- http://www.mathworks.com/matlabcentral/fileexchange/26242-vchoosekro as fast C-Mex function,
- http://www.mathworks.com/matlabcentral/fileexchange/24325-combinator-combinations-and-permutations as general M-functions for combinations/permutations with or without repetitions and ordering.
Matrix with all possibilities
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Dear all,
I would like to create a matrix with all possibilities, such as the following: [1 1 1; 1 1 0; 1 0 1; 0 1 1; 1 0 0; 0 1 0; 0 0 1; 0 0 0]
I have tried to use nchoosek([0 0 0 1 1 1],3) but this function fails in ordering. Furthermore I tried C = npermutek([ones(1,3) zeros(1,3)],3); D = unique(C,'rows'), but this one gives a out of memory error for larger vectors (8 instead of 3). For this function see: http://www.mathworks.com/matlabcentral/fileexchange/11462-npermutek/
How to create such a matrix?
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Answers (4)
Jan
on 28 Dec 2012
Searching the FileExchange for the terms "combinations" and "permutations" helps to find:
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Azzi Abdelmalek
on 28 Dec 2012
Edited: Azzi Abdelmalek
on 28 Dec 2012
out=[]
n=3
for k=1:n
s=[ones(2^(n-k ),1) ;zeros(2^(n-k ),1)]
s=repmat(s,2^(k-1),1)
out=[out s]
end
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Roger Stafford
on 29 Dec 2012
Here is a variation on Azzi's solution:
A = ones(2^n,n);
p = 1;
for k = 0:n-1
A(p+1:2*p,n-k:n) = [zeros(p,1),A(1:p,n-k+1:n)];
p = 2*p;
end
To count up instead of down, swap the 'ones' and 'zeros' calls.
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Antonio Adaldo
on 20 Jan 2021
The matrix that you want is the same as the matrix containing the binary digits of the numbers from zero to seven. For example: "0 0 0" is zero, "0 0 1" is one, "0 1 0" is two, etc.
If you have Communications Toolbox installed, MATLAB offers the function "de2bi" to produce that matrix. For example:
de2bi(0:7)
ans =
0 0 0
1 0 0
0 1 0
1 1 0
0 0 1
1 0 1
0 1 1
1 1 1
Documentation for "de2bi" is found here: https://www.mathworks.com/help/comm/ref/de2bi.html
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