Modelica - iterator with exception? - modelica

Question

Slightly generalised example:
How do I make a for loop with exceptions when I define model equations?
The following works:
model Test
Real[9] q;
equation
q[2] = 1.2;
q[4] = 1.4;
for i in {1,3,5,6,7,8,9} loop
q[i] = 0;
end for;
end Test;
But I would rather like to write something like:
model Test
Real[9] q;
equation
q[2] = 1.2;
q[4] = 1.4;
for i in 1:9 and not in {2,4} loop
q[i] = 0;
end for;
end Test;
Is this possible?

Answer 1

This should be possible, as long as you make sure to have an equation for every unknown.
Probably not the perfect solution, but actually pretty readable:
model LoopException
Real[9] q;
equation
q[2] = 1.2;
q[4] = 1.4;
for i in 1:9 loop
if Modelica.Math.Vectors.find(i, {2, 4}) == 0 then
q[i] = 0;
end if;
end for;
end LoopException;
As an alternative, you could also try to write an "Array Constructor with Iterators" (Modelica Language Spec. Sec. 10.4.1), but that probably gets a bit messy...

Answer 2

With 2 helper functions you can easily emulate what you want:
model Test
Real[9] q;
equation
q[2] = 1.2;
q[4] = 1.4;
for i in allExcept(1:9, {2,4}) loop
q[i] = 0;
end for;
end Test;
Here are the functions you need for that:
function contains
"Check if vector v contains any element with value e"
input Integer vec[:];
input Integer e;
output Boolean result;
algorithm
result := false;
for v in vec loop
if v == e then
result := true;
break;
end if;
end for;
end contains;
function allExcept
"Return all elements of vector v which are not part of vector ex"
input Integer all[:];
input Integer ex[:];
output Integer vals[size(all, 1) - size(ex, 1)];
protected
Integer i=1;
algorithm
for v in all loop
if not contains(ex, v) then
vals[i] := v;
i := i + 1;
end if;
end for;
end allExcept;
Note that Modelica tools usually need to know the size of vectors during translation, especially here when you generate equations. Hence, the following line is required:
output Integer vals[size(all, 1) - size(ex, 1)];
It will fail when all or ex contain duplicate elements.
Therefore the model will not translate, if you try something like
for i in allExcept(1:3, {2, 2}) loop