reshuffle a symmetric matrix

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Muhammad Shafique
Muhammad Shafique 2011-6-13
Hi all, I have a large symmetric matrix (600*600)and need to reshuffle the elements randomly while keeping the matrix symmetric.
Could anyone help? I shall be grateful.
Regards, Shafique

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Andrei Bobrov
Andrei Bobrov 2011-6-13
1.
sz = size(A);
B = zeros(sz);
vtl = nonzeros(tril(reshape(1:numel(A),sz)));
B(tril(true(sz))) = A(vtl( randperm(length(vtl))));
B = B + tril(B,-1).';
2. More variant - don't modify main diagonal
sz = size(A);
B = diag(diag(A));
vtl = nonzeros(tril(reshape(1:numel(A),sz),-1));
B(tril(true(sz),-1)) = A(vtl( randperm(length(vtl))));
B = B + tril(B,-1).';
3. OR main diagonal - zeros (modify last row of the previous cod)
B = B + tril(B,-1).'
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Muhammad Shafique
Muhammad Shafique 2011-6-13
Hi Andrei. I needed to reshuffle the elements only within a triangle but excluding the diagonal. The variant you added does exactly that. Thanks a lot.

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