All about Modelica: An equation-based language for modeling physical systems

Chris, I agree that the symbolic processing is quite important. I've often made the argument that a purely numerical approach just can't compete because of the optimizations and insights that come out of the symbolic analysis will always put it on a better footing (curious to know if you agree). But I'd say another factor in the success of Modelica is the ability to make it approachable by non-programmers. All the graphical aspects, acausal semantics, etc. make it easy to understand for non-programmer engineers as well. This has nothing to do with the results, per se, but is I think a factor in its success.

I've been using Modelica for about 15 years now as an engineer. Mainly 3 different interpreter front ends: Dymola, OpenModelica, and SystemModeler.

At first I was mainly interested in it's ability to symbolically manipulate equations for me. With complex physical systems and interconnections it can become a tremendous chore rearranging systems to provide certain inputs and certain outputs. Modelica and the above compilers allowed me to specify the equations, and in fact automatically generate and interconnect larger and larger systems as one model. Specifying what were inputs and what were outputs became a simple few lines of code. For example, forward and inverse kinematics are the same equations in Modelica, you just specify different input/outputs, and the compiler determines what's the best way to do this. This can have significant challenges sometimes, when things don't easily work, but on the whole the process has been more often than not straightforward.

Interconnection of the models to other simulations has also become more and more a delight. Initially we had to depend on specific interfaces being built, either on the modelica interpreter side, or on the external application side (for example, Mathworks or Dymola), but fortunately the growth in such use prompted the modelica community to partner with industry to foster an open specification (like modelica is) for model exchange, called FMI. Integrating my models with external software is now a relatively straightforward task, still with challenges, but not expensive ones.

I'd highly recommend modelica and the various compilers as a means of creating very effective models; easily readable and therefore maintainable, re-usable, and now more and more deployable.

I, myself, have used them in the truck industry, CNC machine controls, flight systems, and in underwater vehicles and power systems. I routinely interact with people who use modelica in a much wider domain than this, and more and more in on-board systems, such as controllers. For example, I believe northern Germany uses modelica for its power controls for a significant portion of their country's energy supply.