MATLAB: Identifying lab id within a parfor

labindexnumlabParallel Computing Toolboxparfor

Hello all,

I have an problem that I would like to run in parallel using a parfor. Within the parfor I have to call an external program that runs some calculations using system('external_command result_file_name'). This external program saves the result into a text file that I have to read after execution.

In order for the different iterations not overwrite the results of each other, I would like to know what is the labid running each iteration such that I can compose the file name such as file_name_labid.

I have tried the function labindex but it always returns 1 within a parfor. Is there any other way I can get the labid?

Many thanks,

Best Answer

As mentioned elsewhere, LABINDEX will not work for this purpose. You could either use

t = getCurrentTask(); t.ID

to find out which task you're running. Each worker has a unique task ID which remains the same for the duration of the MATLABPOOL.

Or, my personal preferred solution would be to use TEMPNAME to generate a unique filename to write the output to.

Related Solutions

MATLAB: Saving within SPMD or parfor

The problem with the save command is that it needs to inspect the contents of the workspace in which it is running. That's not allowed inside parfor and spmd. There's more on this constraint in the documentation. As you note, the constraint is about the body of the block itself, not a fundamental constraint on workers calling save or load, and that's because it's an analysis constraint.

MATLAB: In parfor, how to create a temp folder for every worker

Hi,

I would use the process ID for that:

matlabpool open 4 
parfor i=1:20
    w=getCurrentWorker;
    mydir = fullfile(tempdir,['myfolder',num2str(w.ProcessId)]);
    disp(mydir)
end

(Note: tempdir is a MATLAB function not the variable from your example)

Best Answer

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MATLAB: Saving within SPMD or parfor

MATLAB: In parfor, how to create a temp folder for every worker

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