Paul Sanchez wrote:
> One problem which remains with using Ruby for discrete event simulation 
> is that the random number generator, although of good quality, is 
> implemented as a System method instead of as a class from which multiple 
> generator objects can be instantiated.  This seriously limits its use in 
> designed experiments.  That's the main reason why I haven't translated 
> any of my own work over from C or Java.

Not standard, but available:

http://raa.ruby-lang.org/search.rhtml?search=random