MATLAB: Problems repeating matrix in desired order

repeatrepeat matrix

Hi, I’m relatively new to Matlab and I’m incredibly stuck on how to do what I feel like should be a simple operation. I want to take a 3 dimensional matrix and repeat it a certain number of times to create a 4 dimensional matrix, but the repeat function is not organizing them the way I’d like and I cannot figure out a way to repeat the matrix in the desired order. For example, if I have a 3 dimensional matrix where (:,:,1) = [1 2; 3 4] and (:,:,2) = [5 6; 7 8], I want to create a 4 dimensional matrix where all the (:,:,1,1), (:,:,2,1), etc. data is the [1 2; 3 4] matrix and the (:,:,1,2),(:,:,2,2), etc. data is the [5 6; 7 8] matrix. Currently, however, what I get is a 4D matrix where (:,:,1,1) = [1 2;3 4] and (:,:,2,1) = [5 6; 7 8] and so on. Thanks in advance!

Best Answer

A(:,:,1) = [1,2;3,4];
A(:,:,2) = [5,6;7,8];
N = 2;
repmat(permute(A,[1,2,4,3]),[1,1,N,1])
which gives exactly the output that you requested:
ans(:,:,1,1) =
   1   2
   3   4
ans(:,:,2,1) =
   1   2
   3   4
ans(:,:,1,2) =
   5   6
   7   8
ans(:,:,2,2) =
   5   6
   7   8
The permute rearranges the array so that the third dimension becomes the fourth dimension (which is where you want it in the output). The repmat is used to then repeat this new array N times along the third dimension.
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