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Attributes and the keyword "parameter."
Attributes and the keyword "parameter."
I'm trying to get a complete grasp on the syntax of variable declarations.
If the keyword "parameter" is used, like this:
parameter Modelica.SIunits.Length d(unit="unit", start=1.0, min=0) = 0.06 "diameter of shell";
OpenModelica does not throw any warnings or errors when I check the model.
What is the point of specifying a start or a min for a parameter?
Assuming start is the same thing as assignment with an equals sign, which one takes priority here?
Thank you
Re: Attributes and the keyword "parameter."
I did some testing in OMEdit.
I can check (without errors/warnings) and run code with the following line:
CelestialBody moon(name = "moon", mass(unit="kg, start = 7000)= 7.382e+22, radius = 1738000.0);
The actual moon.mass will be 7.382e+22 at start. If I change the line to:
CelestialBody moon(name = "moon", mass(unit="kg", start = 7000), radius = 1738000.0);
The checker will complain that there aren't enough equations (implying that moon.mass isn't defined?).
Am I to conclude that, for parameters, start does nothing? Is this an error in OpenModelica? Do min and max have any meaning here?
Re: Attributes and the keyword "parameter."
min and max are basically shortcuts for writing
Code:
assert(x <= maxValue, "...");
assert(x >= minValue, "...");
Start values are more complicated. I suggest reading some literature. Sometimes it is used as a guess value for the initial solver. And sometimes it is used as an initial equation (fixed=false vs. fixed=true).
The following is a nonsense start-value which is also ignored because it is not used to calculate the start-value of a state or initial value. x is always 25 
Code:
Real x(start = 15) = 25;
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