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Nactation sequence

Posted By: Nack Ballard
Date: Friday, 16 October 2015, at 3:34 a.m.

In Response To: Very Interesting Variations thanks!! (Konstantin)





White is Player 1

score: 0
pip: 115
Unlimited Game
Jacoby Beaver
pip: 144
score: 0

Blue is Player 2
XGID=--abBCCBBA---Ab--b-dabAa--:1:-1:-1:65:0:0:3:0:10

[ j J53] "<=0.6

[Konstantin] Btw what is the meaning of the stuff in the brackets? e.g. [ j J53] ??

Those are "nacbracs," which is short way of saying "Nactation brackets."

Within the brackets, the best play ( j = 11/5 8/3*) is listed first, followed by the second best play (J = 11/6 11/5), and with it the relative margin (error size) in thousandths; i.e., "53" means that j is better than J by .053.

After the brackets, there are some symbols denoting the bot, and the ply/depth for checker play and cube, followed by the number of rollout trials in thousands rounded down. (If it is less than 1000, I round the hundreds down instead, thus 648 is designated 0.6.)

However, let's back up a step. In case you don't know Nactation, it is a system whereby one uses a single letter to represent a backgammon move.

The five different best plays from the variants diagrammed in my recent post are listed below, in alphabetical order. "J" means to "Jump" checkers over the bar (on the near side), "K" means "Kill" (hit twice), and "S" means "Split" (-and-down).

.....J ...=.. 8/3* 8/2
.....j ...=.. 8/3* 11/5
.....J ..=.. 11/6 11/5
.....K ..=.. 22/16* 8/3*
.....S ...=.. 22/16* 16/11

Lower case -- and even less often, italics -- are used to distinguish plays within the same family. (There are three moves above that "jump.") A symbol or digit can sometimes be used instead of a non-capital letter, but not in this case.

When someones brings a Nactation question to bgonline, it will often involve a non-capital solution. That is because s/he is less likely to bother asking unless it is an unusual or offbeat situation.

To give you an idea of what is typical with Nactation, I've provided a sequence (perfectly played, according to XGR++), beneath the diagram below, that derives your feature problem starting with the opening position and ending with Blue to play his 65. White's rolls/plays are in gray, Blue's are in blue.
White is Player 1

score: 0
pip: 115
Unlimited Game
Jacoby Beaver
pip: 144
score: 0

Blue is Player 2
XGID=--abBCCBBA---Ab--b-dabAa--:1:-1:-1:65:0:0:3:0:10


65R-62S-31P-43P-53D-42P-21P-62R-545-41Z-62H-42Z
-63H-31@-42P-54D-F-63r-32-61K-55H-32H-C-33D-65

For more info, click on the links below, and/or I'll be happy to answer your questions for both.

Nack

Nactation tutorial ĦE explanation of nacbracs

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