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Cube sent - extreme effect on winning chances - why?

Posted By: Tenland
Date: Sunday, 11 November 2012, at 4:19 a.m.

I'm going thru positions in the backgammon encyclopedia, rolling many of them out in XG to make sure I'm learning the right things.

I encountered a strange one. According to XG roller ++, this is a pretty close no double, but according to the rollout, doubling would be a mega blunder. A surprising result to me, given that rolling the prime one pip forward (although very unlikely to occur on this roll) would imply a market loss, and that the no-double winning chances exceed 80 % (albeit with some gammons lost). However, the winning and gammon chances for the opponent would increase very radically after a double according to the rollout (much more slightly according to xg roller++).

Does anyone have an explanation? I'm puzzled...





White is Player 2

score: 0
pip: 54
Unlimited Game
pip: 152
score: 0

Blue is Player 1
XGID=a-----BBBBBB-A---A--Acccb-:0:0:1:00:0:0:0:0:10
Blue on roll, cube action?

Analyzed in Rollout No double Double/Take
Player Winning Chances: 80,44% (G:0,00% B:0,00%) 68,26% (G:0,00% B:0,00%)
Opponent Winning Chances: 19,56% (G:6,60% B:0,05%) 31,74% (G:14,85% B:0,10%)
Cubeless Equities +0,542 +0,431
Cubeful Equities
No double:+0,796±0,046 (+0,750..+0,843)
Double/Take:+0,302 (-0,495)±0,089 (+0,213..+0,390)
Double/Pass:+1,000 (+0,204)
Best Cube action: No double / Take
Percentage of wrong pass needed to make the double decision right: 41,5%
Rollout details
1296 Games rolled with Variance Reduction.
Dice Seed: 2
Moves: 3-ply, cube decisions: XG Roller
Double Decision confidence:100,0%
Take Decision confidence:100,0%
Duration: 38 minutes 13 seconds

eXtreme Gammon Version: 2.03

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