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Re: [Bug-gnubg] Possible cube evaluation problem

 From: Philippe Michel Subject: Re: [Bug-gnubg] Possible cube evaluation problem Date: Wed, 21 Mar 2018 22:52:48 +0100 User-agent: Mutt/1.9.4 (2018-02-28)

```On Mon, Mar 19, 2018 at 11:30:28AM +0100, Terje Pedersen wrote:
> Hi!
>
> One of my users was upset that a position which XG evaluated as
> Double/Take was evaluated to a No Double/Take by Gnu. The score 2A-5A
> may make the cube action a bit tricky.
>
> XGID=-AAbB-EBBB-----a--acbbbb--:0:0:1:00:3:0:0:5:10
>
> Analyzed in 4-ply
> Player Winning Chances:   74.79% (G:2.12% B:0.01%)
> Opponent Winning Chances: 25.21% (G:1.40% B:0.01%)
>
> Cubeless Equities: No Double=+0.5233, Double=+1.6234
>
> Cubeful Equities:
>        No double:     +0.8108 (-0.0040)
>        Double/Take:   +0.8149
>        Double/Pass:   +1.0000 (+0.1851)
>
> Best Cube action: Double / Take
>
> eXtreme Gammon Version: 2.19.211.pre-release, MET: Kazaross XG2
>
> Gnu:
>
> tu0iAAxlvm0AAA:cAmgAAAAGAAE
>
> Cube analysis
> 2-ply cubeless equity  +0.506 (Money:  +0.487)
>   0.739 0.021 0.000 - 0.261 0.012 0.000
> Cubeful equities:
> 1. No double            +0.912
> 2. Double, pass         +1.000  ( +0.088)
> 3. Double, take         +0.742  ( -0.169)
> Proper cube action: No double, take (65.7%)

It looks like there is something wrong with the even-ply cubeful
evaluations at the score:

1-ply; ND 0.77 DT 0.76
2-ply: ND 0.91 DT 0.74
3-ply: ND 0.81 DT 0.80
4-ply: ND 0.86 DT 0.75
rollout: ND 0.84 DT 0.86

The equities are a bit off and the cube action slightly wrong, but the
results for 3-ply and even 1-ply are reasonable. The numbers at even
plies lead to the same small error on actual play but are really