The PARFOR loop cannot run due to the way the variable is used

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Anas Khan
Anas Khan 2022-10-29
编辑： Matt J 2022-10-29
I do not believe there is a way to further vectorize this code. Please let me know if that is untrue. I would like to parallelize the below code. The goal of the routine is to take the structure array "data", extract values from the fields "goPower" and "ngPower" for each element in the struct, perform some operation, and store the result in a 2-D matrix of size 1501 x number_of_elements_in_struct. (1501x7) for example. I expect MatLab to distribute iterations of the PARFOR loop (corresponding to permi looping index) to workers and have each worker perform the inside loop separately. Since each "subject" is different and each iteration of permi does something different, I don't think I have any dependencies. MatLab still says "The PARFOR loop cannot run due to the way the variable "diff" is used. What am I doing wrong?
parfor permi = 1:npermutations
for subject = 1:numel(data)
% Get indices for subsampled set of Go trials = to # of No-Go trials
idxs = randsample(size(data(subject).goPower,2),size(data(subject).ngPower,2),true);
% Combine trials
allTrials = cat(3,data(subject).goPower(:,idxs,:),data(subject).ngPower);
% Making mapping vector
mapping = [ones(size(allTrials,3)/2,1); ones(size(allTrials,3)/2,1)+1];
% Shuffle the mapping vector
new_map = mapping(randperm(numel(mapping)));
% Calculate mean difference
diff(:,subject) = mean( mean( allTrials(:,new_map==2,:) ,2) - mean( allTrials(:,new_map==1,:) ,2) ,3);
end
% Store values for this iteration
perm_diffs(permi,:) = mean(diff,2);
end

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采纳的回答

Matt J
Matt J 2022-10-29
编辑：Matt J 2022-10-29
Pre-allocate temporary variables like diff within the parfor loop.
parfor permi = 1:npermutations
diff=nan(M,N); %pre-allocate diff
for subject = 1:numel(data)

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