Modelica Coding Standards / Modelica When Statement - modelica

Question

Greeting Everyone,
Happy New Year 2020
I am using Openmodelica 1.14 release version on 64 bit windows 7 system.
I am facing some trouble with ‘when’ statement in OMSimulator. While searching for solution, I came across a closed ticket #2664 in Openmodelica. I can still see the reported issue in the current release version of Openmodelica.
I am including the relevant files of ticket # 2664.
model SimpleTest "just a simple model - Compilation etc."
Modelica.Blocks.Interfaces.IntegerInput u annotation(Placement(visible = true, transformation(origin = {-100, 40}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {-80, 40}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
Modelica.Blocks.Interfaces.IntegerOutput y annotation(Placement(visible = true, transformation(origin = {100, 20}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {100, 20}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
algorithm
when change(u) then
y := y + 2;
end when;
annotation(Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2})), Diagram(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2}), graphics = {Rectangle(origin = {-6.15, 2.93}, fillColor = {0, 133, 199}, fillPattern = FillPattern.HorizontalCylinder, extent = {{-77.89, 83.75}, {88.14, -92.53}})}));
end SimpleTest;
Is SimpleTest.mo as per Modelica standards?
While compilation of SimpleTest.mo , it throws a Translation Warning
Assuming fixed start value for the following 1 variables:
y:DISCRETE(flow=false fixed = false ) SimpleTest type: Integer
How to avoid this error?

Answer 1

It is just a warning. When you define a discrete variable like this such that it depends on it's previous value in a when condition, it has to have a fixed start value. Just providing a start value kind of is a guess value for the compiler, when you fix it you tell the compiler that it has to use this value for the initialization.
If you don't provide a start value it is set to zero, if you don't fix it, the compiler fixes it automatically (resulting in the warning).
Simple example:
Integer y(start=0, fixed=true);
Applied on your model:
model SimpleTest "just a simple model - Compilation etc."
Modelica.Blocks.Interfaces.IntegerInput u annotation(Placement(visible = true, transformation(origin = {-100, 40}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {-80, 40}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
Modelica.Blocks.Interfaces.IntegerOutput y(start=0, fixed=true) annotation(Placement(visible = true, transformation(origin = {100, 20}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {100, 20}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
algorithm
when change(u) then
y := y + 2;
end when;
annotation(Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2})), Diagram(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {2, 2}), graphics = {Rectangle(origin = {-6.15, 2.93}, fillColor = {0, 133, 199}, fillPattern = FillPattern.HorizontalCylinder, extent = {{-77.89, 83.75}, {88.14, -92.53}})}));
end SimpleTest;