reshuffle a symmetric matrix

2011 6 13
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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

3 个投票

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
Dear Andrei,
Many thanks for taking the trouble to help. Your solution works great but it would be perfect if the values of main diagonal could be kept from getting into triangles.
Your help is immensely appreciated.
Regards,
Shafique
Andrei Bobrov
Andrei Bobrov 2011-6-13
Hi! Muhhammad! Do you want to modify the elements of the matrix without affecting the main diagonal?
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.
Andrei Bobrov
Andrei Bobrov 2011-6-13
Muhhammad! Point 2.

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