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Problem with parfor loop

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B.E.
B.E. on 3 Mar 2021
Edited: B.E. on 5 Mar 2021
Hello,
I need help, I have this problem when I use parfor loop for this code, where x a square matrix of order N = 75692 of size approximately equal to 13 Gb and t a row vector of
N=length(t);
alpha= [2.4e-7, 2.5e-7, 2.5e-7, 2.3e-6];
beta = [0.5, 0.8, 0.6, 0.5 ];
YT=zeros(N,4);
YD=zeros(N,4);
parfor ima1:4
[YT(:,ima),YD(:,ima)]=f(t,x,alpha(ima),beta(ima));
end
Error using distcomp.remoteparfor/getCompleteIntervals (line 133)
  2 Comments
B.E.
B.E. on 3 Mar 2021
The complete message is
Error using distcomp.remoteparfor/getCompleteIntervals (line 133)
The parallel pool that parfor was using has shut down. To start a new parallel pool, run your parfor
code again or use parpool.
Error in Code_Method_of_Caracteristics (line 83)
parfor ima=2:4
A write error occurred while sending to worker 19.

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Answers (1)

Edric Ellis
Edric Ellis on 4 Mar 2021
That error basically means a worker crashed while trying to run the parfor loop. You mention that x is large. If you are using the 'local' cluster, then please be aware that x must be copied to each of the worker processes. This can cause a large amount of memory usage, and it's possible (probable?) that this is causing the workers to shut down.
If you're using a recent version of MATLAB, you might be able to use parpool('threads'), which uses multiple computational threads in a single process, and can avoid some memory duplication. (But not all MATLAB functions can operate in this environment).
Otherwise, you are going to be constrained by the memory on your system. Transferring x to the workers from the client incurs additional duplication while the messages are in transit, so if you're only just exceeding the memory, and you can build x directly on the workers by executing a function, then the following pattern might help:
xC = parallel.pool.Constant(@myFunctionThatBuildsX); % build 'x' directly on the worker
parfor ...
[YT(:,ima),YD(:,ima)]=f(t,xC.Value,alpha(ima),beta(ima));
end
  5 Comments
B.E.
B.E. on 5 Mar 2021
The same error with the single worker
Error using distcomp.remoteparfor/getCompleteIntervals (line 133)
The parallel pool that parfor was using has shut down. To start a new parallel pool, run your parfor
code again or use parpool.
Error in Code_Method_of_Caracteristics (line 83)
parfor ima=1:4
A write error occurred while sending to worker 1.

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