random matrix with fix summation

Hello

please.

this is my simple code that create (3*3) random matrix that all elements are 0 or 1.

a=randi([0,1],[500,500])

but is there any way that I define the number of elements that are 1. for example number of elements that are 1 be 7000 or in other word summation of matrix "a" be 7000

Thank you.

Answer 1

[Matt J]

For older versions of MATLAB without the randperm(n,k) syntax enabled,

      n=500^2;
      m=7000;

      idx=randperm(n);
      z=[ones(1,m), zeros(1,n-m)];

      a=reshape(z(idx),500,500);

[fatema saba]

Thank you Matt and Adam. it is splendid

Answer 2

[Adam]

You can just create 7000 random indices instead and place the 1s at those indices

e.g. if you have a [500,500] matrix you have 250000 indices so create 7000 random indices from 1 to 250000 and then just assign 1s to all those indices of a 500 x 500 matrix.

[Mohammad Abouali]

just change "... so create 70 random indices ..." to "... so create 7000 random indices ..."

[Matt J]

+1. This is really the way to go with a current MATLAB version.