Re: [Bug-gnubg] Bug: 1-sided database

[Joern Thyssen]

On Wed, Sep 24, 2003 at 08:59:10AM -0400, Christopher D. Yep wrote
> Win XP
> No-panels build, 030923 (1.1395)
> (Problem also occurs in older versions of gnubg)
> 
>     GNU Backgammon  Position ID: +L4PAAAGAAAAAA
>                     Match ID   : cAkAAAAAAAAA
>     +24-23-22-21-20-19------18-17-16-15-14-13-+  O: gnubg
>     |          O  O  O |   |                  |  0 points
>     |          O  O  O |   |                  |
>     |          O  O  O |   |                  |
>     |          O  O  O |   |                  |
>     |          O  O  O |   |                  |
>     |                  |BAR|                  |v (Cube: 1)
>  XX |                  |   |                  |
>  XX |                  |   |                  |
> XXX |                  |   |                  |
> XXX |    X             |   |                  |  On roll
> XXX |    X             |   |                  |  0 points
>     +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: Chris
> 
> Cube analysis
> 2-ply cubeless equity  +1.737654
>   100.0000%  73.7654%   0.0000% -   0.0000%   0.0000%   0.0000%
> Cubeful equities:
> 1. Double, pass         +1.000000
> 2. Double, take         +3.475309  ( +2.475309)
> 3. No double            +1.000000  ( +0.000000)
> Proper cube action: Double, pass
> 
> (0-ply and 1-ply evals. give 73.7657% and 73.7655% gammons, which is fine 
> since I don't expect the bearoff database to store 6-digit precision.)
> 
> I assume this is just a problem with the bearoff database (i.e. the 1-sided 
> database) and not the version of gnubg.  I'm just using the standard 
> 1-sided and 2-sided bearoff databases that most users use (I haven't had 
> time to create larger ones yet).  The problem appears to occur when player 
> 1 (player not on roll) has 15 checkers, all on the 4-6 points (e.g. if you 
> move a checker from the 4 point to the 3 point, this bug goes away).
> 
> Correct numbers are 72.2222% gammons, 

hmm, I get:

26/36 + 10/36 * 2/36 = 956/1296 = 73.7654321% gammons

Which is the same as the database. Did you notice that 2-1 loses gammon
for O?

Jørn

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