MATLAB: Optimizing a nested loop by summation

nested loopssummation

Does anyone have a suggestion on how I can optimize this nested loop? Is it possible to do this faster by just using sum? O, L, and W are of arbitrary size.
A = zeros(size(W));
for m = 1:size(O,1)
for pix = 1:NumPixels
A = A + O(m,pix) .* ( L(:,:,m,pix) ./ W ) ./ (sum( sum( L(:,:,m,pix) , 1 ) , 2 ) );
end
end

Best Answer

A = zeros(size(W));
for m = 1:size(O,1)
    for pix = 1:NumPixels
        L1 = L(:,:,m,pix);
        A = A + O(m,pix)* L1./W / sum(L1(:));
    end
end
without loop
s = size(L);
L1 = reshape(L,s(1),s(2),[]);
out = sum(bsxfun(@times,bsxfun(@rdivide,...
                    bsxfun(@rdivide,L1,W),sum(sum(L1,2))),reshape(O,1,1,[])),3);
ADD [8:27MDT 16.12.2011]
s = size(L);
L1 = reshape(L,prod(s(1:2)),[]);
A1 = reshape( bsxfun(@times,L1, 1./(W(:)*sum(L1)))*O(:),s(1),[])
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