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About Preallocating for speed

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Hari il 14 Feb 2017
Risposto: Alexandra Harkai il 14 Feb 2017
What is a more efficient way of writing this code?
NumberedOD = [];
for a = 1:(N-1)
for b = (a+1) :N
NumberedOD = [NumberedOD;a, b];
My aim is to get a list of numbers like this:
1 2
1 3
1 N
2 3
2 4
  1 Commento
Adam il 14 Feb 2017
Modificato: Adam il 14 Feb 2017
Purely from a pre-allocation perspective you can work out the number of elements there will be in that matrix - it is fixed and calculable so you can preallocated a zeros matrix. I'm sure there is a quicker vectorized way to do it though, I just don't have time to think about it myself right now. I'm sure someone will suggest one though.

Accedi per commentare.

Risposta accettata

Alexandra Harkai
Alexandra Harkai il 14 Feb 2017
NumberedOD = nchoosek(1:N, 2);

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