[Bug-gnubg] Bug in gammon price calculations using inverted asymmetric MET's

[Maik Stiebler]

Hi folks,

I tried to do some analysis using the Jacobs-Trice 100 MET and got a 
surprising result.

Upon investigation, I found that in non-variance-reduced, non-truncated 
rollouts, the rollout match equity given by gnubg did not match my hand 
calculation based on the cube statistics info. I suspect that on 
inversion of the match equity table, the gammon values don't get 
inversed. This seems to influence not only rollouts, but also evals. I 
will refrain from an awkward description of my debugging process until 
you tell me this is not a known bug and just give you a symptomatic 
example (sorry for the German, I hope it's easy enough to follow):

In the following positions, the 6-away player is supposed to be the 
shark. In the first setup, I can use JT-100 MWC directly, in the second, 
mirrored setup, I have to invert, which I do via menu Analyze->Match 
equity table. The analyses should be the same, but they aren't. This is 
from Version GNU Backgammon 0.91-dev-mingw 20130315 with the 
experimental NN, but the bug also manifested in a version of gnubg from 
2011.


 GNU Backgammon  Position ID: ZtsNAGDbzQ0AIA
                 Match ID   : MIHyABAAIAAE
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     O: gnubg1
 |                O |   | O     O  O  O  O |     1 Punkt
 |                O |   | O     O  O  O  O |     Wurf 54
 |                  |   | O        O       |
 |                  |   |                  |
 |                  |   |                  |
^|                  |BAR|                  |     7-Punkte-Match (Doppler: 1)
 |                  |   |                  |
 |                  |   |                  |
 |                X |   |                  |
 |             X  X | X | X  X  X     X    |
 |             X  X | X | X  X  X     X  O |     4 Punkt
 +13-14-15-16-17-18------19-20-21-22-23-24-+     X: gnubg2


Doppler-Analyse
2-ply MWC ohne Doppler  31.92% (Money:  +0.190)
  0.512 0.219 0.001 - 0.488 0.054 0.000
Cubeful equities:
1. Kein Doppel          32.57%
2. Doppel, Aufgabe      39.30%  (  6.73%)
3. Doppel, Annahme      31.85%  ( -0.72%)
Proper cube action: Kein Doppel, Annahme (9.7%)




 GNU Backgammon  Position ID: ZtsNAGDbzQ0AIA
                 Match ID   : cAngAEAACAAE
 +13-14-15-16-17-18------19-20-21-22-23-24-+     O: gnubg1
 |             O  O | O | O  O  O     O  X |     4 Punkt
 |             O  O | O | O  O  O     O    |
 |                O |   |                  |
 |                  |   |                  |
 |                  |   |                  |
v|                  |BAR|                  |     7-Punkte-Match (Doppler: 1)
 |                  |   |                  |
 |                  |   |                  |
 |                  |   | X        X       |
 |                X |   | X     X  X  X  X |     Am Wurf
 |                X |   | X     X  X  X  X |     1 Punkt
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     X: gnubg2


Doppler-Analyse
2-ply MWC ohne Doppler  32.34% (Money:  +0.190)
  0.512 0.219 0.001 - 0.488 0.054 0.000
Cubeful equities:
1. Kein Doppel          32.71%
2. Doppel, Aufgabe      39.30%  (  6.59%)
3. Doppel, Annahme      32.38%  ( -0.33%)
Proper cube action: Kein Doppel, Annahme (4.7%)



Cheers,

Maik