| 1. |
- Baltz, Andreas, et al.
(författare)
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Exact and heuristic algorithms for the Travelling Salesman Problem with Multiple Time Windows and Hotel Selection
- 2015
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Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 66:4, s. 615-626
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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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| 2. |
- Holmberg, Kaj
(författare)
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Formation of student groups with the help of optimisation
- 2019
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Ingår i: Journal of the Operational Research Society. - : TAYLOR & FRANCIS LTD. - 0160-5682 .- 1476-9360. ; 70:9, s. 1538-1553
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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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| 3. |
- Pazirandeh, Ala, 1983, et al.
(författare)
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Improved coordination during disaster relief operations through sharing of resources
- 2018
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Ingår i: Journal of the Operational Research Society. - : Informa UK Limited. - 0160-5682 .- 1476-9360. ; 69:8, s. 1227-1241
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Tidskriftsartikel (refereegranskat)abstract
- Abstract In this paper, we focus on coordination dynamics between nonprofit organizations in the short-term, nonprofit, and competitive settings in disaster relief operations. Sharing resources across organizations can be a key to better coordination. Thus, we tested the link between resource sharing, aspects impacting resource sharing, and operational performance of the organizations using 101 data points. Data was collected through a survey from HOs within the Southeast Asian region and was analyzed using the Structural Equation Modeling-Partial Least Square (SEM-PLS) approach. The results show that resource sharing can improve organizational performance in this horizontal and competitive context, and that complementarity of resources between organizations increases their willingness to share resources. Complementarity of resources can also improve the interdependencies between organizations, which is not perceived very highly in the current highly competitive settings.
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| 4. |
- Petropoulos, Fotios, et al.
(författare)
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Forecast combinations for intermittent demand
- 2015
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Ingår i: Journal of the Operational Research Society. - : Taylor & Francis. - 0160-5682 .- 1476-9360. ; 66:6, s. 914-924
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Tidskriftsartikel (refereegranskat)abstract
- Intermittent demand is characterised by infrequent demand arrivals, where many periods have zero demand, coupled with varied demand sizes. The dual source of variation renders forecasting for intermittent demand a very challenging task. Many researchers have focused on the development of specialised methods for intermittent demand. However, apart from a case study on hierarchical forecasting, the effects of combining, which is a standard practice for regular demand, have not been investigated. This paper empirically explores the efficiency of forecast combinations in the intermittent demand context. We examine both method and temporal combinations of forecasts. The first are based on combinations of different methods on the same time series, while the latter use combinations of forecasts produced on different views of the time series, based on temporal aggregation. Temporal combinations of single or multiple methods are investigated, leading to a new time-series classification, which leads to model selection and combination. Results suggest that appropriate combinations lead to improved forecasting performance over single methods, as well as simplifying the forecasting process by limiting the need for manual selection of methods or hyper-parameters of good performing benchmarks. This has direct implications for intermittent demand forecasting in practice.
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| 5. |
- Trapero, Juan R., et al.
(författare)
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On the identification of sales forecasting models in the presence of promotions
- 2015
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Ingår i: Journal of the Operational Research Society. - : Taylor & Francis. - 0160-5682 .- 1476-9360. ; 66:2, s. 299-307
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Tidskriftsartikel (refereegranskat)abstract
- Shorter product life cycles and aggressive marketing, among other factors, have increased the complexity of sales forecasting. Forecasts are often produced using a Forecasting Support System that integrates univariate statistical forecasting with managerial judgment. Forecasting sales under promotional activity is one of the main reasons to use expert judgment. Alternatively, one can replace expert adjustments by regression models whose exogenous inputs are promotion features (price, display, etc). However, these regression models may have large dimensionality as well as multicollinearity issues. We propose a novel promotional model that overcomes these limitations. It combines Principal Component Analysis to reduce the dimensionality of the problem and automatically identifies the demand dynamics. For items with limited history, the proposed model is capable of providing promotional forecasts by selectively pooling information across established products. The performance of the model is compared against forecasts provided by experts and statistical benchmarks, on weekly data; outperforming both substantially.
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| 6. |
- Zhang, Changyong
(författare)
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An Origin-Based Model for Unique Shortest Path Routing
- 2016
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Ingår i: Journal of the Operational Research Society. - : Springer. - 0160-5682 .- 1476-9360. ; 68
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Tidskriftsartikel (refereegranskat)abstract
- Link weights are the main parameters of shortest path routing protocols, the most commonly used protocols for IP networks. The problem of optimally setting link weights for unique shortest path routing is addressed. Due to the complexity of the constraints involved, there exist challenges to formulate the problem in such a way based on which a more efficient solution algorithm than the existing ones may be developed. In this paper, an exact formulation is first introduced and then mathematically proved correct. It is further illustrated that the formulation has advantages over a prior one in terms of both constraint structure and model size for a proposed decomposition method to solve the problem.
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