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Barrett W. Thomas

Bio: Barrett W. Thomas is an academic researcher from University of Iowa. The author has contributed to research in topics: Vehicle routing problem & Markov decision process. The author has an hindex of 27, co-authored 67 publications receiving 1993 citations.


Papers
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Journal ArticleDOI
TL;DR: The stochastic p-hub center problem with chance constraints is presented, which is used to model the service-level guarantees of small package delivery companies and discusses analytical results, proposed solution heuristics, and the results from computational experiments.

156 citations

Journal ArticleDOI
TL;DR: This work introduces a multi-vehicle dynamic pickup and delivery problem with time constraints that incorporates key features associated with same-day delivery logistics and incorporates information about future requests into routing decisions to make better informed decisions.
Abstract: Same-day delivery for online purchases is a recent trend in online retail We introduce a multi-vehicle dynamic pickup and delivery problem with time constraints that incorporates key features associated with same-day delivery logistics To make better informed decisions, our solution approach incorporates information about future requests into routing decisions We also introduce an analytical result that identifies when it is beneficial for vehicles to wait at the depot We present a wide range of computational experiments that demonstrate the value of our approach The results show that more requests can be filled when time windows are evenly spread throughout the day compared to when many requests' time windows occur late in the day However, the anticipation of future requests is most valuable when many requests' time windows occur late in the day As a result of increased flexibility, experiments also demonstrate that the value of anticipating the future decreases when the number of vehicles or the

149 citations

Journal ArticleDOI
01 Dec 2018-Networks
TL;DR: This paper analyze how drones can be combined with regular delivery vehicles to improve same-day delivery performance and reveals that geographical districting is highly effective increasing the expected number of sameday deliveries and a combination of drone and vehicle fleets may reduce routing costs significantly.
Abstract: In this paper, we analyze how drones can be combined with regular delivery vehicles to improve same-day delivery performance. To this end, we present a dynamic vehicle routing problem with heterogeneous fleets. Customers order goods over the course of the day. These goods are delivered either by a drone or by a regular transportation vehicle within a delivery deadline. Drones are faster but have a limited capacity as well as charging times. Vehicles capacities are unlimited but vehicles are slow due to urban traffic. To decide whether an order is delivered by a drone or by a vehicle, we present a policy function approximation based on geographical districting. Our computational study reveals two major implications: First, geographical districting is highly effective increasing the expected number of sameday deliveries. Second, a combination of drone and vehicle fleets may reduce routing costs significantly.

136 citations

Journal ArticleDOI
TL;DR: A variant of simulated annealing incorporating a variable penalty method to solve the traveling-salesman problem with time windows (TSPTW) compares favorably with benchmark results in the literature, obtaining best known results for numerous instances.
Abstract: This paper describes a variant of simulated annealing incorporating a variable penalty method to solve the traveling-salesman problem with time windows (TSPTW). Augmenting temperature from traditional simulated annealing with the concept of pressure (analogous to the value of the penalty multiplier), compressed annealing relaxes the time-window constraints by integrating a penalty method within a stochastic search procedure. Computational results validate the value of a variable-penalty method versus a static-penalty approach. Compressed annealing compares favorably with benchmark results in the literature, obtaining best known results for numerous instances.

134 citations

Journal ArticleDOI
TL;DR: This paper introduces a variant of the orienteering problem in which travel and service times are stochastic, and discusses special cases of the problem that can be solved exactly and heuristics for general problem instances.
Abstract: In this paper, we introduce a variant of the orienteering problem in which travel and service times are stochastic. If a delivery commitment is made to a customer and is completed by the end of the day, a reward is received, but if a commitment is made and not completed, a penalty is incurred. This problem reflects the challenges of a company who, on a given day, may have more customers than it can serve. In this paper, we discuss special cases of the problem that we can solve exactly and heuristics for general problem instances. We present computational results for a variety of parameter settings and discuss characteristics of the solution structure.

117 citations


Cited by
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Journal Article
TL;DR: This book by a teacher of statistics (as well as a consultant for "experimenters") is a comprehensive study of the philosophical background for the statistical design of experiment.
Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

13,333 citations

Journal ArticleDOI
TL;DR: The rationale underlying the iterated racing procedures in irace is described and a number of recent extensions are introduced, including a restart mechanism to avoid premature convergence, the use of truncated sampling distributions to handle correctly parameter bounds, and an elitist racing procedure for ensuring that the best configurations returned are also those evaluated in the highest number of training instances.

1,280 citations

Journal ArticleDOI
TL;DR: This survey classifies routing problems from the perspective of information quality and evolution and presents a comprehensive review of applications and solution methods for dynamic vehicle routing problems.

1,066 citations

Journal ArticleDOI
TL;DR: This classification is the first to categorize the articles of the VRP literature to this level of detail and is based on an adapted version of an existing comprehensive taxonomy.

800 citations