Re: [vox-tech] Re: random number in C

[eric nelson <en77@MAPSpacbell.net>]

Not an expert on this, but I think the kernel adds entropy, from keypresses 
and other things considered 'random', so results are not entirely 
deterministic.  You can look at the code in the random driver, random.c in 
/usr/src/linux/drivers/char for some background.
After all, random is used to generate keys used in security, and those 
hackers are pretty smart, and repeatable random sequences would allow certain 
attacks.

On Tuesday 02 April 2002 06:26 pm, you wrote:
> > Date: Tue, 2 Apr 2002 14:47:20 -0800
> > [CODE SNIPPED]
>
> So this is when the program is seeded to /dev/random:
> >    p@satan% ./ising2-jfunc 4.0
> >    T: 4.0e+00  beta: 2.500e-01  trials: 1000  N: 10  M: 10  seed:
> > 3497451914 Average Energy: -1.273893
> >    Average magnetization: 0.425220
> >    Average |magnetization|: 0.531100
> >    Average magnetic susceptibility: 34.746600
>
> And this is when the code is seeded to 1:
> >    T: 4.0e+00  beta: 2.500e-01  trials: 1000  N: 10  M: 10  seed:
> > 3497451914 Average Energy: -1.326747
> >    Average magnetization: 0.495320
> >    Average |magnetization|: 0.495320
> >    Average magnetic susceptibility: 28.645040
>
> And you've established that if you run it repeatedly you keep getting the 
same thing:
> >    T: 4.0e+00  beta: 2.500e-01  trials: 1000  N: 10  M: 10  seed:
> > 3497451914 Average Energy: -1.326747
> >    Average magnetization: 0.495320
> >    Average |magnetization|: 0.495320
> >    Average magnetic susceptibility: 28.645040
>
> BUT four hours earlier:
> > Date: Tue, 2 Apr 2002 10:05:34 -0800
>
> This is when you seed it to /dev/random:
> > 	T: 4.0e+00  beta: 2.500e-01  trials: 1000000
> >	N: 10  M: 10  seed: 208006379
> >	Average Energy: -1.057143
> >	Average magnetization: 0.002008
> >	Average |magnetization|: 0.251765
> >	Average magnetic susceptibility: 8.948655
>
> And this is when you seed it to 1:
> >	T: 4.0e+00  beta: 2.500e-01  trials: 1000000
> >	N: 10  M: 10  seed: 208006379
> >	Average Energy: -1.050182
> >	Average magnetization: 0.030723
> >	Average |magnetization|: 0.246092
> >	Average magnetic susceptibility: 8.692724
>
> Why did 4 hours of time change the results when you seed it to 1 ???
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