[ View Thread ] [ Post Response ] [ Return to Index ] [ Read Prev Msg ] [ Read Next Msg ]

BGonline.org Forums

Backgammon Position --- there's more to the story!

Posted By: Timothy Chow
Date: Monday, 2 March 2015, at 5:15 p.m.

In Response To: Backgammon Position (Stick)

It turns out that the Jacoby rule makes a significant difference.

As you can see from the rollouts below, the equity of the safe play 8/6 is not very sensitive to the Jacoby rule. Furthermore, if we examine the rollout statistics (not shown here), we find that they are very similar in both cases. Sure, both players end up winning the occasional undoubled gammon if there is no Jacoby rule, but it's rare enough that it doesn't make an appreciable difference.

However, the rollout statistics differ rather dramatically after the banana split. Without Jacoby, White ultimately wins an undoubled G/BG over 10% of the time, and cashes a single point about 21% of the time. On the other hand, if the Jacoby rule is in force, White still doesn't have a double from the bar, and so ends up cashing a single point a whopping 39% of the time. All those pseudocubeless gammons are illusory; White collects more than one point only about 25% of the time, and that's including single wins with the cube turned.





White is Player 2

score: 0
pip: 123
Unlimited Game
Jacoby
pip: 160
score: 0

Blue is Player 1
XGID=--aBBBC-A---ba-a-c-cBAbbAA:0:0:1:52:0:0:1:0:10
Blue to play 52

1.Rollout1Bar/20 4/2* eq: -0.211
Player:
Opponent:		44.26% (G:16.67% B:0.94%)
55.74% (G:30.22% B:2.80%)		Conf.: ± 0.008 (-0.220...-0.203) - [100.0%]
Duration: 2 hours 33 minutes
2.Rollout2Bar/20 8/6eq: -0.270 (-0.058)
Player:
Opponent:		43.73% (G:14.40% B:0.66%)
56.27% (G:18.25% B:0.70%)		Conf.: ± 0.007 (-0.277...-0.263) - [0.0%]
Duration: 49 minutes 45 seconds
1 5184 Games rolled with Variance Reduction.
Rolled for both No double and Double
Dice Seed: 271828
First 3 moves: 3-ply, cube decisions: XG Roller+
Remaining moves: 3-ply, cube decisions: XG Roller

2 5184 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.19.208.pre-release
White is Player 2

score: 0
pip: 123
Unlimited Game
pip: 160
score: 0

Blue is Player 1
XGID=--aBBBC-A---ba-a-c-cBAbbAA:0:0:1:52:0:0:0:0:10
Blue to play 52

1.Rollout1Bar/20 8/6eq: -0.260
Player:
Opponent:		43.76% (G:14.63% B:0.67%)
56.24% (G:17.99% B:0.70%)		Conf.: ± 0.007 (-0.267...-0.253) - [98.4%]
Duration: 54 minutes 14 seconds
2.Rollout2Bar/20 4/2* eq: -0.272 (-0.012)
Player:
Opponent:		44.10% (G:16.94% B:0.99%)
55.90% (G:31.47% B:3.28%)		Conf.: ± 0.009 (-0.281...-0.263) - [1.6%]
Duration: 2 hours 21 minutes
1 5184 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

2 5184 Games rolled with Variance Reduction.
Rolled for both No double and Double
Dice Seed: 271828
First 3 moves: 3-ply, cube decisions: XG Roller+
Remaining moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.19.208.pre-release

Messages In This Thread

 

Post Response
Your Name:
Your E-Mail Address:
Subject:
Message:

If necessary, enter your password below:

Password:
 

 

[ View Thread ] [ Post Response ] [ Return to Index ] [ Read Prev Msg ] [ Read Next Msg ]

BGonline.org Forums is maintained by Stick with WebBBS 5.12.