linear combination of vector and permutation

11 views (last 30 days)
Hi, i' m developing a program where I find myself with this problem that I couldn't solve nem with combntns(v,k) or with nchoosek .
Anyone here to help me?
Let A=[-1,1] and B=3
I need to find all possible combinations taking from B to B vector element A ( It can be with repetition of the vector element )
I have done it manually, but I need it automatically, or a Matlab function does it.
Let A and B the output of this function has to be:
Out=[-1,-1,-1;
-1,-1, 1
-1, 1,-1
-1, 1, 1
1,-1,-1
1,-1, 1
1, 1,-1
1, 1, 1],

Accepted Answer

Torsten
Torsten on 3 Oct 2022
values = [-1 1]; %// data
k = 3; %// data
n = numel(values); %// number of values
combs = values(dec2base(0:n^k-1,n)-'0'+1) %// generate all tuples
combs = 8×3
-1 -1 -1 -1 -1 1 -1 1 -1 -1 1 1 1 -1 -1 1 -1 1 1 1 -1 1 1 1
  2 Comments
Matt J
Matt J on 4 Oct 2022
Edited: Matt J on 4 Oct 2022
This approach is rather slow, if that matters...
values = -2:2; %// data
k = 9;
timeit(@()version1(values,k))
ans = 0.5780
timeit(@()version2(values,k))
ans = 0.0763
function version1(values,k)
n = numel(values); %// number of values
combs = values(dec2base(0:n^k-1,n)-'0'+1); %// generate all tuples
end
function version2(A,B)
[Out{1:B}]=ndgrid(A);
Out=reshape( cat(B+1,Out{:}),[],B);
end

Sign in to comment.

More Answers (2)

Matt J
Matt J on 3 Oct 2022
Edited: Matt J on 3 Oct 2022
One way:
A=[-1,1];B=3;
[Out{1:B}]=ndgrid(A);
Out=reshape( cat(B+1,Out{:}),[],B)
Out = 8×3
-1 -1 -1 1 -1 -1 -1 1 -1 1 1 -1 -1 -1 1 1 -1 1 -1 1 1 1 1 1

James Tursa
James Tursa on 4 Oct 2022
Edited: James Tursa on 4 Oct 2022
Another way very similar to Torsten's method, limited to two desired values:
n = 3;
2*(dec2bin(0:2^n-1)-'0')-1
ans = 8×3
-1 -1 -1 -1 -1 1 -1 1 -1 -1 1 1 1 -1 -1 1 -1 1 1 1 -1 1 1 1

Categories

Find more on Creating and Concatenating Matrices in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by