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| XGID=-b----EDB---cB-c--Bb-bab--:0:0:1:54:1:0:1:2:10 | |||||
| Blue to play 54 | |||||
| 1. | Rollout1 | 13/9 13/8 | eq: +0.072 | |||
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| 2. | Rollout1 | 18/14 18/13 | eq: +0.056 (-0.016) | |||
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| 3. | Rollout1 | 7/2 6/2 | eq: +0.051 (-0.021) | |||
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| 4. | Rollout1 | 8/3 7/3 | eq: +0.017 (-0.055) | |||
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| 1 5184 Games rolled with Variance Reduction. Dice Seed: 36091569 Moves: 3-ply, cube decisions: XG Roller | ||||||
Igor: Nack, can you explain why bringing two down is best at GS? I must admit I don't understand this.
Scotty: Great question! I am pondering the same thing. I would guess that one should tend towards avoiding blots at this score.
It is indeed a great question. Let's start by isolating percentages for wins and gammons lost from the rollout above.
.....Play......Win.....G loss......Net.......Diff..........x .02
..... D.......62.76.......9.17.....53.60
..... R.......62.97.....10.17.....52.80.....(–0.80).....(–.016)
..... 2pt.....61.92.......9.36.....52.56.....(–1.04).....(–.0208)
..... 3pt.....61.30.....10.45.....50.85.....(–2.75).....(–.055)
The shortcut for figuring out relative equities at gammon save is to subtract gammon losses from wins, then double (and divide by 100 to restore a percentage like 62.76 to its actual 0.6276). Those results appear in blue, and you can double-check these against the relative equities in the Gammon Save rollout (at the top of this post).
D (Down, 13/9 13/8) wins more games and loses fewer gammons than making the 2pt (7/2 6/2). If Blue plays D, then subsequently (the 31/36 of the time that he is not hit), Blue's follow-up plays will be somewhat natural and with few real choices, less swingy.
By contrast, if Blue makes the 2pt, he will often find himself in conflict, having to hold back some attacking plays (for fear of a backfire that would get himself gammoned) that would be compelling for money (in the other part because of the supplemental upside of winning a gammon), and that will be much more the case after making the 2pt than after D.
For example, suppose White responds with 52C (Cross, 24/22 10/5, best), and Blue rolls his own 52. The double-hitting play of K (Kill, 8/3*/1*) is a "wipeout" (opposite of whopper) for Money, whereas at Gammon Save K is a blunder -- huge swing. The problem is that due to the score Blue must forgo follow-up plays that otherwise flow naturally from making the 2pt (additionally noting that one is more willing to break the 8pt when it is 6 pips away from the owned 2pt). The value of making a deep inside point is largely squandered at Gammon Save.
It is true that D gets hit with 5 numbers. If that were not the case, D would be right at Gammon Save by a significantly larger margin than it is in the featured position.
Consider that on the very first move of the game, 64P is best (tied) for money but at Gammon Save is –.034 (equivalent to a money error of –.049). Granted, the option of replying with D doesn't exist without leaving a direct shot, but the idea of eschewing P is similar. Given the opportunity, you'll be much less willing to attack at GS (than for Money); it is therefore illogical to make the 2pt in the first place.
Reviewing four-score positions I've posted over the years, we can see that the Gammon Save score supports plays that make or keep a non-deep anchor in the opponent's board (20pt, 21pt or 22pt) -- 11a, 11b, 22a+b, 33, 44a, 44bcdefghijk, 55, 21, 41, 43, 53, 64. The only GS positions from this group where such a play isn't made is when it isn't possible (66, 54, 65). That basic element is one you probably knew already, but there's much more to learn. Clicking on these links and studying each of the positions (at Gammon Save, and for that matter at all four scores) is a great way of learning the boundaries and nuances of AtS checker play.
Hope that helps.
Nack