[Bug-gnubg] Strange bearoff analysis

[Jim Segrave]

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.

-- 
Jim Segrave           address@hidden