Re: [Bug-gnubg] Strange bearoff analysis

[Nis Jorgensen]

--On 12 June 2003 20:21 +0200 Jim Segrave <address@hidden> 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.

All correct.

Furthermore, it seems like both evaluations are wrong - since you will 
clearly loose in approximately 5/6  * (1 - 5/6^2) (you roll no double, your 
opponents rolls at least one double in two rolls) ~ 25% of the games.

My gnubg is a little outdated, and I don't get this result.

I assume this is reproducible - since I can see you are entering the 
match+position ID's manually.

Did you restart gnubg (to clear the cache)?

What does an eval of the two resulting positions tell you?

--
Nis Jorgensen
Amsterdam