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Meaning of "cubeless" in gnubg

Posted By: Maik Stiebler
Date: Tuesday, 15 September 2009, at 7:58 a.m.

In Response To: Meaning of "cubeless" in gnubg (Timothy Chow)

If I understand this correctly, this means in particular that the "cubeless" numbers are based on cubeful checker-play. It follows that the "cubeless" numbers are not reliable approximations to the equity of a cubeless backgammon game played by optimal players.

I think your understanding is correct, but the conclusion a bit harsh, given that bots never give us anything really reliable anyway, except in endgame situations which are in the database. Usually I think the effect of cubeful vs. cubeless play is just one of many contributions to systematic uncertainty.

So what is this "cubeless" number good for

It cannot hurt to have the extra information. While the cubeful numbers may usually be more useful, there may also be cases where gnubg butchers the cube decisions in a rollout to the extent that adjusted cubeless numbers are more reliable.

By the way, the cubeless equity number that gnubg computes for cubeful rollouts in matches is rather nonsensical, seemingly because it mixes up emg normalizations from different cubelevels (see http://lists.gnu.org/archive/html/bug-gnubg/2008-12/msg00024.html and Christian Anthon's reply). The w/g/bg distribution is what you want to look at if you are interested in quasi cubeless numbers.

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