the dorbel daily

Wednesday 27 July 2011

A Reader Writes, Part 3.........

Dear Dorbel, In the position below, I moved 23/14. It looks to me like this only leaves a hit by a 4 or a 65 and if I am missed I should get in easily. However, Gnu thinks that I should play 23/18, 6/2.
It looks as if I leave the checker back on the 18 it will be much more likely to be hit after my next roll, if opponent gets a checker out to my 7, 8 or 9pt. I cant see the advantage of staying back.
Thanks as always,

Position ID: s90AAg73nAcAEA

It's the Crawford game in a five point match and Blue leads 4-0.

Yes I see what you mean.
"Only" a 4 and a 6-5 to hit is a lot of only, 17 shots or 47%. "If missed, should get in easily" is also questionable, as only 10 numbers (28%) get you home next turn. Sometimes it is right to take a direct shot when racing a straggler home, but these usually happen when your opponents home board is weak but about to get stronger, which doesn't apply here. Keeping the shots down with 23/18, 6/2 is clearly best. You may be able to hit something next turn to smooth your way home, or find a relatively safe point to land on. I agree that you may have to face more than 17 shots next turn, but you are just as likely to be facing the same or less or even none at all.
Your play is a small but clear error. If it left fewer shots or got you closer to home, it might be right.

Gnu's 2-ply analysis suggests that the two plays are very close (o.010), but a rollout shows that in fact 23/14 is an error costing 0.032. This translates to 52.4 game wins by staying back and 50.8 by running all the way. Can we draw a golden rule from this that stayng back has to be always best? Not really, reduce the shots and get the straggler closer to home, change the home boards a bit, any of these might make leaving the direct shot better or very close to equal. In the end, it's our old friend "pay now or pay later" and all you can do is add up what you risk and what you stand to gain by giving the shots straight away. If you do that and make a mistake, that's fine. It was probably, as here, a close decision anyway. If you fail to add up the hitting numbers and the number of rolls that get you home safely, then you will be making a guess and serve you right if you get it wrong. These crunch positions demand a lot of thought. Don't shirk it.

Have a look at this close relative to our starter position. How would you play 6-5 here?

Position ID: s90ABA73nAcAEA

Taking the immediate risk with 23/12 is more attractive. It's only 16 shots, but much more importantly, Blue gets a lot closer to home. Now 20 numbers get him to safety next turn and this is just enough to tip the balance and make "pay now" the correct choice. It's very close though, the rollout makes that play best by just 0.009.

Thanks to A. Reader for the position. Until tomorrow, enjoy the game!

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