from the sociology literature, such as Read’s New Guinean tribes, and much more recent ones involving senate bill co-sponsorship. The synthetic data involves both Erdős-Rényi and Barabási-Albert graphs.
We find that under all our measures, real-world networks are more balanced than random networks. We also show that some measures behave better than others in terms of axioms. We make some recommendations for measures to be used in future work.
Everyone welcome!
CMSS Seminar: José A. Rodrigues-Neto
Speaker: José A. Rodrigues-Neto
Affiliation: Australian National University
Title: Self-Consistency and Common Prior in Non-Partitional Knowledge Models
Date: Tuesday, 22 Sep 2015
Time: 5:00 pm
Location: CAG15/114-G15 (Commerce A)
In non-partitional models of knowledge with objective and subjective state spaces, the issue of self-consistency arises. The present paper defines a multigraph G_j for each player j, and also a global multigraph G. The posteriors of player j are self-consistent if and only if all cycle equations associated with cycles in G_j are satisfied. Similarly, the posteriors of all players are consistent with a common prior when all cycle equations corresponding to the cycles in G are satisfied. In particular, the self-consistency of player j is automatic when G_j is acyclic. Consistency always holds when G is acyclic, regardless of any probabilistic information. There is a simple formula to check for the acyclicity of G_j , and another formula to check for the acyclicity of G.
This is a joint paper with Luciana C. Fiorini.
Everyone welcome!
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