random matrix with fix summation

Question

fatema saba 2015-1-15

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编辑： Adam 2015-1-15

采纳的回答： Matt J

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.

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Answer 1

Matt J 2015-1-15

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编辑：Matt J 2015-1-15

在 MATLAB Online 中打开

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);

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fatema saba 2015-1-15

Thank you Matt and Adam. it is splendid

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Answer 2

Adam 2015-1-15

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编辑：Adam 2015-1-15

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.