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BGonline.org Forums
Someone please explain this to me
Posted By: Daniel Murphy In Response To: Someone please explain this to me (Max Levenstein)
Date: Thursday, 1 September 2011, at 4:35 a.m.
As Carlo said, the bot reports "cubeless" game outcomes which are estimates assuming of how the game would turn out if the cube is never turned. If you want to know cubeful game outcomes you must try to figure out what the bot actually does in its rollout. In very simple positions this can be deduced from the reported cubeful equity. More complex positions that involve gammons and redoubles (and re-redoubles) are trickier.
Cubeful, after 11/8 3/2 or 11/7 you will double your opponent out unless he rolls 6-6 (ND), 5-5 (D/T) or 4-4 (close D/T). Thus you win nearly all games and only a thimbleful of gammons (he stays on 4-4 or 5-5, double/take):
W G L 97.2% 0.2% 2.8% Approximately, that's your cubeful game outcome. Much different from your bot's cubeless numbers:
W G L 80% 1% 20% If instead you play 7/5*(2) the responses are of three types:
(1) 2/36 of the time opponent hits you with 6-5. You lose. Right there are 5.55% losses.
(2) 9/36 of the time opponent enters without hitting. On 6-6 you can double him in. On the other sixes, double/pass is either right or not wrong by much. You are right at the ND/DP borderline especially after the smaller numbers.
(3) 25/36 of the time opponent fans. Your position is now just barely too good, which means that you're now only a tiny bit better off playing on than cashing, and if you do play on, your gammon wins just barely offset your additional losses. If you have your bot analyze this decision, again the game outcomes may be misleading because they are "cubeless." Although they won't tell you how often you will actually win single games and gammons, Gnubg's "show statistics" rollout feature can, with fair accuracy, I think. These are the results of a 1296 trial rollout:
Win 1 point Win 2 points (single) Win 2 points (gammon) Lose 1 point Lose 2 points 91.35% 0.23% 6.55% 1.54% 0.23% (One trial ended with the cube on 4.)
Summing your equity after all responses -- to simplify I'll say you double out after an entering 6-1 6-2 6-3 6-4 (it is a close decision between double out and play on):
W G L 92.45% 4.55% 7.46 There are your cubeful game outcomes, approximately, after 7/5*(2). And again they are much different from the "cubeless" numbers:
W G L 87% 7.7% 13% Cubefully, in comparison to the best two plays, 7/5*(2) wins about 4.35% more gammons but loses about 4.55% more games, so this play isn't right with a centered cube. If your opponent had the cube, 7/5*(2) would be hugely right because then it would actually win the most games and gammons, and you would actually win most of the cubeless gammons that the bot said you should win.
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