[Bug-gnubg] Bug: Double/Beaver

[Christopher D. Yep]

Windows XP, GUI version
Version 0.14-devel 1.1282 030818 (build Aug 19 2003)

gnubg misinterprets the following evaluation:

    GNU Backgammon  Position ID: 27ZCFADbtgEDQA
                    Match ID   : cAkAAAAAAAAA
    +24-23-22-21-20-19------18-17-16-15-14-13-+  O: gnubg
    | O  O  O  O  O  O |   | O           O  X |  0 points
    | O  O  O  O  O    |   |                X |
    |                  |   |                  |
    |                  |   |                  |
    |                  |   |                  |
    |                  |BAR|                  |v (Cube: 1)
    |                  |   |                  |
    |                  |   |                  |
    |                  |   |                  |
    | X  X  X  X  X  X |   |                  |  On roll
    | X  X  X  X  X  X | X |          O  O    |  0 points
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: Chris

Cube analysis
2-ply cubeless equity  -0.038
   38.3%  28.2%   6.2% -  61.7%  14.7%   0.0%
Cubeful equities:
1. Double, take         -0.236
2. Double, pass         +1.000  ( +1.236)
3. No double            -0.389  ( -0.153)
Proper cube action: Double, beaver

[Jacoby rule used above]
Correct cube action, based on the above numbers is actually 
no-double/beaver.  Double/beaver is worth -.472 to X which is worse than 
the -.389 he can get from holding the cube.

Note: As an aside, my rollouts of the position are showing that the 
position *may* (with only low statistical significance so far) actually be 
a correct double/beaver, with double/take around -.18 or -.19 (so 
double/take/beaver around -.36 or -.38).  (However this isn't relevant to 
the bug report.)

Chris