How to distribute 100 ones in 100 by 100 matrix randomly in all posibilities

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Amit
Amit 2012-2-10
编辑： Image Analyst 2013-10-15
I want to make binary matrix, and distribute 100 ones in it, randomly in all possibilities.
What command I have to use plz help.

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采纳的回答

Wayne King
Wayne King 2012-2-10
indices = randi(1e4,100,1);
x = zeros(100,100);
x(indices) = 1;
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Walter Roberson
Walter Roberson 2012-2-16
There are 65208469245472575695415972927215718683781335425416743372210247172869206520770178988927510291340552990847853030615947098118282371982392705479271195296127415562705948429404753632271959046657595132854990606768967505457396473467998111950929802400 different matrices
which is about 6.5 * 10^241
It *is* possible to list them all, if you do not need to store them, but it would take a *very* long time to do the listing.
Amit
Amit 2012-2-16
What command I have to use that gives me exactly 100 ones randomly in 100 by 100 binary matrix

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更多回答（2 个）

Jan
Jan 2012-2-16
You can add a test to Wayne's method to check if the indices are unique:
go = true;
while go
indices = randi(1e4,100,1);
go = numel(unique(inidices)) == 100;
% Or:
% go = all(diff(sort(indices)));
end
x = zeros(100,100);
x(indices) = 1;
Another approach, which works since Matlab 2011b:
indices = randperm(1e4, 100);
If this is time-critical, you can try FEX: Shuffle.
Walter Roberson
Walter Roberson 2012-2-16
idx = randperm(100*100);
x = false(100,100); %you said you wanted a _binary_ matrix
x(idx(1:100)) = true;
If you have a new enough version of MATLAB,
idx = randperm(100*100,100);
x = false(100,100);
x(idx) = true;

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