From: Joel VanderWerf <vjoel@...>
Date: 2004-08-15T09:08:54+09:00
Subject: Re: Random variable library?

Charles Mills wrote:
> On Aug 14, 2004, at 4:12 PM, Robert Feldt wrote:
> 
>> Joel VanderWerf wrote:
>>> It's just that if you need arbitrarily many streams of numbers, then 
>>> you want to be able to instantiate more generators. Actually, I 
>>> suppose you could use Kernel#srand to switch between streams. That 
>>> would be slow, because the state vector has to be recreated each 
>>> time, but would save on the space needed for all those state vectors.
> 
> Could you explain this more?

It was a bad idea. After looking more closely at ruby's random.c, I 
don't think it's possible. I naively thought the value returned by 
#srand might be a new seed that encodes the current position in the 
sequence, but of course is does not, because there are 2^19937-1 
distinct positions. So you'd have to save and restore the whole state 
vector. It's better to follow Robert's suggestion to wrap that state in 
an object.