Thus spake Eric Hodel <[EMAIL PROTECTED]>: > David Schultz ([EMAIL PROTECTED]) wrote: > > > Rather than me showing you more semi-meaningful numbers from > > Marsaglia's tests, why don't you look at the following sequence, > > which I get by taking the lowest four bits of the 201st number in > > the rand() sequence for seeds of (0, 1, 2, ...). > > > > f c 9 6 2 f c 8 5 2 e b 8 4 1 e b 7 4 1 d a 7 3 0 d 9 6 3 > f c 9 6 2 f c 8 5 2 e b 8 4 1 e b 7 4 1 d a 7 3 0 d 9 6 3 > f c 9 6 2 f c 8 5 2 e b 8 4 1 e a 7 4 1 d a 7 3 0 d 9 6 3 > f c 9 6 2 f c 8 5 2 e b 8 4 1 e a 7 4 1 d a 7 3 0 d 9 6 3 > f c 9 5 2 f c 8 5 2 e b 8 4 1 e a 7 4 1 d a 7 3 0 d 9 6 3 > f c 9 5 2 f c 8 5 2 e b 8 4 1 e a 7 4 0 d a 7 3 0 d 9 6 3 > f c 9 5 2 f c 8 5 2 e b 8 4 1 e a 7 4 0 d a 7 3 0 d 9 6 3 > f c 9 5 2 f b 8 5 2 e b 8 4 1 e a 7 4 0 d a 7 3 0 d 9 6 3 > f c 9 5 2 f b 8 5 2 e b 8 4 1 e a 7 4 0 d a 7 3 0 d 9 6 3 > f c 9 5 2 f b 8 5 2 e b 8 4 1 e a 7 4 0 d a 6 3 0 d 9 6 3 > f c 9 5 2 f b 8 5 2 e b 8 4 1 e a 7 4 0 d a 6 3 0 d 9 6 3 > f > > > Notice that 'f c 9' repeats in regular intervals and is always > > followed by a 5 or 6. There is a similar pattern for 'e a 7'. I > > think this pretty much demonstrates that the algorithm isn't good > > enough to generate high-quality randomness with respect to > > different seed values. I'm not suggesting that it absolutely must > > be replaced, since most rand() implementations aren't very good in > > the first place, but I'm pointing out that to do a good job of > > fixing it once and for all is harder than you might think. > > A littele modification shows just how similar these sequences are :)
Yeah, I saw the periodicity when I asked less(1) to select particular subsequences. I guess it's a bit more impressive when you select the right modulus. ;-) To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-current" in the body of the message
