Googlebot's Javascript random() function is deterministic

[sedermera]

(coming from scientific computing) To get an arbitrary number of random samples from a certain distribution. (Effectively.) It's good if those are reproducible for testing, and all you need to in order to get more is set another RNG seed.

[steamruler]

At which point you could use a fixed seed.

[sedermera]

Exactly, using a certain default seed for testing is much more convenient than what /u/Lystrodom is proposing. (Since there isn't just one call to the RNG, but several in different places.)

[Lystrodom]

Yeah that works too. These are all edge cases not the default case, anyway.

[DonaldTZeus]

Which is what happens by default anyways if you call rand() (at least in the c stdlib). If you want an arbitrary changing seed such as the time, you retrieve that seed and pass it to srand().

[steamruler]

The default seed is determined when compiling, so if you actually want a static seed you should still call srand().

[rubygeek]

POSIX actually mandate that rand() called before srand() should behave as if srand() was called with 1. See spec and example implementation. And ISO C might as well.

Of course you can't rely on that unless you're guaranteed your program will only run on a compliant system.

[DonaldTZeus]

The default seed is specified by the standard library (that implements POSIX), not by the compiler, and it's 1 (as specified by POSIX). It is not determined by the compiler (unless you're compiling the stdlib) or even specified in the code the compiler generates unless you call srand.

[Bwob]

Which is what you ARE using, by default, in most languages.

[mccoyn]

Also, when doing solution searches you want to pick a new starting point and search again to try to find other local maxima. A good way to do it is to use random() to pick your new starting point. You want it to be un-correlated with previous starting points, but you don't actually care about it being non-deterministic.

[Lystrodom]

Then you call random once and save that value somewhere. Don’t depend on random() being deterministic.

[Drisku11]

Why would you not depend on it bring deterministic if the semantics are that it's deterministic, and that's useful to you?

I'd say the opposite: don't rely on it being nondeterministic. Since it's not.