How to index inside a 4 dimensional matrix in Matlab?

Question

Mathematics

There is a 10x10 matrix, each element of which is an array of 3 elements. To index by matrix elements and write vectors with the same values ​​into it, you need to do this:

for i = 1:10
    for j = 1:10
        matrix(:, :, i, j) = [1; 2; 3];
     end
end

How can you get every 3rd element from each vector from the resulting matrix? And is it generally possible?

Answer 1

How can you get every 3rd element from each vector from the resulting matrix?

Indexes in matlab can be given in the format: start:step:end
For your purpose, simply set step 3 in the corresponding index and get every third element.