Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c++ > #10028 > unrolled thread

Factors Inhibiting Reproducability Of Simulation Results

Back to article view | Back to comp.lang.c++

Contents

  Factors Inhibiting Reproducability Of Simulation Results Chris Gordon-Smith <use.address@my.homepage> - 2011-09-10 14:26 +0000
    Re: Factors Inhibiting Reproducability Of Simulation Results "Paul" <pchristor@yahoo.co.uk> - 2011-09-10 17:04 +0100
    Re: Factors Inhibiting Reproducability Of Simulation Results Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-11 20:41 +0000
      Re: Factors Inhibiting Reproducability Of Simulation Results Miles Bader <miles@gnu.org> - 2011-09-12 10:02 +0900

#10028 — Factors Inhibiting Reproducability Of Simulation Results

I just managed to get my artificial chemistry simulation producing the 
same results when I run it twice with the same parameters. Perhaps some  
members of the group will be interested in the two factors that led to 
differing results:

1)   My graphics library (GTKMM2) calling rand() at random times between 
the calls made by my code
2)   My code storing pointers in an std::set, and then iterating over the 
set. The ordering is dependent on the memory locations of the dynamically 
allocated objects to which the pointers point.

Chris Gordon-Smith
www.simsoup.info

[toc] | [next] | [standalone]

#10034

"Chris Gordon-Smith" <use.address@my.homepage> wrote in message 
news:9d1acbF38fU2@mid.individual.net...
>I just managed to get my artificial chemistry simulation producing the
> same results when I run it twice with the same parameters. Perhaps some
> members of the group will be interested in the two factors that led to
> differing results:
>
> 1)   My graphics library (GTKMM2) calling rand() at random times between
> the calls made by my code
> 2)   My code storing pointers in an std::set, and then iterating over the
> set. The ordering is dependent on the memory locations of the dynamically
> allocated objects to which the pointers point.
>
Congrats on reaching that milestone in your project, it looks like an 
interesting one.
Thanks for the info. :) 


--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

[toc] | [prev] | [next] | [standalone]

#10050

On Sat, 2011-09-10, Chris Gordon-Smith wrote:
> I just managed to get my artificial chemistry simulation producing the 
> same results when I run it twice with the same parameters. Perhaps some  
> members of the group will be interested in the two factors that led to 
> differing results:
>
> 1)   My graphics library (GTKMM2) calling rand() at random times between 
> the calls made by my code

Aargh!  But in a sense that's just another example of the brokenness
of rand(). You usually want a PRNG where you keep the state manually.
I assume the TR1 random number stuff can do that.

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .     .
\X/     snipabacken.se>   O  o   .

[toc] | [prev] | [next] | [standalone]

#10052

Jorgen Grahn <grahn+nntp@snipabacken.se> writes:
>> 1)   My graphics library (GTKMM2) calling rand() at random times between 
>> the calls made by my code
>
> Aargh!  But in a sense that's just another example of the brokenness
> of rand(). You usually want a PRNG where you keep the state manually.
> I assume the TR1 random number stuff can do that.

The random state in both TR1 and C++11 is a part of the generator
object, so ... yeah.  [Of course it would be super duper surprising if
this wasn't true!]

-Miles

-- 
`There are more things in heaven and earth, Horatio,
 Than are dreamt of in your philosophy.'

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.c++

csiph-web