How using a script of variables in a parfor loop ?

Hello,

I have gathered the declaration of variables in one and the same script, to simply reduce the number of lines in the main function. The script of variables therefore contains:

Var1 = 2;

Var2 = 3;

....

The loop just reads the script.

parfor i = 1:5

scriptOfVariables

Var3 = Var1 + Var2

end

It seems that parfor does not accept it and I have to write the set of variables directly in the loop.

Any idea to avoid overloading the loop?

[Ive J]

why not save/load the variables in/as mat/struct? Though not sure about overhead issues (should be fine if variables are few).

[Michael cohen]

Thank you for your answer !

Because I don't want then, during the many variable calls, to have to use dot notation each time, which makes the code more cumbersome.

Answer 1

[Matt J]

Does scriptOfVariables use the loop counter i in any way? If not, you should move it outside the loop,

scriptOfVariables;
parfor i = 1:5
 Var3 = Var1 + Var2;
end

Otherwise, you should be using a function instead

parfor i = 1:5
[Var1,Var2]=mfunction(i);
 Var3 = Var1 + Var2;
end

[Michael cohen]

Thank you for your answer !

No, scriptOfVariables does not use the loop counter i in any way. But, in the script there is the declaration of structure type variables.

Var1 = 2;
Var2 = 3;
struct.var(1) = 5;
struct.var(2) = 7;
....

New values are then assigned to them in the parfor loop.

parfor i = 1:5
    scriptOfVariables
    Var3 = Var1 + Var2
    struct.var(1).type = 6;
    ....
end

The concern is that if I take the script out of the loop, Matlab shows me the error below :

Error: Unable to classify the variable 'struct' in the body of the parfor-loop.

For more information, see Parallel for Loops in MATLAB, "Solve Variable

Classification Issues in parfor-Loops".

From what I understand, Matlab cannot recognize structures declared outside the loop and used inside the loop. Reason why I want to insert the script inside the loop..

About your second suggestion, it's simply because of the large number of variables :)

[Stephen23]

"Unable to classify the variable 'struct' in the body of the parfor-loop."

Do not define variables named struct.

[Matt J]

From what I understand, Matlab cannot recognize structures declared outside the loop and used inside the loop.

No, that's not the problem. The problem is that you are not allowed to assign to variables declared outside the loop unless it is a sliced variable. However, you can return the struct from a function:

parfor i = 1:5
    
    [S,Var1,Var2]=declareTemp();
    
    Var3 = Var1 + Var2
    struct.var(1).type = 6;
    ....
end

function [S,Var1,Var2]=declareTemp()

    Var1 = 2;
    Var2 = 3;
    struct.var(1) = 5;
    struct.var(2) = 7;

end

[Michael cohen]

Thanks again for your answer.

Actually, I simplified the example.

The reality is that the struct has multiple fields (S.var, S.coco, S.moo, etc.). So if I don't provide the structure as input parameter of the function you propose, these other fields (other than .var) will all be cleared.

[S,Var1,Var2]=declareTemp(S);

What is surprising is that parfor refuses I provide "S" as input to the declareTemp function, but it accepts the other variables (of type dooble) even though they are also declared in the script before the parfor loop

[S,Var1,Var2]=declareTemp(Var1,Var2);