Parallelizing MATLAB code

Question

Hello I want to use parallelize my MATLAB code to run High computing server. It is code to make image database for Deep learning. To parallelize the code I found the I have to for parfor loop. But I used that with the first loop or with the second loop it shows me error parfor cannot be run due to the variable imdb and image_counter. Anyone please help me to change the code to work with parfor

for i = 1:length(cur_images)
            X = sprintf('image Numb: %d ',i);
            disp(X)
        cur_image = load(cur_images{i,:});
        cur_image=(cur_image.Image.crop);


        %----------------------------------------------

        cur_image = imresize(cur_image, image_size);


        if(rgb < 1)
            imdb.images.data(:,:,1,image_counter) = cur_image;
        else
            imdb.images.data(:,:,1,image_counter) = cur_image(:,:,1); 
            imdb.images.data(:,:,2,image_counter) = cur_image(:,:,2);
            imdb.images.data(:,:,3,image_counter) = cur_image(:,:,3); 
            imdb.images.data(:,:,4,image_counter) = cur_image(:,:,4); 
            imdb.images.data(:,:,5,image_counter) = cur_image(:,:,5); 
            imdb.images.data(:,:,6,image_counter) = cur_image(:,:,6); 
            imdb.images.data(:,:,7,image_counter) = cur_image(:,:,7); 
            imdb.images.data(:,:,8,image_counter) = cur_image(:,:,8); 
            imdb.images.data(:,:,9,image_counter) = cur_image(:,:,9); 
            imdb.images.data(:,:,10,image_counter) = cur_image(:,:,10);

        end


        imdb.images.set(     1,image_counter) = set;             
        image_counter = image_counter + 1;
    end

You just need a tutorial on what you can and can not do in parallel — Ander Biguri
– Ander Biguri, Commented May 9, 2018 at 8:49

Edric · Accepted Answer · 2018-05-09 14:52:58Z

2

The main problem here is that you can't assign to fields of a structure inside parfor in the way that you're trying to do. Also, your outputs need to be indexed by the loop variable to qualify as "sliced" - i.e. don't use image_counter. Putting this together, you need something more like:

% Make a numeric array to store the output.
data_out = zeros([image_size, 10, length(cur_images)]);

parfor i = 1:length(cur_images)
    cur_image = load(cur_images{i, :});
    cur_image=(cur_image.Image.crop);
    cur_image = imresize(cur_image, image_size);

    % Now, assign into 'data_out'. A little care needed
    % here.
    if rgb < 1
        data_tmp = zeros([image_size, 10]);
        data_tmp(:, :, 1) = cur_image;
    else
        data_tmp = cur_image;
    end
    data_out(:, :, :, i) = data_tmp;
end
imdb.images.data = data_out;

answered May 9, 2018 at 14:52

Edric

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2 Comments

Aadnan Farooq A Over a year ago

after loading the size of cur_image is 250x250x10. The data should be store in imdb.images.data like (250x250x10x1) for the first image and (250x250x10x2) for the second image. data_out(:, :, :, i) = data_tmp; and imdb.images.data = data_out; will act like same?

Aadnan Farooq A Over a year ago

There is one more thing is this parfor loop is working another for loop for no of sets. There are 3 sets and for each set this parfor is running. The size of first set is data_out 28x28x61x11028. The size of second and third set is data_out 28x28x61x2048. How can I concatenate it is loop of set?

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