Connecting declared variables in expandable connectors

[modelica-trac-importer]

Reported by eshmoylova on 28 Mar 2017 18:11 UTC
Resolution of ticket #428 changed the text of specification for elaborating expandable connectors in 9.1.3 to:
"One connector in the connect equation must reference a declared component, and if the other connector is an undeclared element in a declared expandable connector it is handled as follows (elements that are only potentially present are not seen as declared)"

Does it mean the following example is illegal?

expandable connector A
end A;

expandable connector B
  input Real x;
end B;

connector RealInput = input Real;

model M
  A a;
  B b;
  RealInput ri;
...
equation
...
  connect(a.x,b.x);
end M

According to the new text, the connect equation should not be allowed because a.x is not seen as declared because it is only potentially existing. What would happen if there was instead a pair of connect equations?

  connect(a.x,ri);
  connect(a.x,b.x);

After the first connect equation a.x is no longer only potentially existing, and it is declared. So is it considered as declared when we process the second equation? I think it should not be because that would make the result dependent on the order of processing. But the specification does not say so explicitly.

Is the paragraph about connecting two expandable connectors correct?
"When two expandable connectors are connected, each is augmented with the variables that are only declared in the other expandable connector (the new variables are neither input nor output). This is repeated until all connected expandable connector instances have matching variables [i.e. each of the connector instances is expanded to be the union of all connector variables.]"

It talks only about variables that are declared. What about the variables that are added to a connector as a result of connection?

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Migrated-From: https://trac.modelica.org/Modelica/ticket/2172

[modelica-trac-importer]

Comment by jmattsson on 3 Apr 2017 13:03 UTC
Replying to [ticket:2172 Elena Shmoylova]:

After the first connect equation a.x is no longer only potentially existing, and it is declared. So is it considered as declared when we process the second equation? I think it should not be because that would make the result dependent on the order of processing. But the specification does not say so explicitly.

I think you may have switched around your example. Did you mean to declare x in A rather than in B?

Even with that change, I disagree. x does not become declared after processing the first connect. It's status doesn't change at that point other than that we note down that it will be present in the flattened model.

It talks only about variables that are declared. What about the variables that are added to a connector as a result of connection?

This should probably be fixed.

[modelica-trac-importer]

Comment by eshmoylova on 4 Apr 2017 14:06 UTC
Replying to [comment:1 Jesper Mattsson]:

Replying to [ticket:2172 Elena Shmoylova]:

After the first connect equation a.x is no longer only potentially existing, and it is declared. So is it considered as declared when we process the second equation? I think it should not be because that would make the result dependent on the order of processing. But the specification does not say so explicitly.
I think you may have switched around your example. Did you mean to declare x in A rather than in B?

You are right. With A and B as written, I should have wrote:

connect(b.x,ri);
connect(a.x,b.x);

And the comment above should refer to b.x.

Even with that change, I disagree. x does not become declared after processing the first connect. It's status doesn't change at that point other than that we note down that it will be present in the flattened model.

Sorry, I just want to make sure I understood your comment correctly. You disagree that x is considered declared after the first connect, right? Does it mean you agree that the example is illegal, that we cannot connect a.x and b.x?

If that's the case I think there might be existing models and libraries out there that would become illegal. I think there should be an explicit example of this illegal case in the Specification, so that it would be easier to understand for the users what has changed.

[modelica-trac-importer]

Comment by kurzbach on 7 Apr 2017 05:25 UTC
In the example above b.x is declared so the second connect is valid.
But what about

model M
 expandable connector C
  Real r;
 end C;
 C c1;
 C c2;
 C c3;
 equation
  connect(c1.r,c2.a);
  connect(c2.a,c3.b);
end M;

c2.a ist introduced by the first connect statement (c.r is declared), but is not declared (as I understand the spec).
That way, the second connect is illegal, but a prominent Modelica tool accepts it.
What is the correct interpretation?

Such an example is missing in the specification.