RE: Re: dynamics: comment about MBdyn...

On Mon, 14 Jul 2003, Tiller, Michael (M.M.) wrote:

[...]
> Dynasim has already released an implementation that supports these
> features and I expect they will have a demo available within the
> next few weeks that includes the support for these features and a
> beta version of a multibody library that utilizes them.

That doesn't help the open source world a lot, does it? :-)

> I just thought I would throw those two things in since we were on
> the topic of Bond Graphs and robots (and since Dr. Masarati
> mentioned Modelica in his original message).

I do appreciate your contributions from the Modelica front!

[...]
> Herman mentions index reduction efforts (I assume that is what he
> means by reduction of sets of DAEs).  Symbolic manipulation gets you
> several other things.  Basic things such as equation sorting can
> help you formulate problems in block-lower-triangular (BLT) form
> which is computationally efficient.  

In Bond Graph discussions, they talk a lot about the determination of
the "causality", which is nothing else than determining an order in
which to solve the numeric equations. As far as I know, they do not
yet have a fully automatic solution to all possible problems. But
indeed, it is mostly a "symbolic" process, although much of the
symbolic operations are converted into linear algebra.

[...]
> Second, one of the big criticisms of Modelica I have seen is that
> there aren't any open source implementations. Ideally, I'd like to
> see some academic groups attempt an implementation.  In an effort to
> support this, I am going to try (no promises) to get our (Ford's)
> internal Modelica parsing and semantic processing tools (very
> limited capability at the moment) released for distribution by the
> Modelica Association as open source.  Hopefully, this might help
> people like Dr. Masarati who are interested in being able to read
> Modelica models into their simulation environments.
Well, parsing is not really the big software hurdle... It's defining
the objects that correspond to the models, as well as the tools to
build systems and prepare them for simulation. (And the numeric
solvers too, of course.)

BTW, do you have any idea about the quality of the DAE solvers in
projects like OCtave and Scilab? (They use some form of DASSL, if I am
not mistaken...)

Herman
-- 
  K.U.Leuven, Mechanical Engineering, Robotics Research Group
<http://people.mech.kuleuven.ac.be/~bruyninc> Tel: +32 16 322480