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Rollout and some analysis: Gammon go, critical decision

Posted By: Timothy Chow
Date: Sunday, 20 May 2012, at 10:44 p.m.

In Response To: Gammon go, critical decision (Timothy Chow)

Two competing rules of thumb come into play here: "When ahead in the race, race" and "Don't volunteer a shot in a mutual holding game."

The racing play is 20/9 and the blot-free play is 8/3 8/2. I decided that 8/3 8/2 was too ugly and that the score should shade me towards the bold 20/9. The rollout says that 20/9 is a big mistake. But see the variant below to see that the decision is more delicate than the raw equities might suggest.





White is Player 2

score: 6
pip: 124
7 point match
pip: 117
score: 4

Blue is Player 1
XGID=-A-BbCB-BC-----c-c-cB-bb--:1:-1:1:65:4:6:0:7:10
Blue to play 65

1.Rollout18/3 8/2eq: +0.233
Player:
Opponent:		 54.24% (G:7.40% B:0.48%)
45.76% (G:7.12% B:0.18%)		Conf: ± 0.007 (+0.226...+0.240)
Duration: 1 hour 48 minutes
2.Rollout120/9eq: +0.156 (-0.077)
Player:
Opponent:		 50.93% (G:6.85% B:0.52%)
49.07% (G:9.20% B:0.47%)		Conf: ± 0.007 (+0.149...+0.163)
Duration: 2 hours 06 minutes
1 1296 Games rolled with Variance Reduction.
Dice Seed: 2
Moves and cube decisions: 3 ply

eXtreme Gammon Version: 1.21, MET: Rockwell-Kazaross

Truncated rollout of variant:





White is Player 2

score: 6
pip: 124
7 point match
pip: 113
score: 4

Blue is Player 1
XGID=-B-BbBB-BC-----c-c-cB-bb--:1:-1:1:65:4:6:0:7:10
Blue to play 65

1.Rollout120/9eq: +0.247
Player:
Opponent:		 56.48% (G:5.87% B:0.12%)
43.52% (G:6.99% B:0.16%)		Conf: ± 0.005 (+0.242...+0.252)
Duration: 2 minutes 30 seconds
2.Rollout18/3 8/2eq: +0.237 (-0.010)
Player:
Opponent:		 55.25% (G:6.59% B:0.13%)
44.75% (G:7.95% B:0.23%)		Conf: ± 0.006 (+0.231...+0.243)
Duration: 2 minutes 39 seconds
1 Truncated at 7 moves using 3 ply.
648 Games rolled with Variance Reduction.
Dice Seed: 2
First 2 moves and cube decisions: 3 ply
Remaining moves: 2 ply, cube decisions: 3 ply

eXtreme Gammon Version: 1.21, MET: Rockwell-Kazaross

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