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T & T 61: Rollout and Commentary

Posted By: Paul Weaver
Date: Wednesday, 15 February 2012, at 1:25 a.m.

In Response To: Reopened case: Tough and tricky 61 (higonefive)

If you read my profile, you will learn that I am an exceptionally humble and modest person. I therefore will not claim that I would have found and made the best play over the board. To find the best play, I consulted XG and got the XG++ eval for a lot of plays to diminish the chance that I would overlook the best play. My rollout result is posted below. More commentary follows:





White is Player 2

score: 0
pip: 105
Unlimited Game
Jacoby Beaver
pip: 131
score: 0

Blue is Player 1
XGID=--ABBBBbB------A-bcdABaba-:0:0:1:61:0:0:3:0:10
Blue to play 61

1.Rollout120/13eq: -0.240
Player:
Opponent:
43.27% (G:9.32% B:0.40%)
56.73% (G:8.05% B:0.15%)
Conf.: 0.011 (-0.250...-0.229) - [100.0%]
Duration: 2 minutes 51 seconds
2.Rollout120/14 3/2eq: -0.286 (-0.046)
Player:
Opponent:
41.57% (G:7.83% B:0.28%)
58.43% (G:6.18% B:0.10%)
Conf.: 0.011 (-0.296...-0.275) - [0.0%]
Duration: 2 minutes 52 seconds
3.Rollout220/14 15/14eq: -0.332 (-0.093)
Player:
Opponent:
40.50% (G:7.36% B:0.25%)
59.50% (G:5.82% B:0.08%)
Conf.: 0.014 (-0.346...-0.318) - [0.0%]
Duration: 1 minute 29 seconds
4.Rollout220/14 6/5eq: -0.332 (-0.093)
Player:
Opponent:
40.08% (G:7.29% B:0.23%)
59.92% (G:7.17% B:0.17%)
Conf.: 0.013 (-0.345...-0.319) - [0.0%]
Duration: 1 minute 24 seconds
5.Rollout215/14 8/2eq: -0.350 (-0.110)
Player:
Opponent:
40.59% (G:8.43% B:0.27%)
59.41% (G:9.06% B:0.14%)
Conf.: 0.014 (-0.364...-0.336) - [0.0%]
Duration: 1 minute 13 seconds
1 1296 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

2 648 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.01

Here's what the position looks like after Blue has made the best play, 20/13. More of my humble BS can be found below the diagram.





White is Player 2

score: 0
pip: 105
Unlimited Game
Jacoby Beaver
pip: 124
score: 0

Blue is Player 1
XGID=--ABBBBbB----A-A-bcd-Baba-:0:0:-1:00:0:0:3:0:10
White on roll, cube action?

eXtreme Gammon Version: 2.01

The first thing to consider in this position is the pip count. After the play, Blue trails by 19 pips. Blue needs to try to get a shot. White's best number is 66, and 20/13 gives Blue a shot after White's 66.

The midpoint is the point on the board that Blue would most like to own, and he has the chance to slot it while White has two blots in her board. He will probably have roughly 16 numbers next turn that cover the 13pt or make the 12pt (62 52 42 32 22 21 53 31 11).

If Blue is able to make the midpoint, not only will it help him get a shot, but it may also force White to waste pips deep in her board, allowing Blue to close some ground in the EPC (effective pip count), whatever that is. Even if Blue is not able to cover the 13pt, he may be able to maintain favorable contact in the position by keeping his blot there next turn while he covers his 2pt with a 6.

Now that you are familiar with the concept, you will encounter this scenario many times in the future: Blue trails in the race while White has blots deep in her home board. To negate the joker effect of some of White's doublets, you can place a Blue blot six or fewer pips from White's outfield point, even if you have little or no chance of covering it next turn. This play is especially effective at DMP and Gammon Go, scores at which losing a gammon costs you nothing.

It took me an hour to write these few paragraphs, and I will not always be able to do this in the future when you encounter a position you do not understand. You can email me and take a lesson, if you like. Although I am very modest, I am also very honest, so I will divulge the fact that I am an outstanding teacher, with more than thirty years of experience teaching backgammon. Last year one of my students improved his PR from 9 to 6 in a seven-month period. This is a claim that my student would be happy to verify.

Hope this commentary is helpful to you. Hope Iancho and others will forgive me for the advertisement, but I figure I've earned the right to present it.

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