Black to Play 6-3
XGID=-BDB-CC-a----------aAcbdd-:1:-1:1:63:0:0:0:0:10
White - Pips 53
Black - Pips 69
In the problem before this one, Problem 37, I identified four criteria that might motivate you to volunteer a direct shot during the last vestiges of contact.
- It is near the end of contact. If White does not break contact on this turn, he will likely do so on the following turn.
- Black trails in the race. He may have some race equity, but hitting also counts for a lot.
- White has defects in his board. If Black gets hit himself, it may not spell doom.
- Black can place a checker 6 pips away from the last White straggler.
When your blot is 6 pips away from an opponent’s blot, there is a 25% chance he will roll low, and fail to pass. The shots you pick up on those variations may be enough to tip the balance in favor of moving within direct range. Getting hit, however, carries a price. That’s why this sort of play requires that your opponent have some defects in his board. The return shots you get from the bar mitigate the damage, but that does not mean you want to be hit. Quite the opposite.
In the last problem, the decision is close. Only 22 millipoints of equity separate the top two plays. In this position, failing to put a blot 6 pips away is a clear error. In fact, it’s a whopper
with cheese! 20/14 6/3 beats 20/11 by 140 millipoints.
It may be instructive to pause for a moment, and try to identify why the margin is so much larger in this position. For reference, here is the previous position, Problem 37:
Black to Play 3-1
XGID=-BBDB-B--a-A----B-bbcab-d-:1:1:1:31:0:0:0:0:10
White - Pips 71
Black - Pips 81
I see two differences. First, In Problem 37, there is a respectable alternative that does not require leaving a direct shot. In Problem 38, some sort of direct shot is forced. The only question is which one. Second, White’s board is weaker in Problem 38.
Quote:
Originally Posted by bleep69
Are expert players breaking down the move like this OTB? Or is a more general assessment done based on past experience and knowledge of percentages?
Let’s make it clear that I am no expert! There are many regular posters here, such as Z, Grant Hoffman, 911, Tom Cowley, Aaron W., and dozens of others to whom I apologize for not listing your names, who are much better players than I am. My PR is currently around 7.75. My checker play is decent, near 6.5, but my cube decisions are abysmal, averaging between 10 and 12. Perhaps a true expert such as Bill Robertie might comment on the OTB thought process of a top player.
Having said that, I think the answer is a qualified yes and no. Bill has often described taking a cross-section of 36 rolls, dividing them into groups as I did for Problem 37, and trying to put rough estimates on how many wins and gammons each group generates.
There is a limit to how far you can take this OTB. To reach the precision given in the solution for Problem 37 requires using a bot and tabulating equities in a spreadsheet. I selected the top two plays in GnuBg, and then clicked TM (for Temperature Map). For each of the 21 different rolls, I subtracted the equity of the 2nd-best play from the that of the top play. Weighting non-doublets twice as much as doublets, I was then able to find the average equities for each of the categories I was interested in. You can do a similar thing using Analyze > Dice Distribution in XG, but the GnuBg Temperature Map may be easier to use when making side-by-side comparisons.
So this is the homework I had to do in order to really learn what is going on is these sorts of positions. Before I added Problems 37 and 38 to my flashcard set, I had seen a similar thing before. While rare, these positions come up with a predictable frequency, often at the tail end of a holding game. I did all the calculation in order to test out my hypotheses about what was important in the positions. At the end of my exploration, I formulated the guidelines given at the top of this post. They may be flawed, but they are what I now use OTB. They are also completely original.
Mike
Last edited by Taper_Mike; 02-11-2015 at 07:09 PM.