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Sökning: L773:0160 5682 OR L773:1476 9360

  • Resultat 1-10 av 24
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1.
  • Andersson Granberg, Tobias, et al. (författare)
  • Decision support tools for ambulance dispatch and relocation
  • 2007
  • Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 58, s. 195-201
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the development of decision support tools for dynamic ambulance relocation and automatic ambulance dispatching is described. The ambulance dispatch problem is to choose which ambulance to send to a patient. The dynamic ambulance relocation problem occurs in the operational control of ambulances. The objective is to find new locations for some of the ambulances, to increase the preparedness in the area of responsibility. Preparedness is a way of evaluating the ability to serve potential patients with ambulances now and in the future. Computational tests using a simulation model show that the tools are beneficial in reducing the waiting periods for the patients.
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2.
  • Baltz, Andreas, et al. (författare)
  • Exact and heuristic algorithms for the Travelling Salesman Problem with Multiple Time Windows and Hotel Selection
  • 2015
  • Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 66:4, s. 615-626
  • Tidskriftsartikel (refereegranskat)abstract
    • We introduce and study the Travelling Salesman Problem with Multiple Time Windows and Hotel Selection (TSP-MTWHS), which generalises the well-known Travelling Salesman Problem with Time Windows and the recently introduced Travelling Salesman Problem with Hotel Selection. The TSP-MTWHS consists in determining a route for a salesman (eg, an employee of a services company) who visits various customers at different locations and different time windows. The salesman may require a several-day tour during which he may need to stay in hotels. The goal is to minimise the tour costs consisting of wage, hotel costs, travelling expenses and penalty fees for possibly omitted customers. We present a mixed integer linear programming (MILP) model for this practical problem and a heuristic combining cheapest insert, 2-OPT and randomised restarting. We show on random instances and on real world instances from industry that the MILP model can be solved to optimality in reasonable time with a standard MILP solver for several small instances. We also show that the heuristic gives the same solutions for most of the small instances, and is also fast, efficient and practical for large instances.
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3.
  • Caro, F., et al. (författare)
  • School Redistricting : Embedding GISTools with Integer Programming
  • 2004
  • Ingår i: Journal of the Operational Research Society. - : Palgrave Macmillan. - 0160-5682 .- 1476-9360. ; 55:8, s. 836-849
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper deals with a school redistricting problem in which blocks of a city must be assigned to schools according to diverse criteria. Previous approaches are reviewed and some desired properties of a good school districting plan are established. An optimization model together with a geographic information system environment are then proposed for finding a solution that satisfies these properties. A prototype of the system is described, some implementation issues are discussed, and two real-life examples from the city of Philadelphia are studied, one corresponding to a relatively easy to solve problem, and the other to a much harder one. The trade-offs in the solutions are analysed and feasibility questions are discussed. The results of the study strongly suggest that ill-defined spatial problems, such as school redistricting, can be addressed effectively by an interaction between objective analysis and subjective judgement.
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4.
  • Førsund, F.R., et al. (författare)
  • Calculating scale elasticity in DEA models
  • 2004
  • Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 55:10, s. 1023-1038
  • Tidskriftsartikel (refereegranskat)
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5.
  • Gunnarsson (Lidestam), Helene, et al. (författare)
  • A combined terminal location and ship routing problem
  • 2006
  • Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 57:8, s. 928-938
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we consider a combined terminal location and ship routing problem at Södra Cell AB. The purpose is to supply the customers' annual demand for pulp products while minimizing the distribution costs. Customers are supplied with various pulp products from pulp mills in Scandinavia by ships, trains, or lorries. The ship routes go from the pulp mills to terminals in Europe. From each terminal, the products are transported to customers by lorry, train, or barge. Some customers can be supplied directly from the pulp mills by trains or lorries. We have developed a mathematical model to select which terminals to use and, at the same time, determine the shipping routes. The mixed integer programming model was solved directly using a commercial solver. When the number of routes generated is large, the time required to obtain an optimal solution is too long. Hence, we have developed heuristics in order to obtain an acceptable solution in reasonable time. In addition to the basic case, five different scenarios were tested. Our heuristics provide solutions that are within 0.12% of the optimal ones.
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6.
  • Hartley, Roger, et al. (författare)
  • On the design of lottery games
  • 2003
  • Ingår i: Journal of the Operational Research Society. - : Palgrave Macmillan. - 0160-5682 .- 1476-9360. ; 54:1, s. 89-100
  • Tidskriftsartikel (refereegranskat)abstract
    • We describe a model of participation in lottery games designed to address the optimisation of tax revenue in state-sponsored lotteries. The model treats participants dynamically and examines a long-run equilibrium. A novel high frequency approximation is used to turn the problem into a static, state-contingent deterministic programming problem. We demonstrate that the solution of this problem has qualitatively plausible properties and then calibrate the model against the United Kingdom National Lottery (UKNL). The results suggest that the current design of the UKNL may not be maximising tax revenue.
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7.
  • Holmberg, Kaj (författare)
  • Formation of student groups with the help of optimisation
  • 2019
  • Ingår i: Journal of the Operational Research Society. - : TAYLOR & FRANCIS LTD. - 0160-5682 .- 1476-9360. ; 70:9, s. 1538-1553
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the problem of forming groups of students so that the groups are as even as possible with respect to certain aspects and group members are changed as much as possible compared to previous groups, and formulate it as a mixed integer programming problem. We find that standard software cannot solve real life sized instances, so we develop several heuristics and metaheuristics for the problem. Computational tests are made on randomly generated instances as well as real life instances. Some of the heuristics give good solutions in short time, and tests on real life problems indicate that satisfactory solutions can be found within 60 seconds.
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8.
  • Javed, Farrukh, et al. (författare)
  • Tangency portfolio weights under a skew-normal model in small and large dimensions
  • 2024
  • Ingår i: Journal of the Operational Research Society. - : Taylor & Francis Group. - 0160-5682 .- 1476-9360. ; 75:7, s. 1395-1406
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we investigate the distributional properties of the estimated tangency portfolio (TP) weights assuming that the asset returns follow a matrix variate closed skew-normal distribution. We establish a stochastic representation of the linear combination of the estimated TP weights that fully characterizes its distribution. Using the stochastic representation we derive the mean and variance of the estimated weights of TP which are of key importance in portfolio analysis. Furthermore, we provide the asymptotic distribution of the linear combination of the estimated TP weights under the high-dimensional asymptotic regime, i.e., the dimension of the portfolio p and the sample size n tend to infinity such that p/n & RARR;c & ISIN;(0,1). A good performance of the theoretical findings is documented in the simulation study. In an empirical study, we apply the theoretical results to real data of the stocks included in the S & P 500 index.
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9.
  • Lind, Mikael, et al. (författare)
  • Team-based reconstruction for expanding organisational ability
  • 2003
  • Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 54:2, s. 119-129
  • Tidskriftsartikel (refereegranskat)abstract
    • Organisations can be interpreted as a collection of actors who produce value for clients. In order for organisations to stay competitive there is a need for organisations to continuously develop their ability. An organisation’s ability is determined by its ability to effectively apply existing knowledge to create new knowledge and to take action that forms the basis for achieving competitive advantage from knowledge-based assets. One means for developing the organisational ability is to establish a mutually accepted understanding of the context in which the actors are acting. One important part of the organisation’s knowledge creation processes is to facilitate the sharing of personal knowledge. A condition for developing the organisational ability is to expand the amount of shared knowledge to an appropriate level. One type of knowledge that needs to be shared among different actors within the organisation is the knowledge about how and in which order actions are performed (contextual knowledge) in order to satisfy client needs. In this paper an approach for team-based reconstruction, used for moving from personal to shared contextual knowledge, is presented. The approach bears on the foundation of theories about knowledge management for understanding the process of externalisation and theories about language action for understanding organisations. Experiences from three case studies are presented. Team-based reconstruction can be used for (1) moving from personal knowledge to shared contextual knowledge in an efficient way, (2) arriving at a foundation for efficient organisational coordination, (3) arriving at a base for development work, and (4) organisational learning.
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10.
  • Nilsson, Andreas, et al. (författare)
  • A simple improvement on Silver's heuristic for the joint replenishment problem
  • 2008
  • Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 59:10, s. 1415-1421
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we revisit the well-known joint replenishment problem. There is a family of items with a major fixed cost associated with any replenishment of the family and a minor, (item-dependent) setup cost for each item that is included in the replenishment. In contrast with optimization methods and sophisticated (iterative) heuristics that have been presented in the literature, we present a simple (including ease of understanding) improvement routine to be used in conjunction with the original, simple approach advocated by one of the authors 30 years ago. Tests on 48,000 examples reveal that the improvement routine does, indeed, substantially improve performance and with relatively little extra computational effort. Thus, it should be of particular interest to practitioners and for teaching materials.
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