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  • 301.
    Quttineh, Nils-Hassan
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Lidestam, Helene
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Produktionsekonomi. Linköpings universitet, Tekniska högskolan.
    Using rolling horizon techniques in the planning process for a chemical process industry2014Ingår i: Pre-Prints, Vol.1, 18th International Working Seminars on Production Economics, Innsbruck, Austria, February 2014., 2014, s. 381-393Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a mathematical optimization model that can be used as a decision support tool for the supply chain planning at Perstorp Oxo AB, a global company in the process industry. At their site in Stenungsund, Perstorp Oxo AB produce chemicals to customers in a variety of branches and for further refinement at other Perstorp sites in Gent, Castellanza and Perstorp. The customers are mainly in branches such as food and feed, leather and textile, plastic and safety glass production. Since Perstorp Oxo sells products to customers worldwide, two large inventory facilities are located in Antwerp (Belgium) and Tees (United Kingdom) for five product types each and two smaller facilities in Philadelphia (USA) and Aveiro (Portugal) for one type respectively. The developed model is a mixed-integer linear program, where the objective function maximizes the profit. A solution to the model shows the quantities to be transported between the different sites, production rates, inventory levels, setups and purchases from external suppliers, each with its respective cost. Based on actual sales data from Perstorp Oxo AB, we use rolling horizon techniques to simulate how customer demands vary over a time horizon of one year, and show that our optimization model is able to find feasible and profitable production plans. The results show that there is a potential to increase profit margin by using a decision support tool based on an optimization model.

  • 302.
    Quttineh, Nils-Hassan
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    Lidestam, Helene
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Produktionsekonomi. Linköpings universitet, Tekniska fakulteten.
    Ahlstedt, Mårten
    Linköpings universitet.
    Olsson, Sven
    Linköpings universitet.
    Supply Chain Modeling for a Process Industry2017Ingår i: International Journal of Operations Research and Information Systems, ISSN 1947-9328, Vol. 8, nr 2, s. 36-55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Process industries of today differ from other industries in many aspects. The purpose of this paper is to consider these special properties of process industries when developing a mathematical model that can be used as a decision support tool for the supply chain planning for a chemical process industry in Sweden. A mixed-integer linear programming model is developed, and solutions to the model present how the products will be transported between the different sites of the company, the levels of the inventories, the setups and purchases from the external suppliers and also the production rates. The mathematical model takes many special properties regarding process industries into account. By using the results from the model and test different scenarios, the model can be used as an important support tool when making decisions. The decision support tool can for example be used in the company's budget process and thereby improve the chances of future profits increases.

  • 303.
    Quttineh, Nils-Hassan
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Lidestam, Helene
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Produktionsekonomi. Linköpings universitet, Tekniska högskolan.
    Ahlstedt, Mårten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Tekniska högskolan.
    Olsson, Sven
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
    Supply Chain Planning at a Chemical Process Industry2013Ingår i: Proceedings for Decision Science Institute (DSI 2013), The 44th Annual Meeting, 2013, Decision Sciences Institute , 2013, s. 671895 - 1-671895 - 19Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The purpose of this paper is to develop a mathematical optimization model that can be used as a decision support tool for the supply chain planning at Perstorp Oxo AB, a global company in the process industry. At their site in Stenungsund, Perstorp Oxo AB produce chemicals to customers in a variety of branches and for further refinement at other Perstorp sites in Gent, Castellanza and Perstorp. The customers are mainly in branches such as food and feed, leather and textile, plastic and safety glass production. Since Perstorp Oxo sells products to customers worldwide, two large inventory facilities are located in Antwerp (Belgium)and Tees (United Kingdom) for five product types each and two smaller facilities in Philadelphia (USA) and Aveiro (Portugal) for one type respectively. The developed model is a mixed-integer linear program, where the objective function maximizes the profit margin, that is, the difference between the selling price and the cost of production, transportation, inventory carrying and outsourcing. A solution to the model shows the quantities to be transported between the different sites, production rates, inventory levels, setups and purchases from external suppliers, each with its respective cost. The results of a baseline scenario show that there is a potential to increase profit margin by using a decision support tool based on an optimization model.

  • 304.
    Quttineh, Nils-Hassan
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Lundberg, Kristian
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Holmberg, Kaj
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Aircraft Mission Planning2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This paper deals with a Military Aircraft Mission Planning Problem, where the problem is to find time efficient flight paths for a given aircraft fleet that should attack a number of ground targets. Due to the nature of the attack, two aircraft need to rendezvous at the target, that is, they need to be synchronized in both space and time. At the attack, one aircraft is launching a guided weapon, while the other is illuminating the target. Each target is associated with multiple attack and illumination options. Further, there may be precedence constraints between targets, limiting the order of the attacks. The objective is to maximize the outcome of the entire attack, while also minimizing the mission time span. We present two mathematical models for this problem and compare their efficiency on some small test cases. We also provide some heuristic approaches since direct application of a general MIP solver to the mathematical model is only practical for smaller scenarios. The heuristics are compared and they successfully provide solutions to a number of scenarios.

  • 305.
    Quttineh, Nils-Hassan
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Lundberg, Kristian
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Holmberg, Kaj
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Effect Oriented Planning2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The problem setting concerns the tactical planning of a military operation. Imagine a big wide open area where a number of interesting targets are positioned. It could be radar stations or other surveillance equipment, with or without defensive capabilities, which the attacker wishes to destroy. Moreover, the targets are possibly guarded by defending units, like Surface-to-Air Missile (SAM) units. The positions of all units, targets and defenders, are known. We consider the problem of the attacker, where the objective is to maximize the expected outcome of a joint attack against the enemy, subject to a limited amount of resources (i.e. aircraft, tanks). We present a mathematical model for this problem, together with alternative model versions which provide optimistic and a pessimistic approximations. The model is not efficient for large problem instances, hence we also provide heuristic solution approaches and successfully provide solutions to a number of scenarios.

  • 306.
    Raidl, Günther R.
    et al.
    Institute of Logic and Computation, TU Wien.
    Rönnberg, Elina
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    Horn, Matthias
    Institute of Logic and Computation, TU Wien.
    Maschler, Johannes
    Institute of Logic and Computation, TU Wien.
    An A*-Based Algorithm to Derive Relaxed Decision Diagrams for a Prize-Collecting Sequencing Problem2018Konferensbidrag (Refereegranskat)
  • 307.
    Razmara, Gholamreza
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Snow removal routing problems: theory and applications2004Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    The focus of this dissertation is on constructing optimization models and developing solution methods for Snow Removal Routing Problems with Time V\lindows. Two cases, after and during snowfall, are studied. We discuss theoretical aspects of these problems and considerations to be taken when modeling and solving the real-world problem of the Swedish National Road Agency.

    In the case of after snowfall we are concerned with finding a set of routes, with minimal total cost, for homogeneous snowplows, where every road segment is plowed in its associated time window. The routes must start from and end at the same depot, at which a numbers of snowplows are stationed. This case is solved by Dantzig-Wolfe decomposition combined with a column generation procedure. An integer solution to the master problem is found by a greedy algorithm or a variable reduction procedure. The case of generating routes for snowplows during snowfall is studied in two versions; the problems with and without time horizon on the duration of the snowfall. The focus is put on the latter problem, which is solved in two ways using a Dantzig-Wolfe decomposition scheme and a Tabu Search heuristic. The Dantzig-Wolfe master problem, is a Constrained Set Covering Problem and the subproblems are Prize Collecting Connected Subgraph Problems. Further, we show that the Prize Collecting Connected Subgraph Problem is a generalization of Prize Collecting Steiner Tree Problem and thus is NP-hard. An integer solution to the master problem is extracted by a greedy search procedure and the obtained solution is improved by post processing. The solution approaches for both cases are implemented and tested on the real-world problem under consideration and on an artificial, generated problem.

  • 308.
    Razmara, Gholamreza
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Lindberg, Per Olov
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    The Prize Collecting Connected Subgraph Problem - A New NP-Hard Problem arizing in Snow Removal Routing2004Ingår i: Operations Research 2004,2004, Berlin: Springer , 2004Konferensbidrag (Refereegranskat)
  • 309.
    Rönnberg, Elina
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten. Saab AB, Linköping, Sweden.
    Co-allocation of communication messages in an integrated modular avionic system2017Ingår i: Operations Research Proceedings 2017. / [ed] N. Kliewer, J.F. Ehmke, and R. Borndörfer, 2017, s. 459-465Konferensbidrag (Refereegranskat)
    Abstract [en]

    Pre-runtime scheduling of the kind of Integrated Modular Avionic (IMA) system addressed in this paper can be considered as multiprocessor scheduling with additional constraints on precedence relations between tasks and the concurrent scheduling of a communication network with discrete time slots for sending messages. This paper extends an existing constraint generation procedure for such IMA-systems to facilitate co-allocation of messages in the time slots. To send a communication message involves the execution of a set of tasks. Co-allocation of messages means that tasks of the same type that originate from these messages are merged and their total execution requirements are shortened. The reduction of the execution requirements induces capacity savings that can have a positive impact on the feasibility of the problem.

  • 310. Beställ onlineKöp publikationen >>
    Rönnberg, Elina
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Contributions within two topics in integer programming: nurse scheduling and column generation2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Integer programming can be used to provide solutions to complex decision and planning problems occurring in a wide variety of situations. The application of integer programming to solve real world problems requires a modelling phase in which the problem at hand is translated into a mathematical description of the problem, and a solution phase that aims at developing methods for producing solutions to the mathematical formulation of the problem.

    The first two papers of this thesis have their focus on the modelling phase, and the application of integer programming for solving nurse scheduling problems. Common to both papers is that the research has been conducted in collaboration with health care representatives, and that the models presented can be used for providing schedules that can be used by nurses. In the latter paper, a meta-heuristic approach is suggested for providing the schedules.

    The last three papers address method development and specifically the design of column generation methods. The first of these papers presents optimality conditions that are useful in methods where columns are generated using dual solutions that are not necessarily optimal with respect to a linear programming relaxation, and the usefulness of these conditions are illustrated by examples from the literature.

    Many applications of column generation yield master problems of a set partitioning type, and the fourth and fifth paper present methodologies for solving such problems. The characteristics of these methodologies  are that all solutions derived are feasible and integral, where the preservation of integrality is a major distinction from other column generation methods presented in the literature.

    Delarbeten
    1. Automating the self-scheduling process of nurses in Swedish healthcare: a pilot study
    Öppna denna publikation i ny flik eller fönster >>Automating the self-scheduling process of nurses in Swedish healthcare: a pilot study
    2010 (Engelska)Ingår i: HEALTH CARE MANAGEMENT SCIENCE, ISSN 1386-9620, Vol. 13, nr 1, s. 35-53Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Hospital wards need to be staffed by nurses round the clock, resulting in irregular working hours for many nurses. Over the years, the nurses influence on the scheduling has been increased in order to improve their working conditions. In Sweden it is common to apply a kind of self-scheduling where each nurse individually proposes a schedule, and then the final schedule is determined through informal negotiations between the nurses. This kind of self-scheduling is very time-consuming and does often lead to conflicts. We present a pilot study which aims at determining if it is possible to create an optimisation tool that automatically delivers a usable schedule based on the schedules proposed by the nurses. The study is performed at a typical Swedish nursing ward, for which we have developed a mathematical model and delivered schedules. The results of this study are very promising and suggest continued work along these lines.

    Ort, förlag, år, upplaga, sidor
    Springer Science Business Media, 2010
    Nyckelord
    Nurse scheduling, Nurse rostering, Self-scheduling, Preference scheduling, Operations research, Integer linear programming
    Nationell ämneskategori
    Matematik
    Identifikatorer
    urn:nbn:se:liu:diva-59720 (URN)10.1007/s10729-009-9107-x (DOI)000281585200004 ()
    Anmärkning
    The original publication is available at www.springerlink.com: Elina Rönnberg and Torbjörn Larsson, Automating the self-scheduling process of nurses in Swedish healthcare: a pilot study, 2010, HEALTH CARE MANAGEMENT SCIENCE, (13), 1, 35-53. http://dx.doi.org/10.1007/s10729-009-9107-x Copyright: Springer Science Business Media http://www.springerlink.com/ Tillgänglig från: 2010-09-24 Skapad: 2010-09-24 Senast uppdaterad: 2018-06-25
    2. Automatic scheduling of nurses: What does it take in practice?
    Öppna denna publikation i ny flik eller fönster >>Automatic scheduling of nurses: What does it take in practice?
    2013 (Engelska)Ingår i: Systems Analysis Tools for Better Healthcare Delivery / [ed] Panos M. Pardalos, Pando G. Georgiev, Petraq Papajorgji, Britta Neugaard, New York, NY: Springer Science+Business Media B.V., 2013, s. 151-178Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This book presents some recent systems engineering and mathematical tools for health care along with their real-world applications by health care practitioners and engineers. Advanced approaches, tools, and algorithms used in operating room scheduling and patient flow are covered. State-of-the-art results from applications of data mining, business process modeling, and simulation in healthcare, together with optimization methods, form the core of the volume. Systems Analysis Tools for Better Health Care Delivery illustrates the increased need of partnership between engineers and health care professionals. This book will benefit researchers and practitioners in health care delivery institutions, staff members and professionals of specialized hospital units, and lecturers and graduate students in engineering, applied mathematics, business administration and health care. 

    Ort, förlag, år, upplaga, sidor
    New York, NY: Springer Science+Business Media B.V., 2013
    Serie
    Springer Optimization and Its Applications, ISSN 1931-6828 ; 74
    Nyckelord
    Mathematics, Practice of medicine, Mathematical optimization, Optimization, Operations Research, Management Science, Health Administration, Mathematical Modeling and Industrial Mathematics, Mathematical Modeling and Industrial Mathematics, Medical care, Hospital care, Matematiska modeller, Hälso- och sjukvård
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-76079 (URN)10.1007/978-1-4614-5094-8_8 (DOI)978-1-4614-5093-1 (ISBN)978-1-4614-5094-8 (ISBN)
    Tillgänglig från: 2012-03-26 Skapad: 2012-03-26 Senast uppdaterad: 2018-06-25Bibliografiskt granskad
    3. Column generation using non-optimal dual solutions: Optimality conditions and over-generation
    Öppna denna publikation i ny flik eller fönster >>Column generation using non-optimal dual solutions: Optimality conditions and over-generation
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Column generation is a linear programming method that, when combined with appropriate integer programming techniques, has been successfully used for solving huge integer programs. The use of a dual solution to the restricted master problem is essential when new columns are derived by solving a subproblem. Even if the problem to be solved is an integer programming one, this dual solution is usually optimal with respect to the linear programming relaxation of either the original problem or of a restriction thereof formed further down a branch-and-price-tree.

    This paper addresses the situation that arises when columns of a binary problem are generated using any dual solution, and we derive optimality conditions for determining when the master problem has been augmented with enough columns to contain an integer optimal solution to the complete master problem.

    We discuss the concept of over-generation of columns, which means to augment the restricted master problem with a set of columns, to ensure progress of the algorithm and also to make sure that the columns of the restricted master problem eventually comply with the optimality conditions. To illustrate the over-generation strategy, we compare our results with special cases that are already known from the literature, and we make some new suggestions.

    Nyckelord
    Binary program, column generation, optimality conditions, overgeneration
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-76090 (URN)
    Tillgänglig från: 2012-03-26 Skapad: 2012-03-26 Senast uppdaterad: 2018-06-25Bibliografiskt granskad
    4. Column Generation in the Integral Simplex Method
    Öppna denna publikation i ny flik eller fönster >>Column Generation in the Integral Simplex Method
    2009 (Engelska)Ingår i: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 192, nr 1, s. 333-342Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The integral simplex method for set partitioning problems allows onlypivots-on-one to be made, which results in a primal all-integer method. Inthis technical note we outline how to tailor the column generationprinciple to this method. Because of the restriction topivots-on-one, only local optimality can be guaranteed, and to ensureglobal optimality we consider the use of implicit enumeration.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2009
    Nyckelord
    integer programming, set partitioning, column generation, quasi-integrality
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-15287 (URN)10.1016/j.ejor.2007.09.037 (DOI)
    Anmärkning
    Original publication: Elina Rönnberg and Torbjörn Larsson, Column Generation in the Integral Simplex Method, 2009, European Journal of Operational Research, (192), 1, 333-342. http://dx.doi.org/10.1016/j.ejor.2007.09.037. Copyright: Elsevier B.V., http://www.elsevier.com/Tillgänglig från: 2008-10-29 Skapad: 2008-10-29 Senast uppdaterad: 2018-06-25Bibliografiskt granskad
    5. All-integer column generation: Basic principles and extensions
    Öppna denna publikation i ny flik eller fönster >>All-integer column generation: Basic principles and extensions
    2014 (Engelska)Ingår i: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 233, nr 3, s. 529-538Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Column generation is a linear programming method in which a dual solution of the master problem is essential when deriving new columns by solving a subproblem. When combined with appropriate integer programming techniques, column generation has successfully been used for solving huge integer programs. In many applications where column generation is used, the master problem is of a set partitioning type.

    The set partitioning polytope has the quasi-integrality property, which enables the use of simplex pivot based methods for finding improved integer solutions where each integer solution is associated with a linear programming basis a corresponding dual solution. By combining these kinds of simplex pivots with column generation, one obtains a method where each successively found solution to a restricted master problem is feasible, integer, and associated with a dual solution to be used in the column generation step. The column generation subproblem can either be of a regular type, or it can be tailored to produce columns that maintain integrality when pivoted into the basis.

    In this paper, a framework for this kind of column generation, which we here name all-integer column generation for set partitioning problems, is presented. The strategies proposed are primarily of a meta-heuristic nature, but with the proper settings, optimal or near-optimal solutions can be obtained.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2014
    Nyckelord
    Set partitioning, meta-heuristic, column generation, quasiintegrality, surrogate columns, over-generation, all-integer pivots
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-76091 (URN)10.1016/j.ejor.2013.08.036 (DOI)000328180200006 ()urn:nbn:se:liu:diva-102966 (Lokalt ID)urn:nbn:se:liu:diva-102966 (Arkivnummer)urn:nbn:se:liu:diva-102966 (OAI)
    Anmärkning

    On the day of the defence date the status of this article was Manuscript with the title All-integer column generation: A meta-heuristic for set partitioning problems.

    Tillgänglig från: 2012-03-26 Skapad: 2012-03-26 Senast uppdaterad: 2018-06-25Bibliografiskt granskad
    Ladda ner fulltext (pdf)
    Contributions within two topics in integer programming: nurse scheduling and column generation
    Ladda ner (pdf)
    omslag
  • 311. Beställ onlineKöp publikationen >>
    Rönnberg, Elina
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Methods and Applications in Integer Programming: All-Integer Column Generation and Nurse Scheduling2008Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Integer programming can be used to provide solutionsto complex decision and planning problems occurring in a wide varietyof situations. Applying integer programming to a real life problembasically involves a first phase where a mathematical model isconstructed, and a second phase where the problem described by themodel is solved. While the nature of the challenges involved in therespective two phases differ, the strong relationship between theproperties of models, and which methods that are appropriate for theirsolution, links the two phases. This thesis constitutes of threepapers, of which the third one considers the modeling phase, while thefirst and second one consider the solution phase.

     

    Many applications of column generation yield master problems of setpartitioning type, and the first and second papers presentmethodologies for solving such problems. The characteristics of themethodologies presented are that all successively found solutions arefeasible and integral, where the retention of integrality is a majordistinction from other column generation methods presented in theliterature.

     

    The third paper concerns nurse scheduling and describes the results ofa pilot implementation of a scheduling tool at a Swedish nursing ward.This paper focuses on the practical aspects of modeling and thechallenges of providing a solution to a complex real life problem.

    Delarbeten
    1. Column Generation in the Integral Simplex Method
    Öppna denna publikation i ny flik eller fönster >>Column Generation in the Integral Simplex Method
    2009 (Engelska)Ingår i: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 192, nr 1, s. 333-342Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The integral simplex method for set partitioning problems allows onlypivots-on-one to be made, which results in a primal all-integer method. Inthis technical note we outline how to tailor the column generationprinciple to this method. Because of the restriction topivots-on-one, only local optimality can be guaranteed, and to ensureglobal optimality we consider the use of implicit enumeration.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2009
    Nyckelord
    integer programming, set partitioning, column generation, quasi-integrality
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-15287 (URN)10.1016/j.ejor.2007.09.037 (DOI)
    Anmärkning
    Original publication: Elina Rönnberg and Torbjörn Larsson, Column Generation in the Integral Simplex Method, 2009, European Journal of Operational Research, (192), 1, 333-342. http://dx.doi.org/10.1016/j.ejor.2007.09.037. Copyright: Elsevier B.V., http://www.elsevier.com/Tillgänglig från: 2008-10-29 Skapad: 2008-10-29 Senast uppdaterad: 2018-06-25Bibliografiskt granskad
    2. An All-Integer Column Generation Methodology for Set Partitioning Problems
    Öppna denna publikation i ny flik eller fönster >>An All-Integer Column Generation Methodology for Set Partitioning Problems
    2008 (Engelska)Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The set partitioning polytope has the quasi-integrality propertythat enables the use of simplex pivot based methods for finding animproved integer solution, which thereby is associated with a linearprogramming basis and a corresponding dual solution. Presented in thispaper is a framework for an all-integer column generation methodologyfor set partitioning problems that utilises the quasi-integralityproperty of the feasible polytope.In the presented methodology, each successively found solution to arestricted master problem is feasible, integer and associated with acorresponding dual solution, which is then used in the columngeneration step. The column generation problem is tailored to producecolumns that maintain integrality when pivoted into the basis.Furthermore, criteria for verifying optimality are presented.

    Förlag
    s. 23
    Serie
    Report / Department of Mathematics, Universitetet i Linköping, Tekniska högskolan, ISSN 0348-2960
    Nyckelord
    integer programming, column generation, quasi-integrality, surrogate columns, over-generation
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-15256 (URN)
    Tillgänglig från: 2008-10-28 Skapad: 2008-10-27 Senast uppdaterad: 2018-06-25Bibliografiskt granskad
    3. Automating the Self-Scheduling Process of Nurses in Swedish Healthcare: A Pilot Study
    Öppna denna publikation i ny flik eller fönster >>Automating the Self-Scheduling Process of Nurses in Swedish Healthcare: A Pilot Study
    2008 (Engelska)Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Hospital wards need to be staffed by nurses round the clock, resultingin irregular working hours for many nurses. Over the years, thenurses' influence on the scheduling have been increased in order toimprove their working conditions. In Sweden it is common to apply a kindof self-scheduling where each nurse individually proposes a schedule,and then the final schedule is determined through informalnegotiations between the nurses. This kind of self-scheduling is verytime-consuming and does often lead to conflicts.We present a pilot study which aims at determining if it is possibleto create an optimisation tool that automatically delivers a usableschedule based on the schedules proposed by the nurses. The study isperformed at a typical Swedish nursing ward, for which we havedeveloped a mathematical model and delivered schedules. The results ofthis study are very promising.

    Förlag
    s. 29
    Serie
    LiTH-MAT-R, ISSN 0348-2960 ; 2008:8
    Nyckelord
    nurse scheduling, integer linear programming
    Nationell ämneskategori
    Beräkningsmatematik
    Identifikatorer
    urn:nbn:se:liu:diva-57562 (URN)
    Tillgänglig från: 2008-10-28 Skapad: 2008-10-27 Senast uppdaterad: 2018-06-25Bibliografiskt granskad
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    COVER01
  • 312.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    All-integer column generation: Basic principles and extensions2014Ingår i: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 233, nr 3, s. 529-538Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Column generation is a linear programming method in which a dual solution of the master problem is essential when deriving new columns by solving a subproblem. When combined with appropriate integer programming techniques, column generation has successfully been used for solving huge integer programs. In many applications where column generation is used, the master problem is of a set partitioning type.

    The set partitioning polytope has the quasi-integrality property, which enables the use of simplex pivot based methods for finding improved integer solutions where each integer solution is associated with a linear programming basis a corresponding dual solution. By combining these kinds of simplex pivots with column generation, one obtains a method where each successively found solution to a restricted master problem is feasible, integer, and associated with a dual solution to be used in the column generation step. The column generation subproblem can either be of a regular type, or it can be tailored to produce columns that maintain integrality when pivoted into the basis.

    In this paper, a framework for this kind of column generation, which we here name all-integer column generation for set partitioning problems, is presented. The strategies proposed are primarily of a meta-heuristic nature, but with the proper settings, optimal or near-optimal solutions can be obtained.

    Ladda ner fulltext (pdf)
    fulltext
  • 313.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    An All-Integer Column Generation Methodology for Set Partitioning Problems2008Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The set partitioning polytope has the quasi-integrality propertythat enables the use of simplex pivot based methods for finding animproved integer solution, which thereby is associated with a linearprogramming basis and a corresponding dual solution. Presented in thispaper is a framework for an all-integer column generation methodologyfor set partitioning problems that utilises the quasi-integralityproperty of the feasible polytope.In the presented methodology, each successively found solution to arestricted master problem is feasible, integer and associated with acorresponding dual solution, which is then used in the columngeneration step. The column generation problem is tailored to producecolumns that maintain integrality when pivoted into the basis.Furthermore, criteria for verifying optimality are presented.

  • 314.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    An integer optimality condition for column generation on zero-one linear programs2019Ingår i: Discrete Optimization, ISSN 1572-5286, E-ISSN 1873-636X, Vol. 31, s. 79-92Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Column generation is a linear programming method that, when combined with appropriate integer programming techniques, has been successfully used for solving huge integer programs. The method alternates between a restricted master problem and a column generation subproblem. The latter step is founded on dual information from the former one; often an optimal dual solution to the linear programming relaxation of the restricted master problem is used.

    We consider a zero–one linear programming problem that is approached by column generation and present a generic sufficient optimality condition for the restricted master problem to contain the columns required to find an integer optimal solution to the complete problem. The condition is based on dual information, but not necessarily on an optimal dual solution. It is however most natural to apply the condition in a situation when an optimal or near-optimal dual solution is at hand.

    We relate our result to a few special cases from the literature, and make some suggestions regarding possible exploitation of the optimality condition in the construction of column generation methods for integer programs.

    Publikationen är tillgänglig i fulltext från 2020-09-27 15:07
  • 315.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Automating the self-scheduling process of nurses in Swedish healthcare: a pilot study2010Ingår i: HEALTH CARE MANAGEMENT SCIENCE, ISSN 1386-9620, Vol. 13, nr 1, s. 35-53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hospital wards need to be staffed by nurses round the clock, resulting in irregular working hours for many nurses. Over the years, the nurses influence on the scheduling has been increased in order to improve their working conditions. In Sweden it is common to apply a kind of self-scheduling where each nurse individually proposes a schedule, and then the final schedule is determined through informal negotiations between the nurses. This kind of self-scheduling is very time-consuming and does often lead to conflicts. We present a pilot study which aims at determining if it is possible to create an optimisation tool that automatically delivers a usable schedule based on the schedules proposed by the nurses. The study is performed at a typical Swedish nursing ward, for which we have developed a mathematical model and delivered schedules. The results of this study are very promising and suggest continued work along these lines.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 316.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Automating the Self-Scheduling Process of Nurses in Swedish Healthcare: A Pilot Study2008Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Hospital wards need to be staffed by nurses round the clock, resultingin irregular working hours for many nurses. Over the years, thenurses' influence on the scheduling have been increased in order toimprove their working conditions. In Sweden it is common to apply a kindof self-scheduling where each nurse individually proposes a schedule,and then the final schedule is determined through informalnegotiations between the nurses. This kind of self-scheduling is verytime-consuming and does often lead to conflicts.We present a pilot study which aims at determining if it is possibleto create an optimisation tool that automatically delivers a usableschedule based on the schedules proposed by the nurses. The study isperformed at a typical Swedish nursing ward, for which we havedeveloped a mathematical model and delivered schedules. The results ofthis study are very promising.

  • 317.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Column generation using non-optimal dual solutions: Optimality conditions and over-generationManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Column generation is a linear programming method that, when combined with appropriate integer programming techniques, has been successfully used for solving huge integer programs. The use of a dual solution to the restricted master problem is essential when new columns are derived by solving a subproblem. Even if the problem to be solved is an integer programming one, this dual solution is usually optimal with respect to the linear programming relaxation of either the original problem or of a restriction thereof formed further down a branch-and-price-tree.

    This paper addresses the situation that arises when columns of a binary problem are generated using any dual solution, and we derive optimality conditions for determining when the master problem has been augmented with enough columns to contain an integer optimal solution to the complete master problem.

    We discuss the concept of over-generation of columns, which means to augment the restricted master problem with a set of columns, to ensure progress of the algorithm and also to make sure that the columns of the restricted master problem eventually comply with the optimality conditions. To illustrate the over-generation strategy, we compare our results with special cases that are already known from the literature, and we make some new suggestions.

  • 318.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    Integral Simplex Methods for the Set Partitioning Problem: Globalisation and Anti-Cycling2018Ingår i: Open Problems in Optimization and Data Analysis / [ed] Panos M. Pardalos, Athanasios Migdalas, Cham: Springer, 2018, s. 285-303Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The set partitioning problem is a generic optimisation model with many applications, especially within scheduling and routing. It is common in the context of column generation, and its importance has grown due to the strong developments in this field. The set partitioning problem has the quasi-integrality property, which means that every edge of the convex hull of the integer feasible solutions is also an edge of the polytope of the linear programming relaxation. This property enables, in principle, the use of solution methods that find improved integer solutions through simplex pivots that preserve integrality; pivoting rules with this effect can be designed in a few different ways. Although seemingly promising, the application of these approaches involves inherent challenges. Firstly, they can get be trapped at local optima, with respect to the pivoting options available, so that global optimality can be guaranteed only by resorting to an enumeration principle. Secondly, set partitioning problems are typically massively degenerate and a big hurdle to overcome is therefore to establish anti-cycling rules for the pivoting options available. The purpose of this chapter is to lay a foundation for research on these topics.

  • 319.
    Rönnberg, Elina
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Torbjörn
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Bertilsson, Ann
    Linköpings universitet, Matematiska institutionen. Linköpings universitet, Tekniska högskolan.
    Automatic scheduling of nurses: What does it take in practice?2013Ingår i: Systems Analysis Tools for Better Healthcare Delivery / [ed] Panos M. Pardalos, Pando G. Georgiev, Petraq Papajorgji, Britta Neugaard, New York, NY: Springer Science+Business Media B.V., 2013, s. 151-178Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This book presents some recent systems engineering and mathematical tools for health care along with their real-world applications by health care practitioners and engineers. Advanced approaches, tools, and algorithms used in operating room scheduling and patient flow are covered. State-of-the-art results from applications of data mining, business process modeling, and simulation in healthcare, together with optimization methods, form the core of the volume. Systems Analysis Tools for Better Health Care Delivery illustrates the increased need of partnership between engineers and health care professionals. This book will benefit researchers and practitioners in health care delivery institutions, staff members and professionals of specialized hospital units, and lecturers and graduate students in engineering, applied mathematics, business administration and health care. 

    Ladda ner fulltext (pdf)
    fulltext
  • 320.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    A new support system for tactical transportation planning2003Ingår i: 5th EUROINFORMS Joint International meeting,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 321.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Experiences with supply chain management in Swedish forest industries2003Ingår i: SMARTLOG, Smart logistics in dynamic value-chains,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 322.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    FlowOpt - Ett flexibelt planeringsverktyg för skoglig logistik2004Ingår i: Skogskonferensen,2004, 2004Konferensbidrag (Refereegranskat)
  • 323.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Forestry planning using OR models in Sweden2003Ingår i: Workshop Taller Nucleo Milenium: Complex engineering systems,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 324.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Integrated logistics management in the forest supply chain2003Ingår i: 2nd Forest Engineering Conference,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 325.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Integrated logistics management in the forestry supply chain2003Ingår i: Symposium for Systems Analysis in Forest Resources,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 326.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Integrated routing and transportation planning2003Ingår i: ROUTE2003, International workshop on vehicle routing and multi-modal transportation,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 327.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Integration in the wood chain towards customer optimized timber - A case study2003Ingår i: IUFRO All Division 5 Conference,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 328.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Kundanpassad virkesproduktion2003Ingår i: Logistikkonferensen,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 329.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Laps Care - An operational system for staff planning in home care2003Ingår i: 5th EUROINFORMS Joint International meeting,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 330.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Modeller för operationsanalys2003Ingår i: Kungl. Skogs- och Lantbruksakademiens Tidskrift, ISSN 0023-5350, Vol. 142, nr 19, s. 27-32Artikel i tidskrift (Refereegranskat)
  • 331.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Optimization and Transportation Scheduling, The Grand Chateau National Park, New Zealand, September 8-10, 2004. (Experiences from developing a decision2004Ingår i: Optimization and Transportation Scheduling,2004, 2004Konferensbidrag (Refereegranskat)
  • 332.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Optimization in forestry2003Ingår i: 18th International Symposium on Mathematical Programming,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 333.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Optimization in forestry2003Ingår i: Mathematical programming, ISSN 0025-5610, E-ISSN 1436-4646, Vol. 97, s. 267-284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optimization models and methods have been used extensively in the forest industry. In this paper we describe the general wood-flow in forestry and a variety of planning problems. These cover planning periods from a fraction of a second to more than one hundred years. The problems are modelled using linear, integer and nonlinear models. Solution methods used depend on the required solution time and include for example dynamic programming, LP methods, branch & bound methods, heuristics and column generation. The importance of modelling and qualitative information is also discussed.

  • 334.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    OR in forestry - 12 open problems2003Ingår i: Symposium for Systems Analysis in Forest Resources,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 335.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Transportation and route planning2003Ingår i: 2nd Forest Engineering Conference,2003, 2003Konferensbidrag (Övrigt vetenskapligt)
  • 336.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Transportation planning with several transportation modes2004Ingår i: CORSINFORMS Joint International Meeting,2004, 2004Konferensbidrag (Refereegranskat)
  • 337.
    Rönnqvist, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Eveborn, Patrik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Scheduler - A system for staff planning2004Ingår i: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 128, nr 1-4, s. 21-45Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Scheduling of staff is an important area, both from an academic and industrial point of view. There has been a lot of attention to develop new and efficient methods and models. In this paper, we consider the problem that given a work-force demand, a set of working rules and regulations find schedules for staff members with individual skills and preferences. The planning horizon is typically one week to several months. The problem both constructs tasks and simultaneously allocates them to staff members. The purpose of this paper is not to develop new theoretical results. Instead it deals with novel applications of known approaches to real-world practice. We describe a general scheduling software called SCHEDULER that includes a number of important features. The model is based on a elastic set-partitioning model and as solution method we use a branch-and-price algorithm. As branching strategy we make use of constraint branching and the column generator is a nested constrained shortest path formulation. An important feature is that only legal schedules are generated and used within the model. The system also allows for task changes within shifts, a general description of legal restrictions, preferences and allowable times. The system is in use at a number of companies and we report on the usage at some companies. We also give some numerical results to illustrate the behavior of some important features.

  • 338.
    Rönnqvist, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Fjeld, Dag
    Puodziunas, M
    The potential of improvement for tactical planning of roundwood transport in Lithuanian state forest enterprises2004Ingår i: Baltic forestry, ISSN 1392-1355, Vol. 10, nr 1, s. 79-88Artikel i tidskrift (Refereegranskat)
  • 339.
    Rönnqvist, Mikael
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Flisberg, Patrik
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Eveborn, Patrik
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Home care operations2004Ingår i: OR/MS today, ISSN 1085-1038, Vol. April, s. 38-43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    No abstract available.

  • 340.
    Rönnqvist, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Frisk, Mikael
    Skogforsk.
    Forsberg, Mathias
    FlowOpt - A flexible decision support tool for strategic and tactical planning in forestry2004Ingår i: TRISTAN 2004, Triennial Symposium on Transportation Analysis,2004, 2004Konferensbidrag (Övrigt vetenskapligt)
  • 341.
    Rönnqvist, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Todoroki, C
    Linkoping Inst Technol, Div Optimizat, S-58183 Linkoping, Sweden New Zealand Forest Res Inst, Rotorua, New Zealand Univ Auckland, Dept Engn Sci, Auckland, New Zealand.
    Allsopp, T
    Linkoping Inst Technol, Div Optimizat, S-58183 Linkoping, Sweden New Zealand Forest Res Inst, Rotorua, New Zealand Univ Auckland, Dept Engn Sci, Auckland, New Zealand.
    Usage of 3D geometry descriptions and transformation techniques in log bucking and curve sawing2000Ingår i: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 95, s. 93-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detailed three dimensional models are nowadays frequently used in cross-cutting (bucking) tree stems into logs and in breakdown processes of logs into boards and flitches. Such models require increasingly sophisticated optimization models to assist planners (or automated decision support systems) in decision making. In this paper we develop two techniques that are linked to each other. The first is concerned with establishing high quality analytic approximations of full trees that are needed in full stem bucking applications. One important aspect is that inaccuracies due to measurement error can be reduced. The second is a transformation technique that makes it possible to apply curve sawing on logs in a standard straight sawing system. Numerical results based on real data are presented that support the usefulness of the techniques.

  • 342.
    Sadoghi, Amirhossein
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Statistik. Linköpings universitet, Tekniska högskolan.
    Burdakov, Oleg
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Grimvall, Anders
    Linköpings universitet, Institutionen för datavetenskap, Statistik. Linköpings universitet, Tekniska högskolan.
    Piecewise Monotonic Regression Algorithm for Problems Comprising Seasonal and Monotonic Trends2011Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In this research piecewise monotonic models for problemscomprising seasonal cycles and monotonic trends are considered.In contrast to the conventional piecewise monotonicregression algorithms, our approach can efficientlyexploit a priori information about temporal patterns. Itis based on reducing these problems to monotonic regressionproblems defined on partially ordered data sets. Thelatter are large-scale convex quadratic programming problems.They are efficiently solved by the GPAV algorithm.

  • 343.
    Sandberg, Richard
    Linköpings universitet, Matematiska institutionen, Optimeringslära.
    A survey of optimization methods for solving the inverse shortest path routing problem2010Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Ruttningen av trafik i IP-nätverk sker ofta med hjälp av bågvikter som bestämmer vilken väg trafiken tar (kortastevägruttning). Problemet här är att avgöra ifall det existerar en uppsättning vikter givet ett önskat ruttningsschema. Den hör rapporten undersöker prestandan hos ett antal modeller och optimeringsprogram avsedda att lösa denna typ av problem som ofta kallas inversa kortastevägruttningsproblemet.

    Undersökningen visar att det existerar en stor skillnad mellan modellerna och optimeringsprogrammen och att modellen baserad på cykelbaser löst med CPLEXdualopt lösaren är snabbast.

    Ladda ner fulltext (pdf)
    A survey of optimization methods for solving the inverse shortest path routing problem
  • 344.
    Skriver, A.J.V.
    et al.
    Department of Operations Research, University of Aarhus, Ny Munkegade Building 530, DK-8000 Århus C, Denmark.
    Andersen, K.A.
    Department of Operations Research, University of Aarhus, Ny Munkegade Building 530, DK-8000 Århus C, Denmark.
    Holmberg, Kaj
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Bicriteria network location (BNL) problems with criteria dependent lengths and minisum objectives2004Ingår i: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 156, nr 3, s. 541-549Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new location model, which is a generalization of the bicritera median problem. We introduce two sum objectives and criteria dependent edge lengths. For this script N sign P complete problem a solution method finding all the efficient solutions is presented. The method is a two-phases approach, which can easily be applied as an interactive method. In Phase 1 the supported solutions are found, and in Phase 2 the unsupported solutions are found. This method can be thought of as a general approach to bi-objective combinatorial optimization (BOCO) problems. © 2003 Elsevier B.V. All rights reserved.

  • 345.
    Sundin, Daniel
    Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Scheduling of Electric Buses with Column Generation2018Självständigt arbete på grundnivå (kandidatexamen), 10,5 poäng / 16 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Column generation has during the last years been popular in vehicle scheduling as it for larger problems can find an optimum faster than using an ordinary mixed-integer programming (MIP) model. We study the problem of finding optimal schedules for electric buses by means of column generation. The motive for this approach is that when the size of the problem becomes very large in terms of variables and different solutions, solving it with a mixed- integer programming model can take a lot time. The purpose of this work is to investigate how the best found integral solution and the solution time vary between different column generation methods and how these methods perform compared to a MIP. This has been done by implementing these methods on a test problem for scheduling of electric buses. The results indicate that column generation methods can be very efficient in terms of time and best found integral solution for larger problems. A modified column generation method has been created in order to accelerate the generation of columns, which is better than standard column generation in terms of solution time and best found integral solution. 

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    Scheduling of Electric Buses with Column Generation
  • 346.
    Svensson, Björn
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Burdakov, Oleg
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    A New Approach For Treating Multiple Eextremal Points In Multi-Linear Least Squares Filter Design2007Ingår i: Proceedings of the {SSBA} Symposium on Image Analysis, 2007, 2007, s. 61-64Konferensbidrag (Övrigt vetenskapligt)
  • 347.
    Svensson, Björn
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Burdakov, Oleg
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Approximate Spectral Factorization for Design of Efficient Sub-Filter Sequences2008Manuskript (preprint) (Övrig (populärvetenskap, debatt, mm))
  • 348.
    Sysoev, Oleg
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Statistik. Linköpings universitet, Filosofiska fakulteten.
    Burdakov, Oleg
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    A Smoothed Monotonic Regression via L2 Regularization2016Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Monotonic Regression (MR) is a standard method for extracting a monotone function from non-monotonic data, and it is used in many applications. However, a known drawback of this method is that its fitted response is a piecewise constant function, while practical response functions are often required to be continuous. The method proposed in this paper achieves monotonicity and smoothness of the regression by introducing an L2 regularization term, and it is shown that the complexity of this method is O(n2). In addition, our simulations demonstrate that the proposed method normally has higher predictive power than some commonly used alternative methods, such as monotonic kernel smoothers. In contrast to these methods, our approach is probabilistically motivated and has connections to Bayesian modeling.

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    Smoothed Monotonic Regression via L2 Regularization
  • 349.
    Sysoev, Oleg
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Statistik och maskininlärning. Linköpings universitet, Filosofiska fakulteten.
    Burdakov, Oleg
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska fakulteten.
    A smoothed monotonic regression via L2 regularization2019Ingår i: Knowledge and Information Systems, ISSN 0219-1377, E-ISSN 0219-3116, Vol. 59, nr 1, s. 197-218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Monotonic regression is a standard method for extracting a monotone function from non-monotonic data, and it is used in many applications. However, a known drawback of this method is that its fitted response is a piecewise constant function, while practical response functions are often required to be continuous. The method proposed in this paper achieves monotonicity and smoothness of the regression by introducing an L2 regularization term. In order to achieve a low computational complexity and at the same time to provide a high predictive power of the method, we introduce a probabilistically motivated approach for selecting the regularization parameters. In addition, we present a technique for correcting inconsistencies on the boundary. We show that the complexity of the proposed method is O(n2). Our simulations demonstrate that when the data are large and the expected response is a complicated function (which is typical in machine learning applications) or when there is a change point in the response, the proposed method has a higher predictive power than many of the existing methods.

    Ladda ner fulltext (pdf)
    fulltext
  • 350.
    Sysoev, Oleg
    et al.
    Linköpings universitet, Institutionen för datavetenskap. Linköpings universitet, Tekniska högskolan.
    Burdakov, Oleg
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Grimvall, Anders
    Linköpings universitet, Institutionen för datavetenskap. Linköpings universitet, Tekniska högskolan.
    A segmentation-based algorithm for large-scale partially ordered monotonic regression2011Ingår i: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 55, nr 8, s. 2463-2476Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Monotonic regression (MR) is an efficient tool for estimating functions that are monotonic with respect to input variables. A fast and highly accurate approximate algorithm called the GPAV was recently developed for efficient solving large-scale multivariate MR problems. When such problems are too large, the GPAV becomes too demanding in terms of computational time and memory. An approach, that extends the application area of the GPAV to encompass much larger MR problems, is presented. It is based on segmentation of a large-scale MR problem into a set of moderate-scale MR problems, each solved by the GPAV. The major contribution is the development of a computationally efficient strategy that produces a monotonic response using the local solutions. A theoretically motivated trend-following technique is introduced to ensure higher accuracy of the solution. The presented results of extensive simulations on very large data sets demonstrate the high efficiency of the new algorithm.

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