Erik Rolland

The Design of Reverse Distribution Networks: Models and Solution Procedures

Reverse distribution, or the management of product return flows, induced by various forms of reuse of products and materials, has received growing attention throughout this decade. In this paper we discuss reverse distribution, and propose a mathematical programming model for a version of this problem. Due to the complexity of the proposed model, we introduce a heuristic solution methodology for this problem. The solution methodology complements a heuristic concentration procedure, where sub-problems with reduced sets of decision variables are iteratively solved to optimality. Based on the solutions from the sub-problems, a final concentration set of potential facility sites is constructed, and this problem is solved to optimality. The potential facility sites are then expanded in a greedy fashion to obtain the final solution. This ‘‘heuristic expansion’’ was also performed using the solution found with a greedy heuristic to provide a short-list of potential facility sites. Computational tests demonstrate a great deal of promise for this solution method, as high-quality solutions are obtained while expending modest computational effort. � 2003 Published by Elsevier Science B.V.

An efficient tabu search procedure for the p-Median Problem

Abstract In this paper we present a new solution heuristic for the p-Median Problem. The algorithm is based on tabu search principles, and uses short term and long term memory, as well as strategic oscillation and random tabu list sizes. Our proposed procedure is compared with two other move heuristics: a well-known interchange heuristic and a recent hybrid heuristic. In computational tests on networks ranging in size up to 500 nodes the new heuristic is found to be superior with respect to the quality of solutions produced.

Tabu search for graph partitioning

In this paper, we develop a tabu search procedure for solving the uniform graph partitioning problem. Tabu search, an abstract heuristic search method, has been shown to have promise in solving several NP-hard problems, such as job shop and flow shop scheduling, vehicle routing, quadratic assignment, and maximum satisfiability. We compare tabu search to other heuristic procedures for graph partitioning, and demonstrate that tabu search is superior to other solution approaches for the uniform graph partitioning problem both with respect to solution quality and computational requirements.

Heuristic concentration and Tabu search: A head to head comparison

Earlier this year two papers applying the metaheuristics Tabu search (TS) and Heuristic concentration (HC) to the p-median problem were published in consecutive volumes of this journal. Here we apply the method of HC to some of the data sets which were used for computational experience in the paper on TS. For these examples, which we regard as being of a particularly challenging character, HC discovers the superior solution (superior to TS) in about 95% of the cases, and, where the optimal solution is known, the optimal solution in about 80% of the cases. No general conclusion on the relative times for the two approaches can be drawn.

A Memory Adaptive Reasoning Technique for Solving the Capacitated Minimum Spanning Tree Problem

In this paper we propose a hybrid memory adaptive heuristic for solving the Capacitated Minimum Spanning Tree (CMST) problem. We augment the problem formulation with additional non-redundant constraints via use of adaptive memory, to improve upon the performance of an elementary heuristic (the Esau-Williams heuristic). Our methodology is tested against many of the previously reported heuristics for the CMST. We conclude that our generalized procedure performs on par with the best of these approaches in terms of solution quality, while expending a very modest amount of computational effort.

Tabu Search in Audit Scheduling

In this paper, we present a heuristic procedure based on tabu search (TS) and intelligent memory structures for solving this problem. The TS method starts with a feasible schedule generated by a greedy forward dispatching procedure, then through a series of intensification and diversification steps it improves on the initial schedule. The improvement in the value of the objective function is observed interactively. The search can be terminated as the improvement in the value of the objective function stabilizes. Application of the TS method to different audit scheduling problems has consistently improved the value of the cost minimization objective function.

Efficient Algorithms for Solving the Shortest Covering Path Problem

The Shortest Covering Path Problem (SCPP) is one of identifying the least cost path from a pre-specified starting node to a pre-specified terminus node. The path is constrained by the condition that it must cover every node in the network. A node is considered to be covered if it is within some pre-specified covering distance of a node on the path. This SCPP has many potential applications, especially in hierarchical network design, and bi-modal routing problems. In this paper we introduce two efficient algorithms for solving the SCPP. The first is a heuristic based upon a Lagrangian relaxation of the problem. The second is an exact algorithm based upon a branch and bound procedure which utilizes the bounds generated by the Lagrangian relaxation scheme. Computational tests indicate that both procedures are very efficient. The heuristic identified and verified the optimal solution for 135 of the 160 test problems solved. The optimal solution to the remaining 25 problems was readily identified by the exact algorithm.

Knowledge-sharing in virtual communities: familiarity, anonymity and self-determination theory

Although the role of motivation has been emphasised in knowledge-sharing literature, traditional motivation theories, such as self-determination theory (SDT), have not been actively used as a research framework in knowledge-sharing research. The purposes of this study are twofold. The first objective is to propose a model, based on SDT, to test the effect of the three basic psychological needs – perceived competence, perceived autonomy and perceived relatedness – on knowledge-sharing behaviours in virtual communities. The second objective is to explore the effects of familiarity and anonymity on the basic psychological needs to better understand individuals’ knowledge-sharing behaviours in virtual communities. The results show that perceived competence and perceived relatedness influence knowledge-sharing behaviours in virtual communities; however, perceived autonomy does not influence knowledge-sharing behaviours; familiarity influences positively perceived competence and perceived relatedness, and anonymity influences negatively perceived autonomy and perceived relatedness.

Decision support system induced guidance for model formulation and solution

One of the critical functions of Decision Support System (DSS) is to provide system induced decision guidance for proper model formulation and solution. We show how to incorporate this type of system induced decision guidance into the design of the next generation of DSS. We suggest that a DSS should make decisions, or at least recommendations, regarding what models should be executed to solve problems most effectively and this information should be generated inductively and used deductively. This information then becomes the meta-model to induce the user to make appropriate choices. We provide an example that will illustrate how two specific problem characteristics, namely the tightness of constraints and the linearity of constraints, influence the solution quality and solution times for a specific class of test problems. We argue that a DSS should execute different formulations of the problem that lead to satisficing solutions guiding DSS users in finding the best approach to solve complex problems.

Improving outpatient health care quality: understanding the quality dimensions.

Abstract: Based on literature review, we derive a set of dimensions that influence patient-perceived health care quality. Utilizing outpatient survey data from 222 different physicians, we identified six underlying quality factors and classified them according to the derived dimensions. These quality factors explain approximately 51 percent of the variation in overall patient-perceived health care quality.