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Asked: 2026-05-20T01:12:03+00:00

I have N^2 matrixes. Each one is a 3×3 matrix. One way to concatenation

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I have N^2 matrixes.
Each one is a 3×3 matrix.
One way to concatenation them to a 3Nx3N matrix is to write
A(:,:,i)= # 3x3 matrix i=1:N^2

matrix

B=[A11 A12 ..A1N;A21 ...A2N;...]
But When N is large is a tedious work.
What do you offer?

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1 Answer

  1. Editorial Team

    Here’s a really fast one-liner that only uses RESHAPE and PERMUTE:

    B = reshape(permute(reshape(A,3,3*N,N),[2 1 3]),3*N,3*N).';

    And a test:

    >> N=2;
>> A = rand(3,3,N^2)
A(:,:,1) =
    0.5909    0.6571    0.8082
    0.7118    0.6090    0.7183
    0.4694    0.9588    0.5582
A(:,:,2) =
    0.1791    0.6844    0.6286
    0.4164    0.4140    0.5833
    0.1380    0.1099    0.8970
A(:,:,3) =
    0.2232    0.2355    0.1214
    0.1782    0.6873    0.3394
    0.5645    0.4745    0.9763
A(:,:,4) =
    0.5334    0.7559    0.9984
    0.8454    0.7618    0.1065
    0.0549    0.5029    0.3226

>> B = reshape(permute(reshape(A,3,3*N,N),[2 1 3]),3*N,3*N).'
B =
    0.5909    0.6571    0.8082    0.1791    0.6844    0.6286
    0.7118    0.6090    0.7183    0.4164    0.4140    0.5833
    0.4694    0.9588    0.5582    0.1380    0.1099    0.8970
    0.2232    0.2355    0.1214    0.5334    0.7559    0.9984
    0.1782    0.6873    0.3394    0.8454    0.7618    0.1065
    0.5645    0.4745    0.9763    0.0549    0.5029    0.3226
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