# System Design, Modeling, and Simulation Using Ptolemy II

## Claudius Ptolemaeus

Language: English

Pages: 690

ISBN: 1304421066

Format: PDF / Kindle (mobi) / ePub

This book is a definitive introduction to models of computation for the design of complex, heterogeneous systems. It has a particular focus on cyber-physical systems, which integrate computing, networking, and physical dynamics. The book captures more than twenty years of experience in the Ptolemy Project at UC Berkeley, which pioneered many design, modeling, and simulation techniques that are now in widespread use. All of the methods covered in the book are realized in the open source Ptolemy II modeling framework and are available for experimentation through links provided in the book. The book is suitable for engineers, scientists, researchers, and managers who wish to understand the rich possibilities offered by modern modeling techniques. The goal of the book is to equip the reader with a breadth of experience that will help in understanding the role that such techniques can play in design.

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Model has three parameters, a time constant T, an output impedance Z, and a drive limit L. The model gives the output voltage of a generator over time as the generator gets more or less gas (specified by the drive input), and as the load varies (as specified by the loadAdmittance input). This model exhibits simplified linear and nonlinear dynamics. The nonlinear dynamics is realized by the Limiter actor (see the sidebar on page 57), which limits Figure 1.8: Simplified model of a gas-powered.

NoisePower parameter, for example, and observe the result. If you wish to view the instance rather than the class definition, you can select Open Instance on one of the instances. The window that opens shows only that instance. Each subcomponent that is inherited from the class definition is highlighted with a pink halo. 2.6.1 Overriding Parameter Values in Instances By default, all instances of Channel in Figure 2.32 have the same icon and the same parameter values. However, each instance can.

Director extracts this relationship and defines one iteration of the model to consist of 256 firings of Sinewave, Channel, and SequencePlotter, and one firing of Spectrum. This example implements a multirate model; that is, the firing rates of the actors are not identical. In particular, the Spectrum actor executes at a different rate than the other actors. It is common for the execution of a multirate model to consist of exactly one iteration. The director determines how many times to fire each.

Initial output from the Ramp actor, which has value 1, will not be displayed. During this first iteration, the Expression and SetVariable actor both fire once. The Expression actor sets its output equal to input, unless the input is equal to the value of the iterations parameter (which it doesn’t in this first iteration). The SetVariable actor sets the value of the rate parameter to 1. By default, SetVariable has a delayed parameter with value true, which means that the rate parameter changes.

4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 5 iv Synchronous-Reactive Models 158 5.1 5.2 Fixed-Point Semantics . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 SR Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 5.3 Finding the Fixed-Point . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 5.4 The Logic of Fixed.