I have a matrix. I can't figure out how to subtract row 1 from row 5, row 2 from row 6, row 3 from row 7, row 4 from row 8. My code isn't working.

Question

Hossam Amin 2021-9-18

0
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https://ww2.mathworks.cn/matlabcentral/answers/1456104-i-have-a-matrix-i-can-t-figure-out-how-to-subtract-row-1-from-row-5-row-2-from-row-6-row-3-from-r

评论： Hossam Amin 2021-9-18

A = [2.5 3.5 7.5 8.5 ;...  %1
     9.5 5.5 6.5 1.5;...   %2 
     2.5 3.5 7.5 8.5; ...  %3
     9.5 5.5 6.5 1.5;...   %4
     2.5 3.5 7.5 8.5; ...  %5
     9.5 5.5 6.5 1.5;...   %6
     2.5 3.5 7.5 8.5;...   %7
     9.5 5.5 6.5 1.5];     %8
for i=1:size(A,1)
    for j=1:size(A,1)/2
         tmp(i,:) = A(i,:)-A(j,:)
    end
%   tmp(i,:) = A(i,:)-A(4+j,:)
end

My code is not working very well. I need a loop that can work for any matrix size.

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Answer 1

TADA 2021-9-18

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https://ww2.mathworks.cn/matlabcentral/answers/1456104-i-have-a-matrix-i-can-t-figure-out-how-to-subtract-row-1-from-row-5-row-2-from-row-6-row-3-from-r#answer_790424

在 MATLAB Online 中打开

if the functionality is to subtract the row in index n+4 from the row in index n

A = [2.5 3.5 7.5 8.5 ;...  %1
     9.5 5.5 6.5 1.5;...   %2 
     2.5 3.5 7.5 8.5; ...  %3
     9.5 5.5 6.5 1.5;...   %4
     2.5 3.5 7.5 8.5; ...  %5
     9.5 5.5 6.5 1.5;...   %6
     2.5 3.5 7.5 8.5;...   %7
     9.5 5.5 6.5 1.5];     %8
 
 subtractInterval = 4;
 tmp = A(1:end-subtractInterval, :) - A(subtractInterval+1:end, :)
 size(tmp)
 
 
 A = magic(10);
 tmp = A(1:end-subtractInterval, :) - A(subtractInterval+1:end, :)
 size(tmp)
 