1,721,159 research outputs found
Autonomy, forward non-Zenoness and quadratic stability of bimodal higher-order piecewise linear systems
No full textWe consider bimodal higher-order piecewise linear systems, i.e. the sets of solutions of two higher-order linear differential equations, coupled with inequality constraints involving a polynomial differential operator acting on the trajectories of the system. Under suitable assumptions on the characteristic polynomials of the differential equations and the polynomial associated with the inequality constraint, we prove that a solution always exists and is unique given the initial conditions, that no forward Zeno-behavior is possible, and that the system is quadratically stable. Moreover, we provide an algorithm based on polynomial algebra to compute a Lyapunov function for the system
Data-driven simulation of continuous-time linear time-invariant systems: the autonomous case
No full textWe use orthogonal bases for continuous-time function spaces to state a version of Willems’ lemma (Willems et al., 2005) for autonomous systems. We assume that an infinite number of representation coefficients of a “sufficiently rich” trajectory is given, and we illustrate how to compute solutions to initial and boundary conditions problems from such data.<br/
Orthogonal polynomial bases for data-driven analysis and control of continuous-time systems
No full textWe use polynomial approximation theory to perform data-driven analysis and control of linear, continuous-time invariant systems. We transform the continuous-time input- and state trajectories into discrete sequences consisting of the coefficients of their orthog- onal polynomial bases representations. We show that the dynamics of the transformed input- and state signals and those of the original continuous-time trajectories are de- scribed by the same system matrices. We investigate informativity, quadratic stabilization, and H2-performance problems for continuous-time systems. We deal with the case in which machine-precision accuracy in the representation of continuous-time signals can be achieved from the data using a finite number of basis elements, and the case in which the approximation error is non-negligible
The shortest experiment for linear system identification
Full text linkIn this paper we study the following problem: given an upper bound of the state-space dimension and lag on a linear time-invariant system, design a sequence of inputs so that the system dynamics can be recovered from the resulting input–output data. As our main result we propose a new online experiment design method, meaning that the selection of the inputs is iterative and guided by past data samples. We show that this approach leads to the shortest possible experiments for linear system identification. In terms of sample complexity, the proposed method outperforms offline methods based on persistency of excitation as well as existing online experiment design methods
A “fundamental lemma” for continuous-time systems, with applications to data-driven simulation
Full text linkWe are given one input–output (i-o) trajectory (u,y) produced by a linear, continuous time-invariant system, and we compute its Chebyshev polynomial series representation. We show that if the input trajectory u is sufficiently persistently exciting according to the definition in Rapisarda et al. (2023), then the Chebyshev polynomial series representation of every i-o trajectory can be computed from that of (u,y). We apply this result to data-driven simulation of continuous-time systems.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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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