| 1. |
- Athanasopoulos, George, et al.
(författare)
-
Forecast reconciliation : A review
- 2024
-
Ingår i: International Journal of Forecasting. - : Elsevier. - 0169-2070 .- 1872-8200. ; 40:2, s. 430-456
-
Forskningsöversikt (refereegranskat)abstract
- Collections of time series formed via aggregation are prevalent in many fields. These are commonly referred to as hierarchical time series and may be constructed cross-sectionally across different variables, temporally by aggregating a single series at different frequencies, or even generalised beyond aggregation as time series that respect linear constraints. When forecasting such time series, a desirable condition is for forecasts to be coherent: to respect the constraints. The past decades have seen substantial growth in this field with the development of reconciliation methods that ensure coherent forecasts and improve forecast accuracy. This paper serves as a comprehensive review of forecast reconciliation and an entry point for researchers and practitioners dealing with hierarchical time series. The scope of the article includes perspectives on forecast reconciliation from machine learning, Bayesian statistics and probabilistic forecasting, as well as applications in economics, energy, tourism, retail demand and demography.
|
|
| 2. |
- Arjomandi Rad, Mohammad, et al.
(författare)
-
Correlation-based feature extraction from computer-aided design, case study on curtain airbags design
- 2022
-
Ingår i: Computers in industry (Print). - : Elsevier. - 0166-3615 .- 1872-6194. ; 138
-
Tidskriftsartikel (refereegranskat)abstract
- Many high-level technical products are associated with changing requirements, drastic design changes, lack of design information, and uncertainties in input variables which makes their design process iterative and simulation-driven. Regression models have been proven to be useful tools during design, altering the resource-intensive finite element simulation models. However, building regression models from computer-aided design (CAD) parameters is associated with challenges such as dealing with too many parameters and their low or coupled impact on studied outputs which ultimately requires a large training dataset. As a solution, extraction of hidden features from CAD is presented on the application of volume simulation of curtain airbags concerning geometric changes in design loops. After creating a prototype that covers all aspects of a real curtain airbag, its CAD parameters have been analyzed to find out the correlation between design parameters and volume as output. Next, using the design of the experiment latin hypercube sampling method, 100 design samples are generated and the corresponding volume for each design sample was assessed. It was shown that selected CAD parameters are not highly correlated with the volume which consequently lowers the accuracy of prediction models. Various geometric entities, such as the medial axis, are used to extract several hidden features (referred to as sleeping parameters). The correlation of the new features and their performance and precision through two regression analyses are studied. The result shows that choosing sleeping parameters as input reduces dimensionality and the need to use advanced regression algorithms, allowing designers to have more accurate predictions (in this case approximately 95%) with a reasonable number of samples. Furthermore, it was concluded that using sleeping parameters in regression-based tools creates real-time prediction ability in the early development stage of the design process which could contribute to lower development lead time by eliminating design iterations.
|
|
| 3. |
- Arjomandi Rad, Mohammad, 1987, et al.
(författare)
-
Image regression-based digital qualification for simulation-driven design processes, case study on curtain airbag
- 2023
-
Ingår i: Journal of engineering design (Print). - : Taylor & Francis. - 0954-4828 .- 1466-1837. ; 34:1, s. 1-22
-
Tidskriftsartikel (refereegranskat)abstract
- Today digital qualification tools are part of many design processes that make them dependent on long and expensive simulations, leading to limited ability in exploring design alternatives. Conventional surrogate modelling techniques depend on the parametric models and come short in addressing radical design changes. Existing data-driven models lack the ability in dealing with the geometrical complexities. Thus, to address the resulting long development lead time problem in the product development processes and to enable parameter-independent surrogate modelling, this paper proposes a method to use images as input for design evaluation. Using a case study on the curtain airbag design process, a database consisting of 60,000 configurations has been created and labelled using a method based on dynamic relaxation instead of finite element methods. The database is made available online for research benchmark purposes. A convolutional neural network with multiple layers is employed to map the input images to the simulation output. It was concluded that the showcased data-driven method could reduce digital testing and qualification time significantly and contribute to real-time analysis in product development. Designers can utilise images of geometrical information to build real-time prediction models with acceptable accuracy in the early conceptual phases for design space exploration purposes.
|
|
| 4. |
- Beldar, Pedram, et al.
(författare)
-
Non-identical parallel machines batch processing problem to minimize the makespan : Models and algorithms
- 2024
-
Ingår i: Computers & Operations Research. - : Elsevier. - 0305-0548 .- 1873-765X. ; 168
-
Tidskriftsartikel (refereegranskat)abstract
- This paper studies a parallel heterogeneous machine batching and scheduling problem in which weighted jobs are first batched, and the batches are then assigned and sequenced on machines of varying capacities. The duration of a batch is the longest time needed to process a job, and the objective is that of minimizing the makespan, or the sum of the batches durations on the machine finishing last. The authors develop polynomial-size mathematical formulations and a variable neighborhood search metaheuristic. Extensive computational results suggest that the flow-based formulation outperforms a compact formulation, despite its larger number of variables. The metaheuristic is capable of producing high-quality solutions within a limited computing time.
|
|
| 5. |
- Billing, Erik, et al.
(författare)
-
Composer : A prototype multilingual model composition tool
- 2013
-
Ingår i: MODPROD2013. - Umeå : Umeå universitet.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Composer - A prototype multilingual model composition toolErik Billing and Martin ServinNovember 10, 2012Facing 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.References[1] Modelica Association. Functional mock-up interface, http://www.fmi-standard.org, November 2012.[2] Modelica Association. Modelica and the modelica association, http://www.modelica.org, November 2012.[3] Erik Billing and Martin Servin. Composer, http://imuit.cs.umu.se/composer, November 2012. [4] SCA Packaging. Sca packaging obbola, http://www.scapackaging.com, November 2012.[5] Patrik Törmänen and Hussein Jaffal. Reducing electricity cost - case study. Technical report, UMIT Research Lab, Umeå University, 2011.2
|
|
| 6. |
- Brownlee, Alexander E. I., et al.
(författare)
-
Conflict-free routing of multi-stop warehouse trucks
- 2020
-
Ingår i: Optimization Letters. - : Springer. - 1862-4472 .- 1862-4480. ; 14:6, s. 1459-1470
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- Chokhachian, Ata, 1988-, et al.
(författare)
-
Toward Object-Oriented Knowledge-Based Parametric Design Thinking
- 2015
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
|
| 8. |
- Dansarie, Marcus, doktorand, 1985-
(författare)
-
sboxgates : A program for finding low gate count implementations of S-boxes
- 2021
-
Ingår i: Journal of Open Source Software. - : Open Journals. - 2475-9066. ; 6:62, s. 1-3
-
Tidskriftsartikel (refereegranskat)abstract
- S-boxes are often the only nonlinear components in modern block ciphers. They are commonly selected to comply with very specific criteria in order to make a cipher secure against, for example, linear and differential attacks. An M x N S-box can be thought of as a lookup table that relates an M-bit input value to an N-bit output value, or as a set of N boolean functions of M variables (Schneier, 1996).Although cipher specifications generally describe S-boxes using their lookup tables, they can also be described as boolean functions or logic gate circuits. sboxgates, which is presented here, finds equivalent logic gate circuits for S-boxes, given their lookup table specification. Generated circuits are output in a human-readable XML format. The software can convert the output files into C or CUDA (a parallel computing platform for Nvidia GPUs) source code. The generated circuits can also be converted to the DOT graph description language for visualization with Graphviz (Ellson et al., 2002).
|
|
| 9. |
- Deb, Kalyanmoy, et al.
(författare)
-
A bi-objective constrained optimization algorithm using a hybrid evolutionary and penalty function approach
- 2013
-
Ingår i: Engineering optimization (Print). - : Taylor & Francis. - 0305-215X .- 1029-0273. ; 45:5, s. 503-527
-
Tidskriftsartikel (refereegranskat)abstract
- Constrained optimization is a computationally difficult task, particularly if the constraint functions are nonlinear and non-convex. As a generic classical approach, the penalty function approach is a popular methodology which degrades the objective function value by adding a penalty proportional to the constraint violation. However, the penalty function approach has been criticized for its sensitivity to the associated penalty parameters. Since its inception, evolutionary algorithms have been modified in various ways to solve constrained optimization problems. Of them, the recent use of a bi-objective evolutionary algorithm in which the minimization of the constraint violation is included as an additional objective has received significant attention. In this article, a combination of a bi-objective evolutionary approach with the classical penalty function methodology is proposed, in a manner complementary to each other. The evolutionary approach provides an appropriate estimate of the penalty parameter, while the solution of an unconstrained penalized function by a classical method induces a convergence property to the overall hybrid algorithm. The working of the procedure on a number of standard numerical test problems and an engineering design problem is demonstrated. In most cases, the proposed hybrid methodology is observed to take one or more orders of magnitude fewer function evaluations to find the constrained minimum solution accurately than some of the best reported existing methodologies.
|
|
| 10. |
- Endrias, Dawit H., et al.
(författare)
-
A combinatorial optimization approach for evaluating minimum-zone spatial straightness errors
- 2012
-
Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 45:5, s. 1170-1179
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new and robust approach for the accurate evaluation of minimumzone spatial straightness error from a set of coordinate measurement data points. The algorithm iteratively searches for the specific data points that define the minimum bound of the spatial straightness zone using combinatorial optimization. It is based on the fact that the minimum circumscribed cylinder of a point set, which is equivalent to the minimum spatial straightness zone of the measurement data, will pass through three, four, or five of the data points that constitute the convex hull vertices of the entire data set. Computed results have shown that although the presented approach may lead to increased computational time, it is robust and able to construct the exact minimum circumscribed cylinder for a given point set. The minimum-zone spatial straightness error can thus be evaluated with the best possible accuracy. The advantage of the presented algorithm is demonstrated via comparison with published computed results of existing algorithms.
|
|
