From: Eero Saynatkari <ruby-forum-reg@...>
Date: 2006-01-25T05:35:29+09:00
Subject: Re: problems with standard rand functions

Matthew Moss wrote:
> hist = Hash.new(0)
> 1_000_000.times do |i|
>     hist[rand(6)] += 1
> end
> 
> print hist.map { |k,v| "#{k}:#{v}\n" }.sort.join
> 
> 
> My output:
> 
> 0:166636
> 1:166867
> 2:166866
> 3:166923
> 4:166572
> 5:166136
> 
> Seems pretty uniform to me...
> As I recall (and someone else might know better), Ruby uses the
> Mersenne Twister which is pretty darn random. I haven't seen the Ruby
> source to know how they're presenting it (ie, how they map to a range
> of 0-5, for instance)

It is MT, indeed, but apparently the amount of bits actually
used from the randomization is limited which slightly reduces
the randomness. http://eigenclass.org has some further info.


E


-- 
Posted via http://www.ruby-forum.com/.