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| 4. |
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| 5. |
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| 6. |
- Ari, E. Aysen, et al.
(författare)
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Disaggregation under uncertainty in hierarchical production planning
- 1988
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 35:2, s. 182-186
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Tidskriftsartikel (refereegranskat)abstract
- This study deals with a hierarchical planning system that is used for planning of a single-stage manufacturing system. We consider two decision levels, aggregate and detailed planning, and formulate a model for evaluation of aggregate plans and optimal disaggregation in case of independent stochastic demand. It is shown how the optimal solution can be obtained with the aid of a dynamic programming algorithm. Furthermore, we give conditions that will guarantee optimality of a simple intuitive disaggregation rule
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| 7. |
- Axsäter, Sven
(författare)
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A Capacity Constrained Production-Inventory System with Stochastic Demand and Production Times
- 2010
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Ingår i: International Journal of Production Research. - : Informa UK Limited. - 0020-7543 .- 1366-588X. ; 48:20, s. 6203-6209
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers a simple model of a capacity constrained production-inventory system with Poisson demand. The system is controlled by an S policy. The production time for a unit is modelled as a gamma distributed stochastic variable. Using M/G/1 queuing theory it is very easy to evaluate holding and backorder costs and optimise the ordering policy. The suggested model may be useful when evaluating investments in production.
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| 8. |
- Axsäter, Sven, et al.
(författare)
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A distribution inventory model with transshipments from a support warehouse
- 2013
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Ingår i: IIE Transactions. - 0740-817X. ; 45:3, s. 309-322
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThis article considers a distribution inventory system consisting of N retailers and a regional support warehouse, all being replenished from a central warehouse/outside supplier. For the case where stock-outs occur, the retailers receive transshipments from the support warehouse at an extra cost. A model is presented for cost evaluation and optimization of the reorder points in the system under fill rate constraints. The solution method is designed to handle large real-life systems and is fast enough to be directly implemented in practice. A numerical study illustrates that (i) the model renders near-optimal solutions; (ii) the value of using a support warehouse can be significant even for large transshipment costs; and (iii) significant cost savings can be obtained using the proposed model. Using real data for a sample of 50 representative products, the proposed model reduces the expected holding and transshipment costs by 29% while still meeting target fill rates. [Supplemental materials are available for this article. Go to the publisher's online edition of IIE Transactions to view the supplemental file.]
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| 9. |
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| 10. |
- Axsäter, Sven
(författare)
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A Heuristic for Triggering Emergency Orders in an Inventory System
- 2007
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 176:2, s. 880-891
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers a single-echelon inventory system with a warehouse facing compound Poisson customer demand. Normally the warehouse replenishes from an outside supplier according to a continuous review reorder point policy. However, it is also possible to use emergency orders. Such orders incur additional costs but have a much shorter lead time. We consider standard holding and backorder costs as well as ordering costs. A heuristic decision rule for triggering emergency orders is suggested. The decision rule minimizes the expected costs under the assumption that there is only a single possibility for an emergency replenishment, but the rule is used repeatedly as a heuristic. Given a certain reorder point policy for normal replenishments, our decision rule will always reduce the expected costs. A simulation study illustrates that the suggested technique performs well under different conditions.
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| 11. |
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| 12. |
- Axsäter, Sven
(författare)
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A New Decision Rule for Lateral Transshipments in Inventory Systems
- 2003
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Ingår i: Management Science. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0025-1909 .- 1526-5501. ; 49:9, s. 1168-1179
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with a single-echelon inventory system consisting of a number of parallel local warehouses facing compound Poisson demand. There are standard holding and backorder costs as well as ordering costs at all warehouses. Normally, the warehouses replenish from an outside supplier. However, lateral transshipments between the warehouses are also possible. Such transshipments take no time but incur additional costs. When a demand occurs at a warehouse, the question is whether the whole demand or part of it should be covered by a lateral transshipment from another warehouse. Given a set of alternative decisions, our decision rule minimizes the expected costs under the assumption that no further transshipments will take place. This rule is then used repeatedly as a heuristic. A simulation study illustrates how the suggested technique performs under different conditions.
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| 13. |
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| 14. |
- Axsäter, Sven
(författare)
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A Note on Stock Replenishment and Shipment Scheduling for Vendor-Managed Inventory Systems
- 2001
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Ingår i: Management Science. - 0025-1909. ; 47:9, s. 1306-1310
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- In a recent paper, Cetinkaya and Lee (2000) model integrated inventory control and shipment scheduling in connection with vendor-managed inventory (VMI). The model is optimized by an approximate technique. This note provides a simple procedure for exact optimization, and illustrates that the errors when using the suggested approximate technique may be very large for certain types of problems. We also suggest a new approximation and an adjustment that can be used to improve both the original and new heuristic.
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| 15. |
- Axsäter, Sven
(författare)
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A sequential lot sizing heuristic with optimal average performance
- 1988
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Ingår i: Management science. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0025-1909 .- 1526-5501. ; 34:11, s. 1324-1332
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Tidskriftsartikel (refereegranskat)abstract
- The classical dynamic lot size problem without backlogging is in practice usually solved with the aid of various heuristics. Most heuristics are sequential techniques, i.e. the future demand is considered period for period, and a decision whether to have a set-up or not in a certain period is taken without regarding the future demand. The average performance of a lot sizing heuristic will depend on the demand process. We assume that a typical demand will look like a sequence of independent identically distributed random numbers, and we derive a sequential lot sizing rule with optimal average performance under such circumstances. The optimal decision rule is compared to the Silver-Meal heuristic. We also analyze the situation when the decision rule is allowed to look ahead one period.
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| 16. |
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| 17. |
- Axsäter, Sven
(författare)
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A Simple Decision Rule for Decentralized Two-Echelon Inventory Control
- 2005
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Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273. ; 93-94, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- We consider a two-echelon distribution inventory system with a central warehouse and a number of retailers. The retailers face stochastic demand. The system is controlled by continuous review installation stock (R,Q) policies with given batch quantities. One way to decentralize the system control is to provide a backorder cost to the warehouse, and let the warehouse choose its reorder point so that the sum of the expected holding and backorder costs are minimized. Given the resulting warehouse policy, the retailers similarly optimize their costs with respect to the reorder points. This paper provides a simple approximate technique for determining the backorder cost to be used by the warehouse.
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| 18. |
- Axsäter, Sven
(författare)
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A Simple Procedure for Determining Order Quantities under a Fill Rate Constraint and Normally Distributed Lead-Time Demand
- 2006
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 174:1, s. 480-491
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Tidskriftsartikel (refereegranskat)abstract
- One of the most common practical inventory control problems is considered. A single-echelon inventory system is controlled by a continuous review (R,Q) policy. The lead-time demand is normally distributed. We wish to minimize holding and ordering costs under a fill rate constraint. Although, it is not especially complicated to derive the optimal solution, it is much more common in practice to use a simple approximate two-step procedure where the order quantity is determined from a deterministic model in the first step. We provide an alternative, equally simple technique, which is based on the observation that the considered problem for each considered fill rate has a single parameter only. The optimal solution for a grid of parameter values is stored in a file. When solving the problem for an item we use interpolation, or for parameter values outside the grid special approximations. The approximation errors turn out to be negligible. As an alternative to the interpolation we also provide polynomial approximations.
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| 19. |
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| 20. |
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| 21. |
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| 22. |
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| 23. |
- Axsäter, Sven
(författare)
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Aggregation of Product Data
- 1978
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Ingår i: Operations Research Verfahren. ; 35, s. 29-48
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Tidskriftsartikel (refereegranskat)
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| 24. |
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| 25. |
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| 26. |
- Axsäter, Sven
(författare)
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An improved decision rule for emergency replenishments
- 2014
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Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273. ; 157, s. 313-317
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a new decision rule for emergency replenishments in an inventory system. The decision rule is a generalization of a previous decision rule suggested and evaluated in Axsater (2003, 2007). An improvement step is added to this rule and this often means considerably better performance. The decisions are based on complete information about the system state. An advantage with our decision rule is its generality. It is possible to handle batch ordering, compound Poisson demand and emergency replenishments that take time. The decision rule has also a performance guarantee in the sense that emergency replenishments will always lead to lower expected costs. The rule can also be used in connection with lateral transshipments. (C) 2014 Elsevier B.V. All rights reserved.
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| 27. |
- Axsäter, Sven
(författare)
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An Inventory Model with Lateral Transshipments
- 1991
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Ingår i: Modern production concepts. - Berlin : Encyclopedia of Global Archaeology/Springer Verlag. - 0387536434 ; , s. 345-52, s. 345-352
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Konferensbidrag (refereegranskat)
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| 28. |
- Axsäter, Sven, et al.
(författare)
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Approximate Aggregation of Product Data
- 1983
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Ingår i: Engineering Costs and Production Economics. - 0167-188X. ; 7:2, s. 119-126
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Tidskriftsartikel (refereegranskat)
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| 29. |
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| 30. |
- Axsäter, Sven
(författare)
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Approximate Optimization of a Two-Level Distribution Inventory System
- 2002
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Ingår i: International Journal of Production Economics. - 0925-5273. ; 81-82, s. 545-553
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Tidskriftsartikel (refereegranskat)abstract
- A two-echelon distribution inventory system with a central warehouse and a number of retailers is considered. The retailers face stochastic demand. The system is controlled by continuous review installation stock (R,Q) policies with given batch quantities. There are linear holding costs at all locations and linear backorder costs at the retailers. We present a simple technique for approximate optimization of the reorder points. The technique means that we use normal approximations both for the retailer demand and the demand at the warehouse, i.e., the orders from the retailers.
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| 31. |
- Axsäter, Sven, et al.
(författare)
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Approximating general multi-echelon inventory systems by Poisson models
- 1994
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Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273 .- 1873-7579. ; 35:1-3, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- We consider a continuous review two-level inventory system with a central warehouse and a number of retailers. The demand processes at the retailers are different compound Poisson processes. We present and evaluate an approximate optimization technique, where the real demand is replaced by "equivalent" Poisson demand such that the ratio between mean and standard deviation is the same as for the real distribution. The solution of the Poisson model is then scaled back to the original problem.
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| 32. |
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| 33. |
- Axsäter, Sven
(författare)
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Batch Quantities when Forecasts are Improving
- 2011
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Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273. ; 133:1, s. 212-215
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the choice of initial batch quantities when demand forecasts are improving. We assume that the standard deviation of the demand per period is decreasing exponentially and approaching a long-run value. A discrete time stochastic single-level inventory model is considered. There are traditional holding and backorder costs as well as an ordering cost. The ordering periods must be determined in advance, and we wish to determine a suitable schedule.
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| 34. |
- Axsäter, Sven
(författare)
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Beslutsstöd för MA
- 1986
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Ingår i: Materialadministration & Transporter.
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Tidskriftsartikel (refereegranskat)
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| 35. |
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| 36. |
- Axsäter, Sven, et al.
(författare)
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Combining items for lot sizing in multi-level assembly systems
- 1987
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Ingår i: International Journal of Production Research. - : Informa UK Limited. - 0020-7543 .- 1366-588X. ; 25:6, s. 795-807
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Tidskriftsartikel (refereegranskat)abstract
- Many manufacturing firms are faced with the problem of planning the production/purchase quantities for items in single product, multi-level assembly production/inventory systems. Such systems are characterized by a single product, or end item, used to satisfy customer demand, which is assembled from a number of component items which, in turn, may be assembled from one or more other component items, etc. Component items may be either fabricated or purchased. This paper identifies conditions on the cost parameters which, when applicable, allow items to be combined for purpose of optimization, thereby reducing the size of the problem.
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| 37. |
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| 38. |
- Axsäter, Sven, et al.
(författare)
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Comparison of Echelon Stock and Installation Stock Policies for Two-Level Inventory Systems
- 1996
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Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273 .- 1873-7579. ; 45:1-3, s. 303-310
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Tidskriftsartikel (refereegranskat)abstract
- It is previously known that echelon stock reorder point policies dominate installation stock reorder point policies for serial and assembly multi-level inventory systems. This paper presents worst-case results for the relative cost difference in case of constant demand and no backorders. Furthermore, we analyze distribution systems with stochastic demand by simulation. Depending on the structure of the system either echelon stock or installation stock policies may be advantageous.
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| 39. |
- Axsäter, Sven, et al.
(författare)
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Comparison of echelon stock and installation stock policies with policy adjusted order quantities
- 1997
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Ingår i: International Journal of Production Economics. - 0925-5273 .- 1873-7579. ; 48:1, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Echelon stock and installation stock reorder point policies for multi-level inventory control have been compared in previous studies. It is known that echelon stock policies dominate installation stock policies for serial and assembly systems. Earlier comparisons assume that both policies use the same given order quantities, while each policy is optimized with respect to its reorder points. This paper presents worst case results for the cost ratio when the order quantities can be optimized for each policy.
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| 40. |
- Axsäter, Sven
(författare)
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Continuous review policies for multi-level inventory systems with stochastic demand
- 1993
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Ingår i: Handbooks in Operations Research and Management Science. - 0927-0507 .- 2212-1323. ; 4, s. 175-197
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Tidskriftsartikel (refereegranskat)abstract
- This chapter deals with continuous review policies. This means that the inventory levels are followed continuously and that replenishments may be ordered at any time. If the demand is Poisson (or compound Poisson) it is easy to realize that it is sufficient to consider those moments of time when demands occur. In case of low demand, there are relatively few such events, and it is usually suitable to apply continuous review policies. On the other hand, in case of very high demand, continuous review can lead to high information costs and it may be more practical to review the inventory system periodically. This means that continuous review policies are of special interest for inventory items that naturally have a low demand like—for example, spare parts. The chapter also discusses available models dealing with continuous review policies for multi-level inventory systems and emphasizes the main characteristics of different approaches. Furthermore, two-level systems and consumable items are also discussed in the chapter.
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| 41. |
- Axsäter, Sven
(författare)
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Control theory concepts in production and inventory control
- 1985
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Ingår i: International Journal of Systems Science. - : Informa UK Limited. - 0020-7721 .- 1464-5319. ; 16:2, s. 161-169
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Tidskriftsartikel (refereegranskat)abstract
- The use of efficient production and inventory control systems is of great importance for industry. Therefore this area could be expected to provide many fruitful applications of control theory techniques. However, control theory has traditionally been aimed at applications in other fields, and results have only limited applicability in production and inventory control. This paper gives an overview of earlier research concerning control theory applications in production and inventory control. Areas given special emphasis are those in which control theory seems to have a stronger potential for practical application
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| 42. |
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| 43. |
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| 44. |
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| 45. |
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| 46. |
- Axsäter, Sven, et al.
(författare)
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Decision Sciences
- 2010
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Ingår i: Encyclopedia of Library and Information Systems, Third Edition. - 9780849397127 ; , s. 1450-1450
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Bokkapitel (populärvet., debatt m.m.)
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| 47. |
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| 48. |
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| 49. |
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