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BQ: Just make the 4-point? (some cube comments)
Posted By: Kevin Whyte In Response To: BQ: Just make the 4-point? (Kevin Whyte)
Date: Saturday, 13 August 2011, at 5:26 p.m.
Thanks for all the comments, I wasn't thinking enough about the cube here. The position is somewhat modified from the one I misplayed - to get that one, move the spare on blue's 5 back to the midpoint. There making the 4-point is clear, although I missed it during the game. I was curious how much racing lead blue would need to make 18/13 correct, and so looked at this. In the game it was 7-away, 7-away with the cube centered. I may well have missed a cube there but I doubt by that much - in the modified version it would have been a big mistake to not double, I think.
As for what happens next, it is all pretty unclear to me:
If blue makes the 4-point I count 24 shots, so blue gets hit 2/3 of the time.
-If white misses, say with 54 played 22/13, it's obviously a double (they are still a lot of ways for blue to lose, so I don't think it can be too good, but I'm really bad at estimating gammons). I wouldn't know whether to take, so maybe it's an efficient one.
-If white hits, it's harder to say what is typical. Maybe 61 13/7*,8/7? If that happens I don't think it's a double.
If I were to try to estimate here, I'd put that as 12 shots (all the misses) where blue has an immediate cash. Of the 24 hits, maybe call it 18 wins with 3 of them gammons, and 6 losses with 1 of them a gammon. That comes out to an equity of 26/36. Many of these games will be doubled, so the actual equity must be higher. It can't be as high as 36/36 unless I'm wrong and not only is it still a double but also a drop), so if it's really not even a double then it should be much closer to the 26/36 figure - maybe 28/36?
If blue just safely plays 18/13, then what? Blue is way ahead in the race, if white rolls a typical 8 pips it's 132 to 145 which seems like a borderline pass so around an equity of .55 for blue if I understand things correctly. It's not a race though - white has three men back. There's not so much danger of a serious prime since making the 4-point is about all blue could hope for and white already has a anchor from which to hop that with sixes. That makes me thing white's timing will be fine for a holding game here. If I remember the positions from Woolsey's encyclopedia correctly, a well timed 3-point holding game is a close take/pass too.
If that's right, then the previous suggestion of just playing 18/13 then cashing looks right. Where is the break even point? If the holding game is better than I'm thinking and is a double/take then to get an equity of 28/36 that we got from the pointing play we'd need an equity of 14/36 here undoubled, plus a bit more to make up for giving white the cube. Somewhere around 70% wins given the large number of gammons likely?
That looks pretty close then - if the holding game after 18/13 is good enough to drop (say around 75% cwp given the doubles) then that's right, and if it's below 70% cwp then 32P is better.
There are enough guesses in there that I wouldn't want count on any of that being right. I'm beginning to think that 32P is better, but that just playing 18/13 and then doubling might be more practical, especially if the opponent might get the take/drop decision wrong (certainly I'd have no confidence in my decision there).
I definitely need to be aware of the cube more. I don't often just forget to consider cubing on my roll, but I do seem to forget it a lot when analyzing. Here it didn't even occur to me to ask about the cube decisions next roll when comparing the plays and clearly it's a huge factor.
I've got a RO going, and I'll post it when done.
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