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BGonline.org Forums
Equities in nacbracs, bot symbols
Posted By: Nack Ballard In Response To: 53P-41S-66B-31? (Ian Shaw)
Date: Friday, 13 May 2011, at 5:05 p.m.
The positioning of the equity with respect to the play letter ought to be consistent with cube decision nacbracs, but I can't find a reference post right now.
A cube decision nacbrac has no play letter, only a cube letter. It starts with D (Double), N (no double), R (Redouble), or X (no redouble), then equity in thousandths, and the difference in equity if the other action occurs, which (logically) represents the equities consecutively. For example,
[D 603–14]
... means that the position is a double with an equity of .603, and not to double is .014 lower (i.e., .589). [As 603 is less than 1000, the position is also a take, of course.] One could expand the formatting to [D 603 N 14] or [D 603 N 589], but its unnecessary.
If one were to write the cube nacbrac as [603 D N14], it would be indistinguishable from a play nacbrac. Does it mean that with an equity of .603 it is a Double with No double being .014 worse, or does it mean that with an equity of .603 playing Down is best with Near is .014 worse? Rather than "consistency," I would call that ambiguity or confusion.
In the case of a play decision where you want to include the best-play equity (atypical but we agree it can be useful on occasion), I find it a bit less disruptive to keep the play letters consecutive: i.e., [-688 P c56 E63], as opposed to [P -688 c56 E63], though either way is okay.
Is there a reason for not simply using one of [jsgbx] as a bot prefix? A default setting still be assumed or you could pre-pend a ply number. I would find this easier than remembering the unintuitive /<>^ etc. It would only cost 1 character per line. My rollout would then be:
53P-41S-66B-31
[-688 P c56 E63] 2g5
[-671 P c27 E39] 0g5*4
[-668 P c24 E47] 0geI use "s" for gammon save and "g" for gammon go (and "d" for dmp), so I decided not to use these same letters to also represent the bots. Granted, the score-defining d/s/g is written before (not after) the brackets, but I thought it better to adopt something different, and more botlike. :)
Here are mnemonics for remembering the bot symbols:
~ ................ Suggestive of a sideways S (for Snowie)
/ ................. GnuBG totally "slashed" (to zero) the price of a backgammon program.
< ^ > = + ... XG is the only bot where we regularly use different plies (3-ply, 4-ply, 5-ply, roller, and roller+) for rollouts. Think of the first three as less than 4-ply, 4-ply and greater than 4-ply (and = and + are obvious for roller and roller+). All these symbols have TWO STROKES of the pen, just like an X has.Appending a ply-number before the bot symbol (as you suggest) is possible. Snowie is 3-ply and that GnuBG is 2-ply unless otherwise marked, and it seemed to me (at least until recently) that anything else was applied rarely enough that I just wrote it out as a parenthetical "0-ply" when it occasionally did. If this rash of 0-ply is more than a temporary fad (we'll see), I suppose it makes sense to abbreviate to "0/" for 0-ply Gnu, and 2-ply Gnu can still be "/" or in comparative contexts "/2" would work. Having a number both before and after the bot symbol seems less than ideal to me, though (and it diminishes the chance to further detail later, if necessary). An option is to resort to a backward slash (\) for 0-ply if that alternate setting becomes a staple.
In the same vein, a possibility for the XG symbology is 3<, 4<, 5<, =< (or r<) and +< for 3-ply, 4-ply, 5-ply, roller and roller plus, respectively. But I don't think it's painfully harder to remember <, ^, >, = and + (refer to the earlier mnemonic explanation), which saves a character and again it avoids having a number both before and after the bot symbol.
Nack
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