Re: [Bug-gnubg] Parallel dice streams

[Michael Petch]

Christian may wish to chime in, but I’ll tell you what I am aware of – and I may not fully understand what you are asking. There is a match seed (options/settings/dice/seed) that can be set and it is associated with the dice as you are playing the match. Normally the dice seed is reset between new matches (To get the same dice for each match see this article: http://lists.gnu.org/archive/html/bug-gnubg/2009-08/msg00239.html ). Each game should get different dice (Unless you manually reset the seed during the match yourself). If you do a rollout, there is a separate seed associated with rollouts thus a separate random stream (This seed is set on the rollout page) that should not interfere with the random number stream for the dice being produced for the game.

Now, as for rollouts, rollouts are not entirely deterministic. If you do a rollout with the same seeds the results will most likely be different if you are using a multithreaded version where the Threads are set to something higher than 1. From my experience if you use more than 1 thread, you can do a rollout with a given seed and get one result - If you rollout it out again with the same seed you might get a different result. If this is a problem, then setting thread count to 1 should solve it.

Michael

On 23/08/09 10:37 PM, "bob koca" <address@hidden> wrote:

>  I want to compare the effects of score on a doubling decision for a checker position. So I want to rollout
> 1296 times at two different scores. To hopefully lower variablity for the differenceI used the same seed for each rollout.  Does it mean that the dice will be the same for each game 
> (until one ends of course)? So the 1rst, 2nd, 3rd, ... games have the same dice. Or does it all get messed up as soon
> as one game for one rollout takes longer than its counterpart in the other? I thought it should be the former but a short testing of it 
> (7 rollouts for each with seeds 100, 200, ... 700) does not show a  strong positive correlation like I would have expected.