Extracting the sub-matrix

Question

cikalekli 2021-10-27

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1573158-extracting-the-sub-matrix

编辑： cikalekli 2021-10-28

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 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...

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

David Hill 2021-10-27

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1573158-extracting-the-sub-matrix#answer_818108

在 MATLAB Online 中打开

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

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

cikalekli 2021-10-28

编辑：cikalekli 2021-10-28

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.

请先登录，再进行评论。

Answer 2

James Tursa 2021-10-27

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1573158-extracting-the-sub-matrix#answer_818103

编辑：James Tursa 2021-10-27

在 MATLAB Online 中打开

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

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

cikalekli 2021-10-28

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.

请先登录，再进行评论。