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Rollout: Which bar? #5

Posted By: Timothy Chow
Date: Thursday, 17 April 2014, at 11:59 p.m.

In Response To: Which bar? #5 (Timothy Chow)

I should probably have mentioned this earlier, but better late than never: Walter Trice has an excellent article on Gammon Village entitled "Which Bar Point to Slot?" He makes a number of excellent observations. One that stuck in my mind was that being behind in the race often shades the decision towards slotting the 7pt, on the general principle that priming and/or playing for more contact are usually better than racing when you're behind in the race. This applies especially when you already have a high anchor and are therefore not in danger of getting trapped.

In the position at hand, we see that these general principles can lead you to play 13/7 even in the face of a double shot. (Note that 8/2 sneaks in again as the "no cigar" play.)





White is Player 2

score: 0
pip: 156
Unlimited Game
pip: 171
score: 0

Blue is Player 1
XGID=---a-aE-C---dD---d-eB----A:0:0:1:61:0:0:0:0:10
Blue to play 61

1.Rollout1Bar/24 13/7eq: -0.102
Player:
Opponent:
47.10% (G:13.07% B:0.45%)
52.90% (G:13.03% B:0.53%)
Conf.: 0.008 (-0.110...-0.094) - [100.0%]
Duration: 2 hours 04 minutes
2.Rollout1Bar/24 8/2eq: -0.124 (-0.022)
Player:
Opponent:
46.29% (G:11.68% B:0.34%)
53.71% (G:11.39% B:0.47%)
Conf.: 0.007 (-0.131...-0.117) - [0.0%]
Duration: 1 hour 48 minutes
3.Rollout2Bar/18eq: -0.150 (-0.048)
Player:
Opponent:
45.95% (G:9.17% B:0.23%)
54.05% (G:9.74% B:0.40%)
Conf.: 0.018 (-0.168...-0.133) - [0.0%]
Duration: 29 minutes 27 seconds
1 5184 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

2 1296 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10


Here is Igor's excellent suggested variant, illustrating the limits of this line of reasoning.





White is Player 2

score: 0
pip: 158
Unlimited Game
pip: 171
score: 0

Blue is Player 1
XGID=-a---aE-C---dD---d-eB----A:0:0:1:61:0:0:0:0:10
Blue to play 61

1.Rollout1Bar/18eq: -0.123
Player:
Opponent:
46.39% (G:8.85% B:0.31%)
53.61% (G:9.39% B:0.31%)
Conf.: 0.007 (-0.130...-0.116) - [98.1%]
Duration: 1 hour 59 minutes
2.Rollout1Bar/24 13/7eq: -0.133 (-0.010)
Player:
Opponent:
46.59% (G:11.23% B:0.38%)
53.41% (G:12.76% B:0.50%)
Conf.: 0.007 (-0.141...-0.126) - [1.9%]
Duration: 2 hours 07 minutes
1 5184 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10


As a bonus, here's another position from my files that I decided wasn't different enough to warrant a separate post.





White is Player 2

score: 0
pip: 161
Unlimited Game
pip: 173
score: 0

Blue is Player 1
XGID=----bAD-C---eD---c-eA---B-:0:0:1:64:0:0:0:0:10
Blue to play 64

1.Rollout124/20 13/7eq: -0.017
Player:
Opponent:
49.34% (G:11.88% B:0.39%)
50.66% (G:11.43% B:0.46%)
Conf.: 0.014 (-0.032...-0.003) - [100.0%]
Duration: 32 minutes 25 seconds
2.Rollout124/20 24/18eq: -0.093 (-0.075)
Player:
Opponent:
47.67% (G:9.26% B:0.36%)
52.33% (G:10.51% B:0.36%)
Conf.: 0.013 (-0.106...-0.079) - [0.0%]
Duration: 32 minutes 12 seconds
3.Rollout124/20 8/2eq: -0.097 (-0.079)
Player:
Opponent:
47.46% (G:11.49% B:0.39%)
52.54% (G:12.44% B:0.58%)
Conf.: 0.015 (-0.112...-0.082) - [0.0%]
Duration: 30 minutes 45 seconds
1 1296 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10

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