Issue with writematrix and parfor

Hello,

I am currently running a 'parfor' loop with writematrix function in it. The writematrix writes some data to multiple sheets of an .xlsx file (each sheet corresponding to data of one particular run). While doing so, I get the following error:

Unable to write to file 'abc.xls'.  Ensure the file is a valid spreadsheet file and is not password protected.

My file is a valid file and is not password protected.

However, if I run a simple 'for' loop, I have no problem and the whole code runs smoothly. My question is two parts 1) How do I use writematrix with parfor such that it does not give the above error? 2) If it is impossible using writematrix, is there any way to save data to a spreadsheet format?

I am desperate for answers :-(

Thanks

[darova]

• If it is impossible using writematrix, is there any way to save data to a spreadsheet format?

Answer 1

[Edric Ellis]

You cannot write to the same file simultaneously from mulitple processes. (This is not a limitation specific to parfor - rather, it's a general limitation). To run in parallel, you must ensure that each worker is writing to a separate file. There are two ways you could do this:

1. Base the file name on the loop iteration
2. Base the file name on the "ID" of the task executing on the worker.

Here's a simple (untested) example:

parfor idx = 1:N
    % Either: base file name on loop iteration
    idxFilename = sprintf('outputFile_%d.xls', idx);
    % Or: base file name on tassk ID
    t = getCurrentTask();
    taskIdFilename = sprintf('outputFile_%d.xls', t.ID);
end