Author: Thuc Duy Vu

Publisher: Stanford University

Published: 2010

Total Pages: 104

ISBN-13:

Knockout tournaments constitute a very common and important form of social institution. They are perhaps best known in sporting competitions, but also play a key role in other social and commercial settings as they model a specific type of election scheme (namely, sequential pairwise elimination election). In such tournaments the organizer controls the shape of the tournament (a binary tree) and the seeding of the players (their assignment to the tree leaves). A tournament can involve millions of people and billions of dollars, and yet there is no consensus on how it should be organized. It is usually dependent on arbitrary decisions of the organizers, and it remains unclear why one design receives precedence over another. The question turns out to be surprisingly subtle. It depends among other things on (a) the objective, (b) the model of the players, (c) the constraints on the structure of the tournament, and (d) whether one considers only ordinal solutions or also cardinal ones. We investigate the problem of finding a good or optimal tournament design across various settings. We first focus on the problem of tournament schedule control, i.e., designing a tournament that maximizes the winning probability of a target player. While the complexity of the general problem is still unknown, various constraints -- all naturally occurring in practice -- serve to push the problem to one side or the other: easy (polynomial) or hard (NP-complete). We then address the question of how to find a fair tournament. We consider two alternative fairness criteria, adapted from the literature: envy-freeness and order preservation. For each setting, we provide either impossibility results or algorithms (either exact or heuristic) to find such a fair tournament. We show through experiments that our heuristics are both efficient and effective. Finally, using a combination of analytic and experimental tools we investigate the optimality of ordinal solutions for three objective functions: maximizing the predictive power, maximizing the expected value of the winner, and maximizing the revenue of the tournament. The analysis relies on innovative upper bounds that allow us to evaluate the optimality of any seeding, even when the number of possible seedings is extremely large.