John J. Bartholdi

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.

Single transferable vote resists strategic voting

We give evidence that Single Tranferable Vote (STV) is computationally resistant to manipulation: It is NP-complete to determine whether there exists a (possibly insincere) preference that will elect a favored candiate, even in an election for a single seat. Thus strategic voting under STV is qualitatively more difficult than under other commonly-used voting schemes. Furthermore, this resistance to manipulation is inherent to STV and does not depend on hopeful extraneous assumptions like the presumed difficulty of learning the preferences of the other voters. We also prove that it is NP-complete to recognize when an STV election violates monotonicity. This suggests that non-monotonicity in STV elections might be perceived as less threatening since it is in effect “hidden” and hard to exploit for strategic advantage.

Reducing Labor Costs in an LTL Crossdocking Terminal

A carrier designed for accepting a wide variety of vases employed in the floral trade is conveniently formed from plastic. The carrier configuration provides for ready adaptation to a wide range of vase sizes and shapes and prevents tipping during transportation and delivery of floral arrangements. Two general types of carriers are disclosed, a first type being used generally for most shapes and sizes of floral vase, and the other type being employed specially for a class of irregular shapes, such as for bulky oblong or rectangular vases.

Decentralized Control of Automated Guided Vehicles on a Simple Loop

Abstract A highly decentralized greedy heuristic will enable a fleet of automated guided vehicles to deliver unit loads quickly on a simple loop track.

Spacefilling curves and the planar travelling salesman problem

To construct a short tour through points in the plane, the points are sequenced as they appear along a spacefilling curve. This heuristic consists essentially of sorting, so it is easily coded and requires only <italic>O</italic>(<italic>N</italic>) memory and <italic>O</italic>(<italic>N</italic> log <italic>N</italic>) operations. Its performance is competitive with that of other fast methods.

A Guaranteed-Accuracy Round-off Algorithm for Cyclic Scheduling and Set Covering

The problem of cyclic staff scheduling is solved by a linear programming round-off heuristic for which a bound on the absolute error is established. The quality of the bound is independent of the resource requirements. Moreover, the quality of the bound improves as the matrix of resource availability approximates the property of consecutive ones. The appropriateness of the heuristic is further established by showing that cyclic staff scheduling is NP-complete.

Retrieval Strategies for a Carousel Conveyor

Abstract We analyze algorithms that sequence the retrieval of items from a carousel conveyor, and show how the appropriate algorithm depends on the load to which the carousel is subjected. In general, as the load increases, so does the quality of solutions produced by simple heuristics. We conclude by recommending certain greedy heuristics for the problems of sequencing the retrieval of orders and for sequencing the retrieval of the items within each order.

Task partitioning in insect societies: bucket brigades

Summary: There are many ways in which social insect foragers may organise the collection of resources and their transportation back to the nest. One way is to partition the task into a number of sequential stages in which material is passed from one worker to another in a relay fashion. This relatively new concept is known as task partitioning. In this study, we focus on a particular form of task partitioning, bucket brigades, which we define as a multistage (i.e., three or more stages) partitioned transport scheme that uses only direct transfer between individual workers and without any predetermined transfer locations, other than the first or last stages. We first consider the potential costs and benefits of bucket brigades compared to other transportation schemes. We then use theory and computer simulation to analyse some of these aspects in detail. In one empirical study of a bucket brigade, foragers were generally found to be sequenced from smallest (near the food source) to fastest (nearest the nest). This exactly matches what dynamical systems theory would predict as an ergonomically efficient solution. However, we also demonstrate that a single and simple local rule - larger ants win fights over material - will generate this sequencing as an epiphenomenon that is not necessarily optimal. We use the behaviour of bucket brigades to reveal some general points about the optimality of task partitioning in more detail.