251 |
Understanding grassland dynamics in the steppe zone of Kazakhstan – a remote sensing analysisDara, Andrey 22 January 2020 (has links)
Die Steppen Kasachstans haben seit dem Zusammenbruch der Sowjetunion einen tiefgreifenden Wandel erfahren. Insbesondere die Veränderung der Landnutzung, welche traditionell von der Acker- und Weidenutzung geprägt ist, sowie die daraus resultierenden Effekte auf das Feuerregime sind aktuell noch nicht ausreichend verstanden. Das Hauptziel dieser Dissertation besteht daher in der Kartierung und Analyse der Veränderungen im Mensch-Umweltsystem des nördlichen Kasachstans seit den 1980er Jahren. Ein auf jährlichen Landsat-Zeitreihen basierender Ansatz wurde entwickelt, um den Zeitpunkt der Aufgabe und Rekultivierung von landwirtschaftlichen Flächen mit hoher räumlicher und zeitlicher Auflösung zu dokumentieren. Dieser Datensatz ermöglichte z.B. die Schätzung des Anteils organischer Kohlenstoffbindungen im Boden auf Basis der Nutzungsgeschichte der letzten Jahrzehnte. Eine Kartierung der Änderungen im Feuerregime zeigte eine siebenfache Zunahme an verbrannter Fläche und eine Verachtfachung von Bränden innerhalb des Untersuchungszeitraumes. Sowohl landwirtschaftliche Feuer als auch die Landaufgabe waren mit einem erhöhten Brandrisiko assoziiert. Darüber hinaus wurde mithilfe von Spektralindizes und einem Random Forest Modell quantifiziert, wie sich der Beweidungsdruck nach dem Zerfall der Sowjetunion verändert hat. Die Analyse ergab einen Rückgang des Beweidungsdrucks in der kasachischen Steppe nach 1992, meist in der Nähe von aufgegebenen Nutzviehhaltestationen. In dieser Dissertation konnte gezeigt werden, wie Landsat-Zeitreihen genutzt werden können, um den Einfluss von Landnutzungsänderungen auf die Ökologie von Steppen besser zu verstehen. Die entwickelten Datensätze ermöglichen es, die Prozesse, die zur Landaufgabe und den damit zusammenhängenden Auswirkungen auf die kasachische Steppe führten, zu entwirren und können zur Entscheidungsfindung in der Landnutzungs- und Naturschutzplanung verwendet werden. / The steppes of Kazakhstan are one of the world regions that experienced massive changes in land-use intensity and widespread land-use change after the breakdown of the Soviet Union. Cropping and grazing regime changes across the steppes of Kazakhstan are understudied, and related spatio-temporal changes, e.g. in fire regimes, are still poorly understood. The main research goal of this thesis was to develop a methodology to map related change at appropriate scales and to provide novel datasets to enhance our understanding of how the coupled human-environment in Northern Kazakhstan has changed since the 1980s. An approach was developed to identify the timing of post-Soviet cropland abandonment and recultivation in northern Kazakhstan. Knowing the timing of abandonment allowed for deeper insights into what drives these dynamics: for example, recultivation after 2007 happened mainly on land that had been abandoned latest. Knowing the timing of abandonment allowed for substantially more precise estimates of soil organic carbon sequestration. Mapping changes in fire regimes highlighted a sevenfold increase in burnt area and an eightfold increase in number of fires after the breakdown of the Soviet Union. Agricultural burning and abandonment were associated with increased fire risk. Grazing probabilities, derived from Landsat using a random forest, were found to provide the best metrics to capture grazing pressure. The analysis revealed a general decline in grazing pressure in the Kazakh steppe after 1992, especially near abandoned livestock stations. Collectively, the dissertation highlights how dense records of Landsat images can be utilized to better understand land use changes and the ecology of steppes across large areas. The datasets developed within this thesis allow to disentangle the processes leading to and the impacts of agricultural abandonment in the temperate Kazakh steppes, and may be used to support decision-making in land-use and conservation planning.
|
252 |
Noisy Bayesian Optimization of Variational Quantum EigensolversIannelli, Giovanni 21 August 2024 (has links)
Der Variationsquanten-Eigensolver (VQE) ist ein hybrider quanten-klassischer Algorithmus, der dazu dient, den Grundzustand eines Hamiltonians mit Hilfe von Variationsmethoden aufzufinden. Er hat ein breites Spektrum an möglichen Anwendungen, von der Quanten Chemie bis hin zu Gittereichtheorien in der Hamiltonformulierung. VQE stützt sich auf Quantencomputer, um die Energie eines Systems in Form von Schaltkreisparametern zu berechnen und minimiert diese parametrisierte Energie mit einer klassischen Optimierungsroutine. Diese Doktorarbeit bebenutzt als Algorithmus eine Bayes'sche Optimierung (BO). Der Algorithmus wurde speziell für die Minimierung der parametrisierten Energie, wie sie mit einem Quantencomputer berechnet wird, entwickelt. Die BO basiert auf der Gaußschen Prozessregression (GPR) und ist ein Algorithmus zum Auffinden des globalen Minimums einer Black-Box Kostenfunktion, z.~B.~der Energie. Die BO arbeitet mit einer sehr geringen Anzahl von Iterationen selbst bei Verwendung von Daten, die durch statistisches Rauschen beeinflusst sind.
Außerdem erwies sich das für diese Arbeit entwickelte GPR-Verfahren als sehr vielseitig, da wir es auch für die Berechnung diskreter Integraltransformationen von verrauschten Daten verwenden konnten. Insbesondere wurde dieses Verfahren zur Rekonstruktion von Parton Verteilungsfunktionen aus Gitter-QCD-Daten verwendet. / The variational quantum eigensolver (VQE) is a hybrid quantum-classical algorithm
used to find the ground state of a Hamiltonian using variational methods. It has a wide range of potential applications, from quantum chemistry to lattice gauge theories in the Hamiltonian formulation. VQE relies on quantum computers to evaluate the energy of the system in terms of circuit parameters, and it minimizes this parametrized energy with a classical optimization routine. This work describes a Bayesian optimization (BO) algorithm specifically designed to minimize the parametrized energy obtained with a quantum computer. BO based on Gaussian process regression (GPR) is an algorithm for finding the global minimum of a black-box cost function, e.g. the energy, with a very low number of iterations even when using data affected by statistical noise.
Furthermore, the GPR procedure developed for this work proved to be very versatile as
we also used it to compute discrete integral transforms of noisy data. In particular, this procedure was used to reconstruct parton distribution functions from lattice QCD data.
|
253 |
Spatial and Temporal Dynamics of Visual Working Memory MaintenanceDegutis, Jonas Karolis 18 December 2024 (has links)
Diese kumulative Dissertation umfasst zwei Studien zu den räumlichen und zeitlichen neuronalen Dynamiken des visuellen Arbeitsgedächtnisses (VA). Die erste Studie untersuchte, wie die oberflächlichen und tiefen Schichten des präfrontalen Kortex (PFC) zur Enkodierung, Aufrechterhaltung und zum Abruf von VA-Informationen bei unterschiedlichen Gedächtnisbelastungen beitragen. Die Ergebnisse zeigten, dass die oberflächlichen PFC-Schichten bei hoher Belastung während der Verzögerung und des Abrufs stärker aktiviert waren. Multivariate Decodierungstechniken zeigten eine dynamische neuronale Kodierung mit drei Clustern generalisierter Aktivitätsmuster in den Phasen der Enkodierung, Verzögerung und des Abrufs. Es gab jedoch keine Generalisierung zwischen diesen Phasen, was auf unterschiedliche neuronale Populationen für jede Phase hinweist. Die zweite Studie untersuchte die Mechanismen, die VA bei Ablenkungen aufrechterhalten. Dabei wurden Daten aus einer früheren Studie erneut analysiert, in der die Teilnehmer drei Arten von Aufgaben ausführten: eine mit einer leeren Verzögerungsphase, eine mit einem Orientierungsablenker und eine mit einem Rauschablenker. Die Studie analysierte die zeitliche Generalisierung der neuronalen Codes in Regionen des visuellen Kortex und prüfte, ob VA und Ablenker dieselben neuronalen Subräume nutzen. Die Ergebnisse zeigten eine dynamische Kodierung während der frühen und späten Verzögerungsphasen. Zudem wurden VA und der Orientierungsablenker in getrennten, nicht überlappenden Subräumen aufrechterhalten, was auf unterschiedliche neuronale Populationen für VA und Ablenker hindeutet. Zusammenfassend erweitert die Dissertation das Verständnis darüber, wie der PFC und visuelle Areale VA-Informationen aufrechterhalten, insbesondere unter unterschiedlichen Belastungen und Ablenkungen. Sie liefert zudem neue Ansätze zur Untersuchung der zeitlichen neuronalen Dynamik dieser Prozesse. / This cumulative thesis covers two scientific studies exploring the spatial and temporal neural dynamics of visual working memory (VWM) processes. The first study examined the contributions of the prefrontal cortex (PFC) layers—superficial and deep—during VWM encoding, maintenance, and retrieval under two memory load conditions. Results revealed heightened activation in the superficial layers of the PFC during high-load trials, particularly in the maintenance and retrieval phases. Using multivariate decoding techniques, the study assessed the temporal stability of neural codes distinguishing high- and low-load trials, identifying a dynamic code with three distinct clusters of generalization during encoding, delay, and retrieval phases. Notably, there was no generalization of neural patterns across these phases, suggesting distinct neural populations for each stage. The second study focused on the mechanisms enabling VWM maintenance in the presence of distractions. Reanalyzing prior data, the study examined VWM trials featuring either a blank delay, an orientation distractor, or a noise distractor. The study explored the temporal generalization of neural codes across visual cortex regions and whether VWM and distractors shared neural subspaces. Findings indicated dynamic neural coding during early and late memory delay periods. Additionally, VWM and orientation distractors were maintained in separate, non-overlapping subspaces, suggesting distinct neural populations for VWM and perceptual distractors. Collectively, this thesis enhances our understanding of how the PFC and visual areas support VWM maintenance and control, particularly under varying loads and distractions. It also introduces novel approaches for investigating the temporal neural dynamics underlying these processes.
|
254 |
On the Efficient Utilization of Dense Nonlocal Adjacency Information In Graph Neural NetworksBünger, Dominik 14 December 2021 (has links)
In den letzten Jahren hat das Teilgebiet des Maschinellen Lernens, das sich mit Graphdaten beschäftigt, durch die Entwicklung von spezialisierten Graph-Neuronalen Netzen (GNNs) mit mathematischer Begründung in der spektralen Graphtheorie große Sprünge nach vorn gemacht. Zusätzlich zu natürlichen Graphdaten können diese Methoden auch auf Datensätze ohne Graphen angewendet werden, indem man einen Graphen künstlich mithilfe eines definierten Adjazenzbegriffs zwischen den Samplen konstruiert. Nach dem neueste Stand der Technik wird jedes Sample mit einer geringen Anzahl an Nachbarn verknüpft, um gleichzeitig das dünnbesetzte Verhalten natürlicher Graphen nachzuahmen, die Stärken bestehender GNN-Methoden auszunutzen und quadratische Abhängigkeit von der Knotenanzahl zu verhinden, welche diesen Ansatz für große Datensätze unbrauchbar machen würde.
Die vorliegende Arbeit beleuchtet die alternative Konstruktion von vollbesetzten Graphen basierend auf Kernel-Funktionen. Dabei quantifizieren die Verknüpfungen eines jeden Samples explizit die Ähnlichkeit zu allen anderen Samplen. Deshalb enthält der Graph eine quadratische Anzahl an Kanten, die die lokalen und nicht-lokalen Nachbarschaftsinformationen beschreiben. Obwohl dieser Ansatz in anderen Kontexten wie der Lösung partieller Differentialgleichungen ausgiebig untersucht wurde, wird er im Maschinellen Lernen heutzutage meist wegen der dichtbesetzten Adjazenzmatrizen als unbrauchbar empfunden. Aus diesem Grund behandelt ein großer Teil dieser Arbeit numerische Techniken für schnelle Auswertungen, insbesondere Eigenwertberechnungen, in wichtigen Spezialfällen, bei denen die Samples durch niedrigdimensionale Vektoren (wie z.B. in dreidimensionalen Punktwolken) oder durch kategoriale Attribute beschrieben werden.
Weiterhin wird untersucht, wie diese dichtbesetzten Adjazenzinformationen in Lernsituationen auf Graphen benutzt werden können. Es wird eine eigene transduktive Lernmethode vorgeschlagen und präsentiert, eine Version eines Graph Convolutional Networks (GCN), das auf die spektralen und räumlichen Eigenschaften von dichtbesetzten Graphen abgestimmt ist. Schließlich wird die Anwendung von Kernel-basierten Adjazenzmatrizen in der Beschleunigung der erfolgreichen Architektur “PointNet++” umrissen.
Im Verlauf der Arbeit werden die Methoden in ausführlichen numerischen Experimenten evaluiert. Zusätzlich zu der empirischen Genauigkeit der Neuronalen Netze liegt der Fokus auf wettbewerbsfähigen Laufzeiten, um die Berechnungs- und Energiekosten der Methoden zu reduzieren. / Over the past few years, graph learning - the subdomain of machine learning on graph data - has taken big leaps forward through the development of specialized Graph Neural Networks (GNNs) that have mathematical foundations in spectral graph theory. In addition to natural graph data, these methods can be applied to non-graph data sets by constructing a graph artificially using a predefined notion of adjacency between samples. The state of the art is to only connect each sample to a low number of neighbors in order to simultaneously mimic the sparse behavior of natural graphs, play into the strengths of existing GNN methods, and avoid quadratic scaling in the number of nodes that would make the approach infeasible for large problem sizes.
In this thesis, we shine light on the alternative construction of kernel-based fully-connected graphs. Here the connections of each sample explicitly quantify the similarities to all other samples. Hence the graph contains a quadratic number of edges which encode local and non-local neighborhood information. Though this approach is well studied in other settings including the solution of partial differential equations, it is typically dismissed in machine learning nowadays because of its dense adjacency matrices. We thus dedicate a large portion of this work to showcasing numerical techniques for fast evaluations, especially eigenvalue computations, in important special cases where samples are described by low-dimensional feature vectors (e.g., three-dimensional point clouds) or by a small set of categorial attributes.
We then continue to investigate how this dense adjacency information can be utilized in graph learning settings. In particular, we present our own proposed transductive learning method, a version of a Graph Convolutional Network (GCN) designed towards the spectral and spatial properties of dense graphs. We furthermore outline the application of kernel-based adjacency matrices in the speedup of the successful PointNet++ architecture.
Throughout this work, we evaluate our methods in extensive numerical experiments. In addition to the empirical accuracy of our neural network tasks, we focus on competitive runtimes in order to decrease the computational and energy cost of our methods.
|
255 |
Automating Geospatial RDF Dataset Integration and EnrichmentSherif, Mohamed Ahmed Mohamed 12 May 2016 (has links)
Over the last years, the Linked Open Data (LOD) has evolved from a mere 12 to more than 10,000 knowledge bases. These knowledge bases come from diverse domains including (but not limited to) publications, life sciences, social networking, government, media, linguistics. Moreover, the LOD cloud also contains a large number of crossdomain knowledge bases such as DBpedia and Yago2. These knowledge bases are commonly managed in a decentralized fashion and contain partly verlapping information. This architectural choice has led to knowledge pertaining to the same domain being published by independent entities in the LOD cloud. For example, information on drugs can be found in Diseasome as well as DBpedia and Drugbank. Furthermore, certain knowledge bases such as DBLP have been published by several bodies, which in turn has lead to duplicated content in the LOD . In addition, large amounts of geo-spatial information have been made available with the growth of heterogeneous Web of Data.
The concurrent publication of knowledge bases containing related information promises to become a phenomenon of increasing importance with the growth of the number of independent data providers. Enabling the joint use of the knowledge bases published by these providers for tasks such as federated queries, cross-ontology question answering and data integration is most commonly tackled by creating links between the resources described within these knowledge bases. Within this thesis, we spur the transition from isolated knowledge bases to enriched Linked Data sets where information can be easily integrated and processed. To achieve this goal, we provide concepts, approaches and use cases that facilitate the integration and enrichment of information with other data types that are already present on the Linked Data Web with a focus on geo-spatial data.
The first challenge that motivates our work is the lack of measures that use the geographic data for linking geo-spatial knowledge bases. This is partly due to the geo-spatial resources being described by the means of vector geometry. In particular, discrepancies in granularity and error measurements across knowledge bases render the selection of appropriate distance measures for geo-spatial resources difficult. We address this challenge by evaluating existing literature for point set measures that can be used to measure the similarity of vector geometries. Then, we present and evaluate the ten measures that we derived from the literature on samples of three real knowledge bases.
The second challenge we address in this thesis is the lack of automatic Link Discovery (LD) approaches capable of dealing with geospatial knowledge bases with missing and erroneous data. To this end, we present Colibri, an unsupervised approach that allows discovering links between knowledge bases while improving the quality of the instance data in these knowledge bases. A Colibri iteration begins by generating links between knowledge bases. Then, the approach makes use of these links to detect resources with probably erroneous or missing information. This erroneous or missing information detected by the approach is finally corrected or added.
The third challenge we address is the lack of scalable LD approaches for tackling big geo-spatial knowledge bases. Thus, we present Deterministic Particle-Swarm Optimization (DPSO), a novel load balancing technique for LD on parallel hardware based on particle-swarm optimization. We combine this approach with the Orchid algorithm for geo-spatial linking and evaluate it on real and artificial data sets. The lack of approaches for automatic updating of links of an evolving knowledge base is our fourth challenge. This challenge is addressed in this thesis by the Wombat algorithm. Wombat is a novel approach for the discovery of links between knowledge bases that relies exclusively on positive examples. Wombat is based on generalisation via an upward refinement operator to traverse the space of Link Specifications (LS). We study the theoretical characteristics of Wombat and evaluate it on different benchmark data sets.
The last challenge addressed herein is the lack of automatic approaches for geo-spatial knowledge base enrichment. Thus, we propose Deer, a supervised learning approach based on a refinement operator for enriching Resource Description Framework (RDF) data sets. We show how we can use exemplary descriptions of enriched resources to generate accurate enrichment pipelines. We evaluate our approach against manually defined enrichment pipelines and show that our approach can learn accurate pipelines even when provided with a small number of training examples.
Each of the proposed approaches is implemented and evaluated against state-of-the-art approaches on real and/or artificial data sets. Moreover, all approaches are peer-reviewed and published in a conference or a journal paper. Throughout this thesis, we detail the ideas, implementation and the evaluation of each of the approaches. Moreover, we discuss each approach and present lessons learned. Finally, we conclude this thesis by presenting a set of possible future extensions and use cases for each of the proposed approaches.
|
256 |
Learning Continuous Human-Robot Interactions from Human-Human DemonstrationsVogt, David 02 March 2018 (has links)
In der vorliegenden Dissertation wurde ein datengetriebenes Verfahren zum maschinellen Lernen von Mensch-Roboter Interaktionen auf Basis von Mensch-Mensch Demonstrationen entwickelt. Während einer Trainingsphase werden Bewegungen zweier Interakteure mittels Motion Capture erfasst und in einem Zwei-Personen Interaktionsmodell gelernt. Zur Laufzeit wird das Modell sowohl zur Erkennung von Bewegungen des menschlichen Interaktionspartners als auch zur Generierung angepasster Roboterbewegungen eingesetzt. Die Leistungsfähigkeit des Ansatzes wird in drei komplexen Anwendungen evaluiert, die jeweils kontinuierliche Bewegungskoordination zwischen Mensch und Roboter erfordern. Das Ergebnis der Dissertation ist ein Lernverfahren, das intuitive, zielgerichtete und sichere Kollaboration mit Robotern ermöglicht.
|
257 |
Interactive 3D Reconstruction / Interaktive 3D-RekonstruktionSchöning, Julius 23 May 2018 (has links)
Applicable image-based reconstruction of three-dimensional (3D) objects offers many interesting industrial as well as private use cases, such as augmented reality, reverse engineering, 3D printing and simulation tasks. Unfortunately, image-based 3D reconstruction is not yet applicable to these quite complex tasks, since the resulting 3D models are single, monolithic objects without any division into logical or functional subparts.
This thesis aims at making image-based 3D reconstruction feasible such that captures of standard cameras can be used for creating functional 3D models. The research presented in the following does not focus on the fine-tuning of algorithms to achieve minor improvements, but evaluates the entire processing pipeline of image-based 3D reconstruction and tries to contribute at four critical points, where significant improvement can be achieved by advanced human-computer interaction:
(i) As the starting point of any 3D reconstruction process, the object of interest (OOI) that should be reconstructed needs to be annotated. For this task, novel pixel-accurate OOI annotation as an interactive process is presented, and an appropriate software solution is released. (ii) To improve the interactive annotation process, traditional interface devices, like mouse and keyboard, are supplemented with human sensory data to achieve closer user interaction. (iii) In practice, a major obstacle is the so far missing standard for file formats for annotation, which leads to numerous proprietary solutions. Therefore, a uniform standard file format is implemented and used for prototyping the first gaze-improved computer vision algorithms. As a sideline of this research, analogies between the close interaction of humans and computer vision systems and 3D perception are identified and evaluated. (iv) Finally, to reduce the processing time of the underlying algorithms used for 3D reconstruction, the ability of artificial neural networks to reconstruct 3D models of unknown OOIs is investigated.
Summarizing, the gained improvements show that applicable image-based 3D reconstruction is within reach but nowadays only feasible by supporting human-computer interaction. Two software solutions, one for visual video analytics and one for spare part reconstruction are implemented.
In the future, automated 3D reconstruction that produces functional 3D models can be reached only when algorithms become capable of acquiring semantic knowledge. Until then, the world knowledge provided to the 3D reconstruction pipeline by human computer interaction is indispensable.
|
258 |
Learning Sampling-Based 6D Object Pose EstimationKrull, Alexander 31 August 2018 (has links)
The task of 6D object pose estimation, i.e. of estimating an object position (three degrees of freedom) and orientation (three degrees of freedom) from images is an essential building block of many modern applications, such as robotic grasping, autonomous driving, or augmented reality. Automatic pose estimation systems have to overcome a variety of visual ambiguities, including texture-less objects, clutter, and occlusion. Since many applications demand real time performance the efficient use of computational resources is an additional challenge.
In this thesis, we will take a probabilistic stance on trying to overcome said issues. We build on a highly successful automatic pose estimation framework based on predicting pixel-wise correspondences between the camera coordinate system and the local coordinate system of the object. These dense correspondences are used to generate a pool of hypotheses, which in turn serve as a starting point in a final search procedure. We will present three systems that each use probabilistic modeling and sampling to improve upon different aspects of the framework.
The goal of the first system, System I, is to enable pose tracking, i.e. estimating the pose of an object in a sequence of frames instead of a single image. By including information from previous frames tracking systems can resolve many visual ambiguities and reduce computation time. System I is a particle filter (PF) approach. The PF represents its belief about the pose in each frame by propagating a set of samples through time. Our system uses the process of hypothesis generation from the original framework as part of a proposal distribution that efficiently concentrates samples in the appropriate areas.
In System II, we focus on the problem of evaluating the quality of pose hypotheses. This task plays an essential role in the final search procedure of the original framework. We use a convolutional neural network (CNN) to assess the quality of an hypothesis by comparing rendered and observed images. To train the CNN we view it as part of an energy-based probability distribution in pose space. This probabilistic perspective allows us to train the system under the maximum likelihood paradigm. We use a sampling approach to approximate the required gradients. The resulting system for pose estimation yields superior results in particular for highly occluded objects.
In System III, we take the idea of machine learning a step further. Instead of learning to predict an hypothesis quality measure, to be used in a search procedure, we present a way of learning the search procedure itself. We train a reinforcement learning (RL) agent, termed PoseAgent, to steer the search process and make optimal use of a given computational budget. PoseAgent dynamically decides which hypothesis should be refined next, and which one should ultimately be output as final estimate. Since the search procedure includes discrete non-differentiable choices, training of the system via gradient descent is not easily possible. To solve the problem, we model behavior of PoseAgent as non-deterministic stochastic policy, which is ultimately governed by a CNN. This allows us to use a sampling-based stochastic policy gradient training procedure.
We believe that some of the ideas developed in this thesis,
such as the sampling-driven probabilistically motivated training of a CNN for the comparison of images or the search procedure implemented by PoseAgent have the potential to be applied in fields beyond pose estimation as well.
|
259 |
Fenchel duality-based algorithms for convex optimization problems with applications in machine learning and image restorationHeinrich, André 21 March 2013 (has links)
The main contribution of this thesis is the concept of Fenchel duality with a focus on its application in the field of machine learning problems and image restoration tasks. We formulate a general optimization problem for modeling support vector machine tasks and assign a Fenchel dual problem to it, prove weak and strong duality statements as well as necessary and sufficient optimality conditions for that primal-dual pair. In addition, several special instances of the general optimization problem are derived for different choices of loss functions for both the regression and the classifification task. The convenience of these approaches is demonstrated by numerically solving several problems. We formulate a general nonsmooth optimization problem and assign a Fenchel dual problem to it. It is shown that the optimal objective values of the primal and the dual one coincide and that the primal problem has an optimal solution under certain assumptions. The dual problem turns out to be nonsmooth in general and therefore a regularization is performed twice to obtain an approximate dual problem that can be solved efficiently via a fast gradient algorithm. We show how an approximate optimal and feasible primal solution can be constructed by means of some sequences of proximal points closely related to the dual iterates. Furthermore, we show that the solution will indeed converge to the optimal solution of the primal for arbitrarily small accuracy. Finally, the support vector regression task is obtained to arise as a particular case of the general optimization problem and the theory is specialized to this problem. We calculate several proximal points occurring when using difffferent loss functions as well as for some regularization problems applied in image restoration tasks. Numerical experiments illustrate the applicability of our approach for these types of problems.
|
260 |
Machine Learning im CAEThieme, Cornelia 24 May 2023 (has links)
Many companies have a large collection of different model variants and results. Hexagon's (formerly MSC Software) software Odyssee helps to find out what information is contained in this data. New calculations can sometimes be avoided because the results for new parameter combinations can be predicted from the existing calculations. This is particularly interesting for non-linear or large models with long run times. The software also helps when setting up new DOEs and offers a variety of options for statistical displays. In the lecture, the number-based and image-based methods are compared. / Viele Firmen können auf eine große Sammlung vorhandener Rechnungen für verschiedene Modellvarianten zurückgreifen. Die Software Odyssee von Hexagon (früher MSC Software) hilft herauszufinden, welche Informationen in diesen Daten stecken. Neue Rechnungen kann man sich teilweise ersparen, weil die Ergebnisse für neue Parameterkombinationen aus den vorhandenen Rechnungen vorhergesagt werden können.
Dies ist besonders interessant für nichtlineare oder große Modelle mit langer Rechenzeit. Die Software hilft auch beim Aufsetzen neuer DOEs und bietet vielfältige Möglichkeiten für statistische Darstellungen. In dem Vortrag werden die zahlenbasierte und bildbasierte Methode gegenübergestellt.
|
Page generated in 0.1298 seconds