Mixed system detection

[Niklas Worschech]

Using the MSL mass with stop and friction with a force (see example below), Dymola detects a mixed system, which is handled as nonlinear system in OpenModelica. When looking at the equations, there is one linear equation, which depends on a boolean variable. Is there a mixed system detection and handling in OpenModelica?

model TestModel
  Modelica.Mechanics.Translational.Components.MassWithStopAndFriction
    massWithStopAndFriction(m=1);
  Modelica.Mechanics.Translational.Sources.Force force;
  Modelica.Blocks.Sources.Sine sine;
equation 
  connect(force.flange, massWithStopAndFriction.flange_a);
  connect(sine.y, force.f);
end TestModel;

[Volker Waurich]

I found no function in the SimCode-generation that generates a SimCode.SES_MIXED().
It seems there is no mixed system type anymore, only SimCode.SES_NONLINEAR and SimCode.SES_LINEAR. There are Boolean attributes which say that such a SimEqSystem is mixed, but not distinction between discrete and continuous vars is available.
Is there any reason for that?

[Lennart Ochel]

I removed the mixed systems a while back, since they were not supported anyway but caused some problems. I will come up with a proper implementation therefore, once I managed the separation of the continuous and discrete simulation.

[Willi Braun]

Currently we assume that all systems can be solved with non-discrete iteration variables what is actually achieved by tearing methods. The mixed system flag indicate that the system has some discrete relation which should switch at events points.

[Nils Menager]

Replying to lochel:
Do you know how long it will take to develop the proper implementation? Because right now, unfortunately, it is not possible to simulate models with friction in an appropriate time with OpenModelica.

[Lennart Ochel]

No, sorry, it's hard to make an estimation. Anyway, I'll try to fix this for the next release.

[Martin Sjölund]

Milestone pushed to 1.9.5

[Martin Sjölund]

Milestone renamed

[Martin Sjölund]

Ticket retargeted after milestone closed

[Martin Sjölund]

Milestone moved to 1.12.0 due to 1.11.0 already being released.

[Francesco Casella]

The milestone of this ticket has been reassigned to "Future".

If you think the issue is still valid and relevant for you, please select milestone 1.13.0 for back-end, code generation and run-time issues, or 2.0.0 for front-end issues.

If you are aware that the problem is no longer present, please select the milestone corresponding to the version of OMC you used to check that, and set the status to "worksforme".

In both cases, a short informative comment would be welcome.