Extracting the sub-matrix

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...

Answer 1

[David Hill]

A = [1 2 3; 4 5 6; 7 8 9];
B=A(1:2,2:3);
E=blkdiag(zeros(2),A);

[cikalekli]

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.

Answer 2

[James Tursa]

You might benefit from going through the onramp tutorials found here:

https://matlabacademy.mathworks.com/details/matlab-onramp/gettingstarted

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:

https://www.mathworks.com/help/matlab/ref/zeros.html?searchHighlight=zeros&s_tid=srchtitle_zeros_1

[cikalekli]

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.