Symmetric matrix element repositioning

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.

Answer 1

[Matt J]

I think this is what you want,

perm=[1 2 3 4 5 6 9 7 8];

Ynew=Y(perm,perm);

[Xuekun Meng]

Got it! Thank you Matt!