Efficient method of summing the values in multiple images on GPU?

pageSum = pagefun(@mtimes,A,ones(size(A,2),1))
% One pagefun gives you the sums of the rows
% repeating again will give the sums for pages
pageSum = pagefun(@mtimes,ones(1,size(pageSum,1)),pageSum)

If you would rather you can write this in one line:

pageSum = ...
pagefun(@mtimes,ones(1,size(A,1)),pagefun(@mtimes,A,ones(size(A,2),1)))

Lastly a simple for loop can work:

for k = size(A,3):-1:1
    tmp = A(:,:,k);
    sumk(k) = sum(tmp(:));
end

I wrote a function to time these methods:

function t = timeGpu(m,n)
% Test the time different methods take to calculate the sum of the elements
% for each page on a GPU array.
% Create a gpuArray m-by-m-by-n
A = rand(m,m,n,'gpuArray');
% Allocate space for timing
t = nan(3,1);
% Time each method
t(1) = gputimeit(@() reshapeIt);
t(2) = gputimeit(@() pageIt);
t(3) = gputimeit(@() loopIt);
t = table(t,'RowNames',{'Reshape','pageIt','loopIt'});
function reshapeIt
    % Method one: use reshaping and sum
    ret = sum(reshape(A,[],size(A,3)));
end
function pageIt
    % Nested calls to pagefun with a matrix multiplication
    % ones'*A*ones, where ones is a column vector.
    vec1 = ones(size(A,2),1);
    ret = pagefun(@mtimes,vec1.',pagefun(@mtimes,A,vec1));
end
function loopIt
    % Just a regular loop through the pages
    for k = size(A,3):-1:1
    tmp = A(:,:,k);
    sumk(k) = sum(tmp(:));
end
end
end

Here is some sample results:

>> t = timeGpu(100,1000)
t = 
                 t    
             _________
    Reshape    0.0010045
    pageIt     0.0079246
    loopIt       0.27821
>> t = timeGpu(100,100)
t = 
                   t     
               __________
    Reshape    0.00035554
    pageIt      0.0014899
    loopIt       0.028113
>> t = timeGpu(1000,100)
t = 
                  t    
               ________
    Reshape    0.009075
    pageIt     0.052044
    loopIt      0.03972

It looks like reshape wins.

Christopher Desmond 2016-7-1

If you have time, would you mind taking a look at another question I have. Its the only other problem I've encountered working with the GPU.

http://www.mathworks.com/matlabcentral/answers/293410-help-with-efficient-collection-of-sub-matrices-on-gpu

Thanks for all of your help.

Brendan Hamm 2016-7-7

Unfortunately, I will not have access to my GPU machine for a few weeks here. I'd be more than happy to make some suggestions on your other post after this though. Likely someone else will get back to you before then.

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Efficient method of summing the values in multiple images on GPU?

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Efficient method of summing the values in multiple images on GPU?

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