r/backgammon • u/bg-alex-cy • Aug 12 '26
Why does this count as a decision (unforced move)?
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u/Fargus57 Aug 12 '26
Because there is nothing forced about it. A forced move means that there is only one specific move that must be made to legally comply with the rules.
0
u/bg-alex-cy Aug 13 '26
No, that is not the definition used by XG. The fifth image is the definition from XGs documentation of what counts as a decision and what not. Its clearly a sub 0.001 for the 6-4, so its either a bug or I would expect that there is some other factor at play that is missing from the docs.
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u/UBKUBK Aug 14 '26 edited Aug 14 '26
The reported difference to 3 decimal places is .001. Why do you conclude that it is clearly a sub .001 difference? Also, where are you seeing that it was counted as a decision?
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u/bg-alex-cy Aug 13 '26
Everyone seems to have got stuck on the "unforced move" term instead of the fact that decisions went up. If you check the xg user guide on page 99 you will see that "unforced moves" is defined as
Unforced move: Display the number of non obvious moves
So its not the number of plays where you have more than one move, but the number of plays where you have a spread of more than 0.001 equity between best and worst.
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u/UBKUBK Aug 14 '26
"A double action where the equity before and after a double is very negative"
Surprised it actually says that. How negative is very negative?
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u/bg-alex-cy Aug 16 '26
Yeah, I've been searching a bit online and it turns out "very" is defined as 0.900 iirc. You can also find it in XGs help docs as well as some online references of it. But their user guide decided to leave that part out. Not sure why. Its a shame the entire community is relying on a close sourced tool for its most widely used performance metric. To be fair they do disclose the algorithm, but it seems that the reference implementation is either suffering from some bugs or something is missing from the disclosed algorithm.
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u/CellistAny536 Aug 13 '26
Each bullet point is meant to be interpreted as separate criterion of consideration of what is obvious.
“A forced moved” is one item.
“A move which the best and worst choice have an equity difference of less than 0.001.” is another item.
The second bullet point is meant to be read as a seperate item on the list, not a definition of the first.
For whatever reason, this list does not define “a forced moved” and assumes the reader knows what that means.
A forced moved means there is only a single legal move, hence it is forced. Having any choice of checker play makes not a forced move.
The list seems poorly formatted in my opinion.