Hi, This position just falls under the special code I wrote ages ago. There might be errors (bugs) there, but please remember that the "exact" is *not* a '8 vs 2 1 0 0 3 cubeless bearoff', since clearing checkers from the back is not the same as bearoff - you *can* move any checker you want. I think that was the point behind the special code ....
-Joseph On 27 February 2012 12:23, Philippe Michel <[email protected]> wrote: > It looks like there are some bugs in the evaluation of backgammon chances in > races, in raceBGprob() in eval.c . For instance, this position : > > +24-23-22-21-20-19------18-17-16-15-14-13-+ O: gnubg (Cube: 2) > | O O O O O | | O | 0 points > | O | | | > | O | | | > | | | | > | | | | > | |BAR| |v > X | 8 | | | > X | X | | | > X | X O | | | > XX | X O O | | | On roll > XX | X O O O | | O | 0 points > +-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: pm > > evaluates as : > > Position ID: pU4AWhz/AAAAAA Match ID: QQkAAAAAAAAA > > Evaluator: Race > > Win W(g) W(bg) L(g) L(bg) Equity Cubeful static: > 1.000 1.000 0.678 0.000 0.000 +2.678 +2.678 > > The backgammon ratio is wrong by about 0.1. > > It is supposed to be computed exactly (not by a net) as the winning chance > of a 8 vs 2 1 0 0 3 cubeless bearoff, either by not-particularly-obvious > internal functions or with the bearoff databases. > > In the example above, it is the internal functions that are used and there > may be a bug in them or, perhaps more likely, they are not used properly. > > If I twist the code in eval.c to only use the databases, I get : > > Win W(g) W(bg) L(g) L(bg) Equity Cubeful static: > 1.000 1.000 0.784 0.000 0.000 +2.784 +2.784 > 1 ply: 1.000 1.000 0.784 0.000 0.000 +2.784 +2.784 > 2 ply: 1.000 1.000 0.744 0.000 0.000 +2.744 +2.744 > 3 ply: 1.000 1.000 0.744 0.000 0.000 +2.744 +2.744 > 4 ply: 1.000 1.000 0.709 0.000 0.000 +2.709 +2.709 > > Now the bg rate is accurate for 0 and 1 ply, but not for deeper searches. > The diminished backgammons surely don't come from misplays by X so there > must be another problem here, either in shorter races or in the collating > process to get the result from higher plies. > > _______________________________________________ > Bug-gnubg mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/bug-gnubg _______________________________________________ Bug-gnubg mailing list [email protected] https://lists.gnu.org/mailman/listinfo/bug-gnubg
