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Re: [Bug-gnubg] Strange bearoff analysis
From: |
Jim Segrave |
Subject: |
Re: [Bug-gnubg] Strange bearoff analysis |
Date: |
Thu, 12 Jun 2003 23:29:09 +0200 |
User-agent: |
Mutt/1.2.5.1i |
On Thu 12 Jun 2003 (19:12 +0000), Joern Thyssen wrote:
> On Thu, Jun 12, 2003 at 08:21:40PM +0200, Jim Segrave wrote
> >
> > Using gnubg (development tree) from June 4th, still with 0.13b weights.
> > I was analysing a match I played against it with 2 ply more or less
> > Supremo settings when this came up:
> >
> > (jes) set matchid UQnrAFAAKAAA
> > (jes) set board OwAAwCYAAAAAAA
> > GNU Backgammon Position ID: OwAAwCYAAAAAAA
> > Match ID : UQnrAFAAKAAA
> > +24-23-22-21-20-19------18-17-16-15-14-13-+ O: gnubg
> > OO | O O | | | 5 points
> > OO | O O | | |
> > OO | O | | |
> > OO | | | |
> > OO | | | |
> > | |BAR| |v 7 point match
> > XX | | | |
> > XX | | | |
> > XX | | | |
> > XX | X X | | | Rolled 62
> > XX | X X X | | | 5 points
> > +-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: jes (Cube: 2)
> >
> >
> >
> > Analysis and hints both say (this is the hint output, but the analysis
> > is identical in it's values)
> >
> > 1. Cubeful 0-ply 4/off Eq.: +0.906
> >
> > 0.953 0.000 0.000 - 0.047 0.000 0.000
> > 0-ply cubeful [expert]
> > 2. Cubeful 0-ply 4/off 2/off Eq.: -0.925 ( -1.831)
> > 0.037 0.000 0.000 - 0.963 0.000 0.000
> > 0-ply cubeful [expert]
> >
> > Now I simply cannot see how taking two men off is a -1.831 blunder. In
> > fact, there's one case where taking 2 men off matters - gnubg rolls
> > doubles and I follow with double 1's. If I have two pieces on both the 1
> > and 2 points, I will lose, if I have only 3 pieces, I will still win.
>
> I can't reproduce your results. I get:
>
> (jth) set evaluation chequerplay evaluation plies 0
> `eval' and `hint' chequerplay will use 0 ply evaluation.
> (jth) hint
> 1. Cubeful 0-ply 4/off 2/off Eq.: +0.516
> 0.758 0.000 0.000 - 0.242 0.000 0.000
> 0-ply cubeful [expert]
> 2. Cubeful 0-ply 4/off Eq.: +0.500 ( -0.016)
> 0.750 0.000 0.000 - 0.250 0.000 0.000
> 0-ply cubeful [expert]
>
> In both cases O has roughly 1/6*5/6 + 5/6*5/6*1/6 = 25% (approx), so
> this analysis looks right.
>
> Can you try setting up the two resulting positions with gnubg on roll,
> and post the output from "eval", please?
Hmm. On my home machine, I get the above sensible results. The odd
ones come from a copy installed at work. I'm wondering if my bearoff
database or weights file is corrupt in some way. I had a copy built in
March which was installed in /usr/local/bin, where I first saw the
problem. I also had a recent copy which gave the same strange
results. The only thing they'd have in common are the databases in
/usr/local/share. I'll try to look at that tomorrow after work, but I
begin to think there's something very odd there.
--
Jim Segrave address@hidden