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Multivariable Feedback with Geometric Tools
No full textI remember Toni for his personal warmth and innate respect; for a friendship you could feel. He would give important and less important bits of advice, throwing in the odd comment, or dropping a hint, never insisting, to show he meant no offence. I remember how attached he was to us in Bologna. During the first research doctorate the university seats of Bologna, Florence and Padua had formed a consortium, but he would still take the train to Bologna to hold his lectures because he liked to breathe the atmosphere of the city and walk across its main square, Piazza Maggiore. I keep in my library a very simple, clear and attractive small book with a nice friendly hand-written dedication to me by Toni. The book presents feedback in simple terms but reflects Toni’s in-depth knowledge, highlighting the presence of feedback in many branches of the scientific world. Inspired by this book and recalling that many years ago Toni probably read our first paper on geometric tools in Italian, I decided to dedicate this contribution to feedback in geometric terms. In this short monograph I will try to explain how these tools not only enable a neat extension to the multivariable case of the most basic features of feedback control for single variable systems, including the internal model of the exosystem, hence steady-state robustness, but they are just within arm’s reach using a certain number of algorithms available in a specific Geometric Approach toolbox for Matlab. Although this approach sounds didactic and somewhat out of standard, it nevertheless contains an original idea: A proposal to extend model-following control to non minimal phase systems. Being a non optimal, but only pseudo-optimal solution, the proposal explains the detailed illustration of this toolbox and its use in the synthesis of multivariable control systems. The geometric approach to system analysis and control suffered from a very slow and inconsistent growth for about four decades, with papers by numerous authors in many different styles, often aiming to impress readers (or reviewers) with intricate mathematics rather than giving them the most direct insight and feeling
Robust design of standard controllers under plant parameters uncertainty
No full textThis note extends some results concerning the characterization of PID and lead/lag controllers satisfying given H-infinity closed–loop
specifications. In particular, it is shown that: (i) the region of the plane of the free controller parameters where the considered H-infinity constraint is satisfied, is still formed by the union of (a bounded number of) disjoint convex sets even
when the plant parameters are not fixed but belong to given intervals, and
(ii) the determination of these sets entails the repeated solution of an optimization problem. The procedure is applied to find the parameters of a PID
controller for an uncertain electric motor so as to ensure that the H1 norm
of the sensitivity function is less than a prescribed value
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
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