Uninitialized fields of record outputs of functions

[modelica-trac-importer]

Reported by stefanv on 10 Dec 2014 17:34 UTC
Modelica.Media.Water.waterBaseProp_pT returns a record of type Modelica.Media.Common.IF97BaseTwoPhase.

The function handles four different "regions", and in the if-statement branches for those, it doesn't always assign all of the fields of the output record.

Does that make it an incorrect function? If not, what are the returned values of those fields?

Here's a simplified example:

record R
    Real a, b, c;
end R;

function F
    input Integer region;
    output R rec;
algorithm
    if region == 1 then
        rec.a := 1;
        rec.b := 2;
    else
        rec.b := 3;
        rec.c := 4;
    end if;
end F;

For the call, r = F(1), what is the value of r.a ?

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Migrated-From: https://trac.modelica.org/Modelica/ticket/1628

[modelica-trac-importer]

Comment by hubertus on 10 Dec 2014 18:50 UTC
Hi Stefan,

This code was created when Modelica was at version 1.6 and never updated, keep that in mind. I think that all fields should be initialized, so this could be filed as a but for MSL. 

In this particular case it would be great to have a symbolic UNDEFINED, as has been discussed elswehere. What to do with such record entries is maybe worthwhile discussing in the language group. It may be an option to leave it without assignment, I'd prefer to set a symbolic undefined.

Hubertus

[modelica-trac-importer]

Comment by jmattsson on 11 Dec 2014 08:34 UTC
The spec says:
The local variables of a function are not automatically initialized to the implicit default values of the data type (Section ‎12.4.4) ![(e.g. 0.0 for Real) for performance reasons. It is the responsibility of the user to provide explicit defaults or to define the values of such variables before they are referenced.!]
I'd say that it would probably be a good idea to detect uninitialized variables in functions with a simple program flow analysis, give a diagnostic and initialize it to the default value anyway. The first two are tool issues, but the last probably needs a spec update to be allowed.

The same issue occures in Modelica.Electrical.Spice3.Internal.Diode.diodeCalcTempDependencies - out_c.m_tBrkdwnV is left unassigned for some cases.

[modelica-trac-importer]

Comment by jfrenkel on 11 Dec 2014 11:55 UTC
Some links to Tickets with the same issue:

• Undefined protected variable in diodeNoBypassCode function #930
• Uninitialized var in function Modelica.Media.Water.IF97_Utilities.waterBaseProp_dT used #1422
• Uninitialized local variable den2 in Modelica.Blocks.Continuous.Internal.Filter.base.CriticalDamping used #1423
• Uninitialized local variable den1 in Modelica.Blocks.Continuous.Internal.Filter.base.Butterworth used #1424
• Conditionally uninitialized local variable dbrgdb in Modelica.Electrical.Spice3.Internal.Mos2.drainCurRevised used #1425
• Uninitialized local variables in Modelica.Electrical.Spice3.Internal.Mos.mos2CalcNoBypassCode used #1427
• Uninitialized local variable temp in Modelica.Electrical.Spice3.Internal.Bjt.bjtNoBypassCode used #1428
• Conditionally uninitialized output variable Re in Modelica.Fluid.Dissipation.HeatTransfer.HeatExchanger.kc_flatTube used #1429
• Conditionally uninitialized local variables in function Modelica.Media.Water.IF97_Utilities.BaseIF97.Isentropic.hofps4 used. #1430
• Placeholder #1440

Interesting for a "simple programm flow analysis" are #1243 and #1424 with the issue of 0-Dimension Variables.

A disscusion about that was already started in #1440.

[modelica-trac-importer]

Comment by hansolsson on 23 Feb 2015 17:19 UTC
Modelica design:
Library should be updated.

The Modelica function should assign to the entire output, including all fields of it (excluding empty arrays - i.e. all elements of the array should be assigned, not the array).

A tool could use NaN, and invalid pointer for strings to be able to detect it (not as easy for Boolean, Integer, and Enumeration - could use invalid values for Boolean and Enumeration). On the other hand to just run predictably it is better to use zero/empty string/false.

[modelica-trac-importer]

Modified by beutlich on 19 Mar 2015 09:49 UTC

[modelica-trac-importer]

Modified by stefanv on 30 Sep 2015 11:57 UTC

[modelica-trac-importer]

Comment by hubertus on 13 Dec 2015 01:38 UTC
Fixedin 6dcfe04 n trunk

[modelica-trac-importer]

Changelog modified by hubertus on 13 Dec 2015 01:38 UTC
Missing initialization fixed in Water IF97