MATLAB: What is the maximum number of random integers generated by randseed before the number s are repeated

random number generator

I am using a random number generator for a gaussian noise generator in Simulink. However, I am not seeing any errors even after 10^9 bits being compared, when my calculations indicate that I should be seeing an error after 10^8 bits. I wonder if the random number generation is being repeated when such large number of bits are being used…

Best Answer

If you use the default Mersenne twister generator, the period is 2^19936 - 1, according to this page:

http://www.mathworks.com/help/techdoc/ref/randstream.list.html

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MATLAB: Rand(‘seed’,1)

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

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