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XG++ Eval & OTB thinking

Posted By: David Presser
Date: Thursday, 6 November 2014, at 6:50 a.m.

In Response To: Who gets this right over the board (Phil Simborg)

I was the player on roll and I Incorrectly doubled here. I will share my thinking OTB, which was flawed for not paying attention to a significant detail, but helped me learn and approach it better in future times:

My instinct was that this is a clear ND due to the score and my high doubling window for 1 roll position. Nonetheless, I wanted to be certain and decided to crunch the numbers. After calculating my win % {1-(22*26/36^2)} I was planing to find the equity under each scenario (D vs ND). When looking at the ND scenario I was thinking of the next roll after a miss. The cube on White's side is clear, and intuitively I thought it is a take. Then I stopped and thought that if I miss and there is a dbl/take cube action, I prefer to have the cube on 2 before I roll since I can only gain from it. I made a blunder in assuming that a miss results in a dbl/take cube action without giving it too much thought (if you know the ME or just have a sense for it you should know it is a clear pass). This flawed thinking convinced me to send the cube. I was actually "lucky" to have only a 0.036 error as it was a blunder in my solution and consequent conclusion.

I should have kept my hands dirty and compared the equities under each scenario. In fact, it is very close. It is so close that if you give White one fewer number that bears off, the position changes to a marginal dbl as can be seen below. In such positions sometimes you can find smooth shortcuts and sometimes there aren't. When using a shortcut to solve the problem, it is important to pay attention to the details and assumptions.

Btw, my one game rollout proved it to be a double :)





White is Player 2

score: 3
pip: 4
5 point match
pip: 8
score: 0

Blue is Player 1
XGID=---A-A-----------------b--:0:0:1:00:0:3:0:5:10
Blue on roll, cube action?

Analyzed in XG Roller++ No double Double/Take
Player Winning Chances: 55.52% (G:0.00% B:0.00%) 55.52% (G:0.00% B:0.00%)
Opponent Winning Chances: 44.48% (G:0.00% B:0.00%) 44.48% (G:0.00% B:0.00%)
Cubeless Equities +0.110 -0.259
Cubeful Equities
No double:-0.222
Double/Take:-0.259 (-0.036)
Double/Pass:+1.000 (+1.222)
Best Cube action: No double / Take
Percentage of wrong pass needed to make the double decision right: 2.8%

eXtreme Gammon Version: 2.10, MET: Kazaross XG2
White is Player 2

score: 3
pip: 5
5 point match
pip: 8
score: 0

Blue is Player 1
XGID=---A-A----------------aa--:0:0:1:00:0:3:0:5:10
Blue on roll, cube action?

Analyzed in XG Roller++ No double Double/Take
Player Winning Chances: 57.18% (G:0.00% B:0.00%) 57.18% (G:0.00% B:0.00%)
Opponent Winning Chances: 42.82% (G:0.00% B:0.00%) 42.82% (G:0.00% B:0.00%)
Cubeless Equities +0.144 -0.182
Cubeful Equities
No double:-0.222 (-0.041)
Double/Take:-0.182
Double/Pass:+1.000 (+1.182)
Best Cube action: Double / Take

eXtreme Gammon Version: 2.10, MET: Kazaross XG2

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