rand('seed',1)

hi there, can anyone explain me the different between using 'rand('seed',1)' inside the loop and outside the loop? Assuming I generate some random number inside the loop.

Ta,Rak

Answer 1

[Jan]

Seeding the random number generator means initializing it to a certain status. Seeding inside the loop means, that all "random" numbers created inside the loop will be the same in each iteration:

for i = 1:3
  rand('seed', 1);
  disp(rand);
end

Result: 0.51291 0.51291 0.51291

This is not very useful. Seeding RAND outside the loop allows you to reproduce the results:

for j = 1:2
  rand('seed', 1);
  for i = 1:3
    disp(rand);
  end
end

Now you get two series of 3 different numbers:

 0.51291  0.46048  0.3504  0.51291  0.46048  0.3504

[Ricky]

so assumingly if I put it outside the loop, then everytime I execute the programe, I will get the same random number. Is that correct?

[Ricky]

got it now, thanks alot

[Peter Perkins]

Unless you are using an extraordinarily old (from the early 1990's) version of MATLAB, you should not be using rand('seed',1) at all. It most likely does not do what you think it does. If you are using R2011a or newer, see this:

<http://www.mathworks.com/help/techdoc/math/bs1qb_i.html>

Otherwise, see the documentation in whatever version you are using.

Answer 2

[ZHU CHENG-CHIH]

rng(seed)

rng(seed,generator)

s = rng

https://www.mathworks.com/help/matlab/ref/rng.html