Coming in against 2pt anchor - Backgammon Forum - Discuss Backgammon Strategy, Clubs and Books

dehydrogenase · 06-22-2012, 03:56 AM

Please help understand the correct play here. Thank you!

White - Pips 161

Black - Pips 83
Black to Play 4-3

Diagram created with www.BGdiagram.com

gpietoso · 06-22-2012, 09:09 AM

Ok, so 7/4,7/3 is the right move.

I'm not so good at analyzing positions too deeply, but here's what I see.

After this play you leave no shots next roll. Checker distribution in your innerboard is much smoother, letting you play your small/medium rolls inside and use your big rolls to bear in the last 2 checkers.

If you play around with the position you will see that it will always be correct to clear the 7 point as long as there is a gap between it and the preceeding point (up till the 11 point).

Cheers.

dehydrogenase · 06-22-2012, 02:18 PM

That is what I do not like about removing 7pt now:
It will leave 4 indirects for White if Black leaves a shot with 61, 62, 63 next roll. Not many, but why not play safe 10/7 10/6 and leave no shots at all?
After 10/7 10/6 we will have plenty of spares on 6pt to play 5s, and only after the first 6 that we play from 7pt (and remove the 3rd checker from it) we might leave a shot with only one roll 65.

gpietoso · 06-25-2012, 08:06 AM

I see your point and it does make sense.

The only thing I can see favoring 7/4, 7/3 is that he is playing a well timed 2pt holding game, so his board will only improve as you start bearing in/off. Considering his awkard position at the moment, moving 7/4 7/3 reduces the chances of shots later at the price of leaving more shots now.

Inteligent choice, after all, it's better to get hit now then later when his board will be much more threatening.

Cheers.

Taper_Mike · 06-25-2012, 04:28 PM

Quote:

Originally Posted by dehydrogenase

... why not play safe 10/7 10/6 and leave no shots at all?

Are you sure 10/7 10/6 won't leave any shots next time?

uberkuber · 06-25-2012, 04:41 PM

Quote:

Originally Posted by Taper_Mike

Are you sure 10/7 10/6 won't leave any shots next time?

5-5 and 4-4 leave shots next turn I believe. However, having said that, OTB I play 10/7 10/6 without a thought.

Taper_Mike · 06-25-2012, 04:48 PM

Clearing the 10pt is more dangerous that clearing the bar point. When you clear the 10pt, 64, 55 and 44 leave direct shots immediately, and there is the danger of leaving a direct shot later, if you roll a couple of 5s while waiting to clear the 7pt. Even at DMP, where gammons do not count, clearing the bar point is the better play.

When gammons do count, you have an even stronger incentive to clear the 7pt. The sooner you bring your checkers home, the sooner you can bear them off.

Look what happens when you add a third checker to the 7pt. The next turn is spent bringing that 3rd checker in (and presumably moving another checker inside). The turn after, if you are lucky enough not to roll a 5, you can clear the 7pt. Of course, 30% of the time you will roll a 5, and then you will be looking for safe ways to play in your inner board. Two 5s in a row will be awkward, but perhaps you can survive even that. Finally, three or four rolls downstream, you can begin the bear off.

Clearing the 7pt now simplifies the bear in. Afterwards, 11 rolls clear the 10pt safely on the first attempt. Almost a third of the time, then, you will begin bearing off two turns from now. 61, 62 and 63 force you to leave an indirect shot, but so what? We have already seen that clearing the bar point is the much greater risk.

In the rollout below, clearing the bar point wins an extra 2% of all games, with an extra 7% of all games ending in a gammon victory.

Code:

XGID=-AcBBBDB--B-b----d-db-----:1:-1:1:43:0:0:3:0:10

X:Player 1   O:Player 2
Score is X:0 O:0. Unlimited Game, Jacoby Beaver
 +13-14-15-16-17-18------19-20-21-22-23-24-+
 |             O    |   | O  O             | +---+
 |             O    |   | O  O             | | 2 |
 |             O    |   | O                | +---+
 |             O    |   | O                |
 |                  |   |                  |
 |                  |BAR|                  |
 |                  |   |                  |
 |                  |   | X                |
 |                  |   | X           O    |
 | O     X        X |   | X  X  X  X  O    |
 | O     X        X |   | X  X  X  X  O  X |
 +12-11-10--9--8--7-------6--5--4--3--2--1-+
Pip count  X: 83  O: 161 X-O: 0-0
Cube: 2, O own cube
X to play 43

    1. Rollout¹    7/4 7/3                      eq:+0.9865
      Player:   81.67% (G:42.36% B:2.00%)
      Opponent: 18.33% (G:0.71% B:0.02%)
      Confidence: ±0.0035 (+0.9830..+0.9899) - [100.0%]
      Duration: 15 minutes 15 seconds

    2. Rollout¹    10/3                         eq:+0.8744 (-0.1120)
      Player:   79.69% (G:36.67% B:1.42%)
      Opponent: 20.31% (G:1.09% B:0.03%)
      Confidence: ±0.0037 (+0.8707..+0.8782) - [0.0%]
      Duration: 14 minutes 12 seconds

    3. Rollout¹    10/7 10/6                    eq:+0.8518 (-0.1347)
      Player:   79.37% (G:34.90% B:1.17%)
      Opponent: 20.63% (G:0.86% B:0.03%)
      Confidence: ±0.0032 (+0.8486..+0.8550) - [0.0%]
      Duration: 13 minutes 45 seconds


¹  5184 Games rolled with Variance Reduction.
   Dice Seed: 67221381
   Moves: 3-ply, cube decisions: XG Roller


Rollout by Taper_Mike
2012-Jun-25
eXtreme Gammon Version: 2.03
Flashcard PositionID 000600.xgp

uberkuber · 06-25-2012, 09:42 PM

Nice post Mike. My OTB play isn't even 2nd!

**Robertie** · 06-26-2012, 05:19 PM

I think the key idea here is that 7/3 7/4 clears an awkward point now, with no shots, and puts builders on good points. Moving 10/7 10/6 creates a big stack on the 6-point (bad) and causes all fives and sixes to move to the 1-point on future turns (bad and bad). You could easily start the bearoff with a big stack on the ace-point and awkward distribution elsewhere.

Try entering the starting position in XG or Gnu and look at its recommendations for all the rolls for Black. I suspect that pretty much every roll that has small numbers will be used to clear the 7-point, while rolls with 5s or 6s will break the 10-point, even at the cost of leaving an indirect shot.

GrantHoffman · 06-28-2012, 10:29 PM

I would also recommend you look at Position 80 "Clearing Against a 2 point Anchor" in "Understanding Backgammon" by Kit Woolsey and Tami Jones for an excellent discussion that will anyone from reluctantly making the correct play to understanding why the correct play is correct.

Also it is a good book that really helped me when I read it along time ago.