Edward K. Baker

Computational experiments with algorithms for a class of routing problems

Abstract The vehicle routing problem, a generalization of the infamous traveling salesman problem, is a well-known distribution management problem that has been the focus of much research attention. On the other hand, generalizations of arc routing problems, such as the Chinese postman problem, have been comparatively neglected. In a recent paper, we studied a class of capacitated arc routing problems from primarily a theoretical point of view. In this paper, we focus on the development and testing of algorithms for solving the capacitated Chinese postman problem. Extensive computational results are presented and analyzed.

Technical Note-An Exact Algorithm for the Time-Constrained Traveling Salesman Problem

The time-constrained traveling salesman problem is a variation of the familiar traveling salesman problem that includes time window constraints on the time a particular city, or cities, may be visited. This note presents a concise formulation of the time-constrained traveling salesman problem. The model assumes that the distances of the problem are symmetrical and that the triangle inequality holds. Additionally, the model allows the salesman to wait at a city, if necessary, for a time window to open. The dual of the formulation is shown to be a disjunctive graph model, which is well known from scheduling theory. A longest path algorithm is used to obtain bounding information for subproblems in a branch and bound solution procedure. Computational results are presented for several small to moderate size problems.

Solution Improvement Heuristics for the Vehicle Routing and Scheduling Problem with Time Window Constraints

SYNOPTIC ABSTRACTBranch exchange techniques, such as the well-known 2-opt and 3-opt procedures, are among the most powerful heuristics available for the solution of the classic vehicle routing problem. The imposition of time window constraints on customer delivery time within the vehicle routing problem, however, introduces several complexities that can reduce the power of these techniques. In this paper, two test data sets for the vehicle routing and scheduling problem with time window constraints are studied. Initial solutions are obtained using a variety of heuristics. These solutions are then improved using branch exchange procedures modified to incorporate the time window constraints.

Efficient Heuristic Solutions to an Airline Crew Scheduling Problem

Abstract This paper presents an application of efficient, heuristic solution procedures to the airline crew scheduling problem of the Federal Express Corporation. It is demonstrated that near-optimal solutions to this class of very large airline crew scheduling problems may be obtained by using heuristic procedures similar to those used in vehicle routing and scheduling. As a result of this research, the procedures developed here have been implemented and are in use, on a monthly basis, at the Federal Express Corporation.

Using simulation to study the impact of work rules on productivity at marine container terminals

Abstract In this paper, we describe a simulation program that models the transfer of containerized cargo to and from ships. Container port operations are extremely important from an economic standpoint, making them a prime target for productivity improvements. They are also inherently very complex since they are at the center of two or more modes of transportation, involve the interaction of several organizations and support groups, and rely on a variety of stochastic processes. The simulation program allows the operator to specify a wide variety of parameters and the manner in which the simulation is to be executed. The major focus of the paper is on the impact of work crew schedules on container port productivity.

Controlled Rounding of Tabular Data

Controlled rounding is a procedure that perturbs tabular data collected from respondents in such a way as to preserve the anonymity of the respondents while maintaining the integrity of the data. The three-dimensional controlled rounding problem is NP-complete. This paper describes a binary tree search algorithm for solving three-dimensional problems based on linear programming techniques. Computational results obtained from tests with over 31,000 randomly generated tables and 292 real-life tables have shown that this algorithm can effectively find controlled roundings when they exist or determine that no solution exists. The computational results also demonstrate that the running time of the search algorithm can be cut in half by using a heuristic for initializing the simplex basis for the linear programming problems.

Computational results for very large air crew scheduling problems

The airline crew scheduling problem is typically formulated as a set covering problem. The Federal Express Corporation has recently implemented a heuristic crew scheduling system based on this model. The system has been implemented on an IBM 3033 computer. Computational results are presented for crew scheduling problems with up to 3000 rows and 15,000 columns. Results of operational quality are obtained in less than one hour of computer time. This model provides a prototype for a wide variety of large scale crew scheduling applications.

Efficient heuristic algorithms for the weighted set covering problem

Abstract In this paper two heuristic algorithms are presented for the weighted set covering problem. The first algorithm uses a simple, polynomial procedure to construct feasible covering solutions. The procedure is shown to possess a worst case performance bound that is a function of the size of the problem. The second algorithm is a solution improvement procedure that attempts to form reduced cost composite solutions from available feasible covering solutions. Computational results are presented for both algorithms on several large set covering problems generated from airline crew scheduling data.

Experimentation in optimization

Abstract The purpose of this paper is to focus on experimentation issues in optimization. In it, we examine the key factors that impact any computational experiment. Statistical methods of experimentation are reviewed and examples of their use are provided. Complicating factors that arise frequently are also discussed. At the heart of the paper are three diverse case studies which collectively illustrate a host of recurring themes. The paper should be of interest to practitioners as well as researchers.

Extending the Horizons: Advances in Computing, Optimization, and Decision Technologies

This book represents the results of cross-fertilization between OR/MS and CS/AI. It is this interface of OR/CS that makes possible advances that could not have been achieved in isolation. Taken collectively, these articles are indicative of the state-of-the-art in the interface between OR/MS and CS/AI and of the high caliber of research being conducted by members of the INFORMS Computing Society.