POV-Ray : Newsgroups : povray.general : Bug in pseudo random? (gif 716b+) : Re: Bug in pseudo random? (gif 716b+) Server Time
12 Aug 2024 13:19:12 EDT (-0400)
  Re: Bug in pseudo random? (gif 716b+)  
From: Remco de Korte
Date: 2 Feb 1999 11:43:15
Message: <36B72941.78392E6D@xs4all.nl>
It happens with every series of seeds with regular intervals.
I tried it for instance with 1000,2000,3000 which gave a similar result. Then I
tried it with 1000,2001,3000 and lo and behold!
I gues this has something to do with the way seed() works but I wouldn't know
anything about that.
What I don't understand is why you should declare more then one seeds.
Isn't one enough? Anyway, look what happens when you use only one seed. I did
;-)
I guess this isn't really a bug, just a way to uncover that randomness in a
computer is often pseudo (as you mentioned).

Regards,

Remco


Spider wrote:
> 
> Well, I was playing around in pov, using rand() and seed() functions
> when I found this little effect after using it a bit.
> 
> The original idea was to ues the Superpatch in a few aspects(place a lot
> of sphres and use bouded_by from a text object, and thus get text made
> out of bubbles, generally.) when this effetc appeared, I made some
> changes, and switched to normal pov to see if it was still there. Sure
> it was.
> 
> Well, this is the code for the scene :
> 
> camera { location<0,0,-10> look_at<0,0,0> }
> light_source { <-50,150,-50> color rgb 1 }
> light_source { <+50,150,-50> color rgb 1 }
> 
> union {
>   #local Min = <0,-0.0286, 0>+0.1;
>   #local Max = <10,1.6721,4.6715>-0.1;
>   #local S = <seed(1), seed(2), seed(3)>;
>   #local R = seed(4);
>   #local N = 0;
>   #while(N<10000)
>     sphere {
>       Min+(<rand(S.x),rand(S.y),rand(S.z)>*Max)
>       (rand(R)*0.07)+0.03
>     }
>     #local N=N+1;
>   #end
>   translate -5*x
>   pigment {colour rgb 1 }
>   finish {ambient .8}
> }
> At first I thought it was the #local S = <seed(1), seed(2), seed(3)>;
> line that was in error, but no. This worked with other numbers, so the
> error is in seed(1) seed(2) seed(3) generation.
> 
> I just wonder if there is a limitation in the seed() function causing it
> not to work with theese small numbers ???
> 
> If i used a a larger set of numbers, 666, 1999, 2010 3010 and so, it
> worked nicely, but not here.
> 
> Attached is a .gif of the image, 2 colours.
> I'm sorry about the image, but I thought it was small enough to be
> attached here. *smile*
> 
> //Spider
> 
>   --------------------------------------------------------------------------------
>  [Image]


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