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Bar/16 seems clear. It's too early for Black to hit. White's position has not crumbled enough, and Black is not ready to contain the checkers he hits.

After bar/16, if White hits on the 16pt, he will have to make a concession. If instead, Black hits himself, he is the one making a concession.

My second choice would be to slot the 5pt. Hitting is not even on the radar.

Mike

Quote

03-23-2015 , 01:50 PM

#53

uberkuber

veteran

Join Date: Jul 2009 Posts: 3,032

Brag: I never thought about hitting on the 18-pt.
Beat: I never thought about B/16!
Pick: My pick would have been B/20 9/5.
My 2nd pick would have been somehow B/21 13/8, but it's either a brain fart or fancy play syndrom...

Quote

03-23-2015 , 05:32 PM

#54

Karol Szczerek

enthusiast

Join Date: Mar 2015 Posts: 92

Is such massive backgames, long time before final stage, connectivity and timing always comes first. Usual short-term plays, like slotting for aggresive board building or single hits or safe plays to avoid some hits are nothing compared to the risk of getting disconnected or lose timing, which means usually a LOUD game over.

Therefore bar/16 looks automatic to me and I would play it in 1 sec OTB.

Quote

03-24-2015 , 06:43 AM

#55

yogiman

adept

Join Date: Jun 2012 Posts: 784

Code:

    1. bar/16                       Eq.:  -0,196 
       0,516 0,103 0,003 - 0,484 0,278 0,015 CL  -0,156 CF  -0,196 
      
    2. bar/20 9/5                   Eq.:  -0,289 ( -0,093) 
       0,487 0,099 0,003 - 0,513 0,272 0,014 CL  -0,211 CF  -0,289 
      
    3. bar/20 13/9                  Eq.:  -0,370 ( -0,174) 
       0,476 0,092 0,003 - 0,524 0,297 0,019 CL  -0,269 CF  -0,370 
    
    4. bar/21 23/18*                Eq.:  -0,373 (-0,177) 
       0,455 0,103 0,005 - 0,545 0,272 0,016 CL  -0,271 CF  -0,373

With a 3-point board and an extra checker for the 23-point, both moves are a draw.

Code:

    1. bar/21 23/18*                Eq.:  -0,464 
       0,432 0,091 0,004 - 0,568 0,267 0,016 CL  -0,324 CF  -0,464 
      
    2. bar/16                       Eq.:  -0,465 ( -0,001) 
       0,448 0,088 0,003 - 0,552 0,297 0,018 CL  -0,330 CF  -0,465

Placing a builder on the 6-point increases the gain of hitting not enough imo to depart from the general principle for the 3point-backgame to postpone hitting as long as possible.

Code:

    1. bar/21 23/18*                Eq.:  -0,471 
       0,408 0,088 0,003 - 0,592 0,219 0,010 CL  -0,321 CF  -0,471 
     
    2. bar/16                       Eq.:  -0,504 ( -0,033) 
       0,420 0,079 0,003 - 0,580 0,253 0,013 CL  -0,344 CF  -0,504

However, if white has only one point occupied in his outfield, the general rule in this sort of position changes:

White - Pips 136

Black - Pips 229

Code:

    1. bar/21 23/18*                Eq.:  -0,010
       0,572 0,000 0,000 - 0,428 0,173 0,008 CL  -0,038 CF  -0,010
     
    2. bar/16                       Eq.:  -0,123 ( -0,113)
       0,566 0,000 0,000 - 0,434 0,236 0,020 CL  -0,123 CF  -0,123

White - Pips 145

Black - Pips 229

Code:

    1. bar/16                       Eq.:  -0,214
       0,506 0,102 0,004 - 0,494 0,269 0,018 CL  -0,170 CF  -0,214
    
    2. bar/21 23/18*                Eq.:  -0,241 ( -0,027)
       0,474 0,105 0,005 - 0,526 0,231 0,012 CL  -0,184 CF  -0,241

Barring the unusual circumstance that the rest of white's men lag very far behind:

White - Pips 159

Black - Pips 229

Code:

    1. bar/21 23/18*                Eq.:  -0,243
       0,472 0,109 0,005 - 0,528 0,228 0,013 CL  -0,185 CF  -0,243
   
    2. bar/16                       Eq.:  -0,271 ( -0,028)
       0,480 0,104 0,004 - 0,520 0,257 0,018 CL  -0,207 CF  -0,271

Though one could argue that hitting creates a more complex game, to the advantage of the more skillful player.

Quote

03-25-2015 , 07:19 AM

#56

yogiman

adept

Join Date: Jun 2012 Posts: 784

Position ID: wyY4gRkz2zCDAA Match ID: QQkGAAAACAAE

White - Pips 174

Black - Pips 110
Black to Play 4-1
Created with www.BGdiagram.com

Quote

03-25-2015 , 07:55 AM

#57

Kamba

enthusiast

Join Date: Feb 2015 Posts: 93

Playing these sorts of positions when my opponent has 2 points (or more) in my home is definitely my one of my weakest points.

I would play 11/10*/6

I'm not too worried about getting hit on the 18 point; not many rolls do that and all of them leave him exposed for me to hit back.
I may be totally off, but i think leaving my checker on the 18 point gives me a few more options next throw.

Quote

03-25-2015 , 09:12 AM

#58

Fllecha

journeyman

Join Date: Mar 2010 Posts: 321

Here the hindbrain move should Be 18/17*/13 ainec, but adding qf and some reasoning i think it should Be discarded. The problem in any backgame is timing and hitting here improves opponent's timing. He has 2 men out of play and somewhat stripped position, so a move like 18/13 no hit may cause opponent running out of time.

Quote

03-25-2015 , 11:10 AM

#59

Karol Szczerek

enthusiast

Join Date: Mar 2015 Posts: 92

I'd play 18/14, 11/10* OTB.

18/13 seems not good enough. It doesn't improve White's timing, which is good, but his timing isn't that bad at all. He will have some fly shots, which will let him attack when he wants to. And he will want to do it as early as possible, because his 1-pt. renders his usual backgame plan to block a late hit almost impossible.

Out of the hitting numbers 18/14 11/10* gives most return shots, but gives best chance to build another blocking point in front of White's backmen. Ideally, the 8-point.

But again, these kind of positions aren't my strong side.

Quote

03-25-2015 , 04:04 PM

#60

Taper_Mike

adept

Join Date: Sep 2009 Posts: 1,030

Tough problem.

The usual advice is to be wary of hitting too much when your opponent is playing a backgame. Hitting helps guarantee his timing. I think this position may be an exception.

White has made his 1pt. Those checkers cannot be used to build an outside block. That will make it hard to contain a hit checker later. White has 4 checkers holding down his anchors and 2 checkers on the 1pt. That leaves only 9 checkers to build an outside block.

The only use for the 2 checkers on the 1pt is to keep Black dancing when he lands on the roof. For that reason, Black should strive to prevent White from filling in the rest of his board. Hitting will delay White in that task.

Besides, White already trails by 64 pips. That may be enough to time his 4-2 backgame as is. Given that White has obtained decent timing, the price for adding to that is less than it would be otherwise.

18/17*/13

Mike

Last edited by Taper_Mike; 03-25-2015 at 04:13 PM.

Quote

03-25-2015 , 04:35 PM

#61

Robertie

old hand

Join Date: May 2004 Posts: 1,954

With White having made his ace-point, his game is much weaker than it would be with all his checkers in play.

I wouldn't worry too much about his timing here. I'd just hit everything and figure I was increasing my gammon chances. It's 18/17*/13 for me.

Quote

03-25-2015 , 11:22 PM

#62

uberkuber

veteran

Join Date: Jul 2009 Posts: 3,032

I'd hit too, but have no clue which one is better. I'd hesitate between 11/10*/6 and 18/17*/13.

Quote

03-26-2015 , 10:52 PM

#63

Taper_Mike

adept

Join Date: Sep 2009 Posts: 1,030

Quote:

Originally Posted by Robertie

This is a nice heuristic for these sorts of positions. It was silly of me not to mention gammons in my analysis. They must a big part of the reason why hitting plays will dominate the top of the rollout.

With an eye towards gammons, I took another look at this position. I decided that 18*/17/13 is probably the best play even when gammons do not count. I think it wins more games and more gammons.

I am making a DMP rollout to test my theory. I'll post it after Yogiman's analysis appears.

Mike

Quote

03-27-2015 , 02:45 AM

#64

Kamba

enthusiast

Join Date: Feb 2015 Posts: 93

Out of interest, could the guru's tell me why the preference for 18*/17/13 over 11/10*/6?

At my level I can kind of work out why hitting is a good idea, I'd do it every time here, but would be playing 11/10*/6 every time for no other reason than it just looks and feels better to me.

Quote

03-27-2015 , 04:15 AM

#65

Taper_Mike

adept

Join Date: Sep 2009 Posts: 1,030

I like 18/17*/13 because my plan is to disengage. Step 1: get the runner to safety. Step 2: clear the midpoint. I am not necessarily adverse to hitting again if that will make coming home safer.

Getting hit is not a disaster, but I think it would hurt more than it would help. Why volunteer? What specific advantage would be gained by leaving a shot?

Mike

Quote

03-27-2015 , 04:53 AM

#66

yogiman

adept

Join Date: Jun 2012 Posts: 784

As a matter of fact this problem was meant as a dummy, so the QF caused confusion instead of guidance. The obvious move was meant to be 18/17*/13.

White - Pips 174

Black - Pips 110

Code:

    1. 18/17*/13                    Eq.:  +0,561 
       0,662 0,376 0,018 - 0,338 0,041 0,001 CL  +0,676 CF  +0,561 

    2. 11/10*/6                     Eq.:  +0,508 ( -0,053)
       0,658 0,340 0,015 - 0,342 0,046 0,001 CL  +0,625 CF  +0,508
    
    3. 18/13                        Eq.:  +0,399 ( -0,162) 
       0,661 0,233 0,009 - 0,339 0,047 0,001 CL  +0,517 CF  +0,399

Contrary to our expectations, getting a nice 3-point board for white doesn't change the relative value of hitting an awful lot:

White - Pips 180

Black - Pips 110

Code:

    1. 18/17*/13                    Eq.:  +0,268
       0,560 0,351 0,016 - 0,440 0,063 0,001 CL  +0,421 CF  +0,268
      
    2. 18/13                        Eq.:  +0,131 ( -0,137)
       0,560 0,236 0,009 - 0,440 0,070 0,002 CL  +0,293 CF  +0,131
     
    3. 11/10*/6                     Eq.:  +0,131 ( -0,137)
       0,533 0,305 0,013 - 0,467 0,082 0,002 CL  +0,300 CF  +0,131

See how 11/10*/6 has decreased in value. This is because one reason for hitting is to keep white from building an extra homeboard point, which will be more powerful with a straight homeboard (this in reply to Kamba's question, though I am still an aspiring guru). The other reason being to generate more gammons, which is in Taper_Mike's pipeline.

Reducing the pipdifference by moving the 1-point to the 13-point leads to a strong relative value decrease:

White - Pips 174

Black - Pips 134

Code:

    1. 18/17*/13                    Eq.:  +0,541
       0,702 0,267 0,013 - 0,298 0,040 0,001 CL  +0,643 CF  +0,541
     
    2. 18/13                        Eq.:  +0,498 ( -0,043)
       0,726 0,177 0,008 - 0,274 0,045 0,001 CL  +0,592 CF  +0,498

The reason being that white has a worse timing for a backgame, which means that white sooner will have to give up a backgame point before black is compelled to leave a shot. Besides again, because of a smaller pipdifference less gammons will be generated.

Creating a 4-point block by removing the 1-point makes hitting rather arbitrary:

White - Pips 174

Black - Pips 124

Code:

    1. 11/10*/6                     Eq.:  +0,591
       0,712 0,286 0,014 - 0,288 0,033 0,000 CL  +0,689 CF  +0,591
    
    2. 18/14 11/10*                 Eq.:  +0,570 ( -0,021)
       0,712 0,268 0,013 - 0,288 0,035 0,000 CL  +0,669 CF  +0,570
      
    3. 11/10* 11/7                  Eq.:  +0,568 ( -0,024)
       0,705 0,281 0,015 - 0,295 0,037 0,000 CL  +0,669 CF  +0,568
      
    4. 18/17*/13                    Eq.:  +0,567 (-0,024)
       0,696 0,298 0,015 - 0,304 0,034 0,000 CL  +0,671 CF  +0,567
      
    5. 18/13                        Eq.:  +0,542 ( -0,049)
       0,733 0,190 0,008 - 0,267 0,030 0,000 CL  +0,634 CF  +0,542

This in spite of a somewhat better backgame timing than in the previous position. Now there is a greater probability that white has to give up his 4-point instead of his 2-point, and black will have more shot chances in case this happens.

Here is the original problem, with the 4-point moved to the 3-point:

White - Pips 176

Black - Pips 112

Code:

    1. 18/17*/13                    Eq.:  +0,445
       0,615 0,358 0,026 - 0,385 0,039 0,001 CL  +0,576 CF  +0,445
      
    2. 11/10*/6                     Eq.:  +0,409 ( -0,036)
       0,613 0,331 0,022 - 0,387 0,038 0,000 CL  +0,541 CF  +0,409
      
    3. 18/13                        Eq.:  +0,405 ( -0,040)
       0,652 0,250 0,012 - 0,348 0,039 0,001 CL  +0,526 CF  +0,405

In the original problem hitting has an advantage of 0.16 , and now it is 0.04. That is ofcourse because a 23 backgame needs a better timing than a 24 backgame, and as the pipdifference is about equal this shows imo that the extra gammons are a minor factor.

A pipdifference of 40 seems to be a hitting threshold with this type of backgame:

White - Pips 143

Black - Pips 110

Code:

    1. 18/13                        Eq.:  +0,398
       0,691 0,167 0,007 - 0,309 0,054 0,001 CL  +0,500 CF  +0,398
      
    2. 18/17*/13                    Eq.:  +0,354 ( -0,044)
       0,644 0,237 0,008 - 0,356 0,054 0,001 CL  +0,479 CF  +0,354

White - Pips 143

Black - Pips 120

Code:

    1. 18/17*/13                    Eq.:  +0,730
       0,783 0,253 0,011 - 0,217 0,025 0,001 CL  +0,804 CF  +0,730
      
    2. 18/13                        Eq.:  +0,714 ( -0,016)
       0,820 0,147 0,004 - 0,180 0,017 0,000 CL  +0,775 CF  +0,714

To make matters very simple I propose the following gross pipdifferences for the different types of backgames (and I hope I will be corrected). Don't hit below the given pipdifference, in case the front backgame point is 5: 30, if 4: 40, if 3: 60, if 2: 90.

Quote

03-27-2015 , 06:07 AM

#67

Kamba

enthusiast

Join Date: Feb 2015 Posts: 93

Yikes!

I think it will take me years to get the hang of these backgame, pip difference, hit / no hit situations.I am very weak finishing games when my opponent has a couple of points in my home, especially if he has a bit of play left.

Yogiman: this thread (and you doubling one) have been a great help for me, especially your analysis with tweaking the positions.

Gotta say a big thanks.

Would it be very rude of me to request a dedicated backgame thread? :-)

Quote

03-27-2015 , 06:42 AM

#68

yogiman

adept

Join Date: Jun 2012 Posts: 784

Nice words. But two dedicated threads are enough for me. If you start your backgame thread we will respond.

Quote

03-27-2015 , 07:07 AM

#69

Taper_Mike

adept

Join Date: Sep 2009 Posts: 1,030

31k XG Rollout – Double Match Point

At DMP, where gammons do not count, hitting and running to safety is still the top play. Only 2 millipoints behind is the the same running play without the hit. Disengaging seems to be the theme. I think hitting comes out on top because it delays the formation of White’s board. If Black gets hit later on, White may not be ready to contain him.

Code:

XGID=-BbBbBBB--aBcB---aAbb---b-:0:0:1:41:0:0:0:1:10

X:Player 1   O:Player 2
Score is X:0 O:0 1 pt.(s) match.
Pip count  X: 110  O: 174 X-O: 0-0/1
Cube: 1
X to play 41

    1. Rollout¹    18/17* 17/13       eq:+0.283
      Player:   64.16% (G:43.94% B:8.82%)
      Opponent: 35.84% (G:3.04% B:0.08%)
      Confidence: ±0.001 (+0.282..+0.284) - [99.4%]

    2. Rollout¹    18/13              eq:+0.281 (-0.002)
      Player:   64.05% (G:34.75% B:4.90%)
      Opponent: 35.95% (G:3.17% B:0.09%)
      Confidence: ±0.001 (+0.280..+0.282) - [0.6%]

    3. Rollout²    11/10* 10/6        eq:+0.270 (-0.013)
      Player:   63.48% (G:41.96% B:7.99%)
      Opponent: 36.52% (G:3.47% B:0.09%)
      Confidence: ±0.003 (+0.267..+0.273) - [0.0%]

¹  31104 Games rolled with Variance Reduction.
   Dice Seed: 55261301
   Moves: 3-ply, cube decisions: XG Roller

²  5184 Games rolled with Variance Reduction.
   Dice Seed: 55261301
   Moves: 3-ply, cube decisions: XG Roller

Rollout by Taper_Mike
2015-Mar-27
eXtreme Gammon Version: 2.10.199.2658
OpenYourMind.008-d.xgp
[R r2 613] "<=31*5

Mike

Quote

03-28-2015 , 02:06 PM

#70

yogiman

adept

Join Date: Jun 2012 Posts: 784

Position ID: Np45MABsO2AwAw Match ID: cAkGAAAAAAAE

White - Pips 112

Black - Pips 144
Black to Play 4-1
Created with www.BGdiagram.com

Quote

03-28-2015 , 03:58 PM

#71

Taper_Mike

adept

Join Date: Sep 2009 Posts: 1,030

This is an interesting position. My first instinct was to play 13/8, which keeps the board Black needs, and maximizes contact.

Next, I looked at the safe play, 6/2 3/2, which switches to the 2pt, but rejected that. Remaking the 3pt would be both necessary and difficult. Besides, one of the outside points would have to be broken on the following turn anyway, so Black would be sacrificing the 3pt for the benefit of only a one-turn respite. Is White likely to leave a shot if Black holds the midpoint for one more turn? Not likely.

So I was ready to make my first play, when I realized how things might go if Black abandons the midpoint. In many variations, Black will be forced to play his other checker down from the midpoint before White leaves a shot. After that, White would be free to break his anchor, and bring those checkers around one at a time.

I decided, therefore, that breaking the midpoint is not likely to put much pressure on the anchor. In order to that, Black must hold the midpoint, and create enough timing for himself to be able to do that. That’s when I saw 18/13. If hit, Black will usually get many returns. If not, Black will have many flexible moves in the follow up that allow him to keep pressure on White in both outer boards.

The best way to view this position is as a holding game rather than a backgame. In that light, it is easy to see that Black has too many anchors. He does not have the timing to keep them both.

Mike

Quote

03-28-2015 , 05:02 PM

#72

Karol Szczerek

enthusiast

Join Date: Mar 2015 Posts: 92

We don't have timing for the 18-20pt. game. We have to break something. 18/13 feels natural, and I wouldn't hesitate much here. It gives White the opportunity to attack now, which is uncomfortable for him because of weak-ish board. If he doesn't hit, we've released many pips of flexibility for us. At the same time we keep contact everywhere, so White can't release his 16pt., which blocks many pips for him. So most probably, he will run out of time sooner than we.

Quote

03-29-2015 , 09:12 AM

#73

uberkuber

veteran

Join Date: Jul 2009 Posts: 3,032

Wow, I wouldn't have played this OTB but it makes a lot of sense.

Would have played 13/8.

Quote

03-29-2015 , 02:28 PM

#74

yogiman

adept

Join Date: Jun 2012 Posts: 784

White - Pips 112

Black - Pips 144
Black to Play 4-1
Created with www.BGdiagram.com

Code:

    1. 18/13                        Eq.:  -0,389 
       0,383 0,071 0,002 - 0,617 0,077 0,001 CL  -0,239 CF  -0,389 
     
    2. 6/2 3/2                      Eq.:  -0,481 ( -0,092) 
       0,368 0,072 0,002 - 0,632 0,109 0,002 CL  -0,301 CF  -0,481 
      
    3. 13/8                         Eq.:  -0,532 ( -0,142) 
       0,356 0,067 0,002 - 0,644 0,101 0,002 CL  -0,321 CF  -0,532

There is but little to add to Taper_Mike's commentary.

Creating a 4-board by moving checkers from white's 6-point to the 4-point:

White - Pips 108

Black - Pips 144

Code:

    1. 18/13                        Eq.:  -0,411 
       0,381 0,076 0,002 - 0,619 0,102 0,002 CL  -0,262 CF  -0,411 
     
    2. 6/2 3/2                      Eq.:  -0,497 ( -0,086) 
       0,372 0,070 0,002 - 0,628 0,129 0,003 CL  -0,317 CF  -0,497 
     
    3. 13/8                         Eq.:  -0,579 ( -0,168) 
       0,351 0,065 0,002 - 0,649 0,121 0,002 CL  -0,353 CF  -0,579

It is remarkable that the relative values have hardly changed: 0,092 0,142 vs 0,086 0,168. One would expect that leaving a double shot with a white 3-board is much less detrimental than with a white 4-board, so that by comparison the two other moves should be a lot closer to the equity of 18/13. Apparently, being hit in the first case is not so bad, because it is good for the timing and desirably gets a black checker on the 1-point. This is substantiated by the fact that the equity is about unchanged, when the checker on the 6-point is moved to the 24 point (-0,389 vs -0,384):

White - Pips 112

Black - Pips 162

Code:

    1. 18/13                        Eq.:  -0,384 
       0,423 0,107 0,004 - 0,577 0,219 0,004 CL  -0,267 CF  -0,384 
      
    2. 13/8                         Eq.:  -0,455 ( -0,071) 
       0,406 0,088 0,003 - 0,594 0,207 0,006 CL  -0,310 CF  -0,455 
     
    3. 24/20 3/2                    Eq.:  -0,587 ( -0,204) 
       0,359 0,068 0,002 - 0,641 0,179 0,004 CL  -0,395 CF  -0,587

Because of the better timing 13/8 has moved up in value. And weakening the homeboard is very undesirable as the flexibility has increased with the checker on the 24-point, while the chances to hit a shot have increased, also in case white has to hit loose.

Quote

03-30-2015 , 01:18 PM

#75

yogiman

adept

Join Date: Jun 2012 Posts: 784

Quote:

Apparently, being hit in the first case is not so bad, because it is good for the timing and desirably gets a black checker on the 1-point.

Having a fresh look at my own statements this one is not right at all. To be explicit, 18/13 has about the same equity with a white 3-board and 4-board. I think that it is all about not having to break up the 13-point before white flees, and in case black is on the bar both positions facilitate this in their own way. Someone may correct me.

Quote

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