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Snowie vs XG in backgames

Posted By: Daniel Murphy
Date: Monday, 20 December 2010, at 3:06 p.m.

In Response To: Snowie vs XG in backgames (higonefive)

This is Robertie's Problem of the Week #87:

Blue to play 6-2

White175


1O '2O '2O4X '3X1O '1X2O

'2X ' ' '3O1X3O ' ' '4X

Blue217

Position ID: 4DnyIBjgHIwwUw Match ID: cAkZAAAAAAAA

Tim asked for backgame positions where Snowie and XG rollouts disagree. Robertie's Snowie (3-ply?) rollout (not posted) prefers 20/14*. higonfive's XG 3-ply rollout prefers 22/16. Summary:

RankPlayEquity95% confidence interval
1 Bar/23 22/16-0.114-0.099 < -0.114 < -0,129
2 Bar/23 20/14*-0.141 (-0.027)-0.124 < -0.141 < -0.158
3 Bar/23 13/7* -0.175 (-0.061)-0.156 < -0.175 < -0.194

I can add that Gnubg evaluation prefers 20/14* on 2-ply and 22/16 on 3-ply. I'd have played 20/14*, too. Maybe 22/16 is better.

Robertie notes that in the original position (Ballard/Robertie match, score unknown) he played 13/7*. This reminds me of an observation Kit Woolsey made that has been useful to me: when you're playing a backgame, keep the midpoint. Of course, in position #87 you don't have to choose to play a backgame, and Woolsey's comment doesn't mean "never break the midpoint." Still, I've found it useful. In position #87, I rejected 13/7* quickly.

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