MATLAB: Use multiple GPUs for functions

gpugpuarraymultigpusparfor

Dear All, I had my previous question, because it was not clear, now I tried to simplify it. At my disposal there are two GPU devices (GeForce GTX 1070 Ti and GeForce GTX 1060 6GB). I would like to parallelize my calculations on both GPUs. Lets say I have 3D gpuArray and I would like to pass this data in chunks to both GPUs, just in my code function is more difficult, this is an example of what I am trying to achieve, and yes it does not work.
clear;
delete(gcp('nocreate'));
nGPUs = gpuDeviceCount();
parpool('local', nGPUs);
d1=rand(10,10,10);
d=gpuArray(d1);
parfor i =1:nGPUs
c1 = zeros(10,10,10);
c=gpuArray(c1);
  for j=1:10
     c(:,:,j)=d(:,:,j)*2;
  end
end
der=c;
It gives temporary variable error.

Best Answer

Is the question then, why do you get the temporary variable error? The reason is because the variable 'c' is created inside the parfor-loop. It is therefore a temporary variable, meaning that it has no life after the parfor loop. It is both forbidden and illogical to use a temporary variable after the for-loop as you have done at the line,
der=c;
This is because the parfor loop maintains several parallel versions of c. Every parallel worker has its own version of c which might end up carrying a different value at the end of the loop, depending on the parallel operations done to it. So, which of these versions would be assigned to der?
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