Versatile Industrial/Manufacturing Engineer with extensive research experience in the field of optimization algorithms for logistics and transportation problems. Address: Blacksburg, Virginia, United States
ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heu... more ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heuristics with biased-randomization processes. As it will be discussed later, this hybrid scheme represents an efficient, relatively simple, and flexible way to deal with several Combinatorial Optimization Problems in different fields, even when considering realistic constraints.
American journal of medical quality : the official journal of the American College of Medical Quality, Jan 28, 2015
This study demonstrates that it is possible to identify primary care physicians (PCPs) who perfor... more This study demonstrates that it is possible to identify primary care physicians (PCPs) who perform better or worse than expected in managing diabetes. Study subjects were 14 033 adult diabetics and their 133 PCPs. Logistic regression was used to predict the odds that a patient would have uncontrolled diabetes (defined as HbA1c ≥8%) based on patient-level characteristics alone. A second model predicted diabetes control from physician-level identity and characteristics alone. A third model combined the patient- and physician-level models using hierarchical logistic regression. Physician performance is calculated from the difference between the expected and observed proportions of patients with uncontrolled diabetes. After adjusting for important patient characteristics, PCPs were identified who performed better or worse than expected in managing diabetes. This strategy can be used to characterize physician performance in other chronic conditions. This approach may lead to new insights...
International Transactions in Operational Research, 2014
ABSTRACT This paper discusses horizontal cooperation in road transportation and supports the rele... more ABSTRACT This paper discusses horizontal cooperation in road transportation and supports the relevance of this praxis as a way of reducing delivery costs and greenhouse gas emissions. In a competitive market, costs reduction due to economies of scale in short and long run constitutes a key issue for small and medium enterprises. The paper reviews the existing literature on the topic and then examines different scenarios in order to quantify the savings in route costs that can be attained throughout horizontal cooperation. This numerical analysis is based on a set of well-known benchmarks for the Multidepot Vehicle Routing Problem, which has been adapted to illustrate a realistic but seldom considered example of horizontal cooperation. An Iterated Local Search algorithm is proposed to obtain high-quality solutions for this collaborative scenario, while noncollaborative scenarios are solved using a well-tested algorithm for the Capacitated Vehicle Routing Problem. The savings in routing costs—both regarding distance-based and environmental costs—are computed taking into account different geographical distributions of customers with respect to their assigned service providers.
Operations Research and Cyber-Infrastructure, 2009
Abstract In this paper we present SR-GCWS, a simulation-based algorithm for the Capacitated Vehic... more Abstract In this paper we present SR-GCWS, a simulation-based algorithm for the Capacitated Vehicle Routing Problem (CVRP). Given a CVRP instance, the SR-GCWS algorithm incorporates a randomness criterion to the classical Clarke and Wright Savings (CWS) heuristic and ...
ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heu... more ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heuristics with biased-randomization processes. As it will be discussed later, this hybrid scheme represents an efficient, relatively simple, and flexible way to deal with several Combinatorial Optimization Problems in different fields, even when considering realistic constraints.
"This paper describes a simulation–optimization algorithm for the Permutation Flow shop Prob... more "This paper describes a simulation–optimization algorithm for the Permutation Flow shop Problem with Stochastic processing Times (PFSPST). The proposed algorithm combines Monte Carlo simulation with an Iterated Local Search metaheuristic in order to deal with the stochastic behavior of the problem. Using the expected makespan as initial minimization criterion, our simheuristic approach is based on the assumption that high-quality solutions (permutations of jobs) for the deterministic version of the problem are likely to be high-quality solutions for the stochastic version – i.e., a correlation will exist between both sets of solutions, at least for moderate levels of variability in the stochastic processing times. No particular assumption is made on the probability distributions modeling each job-machine processing times. Our approach is able to solve, in just a few minutes or even less, PFSPST instances with hundreds of jobs and dozens of machines. Also, the paper proposes the use of reliability analysis techniques to analyze simulation outcomes or historical observations on the random variable representing the makespan associated with a given solution. This way, criteria other than the expected makespan can be considered by the decision maker when comparing different alternative solutions. A set of classical benchmarks for the deterministic version of the problem are adapted and tested under several scenarios, each of them characterized by a different level of uncertainty – variance level of job-machine processing times. "
ABSTRACT This paper discusses the two-dimensional loading capacitated vehicle routing problem (2L... more ABSTRACT This paper discusses the two-dimensional loading capacitated vehicle routing problem (2L-CVRP) with heterogeneous fleet (2L-HFVRP). The 2L-CVRP can be found in many real-life situations related to the transportation of voluminous items where two-dimensional packing restrictions have to be considered, e.g.: transportation of heavy machinery, forklifts, professional cleaning equipment, etc. Here, we also consider a heterogeneous fleet of vehicles, comprising units of different capacities, sizes and fixed/variable costs. Despite the fact that heterogeneous fleets are quite ubiquitous in real-life scenarios, there is a lack of publications in the literature discussing the 2L-HFVRP. In particular, to the best of our knowledge no previous work discusses the non-oriented 2L-HFVRP, in which items are allowed to be rotated during the truck-loading process. After describing and motivating the problem, a literature review on related work is performed. Then, a multi-start algorithm based on biased randomization of routing and packing heuristics is proposed. A set of computational experiments contribute to illustrate the scope of our approach, as well as to show its efficiency.
ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heu... more ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heuristics with biased-randomization processes. As it will be discussed later, this hybrid scheme represents an efficient, relatively simple, and flexible way to deal with several Combinatorial Optimization Problems in different fields, even when considering realistic constraints.
American journal of medical quality : the official journal of the American College of Medical Quality, Jan 28, 2015
This study demonstrates that it is possible to identify primary care physicians (PCPs) who perfor... more This study demonstrates that it is possible to identify primary care physicians (PCPs) who perform better or worse than expected in managing diabetes. Study subjects were 14 033 adult diabetics and their 133 PCPs. Logistic regression was used to predict the odds that a patient would have uncontrolled diabetes (defined as HbA1c ≥8%) based on patient-level characteristics alone. A second model predicted diabetes control from physician-level identity and characteristics alone. A third model combined the patient- and physician-level models using hierarchical logistic regression. Physician performance is calculated from the difference between the expected and observed proportions of patients with uncontrolled diabetes. After adjusting for important patient characteristics, PCPs were identified who performed better or worse than expected in managing diabetes. This strategy can be used to characterize physician performance in other chronic conditions. This approach may lead to new insights...
International Transactions in Operational Research, 2014
ABSTRACT This paper discusses horizontal cooperation in road transportation and supports the rele... more ABSTRACT This paper discusses horizontal cooperation in road transportation and supports the relevance of this praxis as a way of reducing delivery costs and greenhouse gas emissions. In a competitive market, costs reduction due to economies of scale in short and long run constitutes a key issue for small and medium enterprises. The paper reviews the existing literature on the topic and then examines different scenarios in order to quantify the savings in route costs that can be attained throughout horizontal cooperation. This numerical analysis is based on a set of well-known benchmarks for the Multidepot Vehicle Routing Problem, which has been adapted to illustrate a realistic but seldom considered example of horizontal cooperation. An Iterated Local Search algorithm is proposed to obtain high-quality solutions for this collaborative scenario, while noncollaborative scenarios are solved using a well-tested algorithm for the Capacitated Vehicle Routing Problem. The savings in routing costs—both regarding distance-based and environmental costs—are computed taking into account different geographical distributions of customers with respect to their assigned service providers.
Operations Research and Cyber-Infrastructure, 2009
Abstract In this paper we present SR-GCWS, a simulation-based algorithm for the Capacitated Vehic... more Abstract In this paper we present SR-GCWS, a simulation-based algorithm for the Capacitated Vehicle Routing Problem (CVRP). Given a CVRP instance, the SR-GCWS algorithm incorporates a randomness criterion to the classical Clarke and Wright Savings (CWS) heuristic and ...
ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heu... more ABSTRACT The main goal of this chapter is to present a hybrid scheme which combines classical heuristics with biased-randomization processes. As it will be discussed later, this hybrid scheme represents an efficient, relatively simple, and flexible way to deal with several Combinatorial Optimization Problems in different fields, even when considering realistic constraints.
"This paper describes a simulation–optimization algorithm for the Permutation Flow shop Prob... more "This paper describes a simulation–optimization algorithm for the Permutation Flow shop Problem with Stochastic processing Times (PFSPST). The proposed algorithm combines Monte Carlo simulation with an Iterated Local Search metaheuristic in order to deal with the stochastic behavior of the problem. Using the expected makespan as initial minimization criterion, our simheuristic approach is based on the assumption that high-quality solutions (permutations of jobs) for the deterministic version of the problem are likely to be high-quality solutions for the stochastic version – i.e., a correlation will exist between both sets of solutions, at least for moderate levels of variability in the stochastic processing times. No particular assumption is made on the probability distributions modeling each job-machine processing times. Our approach is able to solve, in just a few minutes or even less, PFSPST instances with hundreds of jobs and dozens of machines. Also, the paper proposes the use of reliability analysis techniques to analyze simulation outcomes or historical observations on the random variable representing the makespan associated with a given solution. This way, criteria other than the expected makespan can be considered by the decision maker when comparing different alternative solutions. A set of classical benchmarks for the deterministic version of the problem are adapted and tested under several scenarios, each of them characterized by a different level of uncertainty – variance level of job-machine processing times. "
ABSTRACT This paper discusses the two-dimensional loading capacitated vehicle routing problem (2L... more ABSTRACT This paper discusses the two-dimensional loading capacitated vehicle routing problem (2L-CVRP) with heterogeneous fleet (2L-HFVRP). The 2L-CVRP can be found in many real-life situations related to the transportation of voluminous items where two-dimensional packing restrictions have to be considered, e.g.: transportation of heavy machinery, forklifts, professional cleaning equipment, etc. Here, we also consider a heterogeneous fleet of vehicles, comprising units of different capacities, sizes and fixed/variable costs. Despite the fact that heterogeneous fleets are quite ubiquitous in real-life scenarios, there is a lack of publications in the literature discussing the 2L-HFVRP. In particular, to the best of our knowledge no previous work discusses the non-oriented 2L-HFVRP, in which items are allowed to be rotated during the truck-loading process. After describing and motivating the problem, a literature review on related work is performed. Then, a multi-start algorithm based on biased randomization of routing and packing heuristics is proposed. A set of computational experiments contribute to illustrate the scope of our approach, as well as to show its efficiency.
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