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Rollouts

Posted By: Wolfgang
Date: Monday, 27 October 2014, at 6:49 p.m.

In Response To: A backgammon position (Wolfgang)

Thank you for your reasoning! Indeed, there is a huge QF due to my question and due to the simultaneous presentation. I overlooked that.
Position 2 is an original postion which occured when I played a match (unlimited session) with XG2. The other positions are variations of position 2. They were created "artificially".

Rollouts:

Position 1:




White is Player 2

score: 0
pip: 110
Unlimited Game
Jacoby Beaver
pip: 118
score: 0

Blue is Player 1
XGID=--aB--D-CC-AbB---b-ccb-b--:0:0:1:41:0:0:3:0:10
Blue to play 41

1.Rollout19/5 6/5eq: +0,459
Player:
Opponent:
62,91% (G:4,86% B:0,13%)
37,09% (G:5,55% B:0,09%)
Conf.: 0,006 (+0,453...+0,465) - [100,0%]
Duration: 14 minutes 27 seconds
2.Rollout111/7 8/7eq: +0,338 (-0,121)
Player:
Opponent:
59,03% (G:3,51% B:0,09%)
40,97% (G:4,56% B:0,06%)
Conf.: 0,006 (+0,332...+0,344) - [0,0%]
Duration: 15 minutes 53 seconds
1 2592 Games rolled with Variance Reduction.
Dice Seed: 7134413
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10

To me, this position is the easiest to solve. Making the golden 5-point uses the checkers very efficiently. The valuable 9-point doesn't have to be cleared in this context.

Position 2:




White is Player 2

score: 0
pip: 111
Unlimited Game
Jacoby Beaver
pip: 129
score: 0

Blue is Player 1
XGID=-a-B--C-CB-AbD---b-ccb-b--:0:0:1:41:0:0:3:0:10
Blue to play 41

1.Rollout111/7 8/7eq: +0,108
Player:
Opponent:
52,17% (G:4,17% B:0,12%)
47,83% (G:8,92% B:0,11%)
Conf.: 0,007 (+0,101...+0,116) - [100,0%]
Duration: 22 minutes 06 seconds
2.Rollout19/5 6/5eq: +0,022 (-0,087)
Player:
Opponent:
49,28% (G:4,26% B:0,13%)
50,72% (G:15,14% B:0,20%)
Conf.: 0,007 (+0,015...+0,028) - [0,0%]
Duration: 19 minutes 26 seconds
1 2592 Games rolled with Variance Reduction.
Dice Seed: 24754213
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10

This is the original position which occured in the match. I made the barpoint, and flagged this move using CRTL+F in order to analyze it afterwards, since I wasn't completely sure.
Yet, making the barpoint leaves no blots, maintains the 9-point, and results in a small 4-point prime which provides a probably good blocking structure.

Position 3:




White is Player 2

score: 0
pip: 110
Unlimited Game
Jacoby Beaver
pip: 129
score: 0

Blue is Player 1
XGID=--aB--C-CB-AbD---b-ccb-b--:0:0:1:41:0:0:3:0:10
Blue to play 41

1.Rollout19/5 6/5eq: +0,151
Player:
Opponent:
53,03% (G:4,80% B:0,16%)
46,97% (G:13,21% B:0,17%)
Conf.: 0,007 (+0,145...+0,158) - [100,0%]
Duration: 20 minutes 20 seconds
2.Rollout111/7 8/7eq: +0,120 (-0,032)
Player:
Opponent:
52,49% (G:3,96% B:0,12%)
47,51% (G:9,34% B:0,11%)
Conf.: 0,007 (+0,112...+0,127) - [0,0%]
Duration: 22 minutes 00 second
1 2592 Games rolled with Variance Reduction.
Dice Seed: 24754213
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10

This is a variation of position 2 insofar as White's backchecker stepped up one pip from the 24-point to the 23-point. Over the board, I would definitely make the barpoint for the same reasons as given in position 2. Yet, this is wrong, as the rollout indicates that making the 5-point is better. To be honest, I still do not understand it.
One reason for the 5-point might have something to do with the fact that Blue will have a stripped position which makes it more difficult to make the 5-point subsequently (same situation like in position 2). Moreover, to make the 5-point may be justified, since White has only a limited number of hits (52 and 54). I admit that this explanation is not very suitable.

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