the dorbel daily

Sunday 22 May 2011

The Bear In, Part One

The Bear In. This just describes the phase of the game where we are moving our last outfield checkers into the home board. The easiest of these come when there is no more contact. All the opponent's checkers have passed ours and there is no more chance of hitting. The game has become a pure race and we can divide these for convenience into two types, the first of which is the race where all we are trying to do is save the gammon. Our only aim is to get all the checkers home and bear one off. Two techniques help us to do this and they occasionally conflict. Cross-overs are vital, a cross-over just being where a checker moves from one quadrant of the board to another and we must always maximise crossovers. However, what we don't want to do is to waste any pips, so we try to avoid putting checkers deep inside the board and ideally pile everything onto the 6pt.

Here's an example of the sort of thing that I mean. Blue has to play 6-1 from the bar.

Position ID: u20AABD2bDgABA

Blue enters with the 6 and has a choice of ones. Both 19/18 and 13/12 achieve a crossover, but 13/12 is best. It means that Blue can use a six with perfect efficiency on the next turn and it also diversifies the mini-stack on the midpoint. The more points you occupy the more choice you have next turn. How important is this? Not very, the better play trims Blue's gammon losses from 93.2% to 92.4%, but you may as well have everything that you can get!
This next one is pretty easy, 3-3 to play

Position ID: 2xYAAIQ9Gw4CAA

The correct play is 13/10(2), 9/6(2), four cross-overs, no wastage.

Position ID: qwAAQNifGSAAAA

Now Blue rolls another terrific 3-3. 18/6 brings a man exactly to the 6pt with no wastage, but sometimes as I said, the two main rules conflict and here 18/12, 8/5(2) is better, achieving three cross-overs rather than two. It wastes two pips, but with the end of the game so close it is essential for Blue to get down to only three checkers in the outfield and maximise his chances of getting a man off in two (and sometimes one) rolls. With the finishing post in sight, you do need to start thinking of specific rolls next turn, as this next position neatly demonstrates.


With White certain to be off in two rolls, Blue must maximise his chances of getting a man off next roll. What's his best play? I'll give you the answer tomorrow, so plenty of time to read the numbers. Until then, enjoy the game!

1 comment:

ah_clem said...

Blue will have to leave at least two checkers in the outfield, which means that only doublets will save the gammon. 66 and 55 will do it no matter what blue plays this time. Can blue make some other doublet work too?

Yes. By leaving a checker on the 12-point blue can save gammon with 44. 10/6 10/7, 10/6 6/3, 10/3, and 10/6 5/2 all allow blue to bear off a checker with 44.

I'm not seeing a way to make 33 work, so all these plays should be equal. The "obvious" play of 12/9 10/6 doesn't allow blue to save gammon with a 44, so it should be about 1.5% worse than the other plays.