how to flip a general square matrix ( it could have even or odd number of rows/cols ) from it's center in matlab ?

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fatema hamodi 2019-1-15

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评论： fatema hamodi 2019-1-16

采纳的回答： Stephen23

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hi all

I have a general matrix , I want to flip the last half of it starting from it's center in matlab

To be clear ,I attach an image

I try the following

A=[1,2,3,4,5;6,7,8,9,10;11,12,13,14,15;16,17,18,19,20;21,22,23,24,25]
num_of_row=length(A(:,1))
if( mod(2,num_of_row)==0)
    k=M/2;
else
    k=(M-1)/2;
end
fliplr(A)

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Stephen23 2019-1-16

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https://ww2.mathworks.cn/matlabcentral/answers/439864-how-to-flip-a-general-square-matrix-it-could-have-even-or-odd-number-of-rows-cols-from-it-s-cen#answer_356614

>> M = [1,2,3,4,5;2,6,7,9,10;3,7,11,12,13;4,9,12,16,20;8,10,13,20,25]
M =
    1    2    3    4    5
    2    6    7    9   10
    3    7   11   12   13
    4    9   12   16   20
    8   10   13   20   25
>> X = [5,4,1,2,3]; 
>> Z = M(X(end:-1:1),X)
Z =
   13   12    3    7   11
   10    9    2    6    7
    5    4    1    2    3
   20   16    4    9   12
   25   20    8   10   13

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Stephen23 2019-1-16

编辑：Stephen23 2019-1-16

"but why this way doesn't work in general "

What I showed does work in general: any valid set of indices can be used to move around the rows and columns of any matrix, exactly as I showed in my answer.

For some unknown reason you tried to use the matrix data itself as indices, which is totally unrelated to anything in my answer, and totally unrelated to anything in your question.

"Subscript indices must either be real positive integers or logicals."

That error message tells us that the indes values that you used are not valid indices for that matrix. If X is supposed to be a set of indices, why are you creating this by concatenting a (whatever that is) with the first row of the matrixc data?:

  X = [a,row_1(1:mid-1)];
% ^                         supposed to be indices, for M(X(end:-1:1),X).
%      ^                    what is this?
%        ^^^^^              why are you using matrix data as indices?

Unless you expect the first row to contain indices, this does not make sense. You certainly did not explain this in your question or any of your images. Please explain what you are trying to achieve.

fatema hamodi 2019-1-16