PTOLEMY II - CiteSeerX

2.10 Hybrid Systems and Modal Models
Using Vergil
Hybrid systems are models that combine continuous dynamics with discrete mode changes. They
are created in Ptolemy II by creating a ModalModel, found in the HigherOrderActors library. We start
by examining a pre-built modal model, and conclude by illustrating how to construct one. Modal models
can be constructed with other domains besides CT, but this section will concentrate on CT. Feel free
to examine other examples of modal models given in the quick tour, figure 2.3.
2.10.1 Examining a Pre-Built Model
Consider the bouncing ball example, which can be found under “Bouncing Ball” in figure 2.3 (in
the “Hybrid Systems” entry). The top-level contents of this model is shown in figure 2.54. It contains a
Ball Model, a TimedPlotter, and PeriodicSampler, and an Animate Ball composite actor. The Ball
Model is an instance of the ModalModel found in the HigherOrderActors library, but renamed. If you
execute the model, you should see a plot like that in the figure and a 3-D animation that is constructed
using the GR (graphics) domain. The continuous dynamics correspond to the times when the ball is in
the air, and the discrete events correspond to the times when the ball hits the surface and bounces.
FIGURE 2.53. Discrete-event model with feedback, which requires a delay actor such as TimedDelay.
Notice the library of domain-specific actors at the left.
82 Ptolemy II