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  • 1.
    Karakitsiou, Athanasia
    et al.
    Department of Business Administration, Educational Technological Institute of Central Macedonia, Serres, Greece .
    Kourgiantakis, Markos
    Department of Business Administration, Technological Educational Institute of Crete, Heraklion, Greece.
    Mavrommati, Athanasia
    Department of Economics, University of Ioannina, Ioannina, Greece .
    Migdalas, Athanasios
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Regional efficiency evaluation by input-oriented data envelopment analysis of hotel and restaurant sector2018In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Karakitsiou, Athanasia
    et al.
    DSS Laboratory Department of Production and Industrial Engineering, Technical University of Crete.
    Mavrommati, Athanasia
    Department of Production Engineering and Management, Technical University of Crete.
    Migdalas, Athanasios
    DSS Laboratory Department of Production and Industrial Engineering, Technical University of Crete.
    Efficient Minimization over Products of Simplices and its Application to Nonlinear Multicommodity Network Problems2005In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505, Vol. 4, no 2, p. 99-118Article in journal (Refereed)
    Abstract [en]

    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

  • 3.
    Karakitsiou, Athanasia
    et al.
    Department of Business Administration, Technological Educational Institute of Central Macedonia.
    Migdalas, Athanasios
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Convex optimization problems in supply chain planning and their solution by a column generation method based on the Frank Wolfe method2016In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505, Vol. 16, no 3, p. 401-421Article in journal (Refereed)
    Abstract [en]

    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

  • 4.
    Karakitsiou, Athanasia
    et al.
    DSS Laboratory Department of Production and Industrial Engineering, Technical University of Crete.
    Migdalas, Athanasios
    DSS Laboratory Department of Production and Industrial Engineering, Technical University of Crete.
    Decentralized Coordination Mechanism for Integrated Production Transportation Inventory Problem in the Supply Chain using Lagragian Relaxation2008In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505, Vol. 8, no 3, p. 257-278Article in journal (Refereed)
    Abstract [en]

    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

  • 5.
    Larsson, Torbjörn
    et al.
    Department of Mathematics, Institute of Technology, Linköping University.
    Migdalas, Athanasios
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Michael, Patriksson
    Department of Mathematical Sciences, Chalmers University of Technology.
    A generic column generation principle: derivation and convergence analysis2015In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505, Vol. 15, no 2, p. 163-198Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Marinakis, Yannis
    et al.
    School of Production Engineering and Management, Technical University of Crete, Decision Support Systems Laboratory, Department of Production Engineering and Management, Technical University of Crete.
    Migdalas, Athanasios
    Decision Support Systems Laboratory, Department of Production Engineering and Management, Technical University of Crete.
    Annotated bibliography in vehicle routing2007In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505, Vol. 7, no 1, p. 27-46Article in journal (Refereed)
    Abstract [en]

    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

  • 7.
    Migdalas, Athanasios
    Decision Support Systems Laboratory, Department of Production Engineering and Management, Technical University of Crete.
    Applications of game theory in finance and managerial accounting2002In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505, Vol. 2, no 2, p. 209-241Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Samuelsson, Björn
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Estimating distribution costs in a supply chain network optimisation tool, a case study2016In: Operational Research, ISSN 1109-2858, E-ISSN 1866-1505, Vol. 16, no 3, p. 469-499Article in journal (Refereed)
    Abstract [en]

    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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