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Assembling two matrices into one in a given pattern

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Dario Garic
Dario Garic on 20 Jan 2021
Commented: Jan on 20 Jan 2021
Hello everbody,
I am fairly new to Matlab and I have some difficulties solving a task from university.
The task ist to assemble two matrices into one global matrices in such form:
A = [ 1 2; 1 2 ]
B = [2 3; 2 3]
% Assemble A and B into C
C = [1 2 0; 1 4 3; 0 2 3]
I tried it using a for loop but I can't manage to insert them into the given form in C.
When searching for a solution I came across "indexing" but I couldn't figure out how to use it in my problem.
I am grateful for any and all help!


Jan on 20 Jan 2021
There is an infirnite number of algorithms, which produces C basend on A and B. Without seeing the exact instructions, it is unlikely that the readers guess, what you want to implement.
Dario Garic
Dario Garic on 20 Jan 2021
Hello Jan, thanks for your time!
I can assemble the matrix any way I want, as long as it works.
Yes you are right, I didn't explain the problem efficient enough, sorry!
I have n matrices in the form 2 x 2. I need to assemble those (Matrix A and B) into a global matrix C with the form n+1 x n+1.
For example:
I have n = 2. That means I have to allocate two 2 x 2 matrices into a global matrix 3 x 3.
I know that there is the function blkdiag, but there is a catch to the task. The number from A (2,2) needs to be added with the number in B(1,1) in the global matrix C.
The code should work for any number n.
Does this descripton help?

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Answers (1)

Jan on 20 Jan 2021
Edited: Jan on 20 Jan 2021
A bold guess (although a wrong guess might be more confusing than posting nothing):
A = [1 2; 1 2];
B = [2 3; 2 3];
[s1, s2] = size(A);
C = zeros([s1, s2] + 1);
C(1:s1, 1:s2) = A;
C(2:s1+1, 2:s2+1) = C(2:s1+1, 2:s2+1) + B;
[EDITED after your comment]
List = {[1 2; 1 2], [2 3; 2 3], [4 7; 8 9]};
n = numel(List);
C = zeros(n + 1, n + 1);
for k = 1:n
C(k:k+1, k:k+1) = C(k:k+1, k:k+1) + List{k};


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