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  • 1.
    Aardal, Karen
    et al.
    CORE, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
    Ari, Aysen
    Luleå tekniska universitet.
    On the resemblance between the Kornai-Liptak and cross decomposition techniques for block-angular linear programs1990In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 46, no 3, p. 393-398Article in journal (Refereed)
    Abstract [en]

    In this paper the resemblance is demonstrated between the master- and subproblems generated by the Kornai-Liptak algorithm and the subproblems obtained by using the cross decomposition method on linear optimization problems with block-angular structure. The significance of the similarity between these two algorithms becomes apparent considering the main disadvantage attributed to cross decomposition. In cross decomposition a master problem has to be solved from time to time since the subproblems alone do not always give a converging sequence of primal and dual solutions. But if the cross decomposition algorithm is modified in such a way that the successive primal and dual subproblem solutions are taken into consideration with equal weights, this results in the Kornai-Liptak algorithm for which convergence is guaranteed

  • 2.
    Ari, E. Aysen
    et al.
    Luleå tekniska universitet.
    Axsäter, Sven
    Luleå tekniska universitet.
    Disaggregation under uncertainty in hierarchical production planning1988In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 35, no 2, p. 182-186Article in journal (Refereed)
    Abstract [en]

    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

  • 3.
    Asratian, Armen S.
    et al.
    Luleå tekniska universitet.
    Werra, D. de
    École Polytechnique Fédérale de Lausanne.
    A generalized class-teacher model for some timetabling problems2002In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 143, no 3, p. 531-542Article in journal (Refereed)
    Abstract [en]

    We consider a theoretical model which extends the basic "class-teacher model" of timetabling and which corresponds to some situations which occur frequently in the basic training programs of universities and schools. We are given m teachers T1, ..., Tm and n classes C1, ..., Cn. The set of classes is partitioned into p disjoint subsets G1, ..., Gp in such a way that in addition to the lectures given by one teacher to one class, there are some lectures given by one teacher to the students of all classes in group Gl, 1 ≤ l ≤ p. Such lectures will be called group-lectures. The number alj of one hour group-lectures which teacher Tj must deliver to group Gl and the number bij of one hour class-teaching which Tj must give to class Ci are given. Is there a timetable of t hours (or length t), so that each class Ci and each group Gl receive all their lectures, but no student is scheduled to be taught by more than one teacher in each hour, and no teacher must teach to more than one group or class in each hour? We show that this problem is NP-complete and find some sufficient conditions for the existence of a timetable of length t. We also describe an algorithm for constructing a timetable corresponding to the requirement matrices A = (alj) and B = (bij) and show that under a natural assumption on A and B this algorithm finds a timetable within 7/6 of the optimum length

  • 4.
    Bergman, Bo
    et al.
    Linköping Institute of Technology.
    Klefsjö, Bengt
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    TTT-concept and replacements to extend system life1987In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 28, no 3, p. 302-307Article in journal (Refereed)
    Abstract [en]

    In a number of papers the current authors have illustrated how the Total Time on Test (TTT) concept can be used when analysing the ordinary age replacement problem and different generalization thereof. In this paper we show that the TTT-concept is very useful also when analysing another replacement problem discussed by C. Derman et al. in which the replacements of a vital component, for which there are n space units, are made with the goal of maximizing the expected system life. (12 refs.)

  • 5. Forsberg, Rolf
    Exact evaluation of (R, Q)-policies for two-level inventory systems with Poisson demand1997In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 96, no 1, p. 130-138Article in journal (Refereed)
    Abstract [en]

    In this paper we show how to exactly evaluate holding and shortage costs for a two-level inventory system with one warehouse and N different retailers. Lead-times (transportation times) are constant, and the retailers face different Poisson demand processes. All facilities apply continuous review (R, Q)-policies. We express the policy costs as a weighted mean of costs for one-for-one ordering policies.

  • 6. Forsberg, Rolf
    Optimization of order-up-to-S policies for two-level inventory systems with compound Poisson demand1995In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 81, no 1, p. 143-153Article in journal (Refereed)
    Abstract [en]

    We consider a two-level inventory system with one warehouse and N retailers. Leadtimes are constant, and the retailers face different compound Poisson demand processes. All facilities apply order-up-to-S replenishment policies. We show how to evaluate holding and shortage costs exactly.

  • 7.
    Larsson, Torbjörn
    et al.
    Department of Mathematics, Institute of Technology, Linköping University.
    Migdalas, Athanasios
    Department of Mathematics, Institute of Technology, Linköping University.
    Rönnqvist, Mikael
    Department of Mathematics, Institute of Technology, Linköping University.
    A Lagrangean heuristic for the capacitated concave minimum cost network flow problem1994In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 78, no 1, p. 116-129Article in journal (Refereed)
    Abstract [en]

    We propose a heuristic solution technique for the capacitated concave minimum cost network flow problem based on a Lagrangean dualization of the problem. Despite its dual character the algorithm guarantees the generation of primal feasible solutions which are local optima and therefore candidates of being the global optimum. The Lagrangean dual is solved by a subgradient search procedure and provides a lower bound to the optimal value. The lower bound is, in general, stronger than the one obtained by a linear approximation of the original problem. It can be used as a judgement of the quality of the solution or in a branch and bound procedure. Computational results from randomly generated problems are presented

  • 8. Levén, Erik
    et al.
    Segerstedt, Anders
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    A scheduling policy for adjusting economic lot quantities to a feasible solution2007In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 179, no 2, p. 414-423Article in journal (Refereed)
    Abstract [en]

    A heuristic scheduling policy is introduced for a multi-item, single-machine production facility. The scheduling policy uses the presumed optimal order quantities derived from solving an Economic Lot Size Problem and checks that the quantities obtain a feasible production schedule according to current inventory levels and expected demand rates. If not, the scheduling policy modifies the order quantities to achieve a possible solution without shortages. The scheduling policy is inspired by modification of the similar heuristic Dynamic Cycle Lengths Policy by Leachman and Gascon from 1988, 1991. The main characteristics of this scheduling policy are successive batches of the same item are treated explicitly, due to that it is quite possible that one item be manufactured several times before one other item is manufactured once more; the batches are ordered in increasing run-out time; if the existing situation creates stock-outs with ordinary order quantities, then the order quantities are decreased with a common scaling factor to try to prevent inventory shortages; in case the decrease of the order quantities changes expected run-out times, the batches are reordered after new run-out times; no filling up to an explicit inventory level is done, the filling up is done by the desirable order quantity; to prevent possible excess inventory the policy suggests time periods where no production should be performed. The scheduling policy contains no economical evaluation; this is supposed to be done when the order quantities are calculated, the policy prevents shortages and excess inventory. A numerical example illustrates the suggested scheduling policy. Finally, it is discussed as to how the policy can also take into account stochastic behaviour of the demand rates and compensate the schedule by applying appropriate safety times.

  • 9.
    Marinakis, Yannis
    et al.
    Technical University of Crete, School of Production Engineering and Management, University Campus, 73100 Chania.
    Migdalas, Athanasios
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Sifaleras, Angelo
    University of Macedonia, School of Information Sciences, Department of Applied Informatics.
    A hybrid Particle Swarm Optimization: Variable Neighborhood Search Algorithm for Constrained Shortest Path Problems2017In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 261, no 3, p. 819-834Article in journal (Refereed)
    Abstract [en]

    In this paper, a well known NP-hard problem, the constrained shortest path problem, is studied. As efficient metaheuristic approaches are required for its solution, a new hybridized version of Particle Swarm Optimization algorithm with Variable Neighborhood Search is proposed for solving this significant combinatorial optimization problem. Particle Swarm Optimization (PSO) is a population-based swarm intelligence algorithm that simulates the social behavior of social organisms by using the physical movements of the particles in the swarm. A Variable Neighborhood Search (VNS) algorithm is applied in order to optimize the particles’ position. In the proposed algorithm, the Particle Swarm Optimization with combined Local and Global Expanding Neighborhood Topology (PSOLGENT), a different equation for the velocities of particles is given and a novel expanding neighborhood topology is used. Another issue in the application of the VNS algorithm in the Constrained Shortest Path problem is which local search algorithms are suitable from this problem. In this paper, a number of continuous local search algorithms are used. The algorithm is tested in a number of modified instances from the TSPLIB and comparisons with classic versions of PSO and with other versions of the proposed method are performed. Also, the results of the algorithm are compared with the results of a number of metaheuristic and evolutionary algorithms. The results obtained are very satisfactory and strengthen the efficiency of the algorithm.

  • 10.
    Migdalas, Athanasios
    et al.
    Decision Support Systems Laboratory, Department of Production Engineering and Management, Technical University of Crete.
    Baourakis, George
    Department of Economic Sciences, Mediterranean Agronomic Institute of Chania.
    Kalogeras, Nikos
    Department of Economic Sciences, Mediterranean Agronomic Institute of Chania.
    Meriem, H.B.
    Department of Economic Sciences, Mediterranean Agronomic Institute of Chania.
    Sector modeling for the prediction and evaluation of Cretan olive oil2004In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 152, no 2, p. 454-464Article in journal (Refereed)
    Abstract [en]

    Greece is a major international olive oil producer. Olive oil varieties constitute the major crops for Greek farmers growing certain oriental olive oil varieties. Currently, the olive oil sector in Greece is undergoing substantial changes and the response of farmers and consumers to this will be a vital factor in its success. Throughout the application of the common agriculture policy (CAP), mechanisms, such as production aid, subsidies and marketing orders, were employed to support both producers and consumers. A possible reform of CAP aimed at eliminating or reducing production aid or any kind of subsidies could have a considerable effect on producer and consumer marketing behaviour. In this study a formulated mathematical problem for the olive oil sector on the island of Crete based on the welfare concept and the simulation of the olive oil market equilibrium, subject to specified policy interventions and circumstances was adopted. According to the results obtained, it was concluded that future olive oil policies should not impinge on mechanisms that influence olive oil farmers and consumer behaviour but should emphasize the greater cost effectiveness of production and marketing policies

  • 11.
    Westberg, Ulf
    et al.
    Luleå tekniska universitet.
    Kumar, Dhananjay
    Maintenance scheduling under age replacement policy using proportional hazards model and TTT-plotting1997In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 99, no 3, p. 507-515Article in journal (Refereed)
    Abstract [en]

    The failure characteristics of a system may depend on the total operating time, operating time since the last repair, failure history, operating conditions or on the values of monitored variables. A reliability based approach which takes into consideration values of monitored variables is suggested for estimating the optimum maintenance (or replacement) time interval for a system or threshold values of monitored variables under the age replacement policy. The maintenance cost equation is formed on the basis of the planned and unplanned maintenance costs and the values of monitored variables. The proportional hazards model is used to identify the importance of monitored variables. The reliability function is estimated considering the values of monitored variables. A total time on test (TTT) plot based on this estimate of the reliability function is used to estimate the optimum maintenance (or replacement) time interval for a system or threshold values of monitored variables. This approach is illustrated with an example.

1 - 11 of 11
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