Lagrange's equations of motion are used to obtain a differential algebraic equation representing the nonlinear dynamics of cable systems approximated through the use of multibody modelling. The differential algebr...
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Lagrange's equations of motion are used to obtain a differential algebraic equation representing the nonlinear dynamics of cable systems approximated through the use of multibody modelling. The differential algebraic equation of index 3 is cast as an ordinary differential equation and integrated using the LSODAR software. The cable system consists of an arbitrary number of links between which restoring torques are placed to provide a damping effect. A cable car is introduced to ride upon the cable, where the initial conditions of the cable car system are determined by allowing the original cable system to fall into an equilibrium position. Graphs and animation indicate the chaotic behaviour of both multibody systems, and it is shown that the CPU time increases in a cubic nature as the number of bodies in the system increases. Finally, the accuracy of the results is investigated using a constraint compliance testing procedure.
We propose a deterministic algorithm for approximating a generating partition from a time series using tessellations. Using data generated by Hénon and Ikeda maps, we demonstrate that the proposed method produces...
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We propose a deterministic algorithm for approximating a generating partition from a time series using tessellations. Using data generated by Hénon and Ikeda maps, we demonstrate that the proposed method produces partitions that uniquely encode all the periodic points up to some order, and provide good estimates of the metric and topological entropies. The algorithm gives useful results even with a short noisy time series.
We estimate topological entropy via symbolic dynamics using a data compression technique called the context-tree weighting method. Unlike other symbolic dynamical approaches, which often have to choose ad hoc paramete...
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We estimate topological entropy via symbolic dynamics using a data compression technique called the context-tree weighting method. Unlike other symbolic dynamical approaches, which often have to choose ad hoc parameters such as the depth of a tree, the context-tree weighting method is almost parameter-free and infers the transition structure of the system as well as transition probabilities. Our examples, including a Markov model, the logistic map, and the Hénon map, demonstrate that the convergence is fast: one obtains the theoretically correct topological entropy with a relatively short symbolic sequence.
Experimental and simulated time series are necessarily discretized in time. However, many real and artificial systems are more naturally modeled as continuous-time systems. This paper reviews the major techniques empl...
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Experimental and simulated time series are necessarily discretized in time. However, many real and artificial systems are more naturally modeled as continuous-time systems. This paper reviews the major techniques employed to estimate a continuous vector field from a finite discrete time series. We compare the performance of various methods on experimental and artificial time series and explore the connection between continuous (differential) and discrete (difference equation) systems. As part of this process we propose improvements to existing techniques. Our results demonstrate that the continuous-time dynamics of many noisy data sets can be simulated more accurately by modeling the one-step prediction map than by modeling the vector field. We also show that radial basis models provide superior results to global polynomial models.
Modern techniques invented for data compression provide efficient automated algorithms for the modeling of the observed symbolic dynamics. We demonstrate the relationship between coding and modeling, motivating the we...
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Modern techniques invented for data compression provide efficient automated algorithms for the modeling of the observed symbolic dynamics. We demonstrate the relationship between coding and modeling, motivating the well-known minimum description length (MDL) principle, and give concrete demonstrations of the “context-tree weighting” and “context-tree maximizing” algorithms. The predictive modeling technique obviates many of the technical difficulties traditionally associated with the correct MDL analyses. These symbolic models, representing the symbol generating process as a finite-state automaton with probabilistic emission probabilities, provide excellent and reliable entropy estimations. The resimulations of estimated tree models satisfying the MDL model-selection criterion are faithful to the original in a number of measures. The modeling suggests that the automated context-tree model construction could replace fixed-order word lengths in many traditional forms of empirical symbolic analysis of the data. We provide an explicit pseudocode for implementation of the context-tree weighting and maximizing algorithms, as well as for the conversion to an equivalent Markov chain.
Given a real-world system with behavior which appears complex, it is difficult to separate the effects of chaos, high dimensionality and noise except in the rare cases where a high-quality model is available. Although...
Given a real-world system with behavior which appears complex, it is difficult to separate the effects of chaos, high dimensionality and noise except in the rare cases where a high-quality model is available. Although great progress has been made in modeling such systems, there is little that is rigorous and most algorithms are slow. To gain understanding it seems necessary to idealize in some way, though not, of course, in the traditional way, which is by linearization. In this paper we simplify the problem by assuming that the system outputs symbols from a finite alphabet, rather than outputting a real number. With this simplification and a reasonable assumption which is the discrete analogue of the standard embedding theorem, it is possible to use known results in data compression theory to produce very fast reconstruction algorithms with guaranteed asymptotic optimality. The models that result can be used to simulate and to predict as well as to calculate all the usual dynamically interesting quantities such as topological entropy.
Fourier spectral estimates and, to a lesser extent, the autocorrelation function are the primary tools to detect periodicities in experimental data in the physical and biological sciences. We propose a method which is...
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Fourier spectral estimates and, to a lesser extent, the autocorrelation function are the primary tools to detect periodicities in experimental data in the physical and biological sciences. We propose a method which is more reliable than traditional techniques, and is able to make clear identification of periodic behavior when traditional techniques do not. This technique is based on an information theoretic reduction of linear (autoregressive) models so that only the essential features of an autoregressive model are retained. These models we call reduced autoregressive models (RARM). The essential features of reduced autoregressive models include any periodicity present in the data. We provide theoretical and numerical evidence from both experimental and artificial data to demonstrate that this technique will reliably detect periodicities if and only if they are present in the data. There are strong information theoretic arguments to support the statement that RARM detects periodicities if they are present. Surrogate data techniques are used to ensure the converse. Furthermore, our calculations demonstrate that RARM is more robust, more accurate, and more sensitive than traditional spectral techniques.
We present a method for the design of nonlinear observers of continuous time chaotic systems. We argue that the synchronization of chaotic systems can usefully be viewed as an observer problem. The method incorporates...
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