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Rollout and discussion

Posted By: Timothy Chow
Date: Wednesday, 12 April 2017, at 11:59 p.m.

In Response To: Just your standard early game 22 (Timothy Chow)

A little while ago, Phil Simborg posted a position with the subject line, Without a QF to help, how many would get this 3rd roll play right? In that position, there was a 22 to play, and I said that I would play 6/4(2) 3/1*(2). I don't think that anyone posted a rollout for that position to BGO, and I still haven't plugged Phil's position into a bot (as I've said before, I mostly read BGO from a computer with no bot on it), but I inferred from the discussion that 6/4(2) 3/1*(2) was the bot play in that position.

In case some people don't believe that I would have played 6/4(2) 3/1*(2) OTB in that position, I will mention that in the position below, my OTB play was 6/4(2) 3/1*(2). I think it's instructive to compare the two positions, as well as other early-game 22 decisions. At a normal score, on the second roll of the game, the bot almost always favors 6/4(2) (along with 13/11(2) or 24/22(2)) over 24/20(2), assuming neither play hits. But once you get to the third or fourth roll, priorities can shift. If you've made your 3pt, then 6/4(2) 3/1*(2) becomes a candidate, especially if (as here) you still have 5 checkers on your 6pt. At the same time, if your opponent has started to build her offense, then the need to make a defensive anchor can become more urgent.

Along the lines of Dmitriy's comment, here White has slotted Blue's 5pt, in contrast to Phil's position, where that blot is on Blue's bar point. That means that White's threat to anchor is more serious in the current position than in Phil's position. Also, in the current position, White's priming threat is more serious than in Phil's position; White doesn't have a drop after a hit and a dance. Both of these factors swing the decision away from 6/4(2) 3/1*(2) towards 24/20(2).

Of course, 6/4(2) 3/1*(2) is definitely more gammonish. It might be interesting to see how much you have to change the match score to tilt the balance in favor of 6/4(2) 3/1*(2).





White is Player 2

score: 0
pip: 154
Unlimited Game
pip: 152
score: 0

Blue is Player 1
XGID=-a-B-aE-B---cDa--bbe----B-:0:0:1:22:0:0:0:0:10
Blue to play 22

1.Rollout124/20(2)eq: +0.215
Player:
Opponent:		54.60% (G:12.99% B:0.39%)
45.40% (G:6.94% B:0.35%)		Conf.: ± 0.012 (+0.203...+0.228) - [100.0%]
Duration: 23 minutes 02 seconds
2.Rollout113/11(2) 6/4(2)eq: +0.174 (-0.041)
Player:
Opponent:		53.15% (G:18.97% B:0.79%)
46.85% (G:12.06% B:0.68%)		Conf.: ± 0.016 (+0.158...+0.191) - [0.0%]
Duration: 21 minutes 14 seconds
3.Rollout16/4(2) 3/1*(2) eq: +0.151 (-0.065)
Player:
Opponent:		51.56% (G:20.86% B:0.58%)
48.44% (G:12.23% B:0.53%)		Conf.: ± 0.016 (+0.135...+0.166) - [0.0%]
Duration: 19 minutes 15 seconds
1 1296 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.19.208.pre-release

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