# Generating a design matrix with for loops

4 views (last 30 days)
Anders Larsen on 22 Sep 2021
Answered: Yongjian Feng on 22 Sep 2021
Hello everyone, I am trying to create a design matrix for simulation puposes using for loops with vectors, but I am struggeling with what to write in the inner most loop. The numbers are arbitrary, to get the hang of it, I need to be able to scale it up for vectors with 100 values or more.
The code looks as follows:
a = (1: 3)';
b = (4: 6)';
c = (7: 9)';
for i = a
for j = b
for k = c
e(i, j k)=...
end
end
end
The result should be a matrix with all posibilities of combinations of the 3 vectors and should look like:
e = 1 4 7
1 4 8
1 4 9
1 5 7
1 5 8
1 5 9
1 6 7
1 6 8
1 6 9
2 4 7...
Hope you guys can help, thanks!

Yongjian Feng on 22 Sep 2021
Something like this?
a = (1: 3);
b = (4: 6);
c = (7: 9);
idx = 1;
for i = a
for j = b
for k = c
e(idx, 1) = i;
e(idx, 2) = j;
e(idx, 3) = k;
idx = idx + 1;
end
end
end
e

R2021a

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