Casadi dae builder template and examples

[micahkc]

No description provided.

[JuliusFrontzek]

Thanks for the great work! I am looking forward to this PR.

I would like to give some feedback as I am having three issues with it so far, for which I am providing two simple example models:

model TestModel
    input Real u;
    output Real x2;
    parameter Real c1 = 1.0;
    parameter Real c2 = c1;
    Real x1;
equation
    der(x1) = c1*x1 + u;
    der(x2) = c2*x2;
end TestModel;

When running rumoca ./tests/models/TestModel.mo -t ./tests/templates/casadi_dae.jinja > ./tests/test_model.py on this model, the resulting Python file contains these lines:

        # Declare p

        c1 = dae.add('c1', 'parameter', 'tunable', dict(start = 1.0))
        c2 = dae.add('c2', 'parameter', 'tunable', dict(start = c1))

which throws this error in CasADi:

NotImplementedError: Wrong number or type of arguments for overloaded function 'DaeBuilder_add'.
  Possible prototypes are:
    add(self,str,dict)
    add(self,str,str,dict)
    add(self,str,str,str,dict)
    add(self,str,str,str,MX,dict)
  You have: '(DaeBuilder,str,str,str,str:MX)'

Because instead of a numeric starting value, the MX variable c1 is passed. For now, I can manually replace these alias assignments, but since they're pretty common in flattened Modelica files, I assume that this should be treated differently in the future.

When fixing this error by manually replacing c2 with c1 in the second ode and removing c2 altogether, I run into another problem: The output (which is simply the state x2 in this case) is not recognized, but I assume that this is a known limitation for now.

Finally, when adding exponents in my equations, I get an "UNHANDLED OP" statement in the Python code.
E.g.:

model TestModel2
    Real x1;
equation
    der(x1) = x1 ^ 2;
end TestModel2;

After running rumoca ./tests/models/TestModel2.mo -t ./tests/templates/casadi_dae.jinja > ./tests/test_model2.py the resulting Python file contains this snippet

 dae.eq(der_x1, (x1 UNHANDLED OP: {
    "Exp": {
        "location": {
            "end": 0,
            "end_column": 0,
            "end_line": 0,
            "file_name": "",
            "start": 0,
            "start_column": 0,
            "start_line": 0,
        },
        "text": "",
        "token_number": 0,
        "token_type": 0,
    },
} 2.0))