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Asked by C Zeng on 22 May 2012

Hello, I want to write a code to try every combination of a N-dimentional vector(with entry 0 or 1 or 2). For example, if N=3, all combinations are (0,0,0)(0,0,1)...(2,2,2) and there are 3^N=27.

One brutal way is for commands: for i=0:2->for j=... but I have to write N these for commands, which is not wise. I wonder it there a fast and smart way to try all combinations?

Thanks a lot!

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Answer by Sean de Wolski on 22 May 2012

Accepted answer

[xx yy zz] = ndgrid(0:2); [xx(:) yy(:) zz(:)]

**Generalized** (fixed)

n = 4 [C{1:n}] = ndgrid(0:2); for ii = n:-1:1 M(:,ii) = C{ii}(:); end

Show 6 older comments

C Zeng on 22 May 2012

Can I write like this:

For i=1 to 3^N

[a1,a2,a3,a4]=M(i,:);

then define function and solve the value;

compare and find the maximizer;

end;

It works well I think.

C Zeng on 24 May 2012

Hi, the code does not work and try all combinations:

n = 4

[C{1:n}] = ndgrid(0:2);

reshape(vertcat(C{:}),[],n)

In deed, it has many same combinations.

Sean de Wolski on 25 May 2012

This is true. I messed up on thinking reshape() would account for the order of the cells being stacked. It did not, see update.

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