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RE: [Bug-gnubg] Analysis of race rollouts

From: David Montgomery
Subject: RE: [Bug-gnubg] Analysis of race rollouts
Date: Thu, 31 Oct 2002 10:11:03 -0800

> The power (and limitation) of the OSR is that it is one sided, 
> i.e. plays each 
> side independently, so that it has no notion if it needs to make 
> desperation 
> plays or not. Even if it did, I doubt it is possible to find 
> those moves cheaply.
> -Joseph

It's true that one-sided racing databases that just have the mean 
rolls to bear off can't make desperation plays.

But one-sided racing databases with the probability distribution
of rolls to bear off *can and do* make desperation plays, if you
choose plays by convolving the two distributions.

I believe that it will be very rare for a rollout done in this
manner to differ noticably from the exact cpw from a two-sided 

If a normal approximation is used, you can still get desperation
plays.  Basically the trailer chooses high-variance plays, even 
those which might have a slightly higher mean rolls to bear off.  
This must be less accurate than using the actual single-sided 
distribution, but for positions far from the end of the race, it 
probably doesn't give up much.


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