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Re: [Bug-gnubg] Re: Race database and bearoff DB

From: Joern Thyssen
Subject: Re: [Bug-gnubg] Re: Race database and bearoff DB
Date: Tue, 1 Oct 2002 07:21:45 +0000
User-agent: Mutt/1.4i

On Tue, Oct 01, 2002 at 09:04:29AM +0200, Øystein O Johansen wrote
> Hi,
> Yes, I really agree with Joseph here. Can anyone provide any race positions
> where it misplays the positions? If this is a problem I think we should
> rather make Joseph's osr (*) algorithm available for gnubg. 

I have ported Joseph's OSR code to a local copy of gnubg, but I never
got around testing it.

> This alogorithm
> is very good, and it's not that slow. Basically, what it does is that it
> rolls out each side independently to get a roll distribution for each side.
> These two roll distributions are combined to give the cubeless winning
> chance.
> I have still not seen this routine make any errors in the race evaluation,
> though I have seen the race network make some bad evaluations in tricky
> positions. (I must admit I don't believe this bad evaluations by the race
> network makes the overall strength of gnubg much worse. I really think the
> overall strength still lays in improving the crashed network.)

It's fairly simple to extend the current one sided bear-off database up
to at least 10 points. It takes around 6 hours to generate on my 1GHz
box: 3268760 positions ( x 32 values x 2 bytes/value = 209MB). I'll also
look into extending the exact bear-off database and have it included
cubeful money game values.

Maybe it's possible to make another OS bear-off DB that goes even
further if we restrict it to, say, 10 chequers per point. 

These one-sided bear-off databases can very easily be combined with the
OSR code giving fast and reliable evaluations. Joseph also has an
algorithm for converting OSR evaluations to cubeful equities.

I'll see if I can get it to work.

Unfortunately people would have to generate their own databases since I
don't think we have the necesary band-width/web-space for such files.
Alternatively, we could sell them on CDs from gnubg.org :-)


Joern Thyssen, PhD
Vendsysselgade 3, 3., DK-9000 Aalborg, Denmark
+45 9813 2791 (private) / +45 2818 0183 (mobile) / +45 9633 7036 (work)
Note: new mobile number!

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