How can I generate a matrix with exact number of ones(with respect to random distribution) ?

I need to generate a random matrix(large one) with the exact number of ones? thanks in advance :)

[Roberto]

Please explain... What's the exact number of ones? and please give an example of the desired result!

[mahdi]

I mean for example I need a 5x5 matrix(symmetric) with exact 10 ones but in a random place. (overall number of ones will be 20 because of symmetrically).

Answer 1

[Matt J]

 A=zeros(N);

 A(randperm(numel(A),nOnes))=1; %nOnes is desired number of ones

[mahdi]

Thanks man it is good but I forgot to say something. In addition I need a zero diagonal symmetric matrix which point to the edge between a nodes in graphs. For example I need a triu(A,1), where the number of ones in this matrix is predefined and stand in random places.

[Jos (10584)]

Over 8 years ago I wrote a wrapper function for this cal http://www.mathworks.com/matlabcentral/fileexchange/10924-ntrue/content/ntrue.m ent/ntrue.m

[Matt J]

Same principle, just randomize over the indices of the upper triangle,

 A=zeros(N);
 idx=find(triu(ones(size(A)),1));
 idx=idx(randperm(numel(idx),nOnes));