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.

Answer 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();

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