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Responding to David Presser

Posted By: Paul Weaver
Date: Saturday, 2 November 2013, at 5:18 p.m.

In Response To: Rollout Results and Comments (David Presser)

Thanks, David, for your question. Let's start by taking a look at the two positions below. On the left, Blue has a 41 to play from the opening position. On the right, White rolled an opening 32 or 41 and played 13/8. As you can see, this one seemingly small change swings Blue's play with 41 from splitting to slotting. In a prime-vs-prime position, you have more incentive to split or run a back checker when you lead in the race and more incentive to sit on your 24pt anchor when you trail. This same principle applies to early game positions where you are still anchored on the 24pt.

On the left, Blue leads in the race by 5 pips after the play. On the right, Blue is even in the count after the play. When Blue is far behind in the race, he has less to lose by getting hit. When Blue is ahead in the race, getting hit is more costly. Blue has more motivation to slot on the right than on the left because he no longer leads in the race after the play.

Also, Blue has less motivation to split 24/23 on the right because White has more material in the zone that can be used to attack.

With Blue to play 63 on the right, running (24/15) is now better than splitting (24/18 13/10). Not only 41 and 63, but Blue's 64 54 52 51 32 should probably be played differently on the right than on the left. The moral of the story is that you have to pay attention not only to White's structure, but also to her checker distribution.

 White is Player 2 score: 0 pip: 167 Unlimited GameJacoby Beaver pip: 167 score: 0 Blue is Player 1
XGID=-b----E-C---eE---c-e----B-:0:0:1:41:0:0:3:0:10
Blue to play 41

1.Book124/23 13/9eq: -0.005
 Player:Opponent: 49.62% (G:14.42% B:0.68%)50.38% (G:13.62% B:0.71%) Conf.: ± 0.003 (-0.008...-0.002) - [99.9%]
2.Book213/9 6/5eq: -0.012 (-0.007)
 Player:Opponent: 49.72% (G:14.16% B:0.66%)50.28% (G:14.53% B:1.01%) Conf.: ± 0.003 (-0.015...-0.009) - [0.1%]
1 Generated by Neil Kazaross on 11/24/2009 using eXtreme Gammon 1.04
41670 Games rolled with Variance Reduction.
Dice Seed: 1
Moves and cube decisions: 4-ply

2 Generated by Neil Kazaross on 11/24/2009 using eXtreme Gammon 1.04
41669 Games rolled with Variance Reduction.
Dice Seed: 1
Moves and cube decisions: 4-ply

eXtreme Gammon Version: 2.10

 White is Player 2 score: 0 pip: 162 Unlimited GameJacoby Beaver pip: 167 score: 0 Blue is Player 1
XGID=-b----E-C---dE---d-e----B-:0:0:1:41:0:0:3:0:10
Blue to play 41

1.Rollout113/9 6/5eq: -0.072
 Player:Opponent: 48.71% (G:13.68% B:0.58%)51.29% (G:15.69% B:1.06%) Conf.: ± 0.007 (-0.079...-0.066) - [100.0%]Duration: 1 hour 01 minute
2.Rollout124/23 13/9eq: -0.095 (-0.022)
 Player:Opponent: 47.75% (G:13.40% B:0.59%)52.25% (G:15.07% B:0.70%) Conf.: ± 0.006 (-0.101...-0.089) - [0.0%]Duration: 54 minutes 55 seconds
1 10368 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10

Advancing both back checkers (24/21 24/22) is the best play on the left, giving Blue an equity of -0.079. On the right, this same play has an equity of -0.221. White's additional checker in the zone makes it much more dangerous for Blue to play 24/22 24/21, by .221 – .079 = .142. After Blue plays 32-up (24/22 24/21) in both positions, White's 11 33 55 are much stronger on the right, where White can point on Blue. Also, White does not have to strip her 6pt to hit twice with 21 (6/4*/3*).

By contrast, there is a much smaller swing in the equity of hit-and-down (13/11 6/3*) in the two positions. On the left, hit and down gives Blue an equity of -0.126 compared to -0.166 on the right, a difference of only 0.040, The hit-and-down play helps to negate the effect of White's additional checker in the zone on the right.

31P-11S-32

 White is Player 2 score: 0 pip: 163 Unlimited GameJacoby Beaver pip: 163 score: 0 Blue is Player 1
XGID=-a-a-BD-B---eE---c-cb---B-:0:0:1:32:0:0:3:0:10
Blue to play 32

1.Rollout124/22 24/21eq: -0.079
 Player:Opponent: 48.34% (G:11.75% B:0.52%)51.66% (G:14.05% B:0.56%) Conf.: ± 0.006 (-0.085...-0.073) - [99.0%]Duration: 1 hour 10 minutes
2.Rollout224/21 13/11eq: -0.089 (-0.010)
 Player:Opponent: 47.92% (G:12.61% B:0.55%)52.08% (G:14.10% B:0.71%) Conf.: ± 0.006 (-0.095...-0.083) - [1.0%]Duration: 1 hour 09 minutes
3.Rollout324/22 6/3* eq: -0.105 (-0.026)
 Player:Opponent: 47.18% (G:14.05% B:0.63%)52.82% (G:14.80% B:0.75%) Conf.: ± 0.006 (-0.111...-0.098) - [0.0%]Duration: 1 hour 18 minutes
4.Rollout424/22 13/10eq: -0.111 (-0.032)
 Player:Opponent: 46.95% (G:12.23% B:0.49%)53.05% (G:13.39% B:0.58%) Conf.: ± 0.016 (-0.127...-0.096) - [0.0%]Duration: 10 minutes 13 seconds
5.Rollout46/3* 3/1* eq: -0.116 (-0.037)
 Player:Opponent: 46.79% (G:14.60% B:0.40%)53.21% (G:15.05% B:0.77%) Conf.: ± 0.016 (-0.131...-0.100) - [0.0%]Duration: 10 minutes 30 seconds
6.Rollout413/11 6/3* eq: -0.126 (-0.047)
 Player:Opponent: 47.11% (G:14.87% B:0.75%)52.89% (G:16.26% B:1.10%) Conf.: ± 0.019 (-0.145...-0.106) - [0.0%]Duration: 10 minutes 30 seconds
7.Rollout413/8eq: -0.141 (-0.062)
 Player:Opponent: 46.35% (G:12.60% B:0.49%)53.65% (G:14.51% B:0.73%) Conf.: ± 0.014 (-0.155...-0.126) - [0.0%]Duration: 9 minutes 13 seconds
1 8727 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

2 8726 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

3 8724 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

4 1296 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10

31P-31P-52S-32

 White is NevzatDogan score: 0 pip: 156 Unlimited GameJacoby Beaver pip: 163 score: 0 Blue is peever
XGID=-a-a-BD-B---dE---c-db---B-:0:0:1:32:0:0:3:0:10
Blue to play 32

1.Rollout113/11 6/3* eq: -0.166
 Player:Opponent: 46.64% (G:14.13% B:0.64%)53.36% (G:18.18% B:1.35%) Conf.: ± 0.006 (-0.172...-0.160) - [100.0%]Duration: 1 hour 18 minutes
2.Rollout16/3* 3/1* eq: -0.184 (-0.018)
 Player:Opponent: 45.56% (G:14.48% B:0.42%)54.44% (G:17.27% B:0.96%) Conf.: ± 0.006 (-0.190...-0.178) - [0.0%]Duration: 1 hour 16 minutes
3.Rollout124/22 6/3* eq: -0.188 (-0.022)
 Player:Opponent: 45.96% (G:13.25% B:0.59%)54.04% (G:17.78% B:1.02%) Conf.: ± 0.006 (-0.194...-0.181) - [0.0%]Duration: 1 hour 20 minutes
4.Rollout124/21 13/11eq: -0.208 (-0.042)
 Player:Opponent: 45.73% (G:11.87% B:0.50%)54.27% (G:17.16% B:0.83%) Conf.: ± 0.005 (-0.213...-0.203) - [0.0%]Duration: 1 hour 12 minutes
5.Rollout213/8eq: -0.218 (-0.052)
 Player:Opponent: 44.72% (G:12.09% B:0.50%)55.28% (G:16.75% B:0.85%) Conf.: ± 0.017 (-0.235...-0.201) - [0.0%]Duration: 6 minutes 35 seconds
6.Rollout324/22 24/21eq: -0.221 (-0.056)
 Player:Opponent: 45.25% (G:10.96% B:0.50%)54.75% (G:16.87% B:0.66%) Conf.: ± 0.018 (-0.239...-0.203) - [0.0%]Duration: 6 minutes 14 seconds
7.Rollout424/22 13/10eq: -0.229 (-0.063)
 Player:Opponent: 44.85% (G:11.53% B:0.48%)55.15% (G:17.23% B:0.77%) Conf.: ± 0.017 (-0.246...-0.212) - [0.0%]Duration: 6 minutes 48 seconds
1 10368 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

2 917 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

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

4 916 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.10

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