Update Continuous.mo

[hubertus65]

Better suggestion to fix init issue for Integrators in Modelica.Blocks.Continuous. WARNING: @MartinOtter, I currently don't have a setup to test this immediately, so this is UNTESTED. Please test before committing. It would be nice to have a test when this is in a loop with a non-linear plant + steady-state initialization.

[HansOlsson]

This will not work for two reasons:

• The default for the start-attribute is now "empty", not 0.0 as in Modelica 3.4. Thus for non-steady-state there will be a new start-value, that may cause problems.
• There are also initial equations that weren't modified, so there will now be both a start-value with fixed=true and an initial equation - which is even more problematic.

For Dymola this is likely to be worse than before, since we could previously down-prioritize a start-value if there was an identical (possibly inactive) initial equation (even if not standardized it could at least be explained) - now they differ so we cannot do that.

It may be possible to find a solution that only provides a non-fixed start-value when needed, I will check later.

[MartinOtter]

As Hans explained, your proposed solution is not good.

A (non-backwards) compatible good solution would be, as performed in Rotational.Components. Inertia, where no start or initial equations are defined at all, but "showStartAttribute=true" is provided for the relevant variables often used for initialization:

This is much clearer and the user has a good GUI to select the most important initialization options (and then it is completely clear in the user interface which values are set with fixed = true, fixed = false or not set).

Since it seems overkill to make such a non-backwards compatible change now (which requires an appropriate, probably non-trivial, conversion script), I would suggest to keep the merged solution, but correct the description text for y_start:
Real y_start= 0 "Initial value of output (= state), if initType=initialState or initialOutout)"
instead of the current
Real y_start = 0 "Initial or guess value of output (= state)"

If the block appears in a nonlinear algebraic loop and y is an iteration variable, then, as usual, the user has to make a modifier (y(start=xxx)). One might also explain this in the documentation.