How to find the indices within blocks and sort the blocks thereafter?

Question

Xiaohan Du 2018-6-18

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https://ww2.mathworks.cn/matlabcentral/answers/406136-how-to-find-the-indices-within-blocks-and-sort-the-blocks-thereafter

回答： Prajit T R 2018-6-21

采纳的回答： Prajit T R

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Hi all,

Say I have the following matrix contains 15 elements:

       M =
           6     2     9
           7     2     3
           9     3    10
          10     9     4
           6     3     2

and the following coordinates which represent 4 blocks:

K>> block{:}
ans =
    -1    -1
     0    -1
     0     0
    -1     0
ans =
    -1     0
     0     0
     0     1
    -1     1
ans =
     0    -1
     1    -1
     1     0
     0     0
ans =
     0     0
     1     0
     1     1
     0     1

Now I'd like to separate the elements in M into 4 blocks using information in 'block' as the following picture:

So the result should be:

K>> mBlock{:}
ans =
   2
   2
   3
ans =
   9
   3
  10
ans =
   3
   9
   3
ans =
  10
   4
   2

How can I do it? Thanks a lot!

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Bob Thompson 2018-6-18

What is the logic behind the block creation? Will they always be the same (four quadrants)?

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Answer 1

Prajit T R 2018-6-21

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在 MATLAB Online 中打开

Hi

Here's a code which will work for a size m x n matrix provided that m and n are odd values. To incorporate even values, you have to make some minor tweaks, that's all. You can divide a matrix into 4 quadrants as per your requirement using the following:

M =[6 2 9; 7 2 3; 9 3 10; 10 9 4; 6 3 2]; %The input matrix that needs to be divided
m=5; %number of rows
n=3; %number of coloumns
a=floor(m+1/2); %finding the midline of the rows
b=floor(n+1/2); %finding the midline of the coloumns
q1=M(1:a,1:b) %quadrant-1
q2=M(1:a,2:n) %quadrant-2
q3=M(a:m,1:b) %quadrant-3
q4=M(a:m,2:n) %quadrant-4