How to create symmetric zero and one matrix

Question

I need to create a 100*100 symmetric matrix that has random distribution of zeros and ones, but the diagonal should be all zeros, how can I do that?

randomatlabuser · Answer 1 · 2013-11-26T05:43:57.833

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This is one way to do it:

N = 100; % size of square matrix
p = 0.5; % probability of 0s
A = triu(rand(N)>p, 1); % matrix of 0s and 1s (upper triangular part)
A = A + A'; % now it is symmetric

edited Nov 26 '13 at 05:43

answered Nov 26 '13 at 04:56

randomatlabuser

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score 2 · Accepted Answer · edited May 23 '17 at 10:31

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You can use a uniform distribution to generate your random numbers:

n = 100;
a = round(rand(n,n));

Now set the diagonal entries to zero (as discussed here by Jonas):

a(logical(eye(size(a)))) = 0;

Symmetric component:

aSym = floor((a + a')/2);

Example for n = 5:

aSym =

     0     0     0     0     0
     0     0     1     0     1
     0     1     0     0     1
     0     0     0     0     0
     0     1     1     0     0

Edit: At randomatlabuser's suggestion, added line to calc the symmetric component of the matrix and eliminated loop to zero out entries on the diagonal

edited May 23 '17 at 10:31

Community

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answered Nov 26 '13 at 04:56

Bruce Dean

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Note that the current version returns a matrix that is not symmetric. Also, the loop can be avoided: `a(1:(n+1):end) = 0;` – randomatlabuser Nov 26 '13 at 05:34
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@randomatlabuser, yes thanks for your note on this, I had forgotten the symmetry requirement. I edited my answer to include that. – Bruce Dean Nov 26 '13 at 06:09
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@roybatty, thank you, if you like you can also remove the loop in your answer. – randomatlabuser Nov 26 '13 at 06:14
@randomatlabuser, thanks for your suggestion on the loop (see edit), keep up the great work! – Bruce Dean Nov 26 '13 at 06:27

How to create symmetric zero and one matrix

2 Answers2