Craig A. Tovey

The computational difficulty of manipulating an election

We show how computational complexity might protect the integrity of social choice. We exhibit a voting rule that efficiently computes winners but is computationally resistant to strategic manipulation. It is NP-complete for a manipulative voter to determine how to exploit knowledge of the preferences of others. In contrast, many standard voting schemes can be manipulated with only polynomial computational effort.

Voting schemes for which it can be difficult to tell who won the election

We show that a voting scheme suggested by Lewis Carroll can be impractical in that it can be computationally prohibitive (specifically, NP-hard) to determine whether any particular candidate has won an election. We also suggest a class of “impracticality theorems” which say that any fair voting scheme must, in the worst-case, require excessive computation to determine a winner.

How hard is it to control an election

Some voting schemes that are in principle susceptible to control are nevertheless resistant in practice due to excessive computational costs; others are vulnerable. We illustrate this in detail for plurality voting and for Condorcet voting.

On Honey Bees and Dynamic Server Allocation in Internet Hosting Centers

Internet centers host services for e-banks, e-auctions and other clients. Hosting centers then must allocate servers among clients to maximize revenue. The limited number of servers, costs of reallocating servers, and unpredictability of requests make server allocation optimization difficult Based on the many similarities between server and honey bee colony forager allocation, we pro pose a new decentralized honey bee algorithm which dynamically allocates servers to satisfy request loads. We compare it against an omniscient optimality algorithm, a conventional greedy algorithm, and an algorithm that computes omnisciently the optimal static allocation. We evaluate performance on simulated request streams and commercial trace data Our algorithm performs better than static or greedy for highly variable request loads, but greedy can outperform it under low variability. Honey bee forager allocation, though suboptimal for static food sources, may possess a counterbalancing responsiveness to food source variability.

Auction-Based Multi-Robot Routing.

Recently, auction methods have been investigated as effective, decentralized methods for multi-robot coordination. Experimental research has shown great potential, but has not been complemented yet by theoretical analysis. In this paper we contribute a theoretical analysis of the performance of auction methods for multi-robot routing. We suggest a generic framework for auction-based multi-robot routing and analyze a variety of bidding rules for different team objectives. This is the first time that auction methods are shown to offer theoretical guarantees for such a variety of bidding rules and team objectives.

Automatic generation of linear-time algorithms from predicate calculus descriptions of problems on recursively constructed graph families

This paper describes a predicate calculus in which graph problems can be expressed. Any problem possessing such an expression can be solved in linear time on any recursively constructed graph, once its decomposition tree is known. Moreover, the linear-time algorithm can be generatedautomatically from the expression, because all our theorems are proved constructively. The calculus is founded upon a short list of particularly primitive predicates, which in turn are combined by fundamental logical operations. This framework is rich enough to include the vast majority of known linear-time solvable problems.We have obtained these results independently of similar results by Courcelle [11], [12], through utilization of the framework of Bernet al. [6]. We believe our formalism is more practical for programmers who would implement the automatic generation machinery, and more readily understood by many theorists.

A SIMPLIFIED NP-COMPLETE SATISFIABILITY PROBLEM

3-SAT is NP-complete when restricted to instances where each variable appears in at most four clauses. When no variable appears in more than three clauses, 3-SAT is trivial and SAT is NPcomplete. When no variable appears in more than two clauses, SAT may be solved in linear time.

Individual differences versus social dynamics in the formation of animal dominance hierarchies

Linear hierarchies, the classical pecking-order structures, are formed readily in both nature and the laboratory in a great range of species including humans. However, the probability of getting linear structures by chance alone is quite low. In this paper we investigate the two hypotheses that are proposed most often to explain linear hierarchies: they are predetermined by differences in the attributes of animals, or they are produced by the dynamics of social interaction, i.e., they are self-organizing. We evaluate these hypotheses using cichlid fish as model animals, and although differences in attributes play a significant part, we find that social interaction is necessary for high proportions of groups with linear hierarchies. Our results suggest that dominance hierarchy formation is a much richer and more complex phenomenon than previously thought, and we explore the implications of these results for evolutionary biology, the social sciences, and the use of animal models in understanding human social organization.

Automated process planning for printed circuit card assembly

Printed circuit card assemblies form the core of a vast array of contemporary manufactured products. The technologies for assembling printed circuit cards require a hierarchy of complex decisions for grouping card types and processes, staging components at assembly machines, arranging feeders, and sequencing placement operations. This paper is motivated by the largely unmet needs of industrial process planners for computer aids. Our objective is to develop a framework for the printed circuit card assembly process planning problem and to assess the current state of the research on appropriate models and solution methods. We first provide an overview of the essential elements of printed circuit card terminology, assembly technologies, and assembly system operations. Then we propose a decision hierarchy, survey the published literature, and identify needs for future research.

The Generation of Bidding Rules for Auction-Based Robot Coordination

Robotics researchers have used auction-based coordination systems for robot teams because of their robustness and efficiency. However, there is no research into systematic methods for deriving appropriate bidding rules for given team objectives. In this paper, we propose the first such method and demonstrate it by deriving bidding rules for three possible team objectives of a multi-robot exploration task. We demonstrate experimentally that the resulting bidding rules indeed exhibit good performance for their respective team objectives and compare favorably to the optimal performance. Our research thus allows the designers of auction-based coordination systems to focus on developing appropriate team objectives, for which good bidding rules can then be derived automatically.