MATLAB GPU: arrayfun with indexing
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Hi
I am new to MATLAB GPU computing and have made some initial tests. Now I am looking to parallelize a the following code.
for i=1:n ;where n~1'000'000 and a, b,c of size ~300'000x1
currindices = indices(24,i);
a(currindices ) = a(currindices ) + A(24x24)*(b(currindices )+B(24x24)*c(currindices ));
end
In a test I parallelized this code without any of the indices by using arrayfun and it worked well. Meaning just having the following code in an function that was called by arrayfun:
for i=1:n
a=a+A*(b+B*c)
end
I wonder how to deal with the indexing of the vectors and whether arrayfun still makes sense. The matrices A and B are constant. I read that indexing is rather slow on a GPU.
What would be the best way to parallelize the above code?
Thanks for any help. This whole paralellization does not come natural to me yet.
BR
6 Comments
Joss Knight
on 26 Oct 2017
I don't think you need pagefun. Can't you just do this with indexing and matrix multiplication? It seems indices is the correct shape, namely 24-by-n. So b(indices) and c(indices) return 24-by-n, the multiplies return 24-by-n, and the addition works.
a(indices) = a(indices) + A * (b(indices) + B * c(indices));
If the indices repeat this may not work as you intended, because some elements of a will get one of the answers and not another. You might have to use accumarray in that case.
result = a(indices) + A * (b(indices) + B * c(indices));
a = accumarray(result, indices(:), size(a));
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