Re: [Bug-gnubg] Strange analysis output

[Joern Thyssen]

On Thu, Sep 05, 2002 at 11:03:17AM +0200, Jim Segrave wrote
> On Thu 05 Sep 2002 (10:12 +0200), address@hidden wrote:
> > 
> > 
> > --On 04  Sep 2002  19:24 +0200 Jim Segrave <address@hidden> wrote:
> > 
> > >>From the Annotation window:
> > >
> > >    1. Cubeful 2-ply    5/4 5/1                      Eq.:  +1.033
> > >       0.728 0.371 0.009 - 0.272 0.027 0.000
> > >        2-ply cubeful 100% speed, 8 cand., 0.16 tol. [world class]
> > >*   2. Cubeful 2-ply    8/7 8/4                      Eq.:  +0.950 (
> > >   -0.083)        0.730 0.413 0.016 - 0.270 0.027 0.000
> > >        2-ply cubeful 100% speed, 8 cand., 0.16 tol. [world class]
> > >
> > >The move I made 8/7 8/4 has a
> > >higher probability of a win          0.730 vs 0.728
> > >higher probability of a gammon       0.413 vs 0.371
> > >higher probability of a backgammon   0.016 vs 0.009
> > >and the
> > >same probabilities of being gammoned or backgammoned. So why is the
> > >equity lower? What am I missing or misunderstanding?
> > 
> > The easy answer:because you are doing cubeful evaluation. The numbers 
> > listed are the cubeless winning chances.
> 
> Doh. I knew there was a simple explanation. Dank u wel.
>  
> > Understanding WHY the cubeful equity is so much different in a situation 
> > loke this of course another matter.
> 
> Hmm - I'm trying to work that out for myself now. It may be some time.

I can't offer any explanation beyond Nis'. I can confirm the 2-ply
evaluation by doing a 1296 trial rollout without variance reduction
truncated after 2-ply. So the rollout code and eval code is consistent.

One explanation could be volatility: after hitting, blue has a
relatively good position, 5/4 5/1 often leads to "double, pass" unless
blue rolls something horribly bad (i.e., 66 or 44).

Jørn

-- 
Joern Thyssen, PhD
Vendsysselgade 3, 3., DK-9000 Aalborg, Denmark
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