| 1. |
- Fotedar, Sunney, et al.
(författare)
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Bi-objective optimization of the tactical allocation of job types to machines: mathematical modeling, theoretical analysis, and numerical tests
- 2022
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Ingår i: International Transactions in Operational Research. - : Wiley. - 0969-6016 .- 1475-3995.
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a tactical resource allocation model for a large aerospace engine system manufacturer aimed at long-term production planning. Our model identifies the routings a product takes through the factory, and which machines should be qualified for a balanced resource loading, to reduce product lead times. We prove some important mathematical properties of the model that are used to develop a heuristic providing a good initial feasible solution. We propose a tailored approach for our class of problems combining two well-known criterion space search algorithms, the bi-directional epsilon-constraint method and the augmented weighted Tchebycheff method. A computational investigation comparing solution times for several solution methods is presented for 60 numerical instances.
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| 2. |
- Lean, Hooi Hooi, et al.
(författare)
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On the role of commodity futures in portfolio diversification
- 2023
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Ingår i: International Transactions in Operational Research. - : WILEY. - 0969-6016 .- 1475-3995. ; 30:5, s. 2374-2394
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Tidskriftsartikel (refereegranskat)abstract
- The last two decades have witnessed major financial crises that led investors to seek alternative assets and investment strategies to reduce their portfolio risk. In this article, we provide information on the role of commodity futures in designing portfolios and managing risk based on an appealing operational framework. Using more than 20 years of sample data, we first investigate the conditional mean and volatility dynamics of equity and commodity futures markets within a dynamic conditional correlation model setup. We then form alternative equity-commodity futures portfolios by changing the weights of commodity futures and examine if the diversified commodity-equity portfolios perform superior to the all-equity portfolios and four well-known investment strategies that suit most practitioners. Stochastic dominance approach shows that including commodity futures in diversified portfolios does not always improve the risk-return performance, except for gold in some particular portfolio setups. Accordingly, commodity assets have behaved like financial assets (stocks) and tend to be driven by the same pricing factors in general, which reduces the benefits of diversification.
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| 3. |
- Rönnqvist, Mikael, et al.
(författare)
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Collaboration and optimization in farmland exchanges
- 2023
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Ingår i: International Transactions in Operational Research. - : John Wiley and Sons Inc. - 0969-6016 .- 1475-3995. ; 30:4, s. 1591-1616
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Tidskriftsartikel (refereegranskat)abstract
- To keep businesses competitive in world markets, the number of farms in most countries is decreasing while farm size is increasing, and parcels making up the farm area are extremely fragmented. It is common for farms to expand faster than available arable land near the farm center, leading to longer distances between the farm center and field areas. Consequently, logistic costs increase and affect the farm's profitability and the environment. Moreover, there is often substantial overlap between different farms, which implies that it is possible for farmers to collaborate with each other. We developed and proposed three optimization models to describe different levels of collaboration and sharing restrictions. Many practical considerations need to be weighed, such as the soil type and crops used. We collected detailed information on farms, parcels, and cost drivers in seven large instances for our case study in Sweden. One instance had 1431 farms and 32,091 parcels with 96 crop types. The resulting optimization models were very large; special pre-processing and optimization techniques were developed for their solutions. The theoretical potential for collaboration in logistic cost reduction was very large, ranging from approximately 10% to 50% depending on the form of the collaboration. Because a large part of costs comes from less use of diesel for transport resources, the reduction in cost is directly related to a reduction in CO2 emissions. © 2022 The Authors. International Transactions in Operational Research
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| 4. |
- Zhao, Yixin, et al.
(författare)
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An integer programming column generation principlefor heuristic search methods
- 2020
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Ingår i: International Transactions in Operational Research. - : Wiley-Blackwell. - 0969-6016 .- 1475-3995. ; 27:1, s. 665-695
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in integrating column generation and heuristic approaches to efficiently solve large-scale discrete optimisation problems. We contribute in this direction. Based on the insights from Lagrangian duality theory, we present an auxiliary problem that can be used for finding near-optimal solutions to a discrete column-oriented model. The structure of this auxiliary problem makes it suitable for being addressed with a heuristic search method involving column generation. To this end, we suggest a large neighbourhood search strategy where the repair step is to solve a column generation type subproblem. The suggested search strategy and mathematical models involved need to be tailored to the problem structure. To illustrate important design options and computational behaviour, four applications are studied: bin packing, generalised assignment, a resource allocation problem and the fixed-charge transportation problem.
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