the dorbel daily

Tuesday, 22 February 2011

More Blundering.

It's a good time to remind ourselves of Uncle Jake's minimal guide to good cube action for the trailing player in short matches. Memorise this. It will save you a lot of thinking time.
"Develop some sort of gammon threat and ship it in".
That's it, short and sweet and as near to infallible as you can get in bg. Here's a position that demonstrates it nicely and where I fell asleep and left the cube in the middle.

Red trails 1-2 in a match to five and trails in the race 137 -130.
This is a very clear double and a fairly easy take. What Uncle Jake means by "some sort" of gammon threat is anything that is better than you start with. About 26% of games played to a finish end in a gammon, so you start the game with a 13% chance of a gammon. Red wins about 63% of the games from here, of which 19 will be gammons, so that will do nicely. Of course it is very hard to tag those sort of numbers onto a position, although some people can do it, but like most people I just rely on my sense of smell and this has a definite whiff of gammon about it! Not only that, it is very volatile and this is a vital ingredient. 10 numbers (4-4, 3-3, 2-2, 1-1, 3-2, 3-1, 2-1) put White on the bar and complete the five prime. Red will also hit loose with all his other ones, twos and threes so it is beyond me to say why I didn't double in the match!
For money a double is an error and if Red was leading in the match it would be a big blunder, but for the trailer it's clearly right. The cube has little value for White and her own gammons are partially wasted by overage.

Well, I hit loose and White hit back from the bar, but the dice god gave me a 3-3, almost the best roll possible. How would you play this?

The first three are pretty easy, bar/22, 8/5*(2) and I chose 11/8 for the last one, getting another builder into the zone and slotting the back of the prime. This is a blunder. The checker on the 8pt is vulnerable to 6-2 and 5-3 from the bar and I just don't need that risk, partly because if not hit I have a great cube next turn and partly because my game plan has to be blitzing against the lone man back rather than priming. The clear best play with the last 3 is 7/4, still with three attacking checkers, as Red will break the bar to hit, plus double coverage of the outfield for White's 6-2 and 5-3 from the bar. She should step out with either of these, so note that these rolls have been converted from excellent to very bad if you play 7/4 instead of 11/8. This swing accounts for almost all of the difference between the two plays.
That was a tough play to find I think, so apart from noting that doublets often require a little more thinking time than singletons, let's move on to my third blunder of this game.

By this time I've managed to double White in and have a 3-2 to play in this very strong position. Any ideas?

The first thing to say is that 6/1* is very horrid. Red will hit White loose if she gets up to the 23 pt but no point in hitting on the ace until you have some cover numbers and can go for a close out. I sort of fiddled around at the back without any clear idea in mind and played 24/21, 22/20.
You wouldn't think that you could make a big mistake here, but this play is a blunder.
Two things to think about here. White has what is called a brittle structure, with stacks on the mid and 6pts and three checkers buried on her deuce point. She isn't going to develop this into a prime but if she can point on a Red blot or two she has a chance to get back into the game. Red has to counter that by anchoring 24/22. You will see this time and again. Counter brittle structure with a rock against which it will break. So, that leaves a 3 to play and the best 3 is 13/10, not 6/3. Why leave a shot? To gain a double shot if White throws her magic 6-1, to increase the chances of making the 8pt and to give more hitting numbers if White moves up to the 23pt. As this play also duplicates the 1 that White needs to get to the edge of the prime you it's a bit of a no-brainer, but only if you have engaged your brain in the first place. Before making my nothing play I should have asked myself the pro question, "How do I plan to win from here?" It's a good idea to mutter this under your breath from time to time.
Well, that's about it for today. Thanks for reading, let me know your thoughts on these, or indeed any positions and until the next time, enjoy the game!

Tuesday, 15 February 2011

Put 'Em Where You Want 'Em.

Backgammon is often at its best in tough midgame positional struggles. Here are three interesting positions that a strong player got wrong. See if you can do better.

Red leads 3-0 to 5, but trails 147 - 129 in this game.

Although Red trails in the race his stronger position is enough to make him a small favourite. He has the golden anchor and all his checkers are in play, whereas White has already buried four checkers and so has to play the rest of the game with 11 checkers. In the match, Red chose 10-4 but 20/15, 7/6 is much better even though it leaves a shot.

The theme to keep in mind for this sort of game where you have the golden anchor and you are fighting to prime White’s straggler is this. Ignore shots and put your checkers where you want them. Your anchor (and White’s crappy board) mean that you can leave shots without a serious risk of a bad sequence that gets you cubed. Of course you don’t want to take risks without some gain, but the gains after 20/15, 7/6 are substantial. You free up the spare from the anchor (almost always a useless place for a spare) and you keep two spares aimed at the 5pt.

The next position shows Red making the same sort of mistake, although I grant you that this is a tough play to find.

Red played 7/3, 7/6 giving up his very valuable bar point, but “putting your checkers where you want them” also means leaving your checkers where you want them sometimes and here, with White’s blot inboard, it’s worth keeping the bar and leaving the double shot after 15/11, 15/14. Note that this is better than 15/10, one less shot and duplicates fives and two’s to hit and cover.

And here, in a different shape is the same mistake again.

No need to labour the point. You can see for yourself that 15/14, 3/1, 2/1 is easily the best play as White now has two blots inboard.

The 20pt anchor is a great insurance policy and when your opponent has a weak board as well you can pretty much ignore shots and put your checkers where they will do most good. In these tough positional struggles it's a great guide to finding the right play.

Until the next time, enjoy the game!

Tuesday, 1 February 2011

The Cube's The Thing.

It's so important to get your cube action right. Most games are won by luck anyway, regardless of the checker play skills, so getting the cube to the right level (high in winning games, low in losing ones) is fundamental to success in match and money play.
Expert players carry a library of reference positions in their heads, positions where they know the equity and can compare it to what they face over the board. Here are two quite differing positions, the first commonplace, the second less so, but still essential for success.

Here's the first and it's 0-0 in a match to 7. White is on roll, leading 114-139. What's the correct cube action for both sides?

White leads in the race by 25 pips, she has escaped both her back checkers and if she clears her midpoint next turn she will lose her market, so the double is absolutely clear. Should Red take? If it was just a race Red would have a clear pass, but with his anchor he stands a good chance of getting a shot during the bear-in. Is this enough to give him a take?
I tend to take a few too many of these and I should have passed this one. White has 11 rolls that clear the midpoint immediately and also has a spare 6 and two spare 5s with which she can fiddle around while waiting for a clearing number. My side of the board is important as well. I already have the 5pt (essential!) and I may be able to build a nice board ready for a shot, but may be isn't will. I have to know that a shot will win for me.

Good reference positions are those where the take/pass decision is very close, so that when you come to compare it with what you have on the board, you can say, "Any improvement and I can take, any weakening and I should pass". The above position isn't a good reference, as it is a very clear pass and the take loses 1.2 points on average. The position below is much more useful. The race deficit is still 25 pips in a shorter race (White 100-Red 125) and the take/pass decision is very close indeed.

Although White's race is a bit better, because the race is shorter, her position has weakened in several respects. Now she only has 7 numbers that clear the 13pt immediately and with only one spare 6 and one spare 5 she has less time to wait for a clearing number. Red has improved too, with a solid board already in place and the bar pt slotted. I think this one too is probably a pass, but it's very close, certainly close enough to be a reference.

This next position comes from the same match and I am on the bar trailing 2-3 to 7.

You have to look at these with a view to doubling, even when on the bar against a four (and potentially five) point board. Although White only has 13 shots all the ones play well too. Even dancing isn't fatal yet. White doesn't always cover straight away and has to dig her back men out pretty quickly even when she can make a 5pt board. Giving the cube away in these two way gammonish positions doesn't hurt too much as White can't redouble without putting the the match on the line. This is very much a trailer's double. You shouldn't try this one when level or leading, but any sort of deficit makes for a strong double here. In the match I didn't double ( a large error) and eventually lost an undoubled gammon!
As a reference position it's fairly useful as a minimum double position. Red could actually be a bit weaker than this and still have a correct cube, while at some scores White should even pass. If Red owned the cube it would be a huge redouble of course and a pass.

Well, I hope you find these useful. I'm sure that you'll see something like these every week and in the case of the 20pt anchor positions, every day! Until the next time, enjoy the game.