Array indexing with boolean array - modelica

Question

Given a Real array (e.g. myArray) and a Boolean array (e.g. myMask), I'd like to have:
if myMask[i] == true then myArray[i] = myValueTrue
if myMask[i] == false then myArray[i] = myValueFalse
This does work
model BooleanIndexing
parameter Boolean myMask[3] = {false, true, true};
parameter Boolean myMask_negated[3] = {true, false, false};
Real myArray[3];
parameter Real myValueTrue = 3.0;
parameter Real myValueFalse = 5.0;
equation
myArray[Modelica.Math.BooleanVectors.index(myMask)] = fill(myValueTrue, Modelica.Math.BooleanVectors.countTrue(myMask));
myArray[Modelica.Math.BooleanVectors.index(myMask_negated)] = fill(myValueFalse, Modelica.Math.BooleanVectors.countTrue(myMask_negated));
end BooleanIndexing;
but this does not
model BooleanIndexing
parameter Boolean myMask[3] = {false, true, true};
parameter Boolean myMask_negated[3] = not myMask;
Real myArray[3];
parameter Real myValueTrue = 3.0;
parameter Real myValueFalse = 5.0;
equation
myArray[Modelica.Math.BooleanVectors.index(myMask)] = fill(myValueTrue, Modelica.Math.BooleanVectors.countTrue(myMask));
myArray[Modelica.Math.BooleanVectors.index(myMask_negated)] = fill(myValueFalse, Modelica.Math.BooleanVectors.countTrue(myMask_negated));
end BooleanIndexing;
The only difference is how I initialized myMask_negated.
The errors are, in OpenModelica:
[BooleanIndexing: 9:3-9:139]: Illegal subscript Modelica.Math.BooleanVectors.index({myMask_negated[1], myMask_negated[2], myMask_negated[3]}) for dimensions 3 in component myArray[Modelica.Math.BooleanVectors.index(myMask_negated)].
[BooleanIndexing: 9:3-9:139]: Variable myArray[Modelica.Math.BooleanVectors.index(myMask_negated)] not found in scope BooleanIndexing.
Error occurred while flattening model BooleanIndexing
and in Dymola2018
Translation of BooleanIndexing:
Failed to expand myArray[Modelica.Math.BooleanVectors.index(myMask)].
Errors or failure to expand the equation:
myArray[Modelica.Math.BooleanVectors.index(myMask)] = fill(myValueTrue, Modelica.Math.BooleanVectors.countTrue(myMask));
Found in class BooleanIndexing, C:/workspace/modelica_vehicle/modelica_test/BooleanIndexing.mo at line 8.
Errors or failure to expand vector or matrix expressions.
Translation aborted.
Direct boolean indexing myArray[myMask] seems not to be the solution here.
I cannot see why they are failing and if there are any more elegant solutions.

Answer 1

Both of your versions do not guarantee that the correct number of equations are generated.
myValueTrue and myValueTrue_negated are both parameters, so the user can change the values of the vectors to something which is not complementary.
Hence, I would have recommended to set
final parameter Boolean myMask_negated[3] = not myMask;
but this also does not work, neither in Open Modelica nor in Dymola.
So instead, I recommend to delete myMask_negated and use for loops instead.
Either with two seperate ones:
model BooleanIndexing
parameter Boolean myMask[3] = {false, true, true};
Real myArray[3];
parameter Real myValueTrue = 3.0;
parameter Real myValueFalse = 5.0;
equation
for i in Modelica.Math.BooleanVectors.index(myMask) loop
myArray[i] = myValueTrue;
end for;
for i in Modelica.Math.BooleanVectors.index(not myMask) loop
myArray[i] = myValueFalse;
end for;
end BooleanIndexing;
or with a single for loop using an array constructor, as shown here:
model BooleanIndexing2
parameter Boolean myMask[3] = {false, true, true};
Real myArray[3];
parameter Real myValueTrue = 3.0;
parameter Real myValueFalse = 5.0;
equation
myArray = {if value then myValueTrue else myValueFalse for value in myMask};
end BooleanIndexing2;