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[Bug-gnubg] Use of Two-Sided DB in matches


From: Neil Robins
Subject: [Bug-gnubg] Use of Two-Sided DB in matches
Date: Sat, 5 Sep 2009 05:56:10 +0100

It has occurred to me that in a position like this previously discussed one:
 
http://www.bgonline.org/forums/webbbs_config.pl?noframes;read=47213
 
 GNU Backgammon  Position ID: gwEAQCoAAAAAAA
                 Match ID   : cAmgACAAGAAA
 +13-14-15-16-17-18------19-20-21-22-23-24-+     O: gnubg
 |                  |   | O              O | OOO 2 points
 |                  |   | O              O | OO 
 |                  |   |                  | OO 
 |                  |   |                  | OO 
 |                  |   |                  | OO
v|                  |BAR|                  |     5 point match (Cube: 1)
 |                  |   |                  | XX
 |                  |   |                  | XX 
 |                  |   |                  | XX 
 |                  |   |                  | XX  On roll
 |                  |   | X  X  X     X    | XXX 3 points
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     X: Neil
 
The MWC chance following Double/Take is directly obtainable from the Two-Sided Database. Doubling produces an automatic redouble so the situation is in effect cubeless.
The DB gives Cubeless equity: +0.4707.
 
Therefore where x = MWC/100
x - (1 - x) =  0.4707
x = 0.73535
MWC = 73.535% after Double/Take
This is in very close agreement with the XG rollout.
 
Is there any reason GNU analysis cannot use this exact method?
 
I feel I still get complete nonsense here with the latest windows build.
 
7-ply cubeless MWC  67.39% (Money:  +0.387)
  0.694 0.000 0.000 - 0.306 0.000 0.000
Cubeful equities:
1. No double            70.06%
2. Double, pass         75.08%  (  5.01%)
3. Double, take         69.36%  ( -0.70%)
Proper cube action: No double, take (12.3%)
 
It also sure worries me to get rollout results that are quite certainly wrong.
 
Rollout details:
Centered 1-cube:
  0.728 0.000 0.000 - 0.272 0.000 0.000 CL  68.25% CF  70.66%
 [0.000 0.000 0.000 - 0.000 0.000 0.000 CL   0.00% CF   0.00%]
Player gnubg owns 2-cube:
  0.732 0.000 0.000 - 0.268 0.000 0.000 CL  81.71% CF  73.16%
 [0.000 0.000 0.000 - 0.000 0.000 0.000 CL   0.00% CF   0.00%]
Full cubeful rollout with var.redn.
129600 games, Mersenne Twister dice gen. with seed 865036646 and quasi-random dice
Play:  2-ply cubeful prune [world class]
keep the first 0 0-ply moves and up to 8 more moves within equity 0.12
Skip pruning for 1-ply moves.
Cube: 2-ply cubeful prune [world class]

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