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  • 1.
    Allen, M. R.
    et al.
    Department of Pure Mathematics, University of Waterloo, Waterloo, Ontario, Canada.
    Cruttwell, G. S. H.
    Department of Mathematics and Statistics, Dalhousie University, Halifax, N.S., Canada.
    Hare, Kathryn E.
    Department of Pure Mathematics, University of Waterloo, Waterloo, Ontario, Canada.
    Rönning, Jan-Olav
    University of Skövde, School of Life Sciences.
    Dimensions of fractals in the large2007In: Chaos, Solitons & Fractals, ISSN 0960-0779, E-ISSN 1873-2887, Vol. 31, no 1, p. 5-13Article in journal (Refereed)
  • 2.
    Amouzgar, Kaveh
    et al.
    University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre. Product Development Department, School of Engineering, Jönköping University, Jönköping, Sweden.
    Strömberg, Niclas
    Department of Mechanical Engineering, School of Science and Technology, University of Örebro, Sweden.
    Radial basis functions as surrogate models with a priori bias in comparison with a posteriori bias2017In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, no 4, p. 1453-1469Article in journal (Refereed)
    Abstract [en]

    In order to obtain a robust performance, the established approach when using radial basis function networks (RBF) as metamodels is to add a posteriori bias which is defined by extra orthogonality constraints. We mean that this is not needed, instead the bias can simply be set a priori by using the normal equation, i.e. the bias becomes the corresponding regression model. In this paper we demonstrate that the performance of our suggested approach with a priori bias is in general as good as, or even for many test examples better than, the performance of RBF with a posteriori bias. Using our approach, it is clear that the global response is modelled with the bias and that the details are captured with radial basis functions. The accuracy of the two approaches are investigated by using multiple test functions with different degrees of dimensionality. Furthermore, several modeling criteria, such as the type of radial basis functions used in the RBFs, dimension of the test functions, sampling techniques and size of samples, are considered to study their affect on the performance of the approaches. The power of RBF with a priori bias for surrogate based design optimization is also demonstrated by solving an established engineering benchmark of a welded beam and another benchmark for different sampling sets generated by successive screening, random, Latin hypercube and Hammersley sampling, respectively. The results obtained by evaluation of the performance metrics, the modeling criteria and the presented optimal solutions, demonstrate promising potentials of our RBF with a priori bias, in addition to the simplicity and straight-forward use of the approach.

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  • 3.
    Athanasopoulos, George
    et al.
    Department of Econometrics and Business Statistics, Monash University, Australia.
    Hyndman, Rob. J.
    Department of Econometrics and Business Statistics, Monash University, Australia.
    Kourentzes, Nikolaos
    epartment of Management Science, Lancaster University Management School, United Kingdom.
    Petropoulos, Fotios
    Information, Decision and Operations Division, School of Management, University of Bath, United Kingdom.
    Forecasting with temporal hierarchies2017In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 262, no 1, p. 60-74Article in journal (Refereed)
    Abstract [en]

    This paper introduces the concept of Temporal Hierarchies for time series forecasting. A temporal hierarchy can be constructed for any time series by means of non-overlapping temporal aggregation. Predictions constructed at all aggregation levels are combined with the proposed framework to result in temporally reconciled, accurate and robust forecasts. The implied combination mitigates modelling uncertainty, while the reconciled nature of the forecasts results in a unified prediction that supports aligned decisions at different planning horizons: from short-term operational up to long-term strategic planning. The proposed methodology is independent of forecasting models. It can embed high level managerial forecasts that incorporate complex and unstructured information with lower level statistical forecasts. Our results show that forecasting with temporal hierarchies increases accuracy over conventional forecasting, particularly under increased modelling uncertainty. We discuss organisational implications of the temporally reconciled forecasts using a case study of Accident & Emergency departments. 

  • 4.
    Barrow, Devon K.
    et al.
    School of Strategy and Leadership, Faculty of Business and Law, Coventry University, Coventry, West Midlands, United Kingdom.
    Kourentzes, Nikolaos
    Lancaster University Management School, Department of Management Science, Lancaster, United Kingdom.
    Distributions of forecasting errors of forecast combinations: Implications for inventory management2016In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 177, p. 24-33Article in journal (Refereed)
    Abstract [en]

    Inventory control systems rely on accurate and robust forecasts of future demand to support decisions such as setting of safety stocks. The combination of multiple forecasts is shown to be effective not only in reducing forecast errors, but also in being less sensitive to limitations of a single model. Research on forecast combination has primarily focused on improving accuracy, largely ignoring the overall shape and distribution of forecast errors. Nonetheless, these are essential for managing the level of aversion to risk and uncertainty for companies. This study examines the forecast error distributions of base and combination forecasts and their implications for inventory performance. It explores whether forecast combinations transform the forecast error distribution towards desired properties for safety stock calculations, typically based on the assumption of normally distributed errors and unbiased forecasts. In addition, it considers the similarity between in- and out-of-sample characteristics of such errors and the impact of different lead times. The effects of established combination methods are explored empirically using a representative set of forecasting methods and a dataset of 229 weekly demand series from a leading household and personal care UK manufacturer. Findings suggest that forecast combinations make the in- and out-of-sample behaviour more consistent, requiring less safety stock on average than base forecasts. Furthermore we find that using in-sample empirical error distributions of combined forecasts approximates well the out-of-sample ones, in contrast to base forecasts. 

  • 5.
    Barrow, Devon
    et al.
    Faculty of Business, Environment and Society, Coventry University, Coventry, West Midlands, United Kingdom.
    Kourentzes, Nikolaos
    Lancaster University Management School, Department of Management Science, Lancaster, United Kingdom.
    The impact of special days in call arrivals forecasting: A neural network approach to modelling special days2018In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 264, no 3, p. 967-977Article in journal (Refereed)
    Abstract [en]

    A key challenge for call centres remains the forecasting of high frequency call arrivals collected in hourly or shorter time buckets. In addition to the complex intraday, intraweek and intrayear seasonal cycles, call arrival data typically contain a large number of anomalous days, driven by the occurrence of holidays, special events, promotional activities and system failures. This study evaluates the use of a variety of univariate time series forecasting methods for forecasting intraday call arrivals in the presence of such outliers. Apart from established, statistical methods, we consider artificial neural networks (ANNs). Based on the modelling flexibility of the latter, we introduce and evaluate different methods to encode the outlying periods. Using intraday arrival series from a call centre operated by one of Europe's leading entertainment companies, we provide new insights on the impact of outliers on the performance of established forecasting methods. Results show that ANNs forecast call centre data accurately, and are capable of modelling complex outliers using relatively simple outlier modelling approaches. We argue that the relative complexity of ANNs over standard statistical models is offset by the simplicity of coding multiple and unknown effects during outlying periods. 

  • 6.
    Bennet, Christian
    et al.
    Göteborgs universitet.
    Sjögren, Jörgen
    University of Skövde, School of Life Sciences.
    Philosophy and mathematics education2013In: Modus Tolland: En festskrift med anledning av Anders Tollands sextioårsdag / [ed] Filip Radovic & Susanna Radovic, Göteborg: Göteborgs universitet , 2013, p. 9-23Chapter in book (Other (popular science, discussion, etc.))
  • 7.
    Bennet, Christian
    et al.
    Göteborgs universitet.
    Sjögren, Jörgen
    University of Skövde, School of Life Sciences. University of Skövde, Health and Education.
    The Viability of Social Constructivism as a Philosophy of Mathematics2013In: Croatian Journal of Philosophy, ISSN 1333-1108, E-ISSN 1847-6139, Vol. XIII, no 39, p. 341-355Article in journal (Refereed)
    Abstract [en]

    Attempts have been made to analyse features in mathematics within a social constructivist context. In this paper we critically examine some of those attempts recently made with focus on problems of the objectivity, ontology, necessity, and atemporality of mathematics. Our conclusion is that these attempts fare no better than traditional alternatives, and that they, furthermore, create new problems of their own.

  • 8.
    Billing, Erik
    et al.
    Umeå universitet, Institutionen för datavetenskap.
    Servin, Martin
    Institutionen för fysik, Umeå universitet.
    Composer: A prototype multilingual model composition tool2013In: MODPROD2013: 7th MODPROD Workshop on Model-Based Product Development / [ed] Peter Fritzson, Umeå: Umeå universitet , 2013Conference paper (Other academic)
    Abstract [en]

    Facing the task to design, simulate or optimize a complex system itis common to find models and data for the system expressed in differentformats, implemented in different simulation software tools. When a newmodel is developed, a target platform is chosen and existing componentsimplemented with different tools have to be converted. This results inunnecessary work duplication and lead times. The Modelica languageinitiative [2] partially solves this by allowing developers to move modelsbetween different tools following the Modelica standard. Another possi-bility is to exchange models using the Functional Mockup Interface (FMI)standard that allows computer models to be used as components in othersimulations, possibly implemented using other programming languages[1]. With the Modelica and FMI standards entering development, there isneed for an easy-to-use tool that supports design, editing and simulationof such multilingual systems, as well as for retracting system informationfor formulating and solving optimization problems.A prototype solution for a graphical block diagram tool for design, edit-ing, simulation and optimization of multilingual systems has been createdand evaluated for a specific system. The tool is named Composer [3].The block diagram representation should be generic, independent ofmodel implementations, have a standardized format and yet support effi-cient handling of complex data. It is natural to look for solutions amongmodern web technologies, specifically HTML5. The format for represent-ing two dimensional vector graphics in HTML5 is Scalable Vector Graphics(SVG). We combine the SVG format with the FMI standard. In a firststage, we take the XML-based model description of FMI as a form for de-scribing the interface for each component, in a language independent way.Simulation parameters can also be expressed on this form, and integratedas metadata into the SVG image. 

    The prototype, using SVG in conjunction with FMI, is implementedin JavaScript and allow creation and modification of block diagrams directly in the web browser. Generated SVG images are sent to the serverwhere they are translated to program code, allowing the simulation ofthe dynamical system to be executed using selected implementations. Analternative mode is to generate optimization problem from the systemdefinition and model parameters. The simulation/optimization result is 

    returned to the web browser where it is plotted or processed using otherstandard libraries.The fiber production process at SCA Packaging Obbola [4] is used asan example system and modeled using Composer. The system consists oftwo fiber production lines that produce fiber going to a storage tank [5].The paper machine is taking fiber from the tank as needed for production.A lot of power is required during fiber production and the purpose of themodel was to investigate weather electricity costs could be reduced byrescheduling fiber production over the day, in accordance with the electricity spot price. Components are implemented for dynamical simulationusing OpenModelica and for discrete event using Python. The Python implementation supports constraint propagation between components andoptimization over specified variables. Each component is interfaced as aFunctional Mock-up Unit (FMU), allowing components to be connectedand properties specified in language independent way. From the SVGcontaining the high-level system information, both Modelica and Pythoncode is generated and executed on the web server, potentially hosted ina high performance data center. More implementations could be addedwithout modifying the SVG system description.We have shown that it is possible to separate system descriptions onthe block diagram level from implementations and interface between thetwo levels using FMI. In a continuation of this project, we aim to integratethe FMI standard also for co-simulation, such that components implemented in different languages could be used together. One open questionis to what extent FMUs of the same component, but implemented withdifferent tools, will have the same model description. For the SVG-basedsystem description to be useful, the FMI model description must remainthe same, or at least contain a large overlap, for a single component implemented in different languages. This will be further investigated in futurework.

  • 9.
    Boström, Henrik
    University of Skövde, School of Humanities and Informatics. University of Skövde, The Informatics Research Centre.
    Maximizing the Area under the ROC Curve with Decision Lists and Rule Sets2007In: Proceedings of the 7th SIAM International Conference on Data Mining / [ed] C. Apte, B. Liu, S. Parthasarathy, D. Skillicorn, Society for Industrial and Applied Mathematics , 2007, p. 27-34Conference paper (Refereed)
    Abstract [en]

    Decision lists (or ordered rule sets) have two attractive properties compared to unordered rule sets: they require a simpler classi¯cation procedure and they allow for a more compact representation. However, it is an open question what effect these properties have on the area under the ROC curve (AUC). Two ways of forming decision lists are considered in this study: by generating a sequence of rules, with a default rule for one of the classes, and by imposing an order upon rules that have been generated for all classes. An empirical investigation shows that the latter method gives a significantly higher AUC than the former, demonstrating that the compactness obtained by using one of the classes as a default is indeed associated with a cost. Furthermore, by using all applicable rules rather than the first in an ordered set, an even further significant improvement in AUC is obtained, demonstrating that the simple classification procedure is also associated with a cost. The observed gains in AUC for unordered rule sets compared to decision lists can be explained by that learning rules for all classes as well as combining multiple rules allow for examples to be ranked according to a more fine-grained scale compared to when applying rules in a fixed order and providing a default rule for one of the classes.

  • 10.
    Brownlee, Alexander E. I.
    et al.
    University of Stirling, United Kingdom.
    Swan, Jerry
    University of York, United Kingdom.
    Senington, Richard
    University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre.
    Kocsis, Zoltan A.
    The University of Manchester, United Kingdom.
    Conflict-free routing of multi-stop warehouse trucks2019In: Optimization Letters, ISSN 1862-4472, E-ISSN 1862-4480Article in journal (Refereed)
    Abstract [en]

    The recent interest in greater vehicular autonomy for factory and warehouse automation has stimulated research in conflict-free routing: a challenging network routing problem in which vehicles may not pass each other. Motivated by a real-world case study, we consider one such application: truck movements in a tightly constrained warehouse. We propose an extension of an existing conflict-free routing algorithm to consider multiple stopping points per route. A high level metaheuristic is applied to determine the route construction and assignment of vehicles to routes. 

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  • 11.
    Chokhachian, Ata
    et al.
    The Technical University of Munich, Germany.
    Hooshyar Yousefi, Bahram
    The Vienna University of Technology, Austria.
    Toward Object-Oriented Knowledge-Based Parametric Design Thinking2015Conference paper (Refereed)
    Abstract [en]

    The parameter, as a variable of differentiation, defines the limits and boundaries of a system and the conditions for its operation. It is through parameters that we are able to produce certain logical relationships between different parts in design procedure. Fundamental to this, however, is the assumption that the object or phenomenawe are modeling is in fact quantifiable. Advances in computational processing have promoted our capacity, and thus faith in the ability, to systematically classify and itemize the world around us. The Parametricism Manifesto concerns itself solely with appearance and arejection of the term Parametricism in certain levels could be clearly visible within the contemporary discourse of Object-oriented and knowledge-based approach that reflects the cognitive attitude of the designer/architect regarding the object-oriented reasoning and analogy. Moreover, instead of having parametric manifestation alternate terms such as digitally intelligent design , algorithmic design, object oriented design , Context-oriented design , Parametric thinking , and even postparametric design have arisen and could be used to describe this vastly differentiated field. What these design theories do share, however, is a predilection and belief in the tool. Nowadays the project fields are information-rich contexts and the tool sets for design are able to interpret, analyze, synthesize and realize these data into the design procedure. This research mainly aims to uncover potentialities of the existing enablers and assistive technologies in context-oriented design in order to have more content-embedded architectural conceptualization solutions.

  • 12.
    Conder, Marston
    et al.
    University of Auckland, New Zealand.
    Stokes, Klara
    University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre. National University of Ireland Maynooth, Co. Kildare, Ireland.
    New methods for finding minimum genus embeddings of graphs on orientable and non-orientable surfaces2019In: Ars Mathematica Contemporanea, ISSN 1855-3966, Vol. 17, no 1, p. 1-35Article in journal (Refereed)
    Abstract [en]

    The question of how to find the smallest genus of all embeddings of a given finite connected graph on an orientable (or non-orientable) surface has a long and interesting history. In this paper we introduce four new approaches to help answer this question, in both the orientable and non-orientable cases. One approach involves taking orbits of subgroups of the automorphism group on cycles of particular lengths in the graph as candidates for subsets of the faces of an embedding. Another uses properties of an auxiliary graph defined in terms of compatibility of these cycles. We also present two methods that make use of integer linear programming, to help determine bounds for the minimum genus, and to find minimum genus embeddings. This work was motivated by the problem of finding the minimum genus of the Hoffman-Singleton graph, and succeeded not only in solving that problem but also in answering several other open questions.

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  • 13.
    Fildes, Robert
    et al.
    Lancaster Centre for Forecasting, Lancaster University, Department of Management Science, United Kingdom.
    Kourentzes, Nikolaos
    Lancaster Centre for Forecasting, Lancaster University, Department of Management Science, United Kingdom.
    Validation and forecasting accuracy in models of climate change2011In: International Journal of Forecasting, ISSN 0169-2070, E-ISSN 1872-8200, Vol. 27, no 4, p. 968-995Article in journal (Refereed)
    Abstract [en]

    Forecasting researchers, with few exceptions, have ignored the current major forecasting controversy: global warming and the role of climate modelling in resolving this challenging topic. In this paper, we take a forecaster's perspective in reviewing established principles for validating the atmospheric-ocean general circulation models (AOGCMs) used in most climate forecasting, and in particular by the Intergovernmental Panel on Climate Change (IPCC). Such models should reproduce the behaviours characterising key model outputs, such as global and regional temperature changes. We develop various time series models and compare them with forecasts based on one well-established AOGCM from the UK Hadley Centre. Time series models perform strongly, and structural deficiencies in the AOGCM forecasts are identified using encompassing tests. Regional forecasts from various GCMs had even more deficiencies. We conclude that combining standard time series methods with the structure of AOGCMs may result in a higher forecasting accuracy. The methodology described here has implications for improving AOGCMs and for the effectiveness of environmental control policies which are focussed on carbon dioxide emissions alone. Critically, the forecast accuracy in decadal prediction has important consequences for environmental planning, so its improvement through this multiple modelling approach should be a priority.

  • 14.
    Griggs, Terry
    et al.
    The Open University, UK.
    Stokes, Klara
    University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre.
    On Pentagonal Geometries with Block Size 3, 4 or 52016In: Symmetries in Graphs, Maps, and Polytopes: 5th SIGMAP Workshop, West Malvern, UK, July 2014 / [ed] Jozef Širáň, Robert Jajcay, Springer, 2016, p. 147-157Chapter in book (Refereed)
  • 15.
    Gundeboina, Saidulu
    University of Skövde, School of Technology and Society.
    Finite Element Analysis of a Washing Machine Cylinder2010Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis a finite element model of a household washing machine cylinder is built and analysed in ABAQUS 6.9-2. The aim is to help Asko appliances in conducting similar analysis for future manufacturing of high capacity cylinders by reducing experimentation. The analysis is mainly concerned with an evenly distributed load at a constant angular velocity. The load is applied with the help of lead plates instead of clothes. The cylinder is loaded with three thin (2 mm) lead plates weighing 2 kg each. The plates with dimensional 370x240x2 mm are mounted with one strip of double sided foam tape inside the cylinder. To estimate the behavior of the cylinder the strains are measured when the cylinder is rotating at 1620 and 2200 revolution per minute (rpm). To validate the model the numerical analyses are compared with experimental results. The results clearly show that the numerical strain values fit with experimental strain values.

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  • 16.
    Hare, Kathryn E.
    et al.
    Department of Pure Mathematics, University of Waterloo, Waterloo, Ontario, Canada.
    Rönning, Jan-Olav
    University of Skövde, Department of Natural Sciences.
    Applications of generalized Perron trees to maximal functions and density bases1998In: Journal of Fourier Analysis and Applications, ISSN 1069-5869, E-ISSN 1531-5851, Vol. 4, no 2, p. 215-227Article in journal (Refereed)
  • 17.
    Hare, Kathryn E.
    et al.
    Department of Pure Mathematics, University of Waterloo, Canada.
    Rönning, Jan-Olav
    University of Skövde, Department of Natural Sciences.
    Fractal dimensions of infinite product spaces2004In: International journal of pure and applied mathematics, ISSN 1311-8080, E-ISSN 1314-3395, Vol. 14, no 2, p. 139-167Article in journal (Refereed)
  • 18.
    Hare, Kathryn E.
    et al.
    Department of Pure Mathematics, University of Waterloo, Waterloo, Ontario Canada.
    Rönning, Jan-Olav
    University of Skövde, Department of Natural Sciences.
    The size of Max(p) sets and density bases2002In: Journal of Fourier Analysis and Applications, ISSN 1069-5869, E-ISSN 1531-5851, Vol. 8, no 3, p. 259-268Article in journal (Refereed)
  • 19.
    Holst, Anders
    et al.
    RISE SICS, Stockholm, Sweden.
    Pashami, Sepideh
    Center for Applied Intelligent Systems Research (CAISR), Halmstad University, Sweden.
    Bae, Juhee
    University of Skövde, School of Informatics. University of Skövde, The Informatics Research Centre.
    Incremental causal discovery and visualization2019In: Proceedings of the Workshop on Interactive Data Mining, WIDM 2019, Association for Computing Machinery (ACM), 2019, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Discovering causal relations from limited amounts of data can be useful for many applications. However, all causal discovery algorithms need huge amounts of data to estimate the underlying causal graph. To alleviate this gap, this paper proposes a novel visualization tool which incrementally discovers causal relations as more data becomes available. That is, we assume that stronger causal links will be detected quickly and weaker links revealed when enough data is available. In addition to causal links, the correlation between variables and the uncertainty of the strength of causal links are visualized in the same graph. The tool is illustrated on three example causal graphs, and results show that incremental discovery works and that the causal structure converges as more data becomes available. 

  • 20.
    Höglund, Marlen
    University of Skövde, School of Humanities and Informatics.
    När kan jag använda mina kunskaper i matematik?: teoretisk och praktisk betydelse för grundskolans matematik2011Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    I skolan anses matematiken vara ett viktigt ämne och den upptar en stor del av skolans undervisningstid. Däremot har det märkts en trend bland eleverna i grundskolan att de mer och mer ifrågasätter varför de över huvud taget måste lära sig matematik. Ren matematik som de läser i skolan kan det många gånger vara svårt att se nyttan med. Påföljande matematik blir då sedan svårare och svårare att ge bra motiveringar till varför man bör kunna.  Många elever och vuxna känner även en ren ångest när man pratar om ämnet matematik. Vad är egentligen matematik, var används den och till vad? Var kommer matematiken ifrån? Hur uppstod den? Är det intressant och relevant för elever att få kunskap om detta? Har matematikundervisningen följt den snabba samhällsutvecklingen och vad behöver vi egentligen lära oss för matematik i grundskolan? Behöver alla få undervisning i matematik? Matematiken finns överallt omkring oss och synen på matematiken eleverna erhållit har formats av hela samhället. Hur mycket påverkar läraren elevernas inställning och vad har föräldrarna för del i det hela? Studien tar upp det matematiska lärandet, matematikens användande och den matematiska fostran.

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  • 21.
    Izquierdo, Milagros
    et al.
    Department of Mathematics, Linköping University, Linköping, Sweden.
    Stokes, Klara
    University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre.
    Isometric point-circle configurations on surfaces from uniform maps2016In: Symmetries in Graphs, Maps, and Polytopes: 5th SIGMAP Workshop, West Malvern, UK, July 2014 / [ed] Jozef Širáň, Robert Jajcay, Springer, 2016, p. 201-212Chapter in book (Refereed)
    Abstract [en]

    We embed neighborhood geometries of graphs on surfaces as point-circle configurations. We give examples coming from regular maps on surfaces with a maximum number of automorphisms for their genus, and survey geometric realization of pentagonal geometries coming from Moore graphs. An infinite family of point-circle v4 configurations on p-gonal surfaces with two p-gonal morphisms is given. The image of these configurations on the sphere under the two p-gonal morphisms is also described.

  • 22.
    Järkehed, Jennie
    et al.
    University of Skövde, School of Humanities and Informatics.
    Mellgren, Hanna
    University of Skövde, School of Humanities and Informatics.
    Från utopi till generell princip: Lärares uppfattningar av individanpassad undervisning i matematik2008Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    According to the Swedish curriculum of 1994 one of the teacher’s assignments is to individualize the teaching. In published official reports, newspaper articles and thesis it appears that students mathematic knowledge is decreasing. Reasons for this could possibly be that focus in the individualized teaching of mathematics turns more towards private schoolwork. According to our experience of individualized teaching in mathematics this statement agrees relatively well. We think that in some cases teachers have a hard time to comply with every student’s conditions and needs. A lack that we think can explain why the students don’t reach the goals in the ninth grade, which are described in the syllabus of mathematics, is despite the fact that the teachers have an assignment to individualize the teaching doesn’t have enough knowledge of the conception to do it. The purpose of this essay is to make researches into teacher’s different conceptions of individualized teaching of mathematics in the early years of school. Through a qualitative methodology with interview as a technique and with a starting point in fenomenografin, was the overarching purpose to contribute with knowledge within the field of education in mathematics. The idea was to contribute to the debate about the necessity of strengthening the student’s knowledge of mathematics. The purpose was also to discuss with implications that could be the consequence of the teacher’s interpretations. The result of the study shows that there are four quality distinct categories of teacher’s conceptions of individualized teaching in mathematics. The conceptions of individualized teaching in mathematics as a general principle of teaching, individualized teaching in mathematics as something that is positive yet impracticable, individualized teaching in mathematics as a method and individualized teaching of mathematics from different students. This study has shown that individualized teaching in mathematic makes the teaching more democratic, the student gets a better presumption to learn the basics of mathematics and that the student gets an increased self-confidence regarding mathematics.

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  • 23.
    Karlsson, Stefan
    Göteborgs universitet.
    Topics on cubic hypersurfaces1998Doctoral thesis, monograph (Other academic)
  • 24.
    Kourentzes, Nikolaos
    Department of Management Science, Lancaster University Management School, Lancaster, Lancashire, United Kingdom.
    Intermittent demand forecasts with neural networks2013In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 143, no 1, p. 198-206Article in journal (Refereed)
    Abstract [en]

    Intermittent demand appears when demand events occur only sporadically. Typically such time series have few observations making intermittent demand forecasting challenging. Forecast errors can be costly in terms of unmet demand or obsolescent stock. Intermittent demand forecasting has been addressed using established forecasting methods, including simple moving averages, exponential smoothing and Croston's method with its variants. This study proposes a neural network (NN) methodology to forecast intermittent time series. These NNs are used to provide dynamic demand rate forecasts, which do not assume constant demand rate in the future and can capture interactions between the non-zero demand and the inter-arrival rate of demand events. This overcomes the limitations of Croston's method. In order to mitigate the issue of limited fitting sample, which is common in intermittent demand, the proposed models use regularised training and median ensembles over multiple training initialisations to produce robust forecasts. The NNs are evaluated against established benchmarks using both forecasting accuracy and inventory metrics. The findings of forecasting and inventory metrics are conflicting. While NNs achieved poor forecasting accuracy and bias, all NN variants achieved higher service levels than the best performing Croston's method variant, without requiring analogous increases in stock holding volume. Therefore, NNs are found to be effective for intermittent demand applications. This study provides further arguments and evidence against the use of conventional forecasting accuracy metrics to evaluate forecasting methods for intermittent demand, concluding that attention to inventory metrics is desirable. 

  • 25.
    Kourentzes, Nikolaos
    et al.
    University of Skövde, School of Informatics. University of Skövde, Informatics Research Environment. Department of Management Science, Lancaster University Management School, Bailrigg, Lancaster, United Kingdom.
    Athanasopoulos, George
    Department of Econometrics and Business Statistics, Monash University, Caulfield East, Australia.
    Elucidate structure in intermittent demand series2020In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860Article in journal (Refereed)
    Abstract [en]

    Intermittent demand forecasting has been widely researched in the context of spare parts management. However, it is becoming increasingly relevant to many other areas, such as retailing, where at the very disaggregate level time series may be highly intermittent, but at more aggregate levels are likely to exhibit trends and seasonal patterns. The vast majority of intermittent demand forecasting methods are inappropriate for producing forecasts with such features. We propose using temporal hierarchies to produce forecasts that demonstrate these traits at the various aggregation levels, effectively informing the resulting intermittent forecasts of these patterns that are identifiable only at higher levels. We conduct an empirical evaluation on real data and demonstrate statistically significant gains for both point and quantile forecasts.

  • 26.
    Kourentzes, Nikolaos
    et al.
    Department of Management Science, Lancaster University Management School, Lancaster University, United Kingdom.
    Barrow, Devon
    Faculty of Business, Environment and Society, Coventry University, United Kingdom.
    Petropoulos, Fotios
    School of Management, University of Bath, United Kingdom.
    Another look at forecast selection and combination: Evidence from forecast pooling2019In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 209, p. 226-235Article in journal (Refereed)
    Abstract [en]

    Forecast selection and combination are regarded as two competing alternatives. In the literature there is substantial evidence that forecast combination is beneficial, in terms of reducing the forecast errors, as well as mitigating modelling uncertainty as we are not forced to choose a single model. However, whether all forecasts to be combined are appropriate, or not, is typically overlooked and various weighting schemes have been proposed to lessen the impact of inappropriate forecasts. We argue that selecting a reasonable pool of forecasts is fundamental in the modelling process and in this context both forecast selection and combination can be seen as two extreme pools of forecasts. We evaluate forecast pooling approaches and find them beneficial in terms of forecast accuracy. We propose a heuristic to automatically identify forecast pools, irrespective of their source or the performance criteria, and demonstrate that in various conditions it performs at least as good as alternative pools that require additional modelling decisions and better than selection or combination. 

  • 27.
    Kourentzes, Nikolaos
    et al.
    Lancaster University Management School, Department of Management Science, Lancaster, Lancashire, United Kingdom.
    Petropoulos, Fotios
    Logistics and Operations Management Section, Cardiff Business School, Cardiff University, United Kingdom.
    Forecasting with multivariate temporal aggregation: The case of promotional modelling2016In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 181, p. 145-153Article in journal (Refereed)
    Abstract [en]

    Demand forecasting is central to decision making and operations in organisations. As the volume of forecasts increases, for example due to an increased product customisation that leads to more SKUs being traded, or a reduction in the length of the forecasting cycle, there is a pressing need for reliable automated forecasting. Conventionally, companies rely on a statistical baseline forecast that captures only past demand patterns, which is subsequently adjusted by human experts to incorporate additional information such as promotions. Although there is evidence that such process adds value to forecasting, it is questionable how much it can scale up, due to the human element. Instead, in the literature it has been proposed to enhance the baseline forecasts with external well-structured information, such as the promotional plan of the company, and let experts focus on the less structured information, thus reducing their workload and allowing them to focus where they can add most value. This change in forecasting support systems requires reliable multivariate forecasting models that can be automated, accurate and robust. This paper proposes an extension of the recently proposed Multiple Aggregation Prediction Algorithm (MAPA), which uses temporal aggregation to improve upon the established exponential smoothing family of methods. MAPA is attractive as it has been found to increase both the accuracy and robustness of exponential smoothing. The extended multivariate MAPA is evaluated against established benchmarks in modelling a number of heavily promoted products and is found to perform well in terms of forecast bias and accuracy. Furthermore, we demonstrate that modelling time series using multiple temporal aggregation levels makes the final forecast robust to model mis-specification. 

  • 28.
    Kourentzes, Nikolaos
    et al.
    Lancaster University Management School, Department of Management Science, Lancaster, Lancashire, United Kingdom.
    Petropoulos, Fotios
    Lancaster University Management School, Department of Management Science, Lancaster, Lancashire, United Kingdom.
    Trapero, Juan R.
    Universidad de Castilla-La Mancha, Departamento de Administracion de Empresas, Ciudad Real, Spain.
    Improving forecasting by estimating time series structural components across multiple frequencies2014In: International Journal of Forecasting, ISSN 0169-2070, E-ISSN 1872-8200, Vol. 30, no 2, p. 291-302Article in journal (Refereed)
    Abstract [en]

    Identifying the most appropriate time series model to achieve a good forecasting accuracy is a challenging task. We propose a novel algorithm that aims to mitigate the importance of model selection, while increasing the accuracy. Multiple time series are constructed from the original time series, using temporal aggregation. These derivative series highlight different aspects of the original data, as temporal aggregation helps in strengthening or attenuating the signals of different time series components. In each series, the appropriate exponential smoothing method is fitted and its respective time series components are forecast. Subsequently, the time series components from each aggregation level are combined, then used to construct the final forecast. This approach achieves a better estimation of the different time series components, through temporal aggregation, and reduces the importance of model selection through forecast combination. An empirical evaluation of the proposed framework demonstrates significant improvements in forecasting accuracy, especially for long-term forecasts. 

  • 29.
    Kourentzes, Nikolaos
    et al.
    Lancaster University Management School Department of Management Science, Lancaster, United Kingdom.
    Rostami-Tabar, Bahman
    Cardiff Business School, Cardiff University, Cardiff, United Kingdom.
    Barrow, Devon K.
    School of Strategy and Leadership, Faculty of Business and Law Coventry University, Coventry, West Midlands, United Kingdom.
    Demand forecasting by temporal aggregation: Using optimal or multiple aggregation levels?2017In: Journal of Business Research, ISSN 0148-2963, E-ISSN 1873-7978, Vol. 78, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Recent advances have demonstrated the benefits of temporal aggregation for demand forecasting, including increased accuracy, improved stock control and reduced modelling uncertainty. With temporal aggregation a series is transformed, strengthening or attenuating different elements and thereby enabling better identification of the time series structure. Two different schools of thought have emerged. The first focuses on identifying a single optimal temporal aggregation level at which a forecasting model maximises its accuracy. In contrast, the second approach fits multiple models at multiple levels, each capable of capturing different features of the data. Both approaches have their merits, but so far they have been investigated in isolation. We compare and contrast them from a theoretical and an empirical perspective, discussing the merits of each, comparing the realised accuracy gains under different experimental setups, as well as the implications for business practice. We provide suggestions when to use each for maximising demand forecasting gains. 

  • 30.
    Kourentzes, Nikolaos
    et al.
    Lancaster University Management School, United Kingdom.
    Sagaert, Yves
    Faculty of Engineering and Architecture of Ghent University, Belgium.
    Incorporating Leading Indicators into Sales Forecasts2018In: Foresight: The International Journal of Applied Forecasting, ISSN 1555-9068, no 48, p. 24-30Article in journal (Refereed)
    Abstract [en]

    Using leading indicators for business forecasting-in contrast to macroeconomic forecasting-has been relatively rare, partly because our traditional time-series methods do not readily allow incorporation of external variables. Nowadays, however, we have an abundance of potentially useful indicators, and there is evidence that utilizing relevant ones in a forecasting model can significantly improve forecast accuracy and transparency. In this article, Nikolaos and Yves show how to find appropriate leading indicators and make good use of them for sales forecasting. 

  • 31.
    Lowe, Robert
    University of Hertfordshire.
    The Evolution of Affective Displays and Related Strategies2007Doctoral thesis, monograph (Other academic)
  • 32.
    Lowe, Robert
    et al.
    Adaptive Systems Research Group, School of Computer Science, University of Hertfordshire.
    Cañamero, Lola
    Adaptive Systems Research Group, School of Computer Science, University of Hertfordshire.
    Nehaniv, Chrystopher L.
    Adaptive Systems Research Group, School of Computer Science, University of Hertfordshire.
    Polani, Daniel
    Adaptive Systems Research Group, School of Computer Science, University of Hertfordshire.
    The Evolution of Affect-Related Displays, Recognition and Related Strategies2004In: Artificial Life IX: Proceedings of the Ninth International Conference on the Simulation and Synthesis of Living Systems / [ed] Jordan Pollack, Mark Bedau, Phil Husbands, Takashi Ikegami, & Richard A. Watson, MIT Press, 2004, p. 176-181Conference paper (Refereed)
  • 33.
    Lowe, Robert
    et al.
    Adaptive Systems Research Group, Faculty of Engineering and Information Sciences, University of Hertfordshire.
    Cañamero, Lola
    Adaptive Systems Research Group, Faculty of Engineering and Information Sciences, University of Hertfordshire.
    Nehaniv, Chrystopher
    Adaptive Systems Research Group, Faculty of Engineering and Information Sciences, University of Hertfordshire.
    Polani, Daniel
    Adaptive Systems Research Group, Faculty of Engineering and Information Sciences, University of Hertfordshire.
    Strategies in the Evolution of Affect Related Displays and Recognition2004In: The Logic of Artificial Life: Abstracting And Synthesizing The Principles Of Living Systems: Proceedings of the 6th German Workshop on Artificial Life, April 14-16, 2004, Bamberg, Germany, IOS Press, 2004, p. 89-95Conference paper (Refereed)
  • 34.
    Lowe, Robert
    et al.
    Adaptive Systems Research Group, Faculty of Engineering and Information Sciences, University of Hertfordshire, United Kingdom.
    Polani, Daniel
    Adaptive Systems Research Group, Faculty of Engineering and Information Sciences, University of Hertfordshire, United Kingdom.
    Preventing bluff agent invasions in honest societies2003In: Advances in Artificial Life: 7th European Conference, ECAL 2003, Dortmund, Germany, September 14-17, 2003. Proceedings / [ed] Wolfgang Banzhaf, Jens Ziegler, Thomas Christaller, Peter Dittrich, Jan T. Kim, Berlin, Heidelberg: Springer, 2003, p. 118-127Conference paper (Refereed)
  • 35.
    Mellin, Jonas
    et al.
    University of Skövde, School of Informatics. University of Skövde, The Informatics Research Centre.
    Andler, Sten F.
    University of Skövde, School of Informatics. University of Skövde, The Informatics Research Centre.
    The effect of optimizing engine control on fuel consumption and roll amplitude in ocean-going vessels: An experimental study2015Report (Other academic)
    Abstract [en]

    We use data-generated models based on data from experiments of an ocean-going vessel to study the effect of optimizing fuel consumption. The optimization is an add-on module to the existing diesel-engine fuel-injection control built by Q-TAGG R&D AB. The work is mainly a validation of knowledge-based models based on a priori knowledge from physics. The results from a simulation-based analysis of the predictive models built on data agree with the results based on knowledge-based models in a companion study. This indicates that the optimization algorithm saves fuel. We also address specific problems of adapting data to existing machine learning methods. It turns out that we can simplify the problem by ignoring the auto-correlative effects in the time series by employing low-pass filters and resampling techniques. Thereby we can use mature and robust classification techniques with less requirements on the data to demonstrate that fuel is saved compared to the full-fledged time series analysis techniques which are harder to use. The trade-off is the accuracy of the result, that is, it is hard to tell exactly how much fuel is saved. In essence, however, this process can be automated due to its simplicity. 

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  • 36.
    Petropoulos, Fotios
    et al.
    Cardiff Business School of Cardiff University, United Kingdom.
    Kourentzes, Nikolaos
    Lancaster University, United Kingdom.
    Commentary: Two Sides of the Same Coin2016In: Foresight: The International Journal of Applied Forecasting, ISSN 1555-9068, no 42, p. 37-39Article in journal (Refereed)
  • 37.
    Petropoulos, Fotios
    et al.
    Lancaster Centre for Forecasting, Lancaster University Management School, Lancaster University, Lancaster, United Kingdom.
    Kourentzes, Nikolaos
    Lancaster Centre for Forecasting, Lancaster University Management School, Lancaster University, Lancaster, United Kingdom.
    Forecast combinations for intermittent demand2015In: Journal of the Operational Research Society, ISSN 0160-5682, E-ISSN 1476-9360, Vol. 66, no 6, p. 914-924Article in journal (Refereed)
    Abstract [en]

    Intermittent demand is characterised by infrequent demand arrivals, where many periods have zero demand, coupled with varied demand sizes. The dual source of variation renders forecasting for intermittent demand a very challenging task. Many researchers have focused on the development of specialised methods for intermittent demand. However, apart from a case study on hierarchical forecasting, the effects of combining, which is a standard practice for regular demand, have not been investigated. This paper empirically explores the efficiency of forecast combinations in the intermittent demand context. We examine both method and temporal combinations of forecasts. The first are based on combinations of different methods on the same time series, while the latter use combinations of forecasts produced on different views of the time series, based on temporal aggregation. Temporal combinations of single or multiple methods are investigated, leading to a new time-series classification, which leads to model selection and combination. Results suggest that appropriate combinations lead to improved forecasting performance over single methods, as well as simplifying the forecasting process by limiting the need for manual selection of methods or hyper-parameters of good performing benchmarks. This has direct implications for intermittent demand forecasting in practice. 

  • 38.
    Petropoulos, Fotios
    et al.
    Lancaster University, United Kingdom.
    Kourentzes, Nikolaos
    Lancaster University, United Kingdom.
    Improving Forecasting via Multiple Temporal Aggregation2014In: Foresight: The International Journal of Applied Forecasting, ISSN 1555-9068, no 34, p. 12-17Article in journal (Refereed)
    Abstract [en]

    In most business forecasting applications, the decision-making need we have directs the frequency of the data we collect (monthly, weekly, etc.) and use for forecasting. In this article, Fotios and Nikolaos introduce an approach that combines forecasts generated by modeling the different frequencies (levels of temporal aggregation). Their technique augments our information about the data used for forecasting and, as such, can result in more accurate forecasts. It also automatically reconciles the forecasts at different levels.

  • 39.
    Petropoulos, Fotios
    et al.
    Logistics and Operations Management Section, Cardiff Business School, Cardiff University, United Kingdom.
    Kourentzes, Nikolaos
    Department of Management Science, Lancaster University Management School, Lancaster University, United Kingdom.
    Nikolopoulos, Konstantinos
    Bangor Business School, Bangor University, United Kingdom.
    Another look at estimators for intermittent demand2016In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 181, p. 154-161Article in journal (Refereed)
    Abstract [en]

    In this paper we focus on forecasting for intermittent demand data. We propose a new aggregation framework for intermittent demand forecasting that performs aggregation over the demand volumes, in contrast to the standard framework that employs temporal (over time) aggregation. To achieve this we construct a transformed time series, the inverse intermittent demand series. The new algorithm is expected to work best on erratic and lumpy demand, as a result of the variance reduction of the non-zero demands. The improvement in forecasting performance is empirically demonstrated through an extensive evaluation in more than 8000 time series of two well-researched spare parts data sets from the automotive and defence sectors. Furthermore, a simulation is performed so as to provide a stock-control evaluation. The proposed framework could find popularity among practitioners given its suitability when dealing with clump sizes. As such it could be used in conjunction with existing popular forecasting methods for intermittent demand as an exception handling mechanism when certain types of demand are observed.

  • 40.
    Petropoulos, Fotios
    et al.
    School of Management, University of Bath, United Kingdom.
    Kourentzes, Nikolaos
    Lancaster University Management School, Lancaster University, United Kingdom.
    Nikolopoulos, Konstantinos
    Bangor Business School, Bangor University, United Kingdom.
    Siemsen, Enno
    Wisconsin School of Business, University of Wisconsin, USA.
    Judgmental selection of forecasting models2018In: Journal of Operations Management, ISSN 0272-6963, E-ISSN 1873-1317, Vol. 60, p. 34-46Article in journal (Refereed)
    Abstract [en]

    In this paper, we explored how judgment can be used to improve the selection of a forecasting model. We compared the performance of judgmental model selection against a standard algorithm based on information criteria. We also examined the efficacy of a judgmental model-build approach, in which experts were asked to decide on the existence of the structural components (trend and seasonality) of the time series instead of directly selecting a model from a choice set. Our behavioral study used data from almost 700 participants, including forecasting practitioners. The results from our experiment suggest that selecting models judgmentally results in performance that is on par, if not better, to that of algorithmic selection. Further, judgmental model selection helps to avoid the worst models more frequently compared to algorithmic selection. Finally, a simple combination of the statistical and judgmental selections and judgmental aggregation significantly outperform both statistical and judgmental selections.

  • 41.
    Pettersson, Kerstin
    University of Skövde, School of Life Sciences.
    Samspel mellan intuitiva idéer och formella bevis: en fallstudie av universitetsstudenters arbete med en analysuppgift2004Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    The aim of this study is to illuminate the interplay between intuitive ideas and formal justification. In a perspective where we focus on the students’ competences we describe the interaction between intuitive ideas and formal structures, as they appear especially in relation to concept definitions and formal proofs. A group of university students have been working on a task in calculus. The task includes the concepts function and derivative and requires of them to use a proof by induction. The discussion between the members of the group has been analyzed in accordance with the principles of intentional analysis, a method by which we regard the students’ activities as intentional. This method of analysis makes the process of interpretation visible. It also makes it possible to make explicit the competences of the students’ and the mathematical content of their actions. In the study examples are given of the interplay between the intuitive ideas and the formal structures and also of the function for this interplay. The students have rich concept images and access to intuitive ideas relevant to the concepts brought to the 4 fore by the task. During the group discussion all components of a complete proof are included in the students’ reasoning. The students create a proof by induction which matches the ordinary pattern for such a proof, but they do not themselves regard it as a proof fitting into the ordinary scheme of argumentation, as they remember it from text-books and teaching. The students put heavy demands upon the formalization of their ideas and these demands are sometimes hampering the problem solving process, but they also encourage the students to expand their search for a solution to the problem at hand.

  • 42.
    Pettersson, Kerstin
    University of Skövde, School of Life Sciences.
    Växelverkan mellan intuitiva idéer och formella resonemang: En fallstudie av universitetsstudenters arbete med en analysuppgift2008In: Nordisk matematikkdidaktikk, ISSN 1104-2176, Vol. 13, no 1, p. 29-50Article in journal (Refereed)
    Abstract [sv]

    Studiens syfte är att visa hur en växelverkan mellan intuitiva idéer och formella resonemang kan gestalta sig i en problemlösningsprocess. Studien visar att universitetsstudenter redan under sitt första år av matematikstudier förmår utnyttja en sådan växelverkan. En grupp studenter har arbetat med en analysuppgift som berör begreppen funktion och derivata samt inkluderar ett induktionsbevis. Studenterna utnyttjar i den kreativa processen intuitiva idéer och formella resonemang i ett dynamiskt samspel. Växlingarna har ett flertal funktioner: att kontrollera intuitiva uppfattningar, att skaffa nya utgångspunkter för problemlösningsprocessen, att ekonomisera resonemang och att driva arbetet vidare.

  • 43.
    Pettersson, Kerstin
    et al.
    University of Skövde, School of Life Sciences.
    Scheja, Max
    Algorithmic contexts and learning potentiality: A case study of students' understanding of calculusManuscript (Other academic)
  • 44.
    Runesson, Ulla
    University of Skövde, School of Humanities and Informatics.
    A collective enquiry into critical aspects of teaching the concept of angles2007In: Nordisk matematikkdidaktikk, ISSN 1104-2176, Vol. 12, no 4, p. 7-25Article in journal (Refereed)
    Abstract [en]

    This paper describes an approach to teaching that enhances pupils’ learning in mathematics. The model described – Learning study – involves teachers and researchers cooperating in an iterative process, gathering data about teaching and pupils’ learning, analysing the data, planning and revising their teaching. A particular theoretical framework was used as a guiding principle when designing and analysing learning. The goal was to identify aspects critical for learning the angle concept. It is demonstrated how the teachers were able to identify the critical aspects and change the teaching in a way that promoted pupils’ learning. What these critical aspects may entail and what teachers and researchers can learn from a Learning study is discussed.

  • 45.
    Rönning, Jan-Olav
    University of Skövde, Department of Natural Sciences.
    A convergence result for square roots of the Poisson kernel in the bidisk1999In: Mathematica Scandinavica, ISSN 0025-5521, E-ISSN 1903-1807, Vol. 84, no 1, p. 81-92Article in journal (Refereed)
  • 46.
    Rönning, Jan-Olav
    University of Skövde, Department of Natural Sciences.
    Convergence results for the square root of the Poisson kernel1997In: Mathematica Scandinavica, ISSN 0025-5521, E-ISSN 1903-1807, Vol. 81, no 2, p. 219-235Article in journal (Refereed)
  • 47.
    Rönning, Jan-Olav
    University of Skövde, School of Engineering Science.
    On convergence for the square root of the Poisson kernel in symmetric spaces of rank 11997In: Studia Mathematica, ISSN 0039-3223, E-ISSN 1730-6337, Vol. 125, no 3, p. 219-229Article in journal (Refereed)
  • 48.
    Rönning, Jan-Olav
    et al.
    University of Skövde, Department of Natural Sciences.
    Svensson, Olof
    Linköpings Universitet, Campus Norrköping, Institutionen för teknik och naturvetenskap.
    Convergence for the square root of the Poisson kernel in rank one symmetric spaces against boundary functions with regularity: Preprint Chalmers och Göteborgs Universitet, (79)2001Manuscript (preprint) (Other academic)
  • 49.
    Sagaert, Yves R.
    et al.
    Univ Ghent, Dept Ind Syst Engn & Prod Design, Ghent, Belgium / Solventure NV, Ghent, Belgium.
    Aghezzaf, El-Houssaine
    Univ Ghent, Dept Ind Syst Engn & Prod Design, Ghent, Belgium / Flanders Make, Lommel, Belgium.
    Kourentzes, Nikolaos
    Univ Lancaster, Sch Management, Dept Management Sci, Lancaster, United Kingdom.
    Desmet, Bram
    Solventure NV, Ghent, Belgium.
    Temporal big data for tactical sales forecasting in the tire industry2018In: Interfaces, ISSN 0092-2102, E-ISSN 1526-551X, Vol. 48, no 2, p. 121-129Article in journal (Refereed)
    Abstract [en]

    We propose a forecasting method to improve the accuracy of tactical sales predictions for a major supplier to the tire industry. This level of forecasting, which serves as direct input to the demand-planning process and steers the global supply chain, is typically done up to a year in advance. The product portfolio of the company for which we did our research is sensitive to external events. Univariate statistical methods, which are commonly used in practice, cannot be used to anticipate and forecast changes in the market; and forecasts by human experts are known to be biased and inconsistent. The method we propose allows us to automate the identification of key leading indicators, which drive sales, from a massive set of macroeconomic indicators, across di erent regions and markets; thus, we can generate accurate forecasts. Our method also allows us to handle the additional complexity that results from short-term and long-term dynamics of product sales and external indicators. For the company we study, accuracy improved by 16.1 percent over its current practice. Furthermore, our method makes the market dynamics transparent to company managers, thus allowing them to better understand the events and economic variables that a ect the sales of their products. 

  • 50.
    Scheja, Max
    et al.
    Stockholm Univ, Dept Educ, S-10691 Stockholm, Sweden.
    Pettersson, Kerstin
    University of Skövde, School of Life Sciences.
    Transformation and contextualisation: exploring students' conceptual understandings od threshold concept in calculus2010In: Higher Education, ISSN 0018-1560, E-ISSN 1573-174X, Vol. 59, no 2, p. 221-241Article in journal (Refereed)
12 1 - 50 of 70
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