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Modellierung von Beobachtungen von dynamischen Systemen mit Gedächtnis
No full textDetecting the governing mathematical rules of a dynamical system from data persists to be a challenge. It becomes particularly difficult when the variables of the system can only be partially observed in the form of a so-called observable function. In this case information about variables that can be vital for the prediction of future states is missing. In order to still formulate the dynamics of the observable, it can be shown that by exploiting its memory terms one can make up for the lost information. This can be placed on a mathematical ground by the delay embedding theorem of Takens and the Mori–Zwanzig formalism (MZ). In this thesis, novel numerical methods for the modelling of the observed dynamics were developed by using Takens and MZ to extend known methods used for memoryless systems. Firstly, the method Sparse Identification of Nonlinear Dynamics (SINDy) was combined with the family of autoregressive (AR) models to define Sparse Identification of Autoregressive Models (SINAR) which seeks a sparse representation of memory-exhibiting dynamics. It was compared to various others theoretically and on examples coming from different fields. Another new numerical method was introduced in which a high-dimensional dynamical system is projected onto a low-dimensional convex polytope using the Scalable Probabilistic Approximation (SPA) algorithm. The projection to the polytope was interpreted as an observable and memory was used to estimate the projected dynamics in a newly introduced method called memory SPA (mSPA). It was shown that mSPA can generate strong prediction accuracy for various dynamical systems while guaranteeing stability by keeping the dynamics inside the polytope. As another contribution of this thesis, the identification of memory-exhibiting dynamics was connected with the field of agent-based modelling. To this end, two new ABMs were defined, the high-dimensional representation of the states of all individual agents was interpreted as the full system state and a low-dimensional statistic as the observable. Then the ABM was translated into the setting introduced before. It was shown in a detailed numerical analysis using SINAR that including memory generally improves the accuracy of the model identification, moreover, that adding a sparsity constraint can improve the model and that the model fitting can strongly depend on the data. The thesis was concluded with a small note on how along the different methods discussed, the seemingly unrelated theoretical perspectives of Takens and Mori–Zwanzig could be connected.Die dominanten mathematischen Regeln eines dynamischen Systems aus Daten zu ermitteln ist weiterhin eine Herausforderung, welche besonders schwierig wird, wenn die Variablen eines Systems nur in Form einer so genannten Observablenfunktion partiell beobachtet werden können. Um trotzdem die Dynamik der Observablen formulieren zu können, ist es möglich, die Gedächtnisterme der Observablen zu benutzen, um das Fehlen der Information über die nicht-beobachtbaren Variablen auszugleichen. Dies kann auf ein mathematisches Fundament gestellt werden durch das (eng.) Delay-Embedding-Theorem von Takens und den Mori–Zwanzig Formalismus (MZ). In dieser Arbeit wurden neue numerische Methoden für die Modellierung der beobachteten Dynamik entwickelt, indem mithilfe von Takens und MZbereits bekannte Methoden für gedächtnislose Dynamiken erweitert wurden. Zunächst wurde die Methode Sparse Identification of Nonlinear Dynamics (SINDy) mit autoregressiven (AR) Modellen kombiniert, um Sparse Identification of Autoregressive Models (SINAR) zu definieren – eine Methode, die eine (eng.) sparse Darstellung einer gedächtniszeigenden Dynamik zu finden versucht. Diese Methoden wurden untereinander und mit anderen auf theoretischer Basis und anhand verschiedener Beispiele verglichen. Eine weitere numerische Methode wurde eingeführt, mit der durch den Scalable Probabilistic Approximation (SPA) Algorithmus eine hochdimensionale Dynamik auf ein niedrigdimensionales Polytop projiziert wird. Die Projektion auf das Polytop wurde als Observable interpretiert und Gedächtnis benutzt, um die projizierte Dynamik mit der neuen Methode memory SPA (mSPA) zu schätzen. Es wurde gezeigt, dass mSPA gute Genauigkeit für verschiedene dynamische Systeme erreichen kann und gleichzeitig Stabilität garantiert, indem die Dynamik innerhalb des Polytops bleibt. Als ein weiterer Beitrag dieser Arbeit wurde die Identifikation von gedächtniszeigender Dynamik mit dem Feld von agentenbasierter Modellierung (ABM) verbunden, wofür zwei neue ABMs definiert wurden. Die hochdimensionale Darstellung der Zustände ihrer einzelnen Agenten wurden als den vollen Systemzustand und eine niedrigdimensionale Statistik als die Observable interpretiert und die ABMs wurden in das zuvor eingeführte Konzept übersetzt. Es wurde mit SINAR u.a. detailliert gezeigt, dass das Hinzunehmen von Gedächtnis im Allgemeinen die Genauigkeit der Modellidentifikation verbessert. Diese Arbeit wurde mit einer Beobachtung dar über abgeschlossen, wie durch die verschiedenen untersuchten Methoden die scheinbar nicht verwandten theoretischen Perspektiven von Takens und Mori–Zwanzig verbunden werden könnten
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Measuring Dependencies between Variables of a Dynamical System Using Fuzzy Affiliations
Get PDFA statistical, data-driven method is presented that quantifies influences between variables of a dynamical system. The method is based on finding a suitable representation of points by fuzzy affiliations with respect to landmark points using the Scalable Probabilistic Approximation algorithm. This is followed by the construction of a linear mapping between these affiliations for different variables and forward in time. This linear mapping, or matrix, can be directly interpreted in light of unidirectional dependencies, and relevant properties of it are quantified. These quantifications, given by the sum of singular values and the average row variance of the matrix, then serve as measures for the influences between variables of the dynamics. The validity of the method is demonstrated with theoretical results and on several numerical examples, covering deterministic, stochastic, and delayed types of dynamics. Moreover, the method is applied to a non-classical example given by real-world basketball player movement, which exhibits highly random movement and comes without a physical intuition, contrary to many examples from, e.g., life sciences
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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