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- Karlsson, Jenny, 1969-, et al.
(författare)
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Short-term harvest planning including scheduling of harvest crews
- 2003
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Ingår i: International Transactions in Operational Research. - : Wiley. - 0969-6016 .- 1475-3995. ; 10:5, s. 413-431
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Tidskriftsartikel (refereegranskat)abstract
- The problem we consider is short-term harvesting planning for a total planning period of 4–6 weeks where we want to decide the harvest sequences or schedules for harvest crews. A schedule is an order or sequence of harvest areas assigned to each crew. The harvesting of areas is planned in order to meet industrial demand. The total cost includes harvesting, transportation, and storage. One considerable cost is due to the quality reduction of logs stored at harvest areas. There are a number of restrictions to be considered. Areas are of varying size and the composition of assortments in each area is different. Each harvest team has different skills, a different home base, and different production capacity. Another aspect is the road network. There is a cost related to road opening (restoring, snow removal). In this paper, we develop a mixed integer programming (MIP) model for the problem. The schedules are represented by 0/1 variables. With a limited number of schedules, the problem can be solved by a commercial MIP solver. We have also developed a heuristic solution approach that provides high-quality integer solutions within a distinct time limit to be used when more schedules are used. Computational results from a major Swedish forest company are presented.
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| 2. |
- Guajardo, Mario, et al.
(författare)
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Joint optimization of pricing and planning decisions in divergent supply chain
- 2013
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Ingår i: International Transactions in Operational Research. - : Wiley-Blackwell. - 0969-6016 .- 1475-3995. ; 20:6, s. 889-916
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Tidskriftsartikel (refereegranskat)abstract
- In divergent supply chains, such as in the oil industry, processing raw materials results in an outflow of multiple products. Final products are stored at international depots, from where they are ready to be shipped to the markets. Even if one company controls the entire chain, when production and sales organizations are decoupled, a relevant problem is to determine the internal prices of products at depots for achieving coordination. We propose an optimization model involving pricing and production decisions, and several constraints commonly used in divergent chains. In our approach, the producer incorporates the sellers behavior by expressing demand as a function of the internal price. As a result, our model serves as a coordination mechanism in trying to get an overall coordinated integrated solution in a decoupled reality. Numerical examples in single and multiple periods problems show the advantages of our approach over cost-based methods.
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| 3. |
- 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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| 6. |
- 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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