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Re: [Bug-gnubg] Strange bearoff analysis


From: Joern Thyssen
Subject: Re: [Bug-gnubg] Strange bearoff analysis
Date: Thu, 12 Jun 2003 19:12:54 +0000
User-agent: Mutt/1.4.1i

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?

Jørn




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