# Extracting the sub-matrix

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cikalekli on 27 Oct 2021
Edited: cikalekli on 28 Oct 2021
Hello, while I'm practising on Matlab about extracting matrix and here there was a thing which I stucked while doing it. (Plus, I also added my code which I have tried to solve but it was not right way to solve it.)
First I've let A = [1 2 3; 4 5 6; 7 8 9] be a matrix of the size 3-by-3. After that I wanted to extract that sub-matrix such as B = [2 3; 5 6] of the size 2-by-2 or something else.
Finally I just wanted to create the following matrix by typing two commands like that:
E =
0 0 0 0 0
0 0 0 0 0
0 0 1 2 3
0 0 4 5 6
0 0 7 8 9
However I could not really understand to pull of this B = [2 3; 5 6] sub matrix from the A matrix to find out matrix E.
I just want to understand its logic please.
Sincerely...

David Hill on 27 Oct 2021
A = [1 2 3; 4 5 6; 7 8 9];
B=A(1:2,2:3);
E=blkdiag(zeros(2),A);
cikalekli on 28 Oct 2021
I'm really, really grateful for that. Now I will understand better by giving different values myself with this code structure. Thank you again, I wish you a wondrous day.

James Tursa on 27 Oct 2021
Edited: James Tursa on 27 Oct 2021
You might benefit from going through the onramp tutorials found here:
Sub-matrices use colon indexing. E.g.,
M(3:5,7:9) is the sub-matrix of M in rows 3 thru 5 and columns 7 thru 9.
This syntax can be used for extracting as well as assigning. E.g.,
M = whatever; % some arbitrary matrix
N = M(3:5,7:9); % extract a sub-matrix of M and store it in a variable called N
M(2:4,5:8) = whatever; % assign something to a sub-matrix of M
Also see the following:
cikalekli on 28 Oct 2021
Ah really thank you for the example and also the site links. As you describe, I will now try to read these links you gave and try to understand them better. Seriously thank you so much for your support.