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Issue with relational operators

#5437  Permalink Top

Issue with relational operators

Jan-23-15 20:22:53

Hello,
I'm facing a problem with relational operators in OpenModelica (1.9.1 r22929).
Here is a small model that produces weird results:

Code:

model Test

  Modelica.Blocks.Continuous.Integrator i1;

  Modelica.Blocks.Nonlinear.Limiter sat(uMin = 0.0, uMax = 100.0);

  Real u(start = 0);

  Real y;

  Boolean b1 = y < 100;

  Boolean b2 = y <= 100;

  Boolean b3 = y == 100;

  Boolean b4 = y >= 100;

  Boolean b5 = y > 100;

equation

  der(u) = 50;

  connect(i1.u, u);

  connect(i1.y, sat.u);

  connect(sat.y, y);

end Test;

After running the simulation for two seconds, 'y' is equal to 100.
The problem is that 'b1', 'b2' and 'b3' are all true although that is illogical.

Is anyone able to reproduce the results?

Thanks

#5438  Permalink Top

Re: Issue with relational operators

Jan-23-15 20:48:38

I tried this in Dymola as well but had to use b3 = y >= 100 and y <= 100 since you are not allowed to compare Real with equality in equation context in Modelica (and also not connect Real values since they are not connectors). Dymola seems to do it OK. OpenModelica does the == better.

Detecting the zero-crossing for y < 100 I guess is the problem. Keep in mind you are dealing with floating point which is not really precise; this model depends on exact values being calculated. https://trac.openmodelica.org/OpenModelica/newticket

#5439  Permalink Top

Re: Issue with relational operators

Jan-23-15 21:47:49

Alright, I'm creating a ticket for the issue.

I was able to reproduce the bug on a smaller model, which narrows the problem to the "if" statement:

Code:

model Test

  Real y;

  Boolean b1 = y < 100.0;

  Boolean b2 = y <= 100.0;

  Boolean b3 = y == 100.0;

  Boolean b4 = y >= 100.0;

  Boolean b5 = y > 100.0;

equation

  y = if time > 2 then 100 else 0;

end Test;

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