Showing papers in "Journal of the Operational Research Society in 2002"
TL;DR: This book is most obviously relevant to practitioners who already have some experience of multiagency facilitation, but might also serve as an introduction to working in this arena, if carefully supplemented with further reading and exploration of the topics it covers.
Abstract: (2002). Business Dynamics—Systems Thinking and Modeling for a Complex World. Journal of the Operational Research Society: Vol. 53, No. 4, pp. 472-473.
2,977 citations
TL;DR: Several of the most important classical and modern heuristics for the vehicle routing problem are summarized and compared using four criteria: accuracy, speed, simplicity and flexibility.
Abstract: Several of the most important classical and modern heuristics for the vehicle routing problem are summarized and compared using four criteria: accuracy, speed, simplicity and flexibility. Computational results are reported.
620 citations
TL;DR: In this note, Goyal's model is amended by considering the difference between unit price and unit cost and an easy analytical closed-form solution is established, which reveals the following two managerial phenomena.
Abstract: In this note, I amend Goyal's model by considering the difference between unit price and unit cost. I then establish an easy analytical closed-form solution to the problem. The theoretical results obtained here reveal the following two managerial phenomena. (1) In certain cases, the economic replenishment interval and order quantity decreases under the permissible delay in payments, which contradicts to Goyal's conclusion. It makes economic sense for some customers to order less quantity (or shorten the replenishment time interval) and to take the benefits of the permissible delay more frequently. (2) If a supplier wants to reduce his/her large level of inventory, then he/she should charge an excessive interest rate on his/her customer's outstanding amount after the credit term expires. Consequently, his/her customers will order to buy more quantity than the classical economic order quantity. As a matter of fact, these two managerial phenomena have been demonstrated in the decision making of using credit cards. For example, most credit card companies provide card holders 25 days of grace period, and charge 18-20% interest on the amount past due (ie, the second phenomenon). However, for a well-established credit card holder, he/she will take the benefit of 25 days of grace period constantly, but will not spend over his/her limit and face an excessive finance charge (ie, the first phenomenon).
443 citations
TL;DR: The authors propose a three-step model by which companies can obtain knowledge from customers that comes from social interactions with firm employees, and identifies cultural changes required to make this process successful.
Abstract: Customer knowledge has received little attention in the knowledge management literature. The authors of this exploratory study argue that practices in marketing and customer relationship management have not been able to capture knowledge from customers that comes from social interactions with firm employees. The authors propose a three-step model by which companies can obtain this knowledge. The model's theoretical base comes from the information retrieval and socialization concepts of the knowledge management literature. The paper identifies cultural changes required to make this process successful.
341 citations
TL;DR: This paper demonstrates that simple deterministic spreadsheet calculations typically do not provide the appropriate information and result in underestimating true bed requirements, and development and use of a more sophisticated, flexible and necessarily detailed capacity models are needed.
Abstract: The internal dynamics of a hospital represent a complex non-linear structure. Planning and management of bed capacities must be evaluated within an environment of uncertainty, variability and limited resources. A common approach is to plan and manage capacities based on simple deterministic spreadsheet calculations. This paper demonstrates that these calculations typically do not provide the appropriate information and result in underestimating true bed requirements. More sophisticated, flexible and necessarily detailed capacity models are needed. The development and use of such a simulation model is presented in this paper. The modelling work, in conjunction with a major UK NHS Trust, considers various types of patient flows, at the individual patient level, and resulting bed needs over time. The consequence of changes in capacity planning policies and management of existing capacities can be readily examined. The work has highlighted the need for evaluating hospital bed capacities in light of both bed occupancies and refused admission rates. The relationship between occupancy and refusals is complex and often overlooked by hospital managers.
304 citations
TL;DR: A survey of OR/MS practitioners is reported on to discover the extent of multimethodology usage and which particular combinations are most commonly utilised.
Abstract: There is now a vast range of techniques and methodologies, both hard and soft, available to the OR/MS practitioner. After a period of concern about methodology choice, ie ‘which method when’, we are now moving towards a pluralistic approach of combining together several methods within an intervention—multimethodology. This paper reports on a survey of OR/MS practitioners to discover the extent of multimethodology usage and which particular combinations are most commonly utilised.
191 citations
TL;DR: A queueing model is used to determine the main characteristics of the access of patients to hospital, such as mean bed occupancy and the probability that a demand for hospital care is lost because all beds are occupied.
Abstract: The aim of this paper is, on the one hand, to describe the movement of patients through a hospital department by using classical queueing theory and, on the other hand, to present a way of optimising the use of hospital resources in order to improve hospital care. A queueing model is used to determine the main characteristics of the access of patients to hospital, such as mean bed occupancy and the probability that a demand for hospital care is lost because all beds are occupied. Moreover, we present a technique for optimising the number of beds in order to maintain an acceptable delay probability at a sufficiently low level and, finally, a way of optimising the average cost per day by balancing costs of empty beds against costs of delayed patients.
185 citations
TL;DR: This paper develops a solution procedure that considers each objective separately and search for a set of efficient solutions instead of a single optimum within the framework of the evolutionary approach known as scatter search.
Abstract: In this paper we address the problem of routing school buses in a rural area. We approach this problem with a node routing model with multiple objectives that arise from conflicting viewpoints. From the point of view of cost, it is desirable to minimise the number of buses used to transport students from their homes to school and back. From the point of view of service, it is desirable to minimise the time that a given student spends en route. The current literature deals primarily with single-objective problems and the models with multiple objectives typically employ a weighted function to combine the objectives into a single one. We develop a solution procedure that considers each objective separately and search for a set of efficient solutions instead of a single optimum. Our solution procedure is based on constructing, improving and then combining solutions within the framework of the evolutionary approach known as scatter search. Experimental testing with real data is used to assess the merit of our proposed procedure.
176 citations
TL;DR: In this paper, the shortcomings of the cost and allocative efficiencies as used in the DEA literature are pointed out, and a new approach to the cost efficiency evaluation is proposed.
Abstract: In this paper we point out the shortcomings of the cost and allocative efficiencies as used in the DEA literature, and propose a new approach to the cost efficiency evaluation
174 citations
TL;DR: A framework for dynamic routing systems based on their degree of dynamism is proposed and the Partially Dynamic Travelling Repairman Problem is introduced and several dynamic policies to minimize routing costs are described.
Abstract: In this paper we propose a framework for dynamic routing systems based on their degree of dynamism. Next, we consider its impact on solution methodology and quality. Specifically, we introduce the Partially Dynamic Travelling Repairman Problem and describe several dynamic policies to minimize routing costs. The results of our computational study indicate that increasing the dynamic level results in a linear increase in route length for all policies studied. Furthermore, a Nearest Neighbour policy performed, on the average, uniformly better than the other dispatching rules studied. Among these, a Partitioning policy produced only slightly higher average route lengths.
168 citations
TL;DR: This work describes an Ant Colony Optimization (ACO) algorithm having a new feature using look-ahead information in the transition rule that shows an improvement in performance.
Abstract: We compare several heuristics for solving a single machine scheduling problem. In the operating situation modelled, setup times are sequence-dependent and the objective is to minimize total tardiness. We describe an Ant Colony Optimization (ACO) algorithm having a new feature using look-ahead information in the transition rule. This feature shows an improvement in performance. A comparison with a genetic algorithm, a simulated annealing approach, a local search method and a branch-and-bound algorithm indicates that the ACO that we describe is competitive and has a certain advantage for larger problems.
TL;DR: The global efficiency approach is introduced as a means to improve the discriminating power of Data Envelopment Analysis (DEA) and the units that can maintain their efficiency score under common weighting structures are dealt with.
Abstract: We introduce in this paper the global efficiency approach as a means to improve the discriminating power of Data Envelopment Analysis (DEA). To discriminate further among the DEA efficient units, we deal only with the units that can maintain their efficiency score under common weighting structures. Then we proceed further to ranking the whole set of DEA efficient units. We compare the global efficiency approach with the multi-criteria DEA and the cross-efficiency approaches on the basis of characteristic numerical examples drawn from the literature.
TL;DR: The Weibull proportional-hazards model is used to determine the optimal replacement policy for a critical item which is subject to vibration monitoring, and the policy is validated using data that arose from subsequent operation of the plant.
Abstract: This paper describes a case study in which the Weibull proportional-hazards model is used to determine the optimal replacement policy for a critical item which is subject to vibration monitoring. Such an approach has been used to date in the context of monitoring through oil debris analysis, and this approach is extended in this paper to the vibration monitoring context. The Weibull proportional-hazards model is reviewed along with the software EXAKT used for optimization. In particular the case considers condition-based maintenance for circulating pumps in a coal wash plant that is part of the SASOL petrochemical company. The condition-based maintenance policy recommended in this study is based on histories collected over a period of 2 years, and is compared with current practice. The policy is validated using data that arose from subsequent operation of the plant.
TL;DR: It is clear that the use of principal components can noticeably improve the strength of DEA models.
Abstract: This research further develops the combined use of principal component analysis (PCA) and data envelopment analysis (DEA). The aim is to reduce the curse of dimensionality that occurs in DEA when there is an excessive number of inputs and outputs in relation to the number of decision-making units. Three separate PCA–DEA formulations are developed in the paper utilising the results of PCA to develop objective, assurance region type constraints on the DEA weights. The first model applies PCA to grouped data representing similar themes, such as quality or environmental measures. The second model, if needed, applies PCA to all inputs and separately to all outputs, thus further strengthening the discrimination power of DEA. The third formulation searches for a single set of global weights with which to fully rank all observations. In summary, it is clear that the use of principal components can noticeably improve the strength of DEA models.
TL;DR: This paper replaces ordinary DEA formulations with stochastic counterparts in the form of a series of chance constrained programming models, with emphasis on technical efficiencies and inefficiencies which do not require costs or prices.
Abstract: This paper replaces ordinary DEA formulations with stochastic counterparts in the form of a series of chance constrained programming models. Emphasis is on technical efficiencies and inefficiencies which do not require costs or prices, but which are nevertheless basic in that the achievement of technical efficiency is necessary for the attainment of ‘allocative’, ‘cost’ and other types of efficiencies.
TL;DR: The paper argues that performance management should embrace four broad functions: formulation of strategy; development of performance measurement instruments; interpreting such measures; and encouraging appropriate organizational responses to performance information.
Abstract: The practice, teaching and research of management is peculiarly vulnerable to fads. A cynic might suggest that this is the result of a lively market in management gurus, in which the latest management concept is promoted as an indispensable tool for the modern manager. However, it might also be the case that some apparent fads do indicate a real change in the preoccupations and needs of managers. The explosion in interest in performance management (PM) since the mid-1990s may indeed be one such case.
TL;DR: The results of a major international survey into the relationship between corporate strategy, supply chain strategy and supply chain performance management are reported and there is evidence of inconsistency in the way many businesses relate their supply chain, corporate, and investment strategy.
Abstract: The results of a major international survey into the relationship between corporate strategy, supply chain strategy and supply chain performance management are reported. Five clearly defined groups are identified: Supply Chain Leaders, Strong and Weak Players, Lagging Players and Non-players. Those business units that report a close link between their supply chain strategy and their supply chain technology, in comparison with those that report a weaker link, displayed a consistent set of characteristics. They rate supply chain strategy as more important for corporate strategy. They have a relatively sophisticated definition of their supply chain strategy. They think their supply chain is more important in achieving competitive advantage, they have invested more in supply chain infrastructure and IT support and they have more formal means of assessing their supply chain performance. There is evidence of inconsistency in the way many businesses relate their supply chain, corporate, and investment strategy.
TL;DR: A method for establishing a berth schedule consisting of berthing times and berthing positions of containerships in port container terminals is addressed and a Lagrangean relaxation model of the discretized model is solved using a sub-gradient optimization technique.
Abstract: A method for establishing a berth schedule consisting of berthing times and berthing positions of containerships in port container terminals is addressed in this paper. Each vessel requires a specific amount of space on the berth during a predetermined length of time for unloading and loading containers. The berth schedule must be constructed in a way to satisfy requests from carriers on berthing times and minimize handling efforts during ship operation. A mixed integer program is formulated for the berth-scheduling problem, which can be solved using a commercial package. In order to overcome the computational load of the mixed integer program, the formulation is converted into another integer linear program in which the solution space of the berth and the time is discretized. A Lagrangean relaxation model of the discretized model is solved using a sub-gradient optimization technique. Results of a numerical experiment are provided and discussed.
TL;DR: A heuristic algorithm for the school bus routing problem is proposed and has shown to be effective with a saving of 29% in total travelling times when comparing to current practice.
Abstract: This paper describes a case study of the school bus routing problem. It is formulated as a multi-objective combinatorial optimisation problem. The objectives considered include minimising the total number of buses required, the total travel time spent by pupils at all pick-up points, which is what the school and parents are concerned with most, and the total bus travel time. It also aims at balancing the loads and travel times between buses. A heuristic algorithm for its solution is proposed. The algorithm has been programmed and run efficiently on a PC. Numerical results are reported using test data from a kindergarten in Hong Kong. It has shown to be effective with a saving of 29% in total travelling times when comparing to current practice.
TL;DR: It is shown for a UK scenario, that large reductions in environmental impact can be achieved for reductions in farm profit which are insignificant relative to the annual variation due to yields and prices.
Abstract: We present a multiple objective linear programming model developed to consider a wide range of farming situations, which allows optimisation of profit or environmental outcome(s) or both. The modelling considers the problem of planning a farming system within a world where environmental considerations are increasing. The objective is to identify the best cropping and machinery options which are both profitable and result in improvements to the environment, depending upon the farm situation of market prices, potential crop yields, soil and weather characteristics. In particular, the model uses a flexible approach to choosing the machinery, timing of operations, crop rotations and levels of inputs. We show for a UK scenario, that large reductions in environmental impact can be achieved for reductions in farm profit which are insignificant relative to the annual variation due to yields and prices.
TL;DR: This paper presents a new type of genetic algorithm for the set covering problem that is an indirect algorithm, ie the actual solutions are found by an external decoder function, and it is shown that results can be further improved by adding another indirect optimisation layer.
Abstract: This paper presents a new type of genetic algorithm for the set covering problem. It differs from previous evolutionary approaches first because it is an indirect algorithm, i.e. the actual solutions are found by an external decoder function. The genetic algorithm itself provides this decoder with permutations of the solution variables and other parameters. Second, it will be shown that results can be further improved by adding another indirect optimisation layer. The decoder will not directly seek out low cost solutions but instead aims for good exploitable solutions. These are then post optimised by another hill-climbing algorithm. Although seemingly more complicated, we will show that this three-stage approach has advantages in terms of solution quality, speed and adaptability to new types of problems over more direct approaches. Extensive computational results are presented and compared to the latest evolutionary and other heuristic approaches to the same data instances.
TL;DR: A well known tool for relative efficiency assessment, namely Data Envelopment Analysis (DEA) is used to measure the performance of the nations participating at the last five Summer Olympic games, considering two inputs (GNP and population) and three outputs (number of gold, silver and bronze medals won).
Abstract: In this paper a well known tool for relative efficiency assessment, namely Data Envelopment Analysis (DEA), is used to measure the performance of the nations participating at the last five Summer Olympic games. The proposed approach considers two inputs (GNP and population) and three outputs (number of gold, silver and bronze medals won). To increase the consistency of the results, weight restrictions are included, guaranteeing a higher valuation for gold medals than for silver medals and higher for the latter than for bronze medals. Variable returns to scale are assumed. The results for the last five Summer Olympics are analysed. For each of them, a performance index as well as benchmarks are computed for each country. In addition, plotting the performance of a specific country for the different games can help identify trends as well as objective successes and disappointments.
TL;DR: A branch-and-bound algorithm and a heuristic procedure which both make use of a lower bound calculation for the discrete time/cost trade-off problem (without time-switch constraints) are proposed.
Abstract: The discrete time/cost trade-off problem assumes the duration of project activities to be discrete, non-increasing functions of the amount of a single non-renewable resource. The problem has been studied under three possible objectives. The so-called deadline problem involves the scheduling of project activities in order to minimize the total cost of the project while meeting a given deadline. The budget problem aims at minimizing the project duration without exceeding a given budget. A third objective involves the generation of the complete efficient time/cost profile over the set of feasible project durations. In this paper we describe a solution procedure for the deadline problem in which three special cases of time-switch constraints are involved. These constraints impose a specified starting time on the project activities and force them to be inactive during specified time periods. We propose a branch-and-bound algorithm and a heuristic procedure which both make use of a lower bound calculation for the discrete time/cost trade-off problem (without time-switch constraints). The procedures have been coded in Visual C++, version 6.0 under Windows 2000 and have been validated on a randomly generated problem set. We also discuss an illustrative example based on a real-life situation.
TL;DR: These variants use a mix of different components, including reactive tabu search concepts; variable neighbourhoods, special data memory structures and hashing functions to efficiently search the various neighbourhood spaces for the Mix Fleet Vehicle Routing Problem.
Abstract: The Mix Fleet Vehicle Routing Problem (MFVRP) involves the design of a set of minimum cost routes, originating and terminating at a central depot, for a fleet of heterogeneous vehicles with various capacities, fixed costs and variable costs to service a set of customers with known demands. This paper develops new variants of a tabu search meta-heuristic for the MFVRP. These variants use a mix of different components, including reactive tabu search concepts; variable neighbourhoods, special data memory structures and hashing functions. The reactive concept is used in a new way to trigger the switch between simple moves for intensification and more complex ones for diversification of the search strategies. The special data structures are newly introduced to efficiently search the various neighbourhood spaces. The combination of data structures and strategic balance between intensification and diversification generates an efficient and robust implementation, which is very competitive with other algorithms in the literature on a set of benchmark instances for which some new best-known solutions are provided.
TL;DR: This paper considers the design and analysis of algorithms for the multi-depot vehicle routing problem with time windows (MDVRPTW), finding that the heuristics with the best results are those with the largest computational efforts.
Abstract: This paper considers the design and analysis of algorithms for the multi-depot vehicle routing problem with time windows (MDVRPTW). Given the intrinsic difficulty of this problem class, approximation methods of the type ‘cluster first, route second’ (two-step approaches) seem to offer the most promise for practical size problems. After describing six heuristics for the cluster part (assignment of customers to depots) an initial computational study of their performance is conducted. Finding, as expected, that the heuristics with the best results (in terms of the routing results) are those with the largest computational efforts.
TL;DR: A unique model for estimating the operating cost of each of three waste-collection systems, including the side-loader system with fixed body, which allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted.
Abstract: In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection.
TL;DR: This paper addresses a shipments-planning problem faced by producers of large volume liquid bulk products by using a mixed integer-programming model and a cost-based heuristic algorithm to derive cost effective solutions.
Abstract: This paper addresses a shipments-planning problem faced by producers of large volume liquid bulk products. Producing origins with limited tank storage capacity supply multiple products by ships (or barges) to consuming destinations that also have limited storage capacity. Timing, origin, destination, and product quantities of shipments have to be determined in a manner that minimizes costs and does not violate storage capacity constraints at both ends (neither stopping production at the origins, nor running out of stock at the destinations). A mixed integer-programming model is used to derive cost effective solutions within a few minutes. A cost-based heuristic algorithm is used to assure that acceptable solutions are obtained quickly.
TL;DR: A heuristic solution method is developed in which the problem is divided into two subproblems, one for assigning container groups into the holds and one for determining a loading pattern of containers assigned to each hold, which shows that the suggested algorithm works better than existing algorithms.
Abstract: We consider a stowage-planning problem of arranging containers on a container ship in the maritime transportation system. Since containers are accessible only from the top of the stack, temporary unloading and reloading of containers, called shifting, is unavoidable if a container required to be unloaded at the current port is stacked under containers to be unloaded at later ports on the route of the ship. The objective of the stowage planning problem is to minimize the time required for shifting and crane movements on a tour of a container ship while maintaining the stability of the ship. For the problem, we develop a heuristic solution method in which the problem is divided into two subproblems, one for assigning container groups into the holds and one for determining a loading pattern of containers assigned to each hold. The former subproblem is solved by a greedy heuristic based on the transportation simplex method, while the latter is solved by a tree search method. These two subproblems are solved iteratively using information obtained from solutions of each other. To see the performance of the suggested algorithm, computational tests are performed on problem instances generated based on information obtained from an ocean container liner. Results show that the suggested algorithm works better than existing algorithms.
TL;DR: A multi-objective version of the Maximum Availability Location Problem is presented, with the assumption of server independence relaxed by adopting the approach of the Queuing Probabilistic Location Set Covering Problem for calculating the probability that all servers in a given region are busy.
Abstract: A multi-objective version of the Maximum Availability Location Problem is presented in this paper. The assumption of server independence is relaxed by adopting the approach of the Queuing Probabilistic Location Set Covering Problem for calculating the probability that all servers in a given region are busy. The first objective seeks to maximize the population receiving coverage within a given distance standard and with a given level of reliability. The second objective chooses those locations which minimize the cost of covering the population. This model is used to obtain sets of good locations using data obtained from the Barbados Emergency Ambulance Service. The solutions obtained from the optimization model are then subject to a detailed analysis by simulation. The results reveal the potentially good performance of the system, when locations derived from the optimization model are used.
TL;DR: Six organisations selected for their success were studied using a grounded theory approach based on interviews with management accountants and operations managers in each of the organisations, and it is clear that they are all making strenuous efforts to use their performance measurement systems but with a focus on the ‘good enough’ rather than the detail.
Abstract: Performance measurement systems along the lines of the EFQM and the balanced scorecard have developed rapidly in recent years, and now occupy much management time and effort. There is limited evide...