Are gpuArray supported within parfor?

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Bharath Lohray 2018-10-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/425885-are-gpuarray-supported-within-parfor

Hi,

I am running the following code and receive an error

Error using gpuArrayTest (line 16)
The following error occurred converting from gpuArray to double:
Conversion to double from gpuArray is not possible.

Line 16 is

parfor i = 1:numel(x_c)

My Code is as follows

%Window Size
W=20;
num_files=3;
% My Code: Read template image from disk - imread > imcrop
im1 = gpuArray(rand(150));
% Actual Code: S = size(template image | im1)
S=[65,62];
[x_c,y_c]=meshgrid(W+1:S(2)-W, W+1:S(1)-W);
max_xcorr_1=zeros(size(x_c),'gpuArray');
% store xcorr results from all filse
max_xcorr_arr=zeros([size(x_c),num_files]);

Loop over a file list.

for j=1:num_files
  % My Code: Read image from disk - imread > imcrop
  im2 = gpuArray(rand(150));
  tic;
  parfor i = 1:numel(x_c)
    x=x_c(i);
    y=y_c(i);
    % Check to see if all pixels in template is not 0 (same).
    if (~max(im1(x-W:x+W,y-W:y+W),[],'all')==0)
      nxc = normxcorr2(im1(x-W:x+W-1, y-W:y+W-1), im2(x-W:x+W-1, y-W:y+W-1));
      % Commenting the line below avoids the gpuArray > double coversion error.
      max_xcorr_1(i)=max(nxc,[],'all');
    end
  end
  max_xcorr_arr(:,:,j)=gather(max_xcorr_1);
  toc
end

However, I do not receive the error if I do one of the following -

I comment out the line `max_xcorr_1(i)=max(nxc,[],'all');`
Reduce the size of the meshgrid to `S=[40, 40]`. The smallest number that I can use without getting the error varies from time to time.
I replace `parfor` with `for`.

I have 8 local MATLAB Workers running. My GPU is an NVIDIA GeForce GTX860M with 4GB of dedicated RAM. My questions are -

Is gpuArray supported within a `parfor`?
Irrespective of the meshgrid size defined by S, The `normxorr2` operation runs on a 2W x 2W sized matrix. So, why does the size S affect the code?
How can I get around this?