Using rng(Random Number Generator) for a specific function in MATLAB

Question

Suppose that we have two m-files :

First one is a function :

function XX = ofx()

for i=1:2
    aa = randperm(5)
end

end

Second one :

rng(0);
for i=1:2
   xx = randperm(3)
end

ofx();

You can see that when we run second code again and again the outputs is the same. Why we have these same outputs in both randperm? I only want same random generator for xx random numbers not ofx function. How can i do that? How can i only use rng for a specific function?

Thanks.

Peter · Accepted Answer · 2014-09-05 18:30:46Z

1

The problem is not the function. The problem is that you want a repeatable sequence of numbers for some uses of the RNG, and non-repeating for other uses. To do this, you need to carefully control the state of the RNG. I would reverse the way you think about them, and have your repeatable case save, then restore the state.

rng_state = rng(0);     % Save (pseudo-) random state of RNG, then seed with known value
for i=1:2
    xx = randperm(3);
end
rng(rng_state);         % Restore saved state so other RNG calls work as expected

ofx();

answered Sep 5, 2014 at 18:30

Peter

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2 Comments

Eghbal Over a year ago

Thank you for answer. Can we reset rng to default values likes we didn't use it? Can we return MATLAB random generator to default not previous condition rng_state?

Peter Over a year ago

Running help rng shows this possibility: rng('default'). You could also use rng('shuffle') to "re-randomize" the rng.

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