| 1. |
- Amankwah, Henry, et al.
(författare)
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A maximum flow formulation of a multi-period open-pit mining problem
- 2014
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Ingår i: Operational Research. - : Springer Berlin/Heidelberg. - 1109-2858 .- 1866-1505. ; 14:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of finding an optimal mining sequence for an open pit during a number of time periods subject to only spatial and temporal precedence constraints. This problem is of interest because such constraints are generic to any open-pit scheduling problem and, in particular, because it arises as a Lagrangean relaxation of an open-pit scheduling problem. We show that this multi-period open-pit mining problem can be solved as a maximum flow problem in a time-expanded mine graph. Further, the minimum cut in this graph will define an optimal sequence of pits. This result extends a well-known result of J.-C. Picard from 1976 for the open-pit mine design problem, that is, the single-period case, to the case of multiple time periods.
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| 2. |
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| 3. |
- Karakitsiou, Athanasia, et al.
(författare)
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Convex optimization problems in supply chain planning and their solution by a column generation method based on the Frank Wolfe method
- 2016
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Ingår i: Operational Research. - : Springer Science and Business Media LLC. - 1109-2858 .- 1866-1505. ; 16:3, s. 401-421
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Tidskriftsartikel (refereegranskat)abstract
- Many problems in supply chain optimization concern the minimization of a differentiable convex objective function subject to a set of linear constraints. The aim of this work is to present a number of such problems and to propose an efficient method for their solution. The proposed method is based on improvements of the well known Frank–Wolfe algorithm. The computational results of the proposed algorithm demonstrate its effectiveness and efficiency
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| 4. |
- Karakitsiou, Athanasia, et al.
(författare)
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Decentralized Coordination Mechanism for Integrated Production Transportation Inventory Problem in the Supply Chain using Lagragian Relaxation
- 2008
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Ingår i: Operational Research. - : Springer Science and Business Media LLC. - 1109-2858 .- 1866-1505. ; 8:3, s. 257-278
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Tidskriftsartikel (refereegranskat)abstract
- This paper is concerned with integrated production, inventory and transportation planning problems directly related to the supply chain management. We establish a Lagrangian based coordination mechanism within the context of the decentralized planning approach. In addition, we demonstrate that dual prices obtained by the described approach might provide enough accuracy in case of sudden changes, such as in a customer’s demand, and thus they could assist agents to find new solutions. Computational results show that the proposed mechanism is able to help organizations to facilitate collaboration, improve business agility and meet business goals
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| 5. |
- Karakitsiou, Athanasia, et al.
(författare)
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Efficient Minimization over Products of Simplices and its Application to Nonlinear Multicommodity Network Problems
- 2005
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Ingår i: Operational Research. - 1109-2858 .- 1866-1505. ; 4:2, s. 99-118
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Tidskriftsartikel (refereegranskat)abstract
- Many problems in portfolio selection, in traffic planning and in computer communicationnetworks can be formulated as nonlinear problems involving minimization of a nonlinearfunction over simplices. Based on the concepts of regularization and partial linearization, wepropose an efficient solution technique for such programs, prove its global convergence anddiscuss the possibilities for parallel implementation. We provide, as an application, analgorithm for traffic assignment which outperforms previous state-of-the-art codes
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| 6. |
- Karakitsiou, Athanasia, et al.
(författare)
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Regional efficiency evaluation by input-oriented data envelopment analysis of hotel and restaurant sector
- 2020
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Ingår i: Operational Research. - : Springer. - 1109-2858 .- 1866-1505. ; 20:4, s. 2041-2058
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyses the efficiency of hotel and restaurant sector across all of the thirteen regions in Greece. For our purpose, DEA models were applied in order to evaluate the tourist efficiency and competitiveness of different regions in Greece. The application of this frontier method permits the calculation of efficiency scores based on a series of inputs (number of local units, number of employees and investments) and output (turnover). For the years, 2002–2013, with respectively constant and variable returns to scale models, the empirical analysis shows the differences in the efficiency performance of the Greek regions. More specifically, Attica and South Aegean can be regarded as “moving ahead” regions, whereas some other like, Thessaly, Central Macedonia, Central Greece and Epirus can be considered as “falling further” regions.
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| 7. |
- Konstantinou, Christos, et al.
(författare)
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Cardinality constrained portfolio optimization with a hybrid scheme combining a Genetic Algorithm and Sonar Inspired Optimization
- 2022
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Ingår i: Operational Research. - : Springer. - 1109-2858 .- 1866-1505. ; 22:3, s. 2465-2487
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Tidskriftsartikel (refereegranskat)abstract
- The constraints and the vast solution space of operational research optimization problems make them hard to cope with. However, Computational Intelligence, and especially Nature-Inspired Algorithms, has been a useful tool to tackle hard and large space optimization problems. In this paper, a very consistent and effective hybrid optimization scheme to tackle cardinality constrained portfolio optimization problems is presented. This scheme consists of two nature-inspired algorithms, i.e. Sonar Inspired Optimization algorithm and Genetic Algorithm. Also, the incorporation of heuristic information, i.e. an expert’s knowledge, etc., to the overall performance of the hybrid scheme is tested and compared to previous studies. More specifically, under the framework of a financial portfolio optimization problem, the heuristic information-enhanced hybrid scheme manages to reach a new optimal solution. Additionally, a comparison of the proposed hybrid scheme with other hybrid schemes applied to the same problem with the same data is performed.
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| 8. |
- Larsson, Torbjörn, et al.
(författare)
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A generic column generation principle: derivation and convergence analysis
- 2015
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Ingår i: Operational Research. - : Springer Science and Business Media LLC. - 1109-2858 .- 1866-1505. ; 15:2, s. 163-198
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Tidskriftsartikel (refereegranskat)abstract
- Given a non-empty, compact and convex set, and an a priori definedcondition which each element either satisfies or not, we want to find an elementbelonging to the former category. This is a fundamental problem of mathematicalprogramming which encompasses nonlinear programs, variational inequalities,saddle-point problems. We present a conceptual column generation scheme, whichalternates between solving a restriction of the original problem and a columngeneration phase which is used to augment the restricted problems. We establishgeneral applicability of the conceptual method, as well as to the three problemclasses mentioned. We also establish a version of the conceptual method in whichthe restricted and column generation problems are allowed to be solvedproximately, and of a version allowing for the dropping of columns. We showsome solution methods (e.g., Dantzig–Wolfe decomposition and simplicialcomposition) are special instances, and present new convergent column generationmethods in nonlinear programming, such as a sequential linear programming typemethod. Along the way, we also relate our quite general scheme in nonlinearprogramming presented in this paper with several other classic, and more recent,iterative methods in nonlinear optimization.
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| 9. |
- Larsson, Torbjörn, et al.
(författare)
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A Lagrangian bounding and heuristic principle for bi-objective discrete optimization
- 2024
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Ingår i: Operational Research. - : SPRINGER HEIDELBERG. - 1109-2858 .- 1866-1505. ; 24:2
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Tidskriftsartikel (refereegranskat)abstract
- Lagrangian relaxation is a common and often successful way to approach computationally challenging single-objective discrete optimization problems with complicating side constraints. Its aim is often twofold; first, it provides bounds for the optimal value, and, second, it can be used to heuristically find near-optimal feasible solutions, the quality of which can be assessed by the bounds. We consider bi-objective discrete optimization problems with complicating side constraints and extend this Lagrangian bounding and heuristic principle to such problems. The Lagrangian heuristic here produces non-dominated candidates for points on the Pareto frontier, while the bounding forms a polyhedral outer approximation of the Pareto frontier, which can be used to assess the quality of the candidate points. As an illustration example we consider a facility location problem in which both CO2 emission and cost should be minimized. The computational results are very encouraging, both with respect to bounding and the heuristically found non-dominated solutions. In particular, the Lagrangian bounding is much stronger than the outer approximation given by the Pareto frontier of the problem's linear programming relaxation.
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| 10. |
- Marinakis, Yannis, et al.
(författare)
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Annotated bibliography in vehicle routing
- 2007
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Ingår i: Operational Research. - 1109-2858 .- 1866-1505. ; 7:1, s. 27-46
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Tidskriftsartikel (refereegranskat)abstract
- One of the most significant problems of supply chain management is the distribution of products between locations, most known as the Vehicle Routing Problem (VRP). The vehicle routing problem is one of the most challenging problems in the field of combinatorial optimization. Dantzig and Ramser first introduced the VRP in 1959. They proposed the first mathematical programming formulation. In 1964 Clarke and Wright proposed an effective greedy heuristic that improved Dantzig and Ramser approach. Since then, hundreds of models and algorithms were proposed for the optimal and approximate solution of the different versions of the VRP. In this paper, we present an annotated bibliography of the vehicle routing problem and its variant
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| 11. |
- Migdalas, Athanasios
(författare)
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Applications of game theory in finance and managerial accounting
- 2002
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Ingår i: Operational Research. - 1109-2858 .- 1866-1505. ; 2:2, s. 209-241
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Tidskriftsartikel (refereegranskat)abstract
- Game theory has been applied during the last two decades to an ever increasing number of important practical problems in economics, industrial organization, business strategy, finance, accounting, market design and marketing; including antitrust analyses, monetary policy, and firm restructuring. In this paper we give insight into the growing role of game theory, and particularly of the principal-agent model, for the important fields of finance and managerial accounting.
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| 12. |
- Samuelsson, Björn
(författare)
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Estimating distribution costs in a supply chain network optimisation tool, a case study
- 2016
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Ingår i: Operational Research. - : Springer Science and Business Media LLC. - 1109-2858 .- 1866-1505. ; 16:3, s. 469-499
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Tidskriftsartikel (refereegranskat)abstract
- In a complex logistic environment it is critical to have efficient methods and tools to evaluate and improve the its efficiency. These tools must support the analysis with accurate results, but they must also be fast and easy enough to be used use in a complex practical setting. In this paper we present and discuss a deterministic single-period single-sourcing LP/MIP based method that the Linde Group has used for more than 100 projects for optimising the logistic network in the air-gas cylinder business. The model, called CSS (cylinder supply structure), includes a multi-echelon logistic network with transportation between plants and warehouses and distribution to several end-customers. The model allows deliveries to customers from all echelons in the supply network. Both the downstream flow of full cylinders and the upstream return of empty cylinders are included in the model. In general, more than 75 % of the total transportation- and distribution costs are caused by the final distribution to customers in a supply network as above. This paper will in particular analyse the distribution part of this model; how it is designed and how the cost is estimated. In order to evaluate the accuracy of the method we use empirical data to compare the model results with empirical results. The results showed that from the beginning the model overestimated the expected distances and costs for the distribution. With a rework and improved method to estimate the distribution cost, the model significantly improved its accuracy
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| 13. |
- Tadaros, Marduch, et al.
(författare)
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Bi- and multi-objective location routing problems: classification and literature review
- 2022
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Ingår i: Operational Research. - : Springer Nature. - 1109-2858 .- 1866-1505. ; 22:5, s. 4641-4683
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Forskningsöversikt (refereegranskat)abstract
- The facility location problem and the vehicle routing problem are highly interdependent and critical parts of any efficient and cost-effective supply chain. The location of facilities heavily affects the design of distribution routes between the facilities and various demand nodes. Within locational analysis, the location-routing problem is a mathematical optimization problem that considers the underlying issues of vehicle routing and simultaneously optimizes the location of facilities and the design of distribution routes. Since, in real-life applications, it is common that decision-makers encounter more than one, often conflicting objectives, the problem can be stated in term of multi-objective optimization. This paper reviews 80 journal articles published in the field of bi- and multi-objective location-routing problems between 2014 and 2020. Included papers are classified based on several factors covering model assumptions and characteristics, objectives, solution approaches, and application area. For each application area, individual papers are presented and discussed. The paper concludes with remarks and suggestions for future research.
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| 14. |
- Tadaros, Marduch, et al.
(författare)
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Location of facilities and network design for reverse logistics of lithium-ion batteries in Sweden
- 2022
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Ingår i: Operational Research. - : Springer. - 1109-2858 .- 1866-1505. ; 22:2, s. 895-915
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Tidskriftsartikel (refereegranskat)abstract
- Estimations of the amount of lithium-ion batteries reaching their end-of-life in 2025 and the amount being recycled indicates large deviations. To enable an efficient recycling process a well-defined and efficient supply chain network for the recovery of discarded lithium-ion batteries must be put in place. This includes analyzing the needs and restrictions of such a network. The aim of this paper is to provide decision support tools, to analyze input, and optimize a future supply chain for discarded lithium-ion batteries. A mixed integer programming model is developed and applied to the Swedish market. The findings show that several aspects will affect a reverse supply chain for discarded lithium-ion batteries, many of which are still uncertain and hard to predict.
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| 15. |
- Tsionas, M., et al.
(författare)
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Effects of the vaccination and public support on covid-19 cases and number of deaths in Sweden
- 2023
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Ingår i: Operational Research. - : Springer. - 1109-2858 .- 1866-1505. ; 23:3
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Tidskriftsartikel (refereegranskat)abstract
- There are large variations between and within countries’ performance in coping with the Covid-19 pandemic. This study assesses the efficiency of different provinces in Sweden in managing the pandemic. Its objective to estimate the relative efficiency of provinces during the pandemic and identify the key determinants of the level and variations in their performance. Performance is measured as efficiency in keeping the number of negative outcomes low and the number of positive outcomes high for given resources. It uses a parametric distance function approach with multi-input, multi-output, and a flexible functional form for estimating the provinces’ efficiency and the variations in this efficiency over time. Variations in their performance are attributed to the observable characteristics of their socioeconomic, locational, demographic, and healthcare resources. The empirical part is based on a panel data of the population in 21 provinces observed on a weekly basis from January 2020 to September 2021. In particular, the paper estimates the effects of public support and vaccinations on a reduction in the number of deaths and the spread of new cases. The level and variations in outcomes are explained by various provinces and local and national policies. The results show large variations in provinces’ performance and their persistence/transitory nature attributed to their observable characteristics. The paper suggests some policy recommendations to help cope with the threat of the pandemic post the removal of restrictions.
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