Matlab: initialize empty array of matrices

Question

I need to create an empty array of matrices, and after fill it with matrices of the same size.

I have made a little script to explain:

result = [];

for i = 0: 4;
    M = i * ones(5,5); % create matrice
    result = [result,M];  % this would have to append M to results
end

Here result is a matrix of size 5*25 and I need an array of matrices 5*5*4.

I have been researched but I only found this line: result = [result(1),M];

Maybe just a typo, but do you not want result = [result,M];. But I guess there might be other problem in terms of dimensions. — mpaskov
– mpaskov, Commented Dec 3, 2016 at 17:16

Suever · Accepted Answer · 2016-12-03 17:12:44Z

3

The issue is that [] implicitly concatenates values horizontally (the second dimension). In your case, you want to concatenate them along the third dimension so you could use cat.

result = cat(3, result, M);

But a better way to do it would be to actually pre-allocate your result array using zeros

result = zeros(5, 5, 4);

And then within your loop fill each "slice" of the 3D array with the values.

for k = 0:4
    M = k * ones(5,5);
    result(:,:,k+1) = M;
end

answered Dec 3, 2016 at 17:12

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