Generate combinations with scaleable code

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Howard Wilton
Howard Wilton 2022-12-29
评论： Howard Wilton 2022-12-29
I have a tight piece of code which generates a 16x4 matrix which essentially is 16 vectors with 4 elements each and i want all the combinations where the vector elements are -1 or 1
[a1,a2,a3,a4] = ndgrid([1 -1],[1 -1],[1 -1],[1 -1]);
a_all_combos = [a1(:),a2(:),a3(:),a4(:)]
clear a1 a2 a3 a4
The code yields the following output:
1 1 1 1
-1 1 1 1
1 -1 1 1
-1 -1 1 1
1 1 -1 1
-1 1 -1 1
1 -1 -1 1
-1 -1 -1 1
1 1 1 -1
-1 1 1 -1
1 -1 1 -1
-1 -1 1 -1
1 1 -1 -1
-1 1 -1 -1
1 -1 -1 -1
-1 -1 -1 -1
However, this code does not scale-up nicely if I want nine-element vectors, yielding a x9 matrix.
Would welcome any suggestions on how to do this concisely.

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采纳的回答

the cyclist
the cyclist 2022-12-29
Ran in:
There happens to be a quite obfuscated way to do this:
n = 9;
a_all_combos = 2*(dec2bin(0:2^n-1) - '0') - 1
a_all_combos = 512×9
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 1 -1 -1 -1 -1 -1 -1 -1 1 -1 -1 -1 -1 -1 -1 -1 -1 1 1 -1 -1 -1 -1 -1 -1 1 -1 -1 -1 -1 -1 -1 -1 -1 1 -1 1 -1 -1 -1 -1 -1 -1 1 1 -1 -1 -1 -1 -1 -1 -1 1 1 1 -1 -1 -1 -1 -1 1 -1 -1 -1 -1 -1 -1 -1 -1 1 -1 -1 1

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