OpenModelica vs Dymola: connect
In general, I target Modelica simulation at OpenModelica for the simple reason that it’s free for me to run anywhere. Having had to retarget one of the simulations at Dymola, I encountered a few differences. This post gives a quick overview of one such difference in using the
I had a situation where I needed to use an existing model and operate on its inputs and outputs. For the purpose of this discussion assume there is a model
Example with output
out. In OpenModelica I’m allowed to do the following:
model UseExample Example e; Real localvar1; equation connect(e.out, localvar1); // The rest of the model here end UseExample;
Now, technically, this may very well be against the Modelica language specification. OpenModelica allows it though, and it is something that I used to make my life a little easier. Dymola, on the other hand, is not so loose around this particular rule and throws an error when compiling the model.
The solution for following the language specification correctly is to have separate models for performing calculations and for connecting models together. For example:
model DoSomething input Modelica.Blocks.Interfaces.RealInput in; Real localvar1; equation // The rest of the model here end DoSomething; model UseExample Example e; DoSomething d; equation connect(e.out, d.in); end UseExample;
Note that this really is a better way of doing things from a modularity and maintainability point of view.