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VERSION:2.0
PRODID:-//University of Liverpool Computer Science Seminar System//v2//EN
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DTSTAMP:20260408T205325Z
UID:Seminar-EcCo-1126@lxserverA.csc.liv.ac.uk.csc.liv.ac.uk
ORGANIZER:CN=Nicos 	Protopapas:MAILTO:N.Protopapas@liverpool.ac.uk
DTSTART:20211013T130000
DTEND:20211013T140000
SUMMARY:Economics and Computation Series
DESCRIPTION:Nicos Protopapas: Truthful aggregations of budget proposals with proportionality guarantees\n\nWe study a participatory budgeting problem, where a set of strategic agents wish to split a divisible budget among different projects, by aggregating their proposals on a single division. Unfortunately, the straight-forward rule that divides the budget proportionally is susceptible to manipulation. In a recent work, Freeman et al.  proposed a class of truthful mechanisms, called moving phantom mechanisms. Among others, they propose a proportional mechanism, in the sense that in the extreme case where all agents prefer a single project to receive the whole amount,the budget is assigned proportionally. While proportionality is a naturally desired property, is defined over a limited type of preference profiles. To address this, we expand the notion of proportionality, by proposing a quantitative framework which evaluates a budget aggregation mechanism according to its worst-case distance from the proportional allocation. Crucially, this is defined for every preference profile. We study this measure on the class of moving phantom mechanisms, and we provide approximation guarantees. For two projects, we show that the Uniform Phantom mechanism is the optimal among all truthful mechanisms. For three projects, we propose a the Piecewise Uniform mechanism, a proportional mechanism which is optimal among all moving phantom mechanisms. Finally, we provide impossibility results regarding the approximability of moving phantom mechanisms\n\nAuthors: Ioannis Caragiannis, George Christodoulou, Nicos Protopapas\n\nhttps://www.csc.liv.ac.uk/research/seminars/abstract.php?id=1126
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