Propagate displayUnits on simple equations

[Francesco Casella]

After the ban on replaceable base classes in Modelica 3.0, input & output connectors are Real and no longer have units. When building components the typical pattern is the following:

model M
  Modelica.SIunits.Temperature T;
  Modelica.Blocks.Interfaces.RealOutput T_out;
  ...
equation
  ...
  T_out = T;
  ...
end M;

It would be great if in this case the unit and displayUnit information was automatically propagated from T to T_out, so that I can see the temperature in degrees Celsius when I'm looking into the connector variable.

This can be trivially implemented by checking all the equations in the form:

a = b;
a + b = 0;

where one of the variables (e.g., a) has a non-empty unit string, while the other (e.g., b) has an empty unit string. In this case, b takes the unit and displayUnit attributes of a.

When implementing this feature, please pay attention to efficiency, see #4362

[Francesco Casella]

@mahge930 reports:

I think this is already supported.

Can you try it with the flags -d=frontEndUnitCheck -d=dumpUnits
-d=frontEndUnitCheck enables the new front end unit check.

-d=dumpUnits notifies you about the units calculated, i.e, exactly what you are looking for.

I know this doesn't work with with -d=newInst right now. That is only because the unit checking is not enabled for NF.

The old front end was used to test this out during the implementation because it had a complete support for many more things. I think we can enable it for the NF whenever needed.

We'll try this out and report. See also #4531.

[Per Östlund]

Move all tickets from NF - New Frontend to New Instantiation so we don't have two different categories for the same thing.

[Martin Sjölund]

Replying to casella:

@mahge930 reports:

Can you try it with the flags -d=frontEndUnitCheck -d=dumpUnits
-d=frontEndUnitCheck enables the new front end unit check.

This only dumps information to stdout. I believe this ticket is requesting to actually update the DAE structure so that OMEdit would show the correct units in the plotting. Possibly we should even output the propagated units in the flat Modelica?

Anyway, this should not be all that difficult to implement; when performing unit checking we have the list of variables with propagated units, so we only need to traverse the DAE structure (only the elements?) and update the units.

[Martin Sjölund]

Actually, I guess the displayUnit would not be propagated since the unit checking does not consider it.

[Martin Sjölund]

​https://github.com/OpenModelica/OMCompiler/pull/2104 updates the DAE with the propagated units (which was already calculated but not returned); displayUnit is not considered though.

[Francesco Casella]

Replying to sjoelund.se:

This only dumps information to stdout. I believe this ticket is requesting to actually update the DAE structure so that OMEdit would show the correct units in the plotting.

Yes.

Possibly we should even output the propagated units in the flat Modelica?

Yes.

Replying to sjoelund.se:

displayUnit is not considered though

It is already better to have unit information rather than no unit information at all. However, the best user experience is obtained if also displayUnit is propagated, otherwise in the above example I would see T in Celsius and T_out in Kelvin, which would be quite puzzling and has no rationale behind it.

[Francesco Casella]

Changed the name to better reflect the currently standing issue

[Francesco Casella]

Rescheduled to 1.14.0 after 1.13.0 releasee

[Francesco Casella]

Releasing 1.14.0 which is stable and has many improvements w.r.t. 1.13.2. This issue is rescheduled to 1.16.0

[Francesco Casella]

Retargeted to 1.17.0 after 1.16.0 release

[Francesco Casella]

Retargeted to 1.18.0 because of 1.17.0 timed release.

[Francesco Casella]

Ticket retargeted after milestone closed