1,720,953 research outputs found
Formal synthesis of analytic controllers: An evolutionary approach
No full textControl design for modern safety-critical cyber-physical systems still requires significant expert-knowledge, since for general hybrid systems with temporal logic specifications there are no constructive methods. Nevertheless, in recent years multiple approaches have been proposed to automatically synthesize correct-by-construction controllers. However, typically these methods either result in enormous look-up tables, require online optimization, or are highly dependent on expert-knowledge. The goal of this thesis is to propose a novel approach that overcomes these limitations, i.e. to propose a framework for automatic controller synthesis, capable of synthesizing closed-form controllers for hybrid systems with temporal logic specifications, without a heavy reliance on expert-knowledge. To this end, we draw inspiration from the human design process and utilize two methods that show great similarities to it, namely evolutionary algorithms and counterexample-guided inductive synthesis (CEGIS). Specifically, we use genetic programming (GP), an evolutionary algorithm capable of evolving entire programs. This makes it possible to automatically discover the structure of a solution. Moreover, it enables the synthesis of compact closed-form controllers, circumventing the need for look-up tables or online optimization. In combination with GP, we use the concept of CEGIS to refine candidate solutions based on counterexamples, until the controller is guaranteed to satisfy the desired specification. In this thesis we propose two CEGIS-based synthesis frameworks, which differ in the employed verification paradigms, namely utilizing either (co-synthesized) Lyapunov-like functions or reachability analysis. Both frameworks result in correct-by-construction compact closed-form controllers, where the use of expert-knowledge is optional. Both frameworks are capable of synthesizing sampled-data controllers, enabling implementation in embedded hardware with limited memory and computation power, forming a stepping stone towards faster automation.Team Tamas Keviczk
Formal synthesis of analytic controllers for sampled-data systems via genetic programming
No full textThis paper presents an automatic formal controller synthesis method for nonlinear sampled-data systems with safety and reachability specifications. Fundamentally, the presented method is not restricted to polynomial systems and controllers. We consider a periodically switched controllers based on a Control Lyapunov Barrier-like function. The proposed method utilizes genetic programming to synthesize these function in analytic form, as well as the controller modes. Correctness of the controller are subsequently verified by means of a Satisfiability Modulo Theories solver. Effectiveness of the proposed methodology is demonstrated on multiple systems.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Tamas Keviczk
Geometric control of an under-actuated balancing robot
No full textBall-balancing robots, or Ballbots, are under-actuated omni-directional mobile robots that balance on top of a single ball. The under-actuated nature arises from the fact that both position and attitude of the robot are actuated by the same actuators. This thesis introduces a geometric approach to the control of ball-balancing robots. In this approach, a new full 3D model is derived using screw theory. Based on this model, a geometric observer and geometric controller are proposed. Two methodologies are implemented, a computed torque controller and a sliding mode controller, that can track the attitude of the robot on either the special orthogonal group SO(3) or the 2-sphere S^2. Position control is achieved through the use of the relation between the desired linear acceleration and the attitude of the robot. The resulting desired attitude is tracked by one of the geometric attitude controllers. Simulation results show the effectiveness of the proposed controllers. The proposed sliding mode controller is shown to be more robust to model uncertainties. The position controller is shown to be able to control the position and follow trajectories, but overall global stability is not guaranteed. Recommendations are made to improve the performance. For the geometric observer, stability is shown under a set of assumptions. The work is concluded with a set of experiments on a real platform.Systems and ControlDelft Center of Systems and ControlMechanical, Maritime and Materials Engineerin
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
Optimal symbolic controllers determinization for BDD storage<sup>⁎</sup>
No full textController synthesis techniques based on symbolic abstractions appeal by producing correct-by-design controllers, under intricate behavioural constraints. Yet, being relations between abstract states and inputs, such controllers are immense in size, which makes them futile for embedded platforms. Control-synthesis tools such as PESSOA, SCOTS, and CoSyMA tackle the problem by storing controllers as binary decision diagrams (BDDs). However, due to redundantly keeping multiple inputs per-state, the resulting controllers are still too large. In this work, we first show that choosing an optimal controller determinization is an NP-complete problem. Further, we consider the previously known controller determinization technique and discuss its weaknesses. We suggest several new approaches to the problem, based on greedy algorithms, symbolic regression, and (muli-terminal) BDDs. Finally, we empirically compare the techniques and show that some of the new algorithms can produce up to ≈ 85% smaller controllers than those obtained with the previous technique.Team Tamas Keviczk
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
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