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SNOWIE ROLLOUTS

Posted By: Matt Ryder
Date: Wednesday, 6 January 2010, at 9:49 p.m.

In Response To: SNOWIE ROLLOUTS (Ray Kershaw)

I'm not sure I fully understand Tim's position here, but I reiterate that it's always possible to derive the cubeless equity from the six probabilities, as these always describe cubeless outcomes.

Here's an example (from XG not Snowie, but I assure you the principle is exactly the same):

is Player 2

score: 0
pip: 55
1
Money session
pip: 69
score: 0

is Player 1
XGID=-BCCCC-------------e-ccabA:0:0:1:43:0:0:0:0:10
to play 43

1.XG Roller+Cannot moveeq: -1.000
Player:
Opponent:		 12.57% (G:0.00% B:0.00%)
87.43% (G:1.60% B:0.02%)

eXtreme Gammon Version: 1.11

Here we see a cubeful equity of -1 (which makes sense as black will turn the cube next turn and it's a clear pass). Note however the six listed probabilities belie this cubeful reality. They suggest that white still has a 12.57% win chance and that black has ancillary gammon (1.6%) and backgammon (0.02%) chances. That's because these numbers are cubeless estimates (and only make sense if the cube is dead).

Cubeless equity for white in this position may be calculated as:

(0.1257 - 0.8743) + (0 - 0.016) + (0 - 0.002) = -0.7666

Hope that clarifies things!

Matt.

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