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OTB & RO

Posted By: John O'Hagan
Date: Monday, 3 September 2018, at 3:09 p.m.

In Response To: Desperate double ATS? (John O'Hagan)

I had this recently in a match against XG. It's tempting to double since lots of my losses will be gammons which will cost me the match regardless if I double or not. I gave it some thought and decided not to turn the cube and that is correct by a lot.

When you're thinking about cubing in such a position, you first have to make sure that you're in the doubling window. If not, it's no double. If you're just barely in the window, it's probably not a double unless the position is super volatile.

So what's the risk from doubling? The RO shows that ~60% of White's wins will be gammons and doubling loses nothing on these. The other 40% are single game losses and you lose your 3% MWC from 11a-Crawford. So the loss from doubling is 40% of 3% or 1.2%.

Now for the gain. If you don't double and win a single game, your MWC at 10a-2a are ~ 8%. Do double and win makes the score 9a-2a with ~10%. The RO shows that about 60% of your wins will be single games so you gain 1.2% by doubling and winning a single game. Now for gammon wins. Don't double and win a gammon makes the score 9a-2a with 10% MWC while double and win a gammon makes it 7a-2a with 16% MWC. 40% of your wins are gammons so you gain 40% of 6% or 2.4%. The total gain (ignoring your slight bg chances) is then 3.6%.

R/R+G is then 1.2/4.8 or 25%. Can Blue win this game 25% of the time? Blue only hits with 8 numbers and loses quite a few of those and seldom wins after the other 28.

Blue isn't in the doubling window so doubling can't be correct.





White is Player 2

score: 11
pip: 80
13 point match
pip: 112
score: 2

Blue is Player 1
XGID=-ABB-CC-----aB-aaAbbb-bbbA:0:0:1:00:2:11:0:13:10
Blue on roll, cube action?

Analyzed in Rollout No double Double/Take
Player Winning Chances: 17.59% (G:6.67% B:0.41%) 16.14% (G:6.28% B:0.36%)
Opponent Winning Chances: 82.41% (G:50.67% B:1.54%) 83.86% (G:40.39% B:0.27%)
Cubeless Equities -1.362 -1.628
Cubeful Equities
No double:-1.315±0.007 (-1.323..-1.308)
Double/Take:-1.628 (-0.312)±0.006 (-1.634..-1.621)
Double/Pass:+1.000 (+2.315)
Best Cube action: No double / Take
Percentage of wrong pass needed to make the double decision right: 10.6%
Rollout details
1296 Games rolled with Variance Reduction.
Moves: 3-ply, cube decisions: XG Roller
Double Decision confidence:100.0%
Take Decision confidence:100.0%
Duration: 5 minutes 44 seconds

eXtreme Gammon Version: 2.10, MET: Kazaross XG2

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