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Symmetric matrix element repositioning

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And Meng
And Meng 2017-1-19
评论： Xuekun Meng 2017-1-20
Hi,
I have a symmetric matrix. I need to reposition the desired diagonal elements and their corresponding elements to the low/right side.
In the following code, the desired diagonal element is 7 and 8. Their diagonal element will be placed at the lower right side of the matrix, e.g.Y(7,7) will be placed at Ynew(8,8). As well as their relevant element, e.g. Y(1,7) will be placed at Ynew(1,8). Is there any way that I can do it more efficiently?
n=9;
%random symmetric matrix
Y=magic(n);
Y=(Y+Y')/2;
% Yrr
Yrr=[Y(7,7) Y(7,8);Y(8,7) Y(8,8)];
% Ytr
Ytr=[Y([1 2 3 4 5 6 9],7) Y([1 2 3 4 5 6 9],8)];
% Ytt
Ytt=[Y([1 2 3 4 5 6 9],[1 2 3 4 5 6 9])];
% Ytr
Yrt=Ytr.';
% new symmetric matrix
Ynew=[Ytt Ytr;Yrt Yrr];
Any advice would be much appreciated. Thanks for reading.

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回答（1 个）

Matt J
Matt J 2017-1-19
编辑：Matt J 2017-1-19
I think this is what you want,
perm=[1 2 3 4 5 6 9 7 8];
Ynew=Y(perm,perm);

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