Bug introduced in 11.3 and fixed in 12.1

I am a bit surprised that I am not getting a boolean output for the following simple Modelica model:

model = ImportString[
    "block Or
        input Boolean u1;
        input Boolean u2;
        output Boolean y;
        y = (u1 or u2);
     end Or;"

sim = SystemModelSimulate[ model, {"y"}, {0,1},
        "Inputs" -> {
            "u1" -> Function[ t, True ],
            "u2" -> Function[ t, False ]

First @ sim[{"y"}]

Function[ t, 1., Listable ]

So, what is returned is the real output (e.g. Boole[y]). Is this a bug?

  • 3
    $\begingroup$ I (as a developer working on system modeling in Wolfram Language) consider it at least an unfortunate behavior. I have reported it in our issue tracker internally. $\endgroup$
    – Malte Lenz
    Commented Jun 10, 2019 at 7:42
  • 1
    $\begingroup$ @Malte Great to hear. It indeed makes wiritng VerificationTest in a test notebook (a great feature btw) a bit more opaque. $\endgroup$
    – gwr
    Commented Jun 10, 2019 at 10:38

1 Answer 1


As Malte Lenz and now officially Wolfram Support have confirmed, this is a bug.

Note, that not only will Boolean outputs be given numerically by SystemModelSimulate, but Boolean inputs also have to be given as 1 or 0 instead of True or False.


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