For Loop in 3D Array

For 2D arrays, the operation that I want to execute is:

a = rand(3,3);
for i = 1:numel(a)
    for j = 1:numel(a)
        out(i,j) = (a(i) - a(j)) /  (a(i) + a(j));
    end
end

Which will turn the out into a skew-symmetric matrix. Now I want to perform the same operation instead the matrix is in 3D, how can I do that? The speed is important since my original matrix is (100,100,726). Thanks!

Answer 1

[Dyuman Joshi]

a = rand(3,3,4);
for k=1:size(a,3)
    y=a(:,:,k);
    for i=1:size(y,1)
        for j=1:size(y,2)
            out(i,j,k)=(y(i) - y(j))/(y(i) + y(j));
        end
    end
end
out

out = 
out(:,:,1) =

         0    0.6498   -0.1418
   -0.6498         0   -0.7248
    0.1418    0.7248         0


out(:,:,2) =

         0   -0.6166   -0.5396
    0.6166         0    0.1154
    0.5396   -0.1154         0


out(:,:,3) =

         0    0.1018    0.1400
   -0.1018         0    0.0387
   -0.1400   -0.0387         0


out(:,:,4) =

         0    0.2123    0.1857
   -0.2123         0   -0.0277
   -0.1857    0.0277         0

[Dyuman Joshi]

It will be skew-symmetric matrix. I have made an edit, take a look at it again.

[MarshallSc]

Thanks, yeah, changing the i and j indices from 1:size(y,1) to numel(y) would do the trick. Thanks again!