In comp.soft-sys.ptolemy, Josu wrote:
Hi
In the Ptolemy II faq, there is a question about Matlab where the next
statement appears
"The CT domain, for example, does not have the notion of "sample
time" (which in Simulink provides the periodic discrete-time support)
nor the support for algebraic loops."
However, in Ptolemy it is possible the use of other directors to
obtain discrete and continuos simulation mixed, isn't it?
Maybe, I am losing something. Can anybody in the list clarify this
point?
Thank you in advance
josu
Hi Josu,
The entire FAQ question is:
--start--
2.2 How are Ptolemy II and Matlab/Simulink different?
Ptolemy II has very little in common with Matlab, which is a
textual, imperative, interactive, scientific programming language.
Ptolemy II works with Matlab, thanks to an interface developed by Zoltan
Kemenczy and others at Research In Motion, Ltd. See
http://ptolemy.eecs.berkeley.edu/ptolemyII/ptIIlatest/ptII/ptolemy/matlab/matlab.htm
Ptolemy II has much more in common with Simulink, which is a
graphical block-diagram language, originally developed for control
system design. Simulink has a rich and expressive model of computation
with continuous-time semantics and support for periodic discrete-time
signals. Some of its principles have been incorporated in the CT
(continuous-time) domain of Ptolemy II, but not all. The CT domain, for
example, does not have the notion of "sample time" (which in Simulink
provides the periodic discrete-time support) nor the support for
algebraic loops. There is also currently no code generation support in
CT (in Simulink, this is provided through the associated product
Real-Time Workshop). Also, the CT domain has implemented fewer ODE
solvers than those provided by Simulink and has a smaller actor library.
Ptolemy II and Simulink both support extension of the actor library
through well-defined interfaces (in Simulink, this is called the
S-function interface). However, Ptolemy II is a more open architecture
in that its infrastructure is open source, and the interfaces to the
core mechanisms in the software are published and documented. The
persistent file format (MoML) is XML in Ptolemy II, which makes it both
more verbose and more portable than the Simulink syntax (MDL files).
Simulink supports one model of computation, whereas Ptolemy II supports
several, and can be extended with new models of computation. Simulink
can also be extended, as for example it has been with the associated
product Stateflow, which supports state-machine modeling. But in
Simulink, the extension is done by defining new blocks using the
S-function interface. As such, additional models of computation added
this way are second class. For example, they cannot define the model of
computation at the top level of the hierarchy, and cannot contain
Simulink models within their own components.
--end--
Professor Lee was the one who wrote the faq, so he would likely do
a better job of addressing this, I'm not that up on the CT domain.
One issue is that there are now two domains with continuous time
semantics, the older "ct" domain and the new "continuous" domain.
The continuous domain is described as:
--start--
The domain models systems with continuous dynamics, including
for example analog circuits and mechanical systems, but also
cleanly supports discrete events, modal behaviors, and signals that
mix continuous-time behaviors with discrete events.
Models for continuous dynamics are equivalent to linear or nonlinear
integral equations. A sophisticated numerical solver for these equations
is integrated with the director.
The clean semantics of the Continuous domain enables its integration
in hierarchical heterogeneous models that use the Synchronous/Reactive (SR)
and Discrete Event (DE) domains. Arbitrary hierarchical mixtures of these
domains are supported, although if SR is at the top level, then the
<i>period</i> parameter of the director must be used so that time advances.
--end--
For more information about the continuous domain, see
http://ptolemy.berkeley.edu/ptolemyII/ptIIlatest/ptII/ptolemy/domains/continuous/doc/
Domain interactions are documented in the following paper:
Antoon Goderis, Christopher Brooks, Ilkay Altintas, Edward
A. Lee, Carole Goble. "Composing Different Models of
Computation in Kepler and Ptolemy II". 2007 Proceedings,
International Conference on Computational Science (ICCS),
April, 2007.
http://chess.eecs.berkeley.edu/pubs/193.html
BTW - I saw your post on google-groups, which gets a feed from
the Usenet comp.soft-sys.ptolemy newsgroup. Our feed to that newsgroup
will be going away shortly. It is best to post to the ptolemy-hackers
mailing list, which then feeds various other lists. To get on
ptolemy-hackers, see
http://ptolemy.eecs.berkeley.edu/mailinglists.htm
_Christopher
--
Christopher Brooks (cxh at eecs berkeley edu) University of California
CHESS Executive Director US Mail: 337 Cory Hall
Programmer/Analyst CHESS/Ptolemy/Trust Berkeley, CA 94720-1774
ph: 510.643.9841 fax:510.642.2718 (Office: 545Q Cory)
home: (F-Tu) 707.665.0131 (W-F) 510.655.5480
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