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RE: [Bug-gnubg] Bearoff dB position, few questions

From: Alain Redlinger
Subject: RE: [Bug-gnubg] Bearoff dB position, few questions
Date: Fri, 26 Jun 2009 15:34:56 +0200

About the side question (purely theoretical):

I think that there are many different equities and winning chances implied in 
match play. If we want to keep things clear, the GWC
***should *** not depend on the score. What has the match score to do with the 
possibilities that a given position leads or not to
winning the game where it occurs? Clearly nothing. 
It is absolutely necessary here to distinguish between Match Winning Chance 
(win or loose) and Game Winning Chances (win/loose
simple, gammon, backgammon).
I would find it ***very*** helpful, at least for a beginner like myself that 
would also like to have a theoretical perspective on
the game and/or software, if in the different dialog boxes of GnuBG, it had 
been made explicit whether, in match play, the term
“equity” refers to match equity or the current game equity (as if it were a 
money game). Currently my understanding is that money
game equity is completely irrelevant to match play, and that in a match 
situation, in every window, the term equity refers to match
equity (even if expressed as NEMG), except when explicitly otherwise mentioned. 
 Am I wrong about this?

De : address@hidden
[mailto:address@hidden De la part de Massimiliano Maini
Envoyé : vendredi 26 juin 2009 13:30
À : address@hidden
Cc : address@hidden; address@hidden
Objet : Re: [Bug-gnubg] Bearoff dB position, few questions

Massimiliano Maini
Product Manager Availability and Schedules
Availability and Shopping
Amadeus IT Group SA
T: +33.(0)

address@hidden wrote on 26/06/2009 12:58:56:

> On Fri, Jun 26, 2009 at 12:37 PM, Misja Alma<address@hidden> wrote:
> > Hi Alain,
> >
> > Yeah you're right that cubeless equities can well be different for
> > matchplay and money play.
> > But not only is the equity different, also the 'Win' percentage is
> > different that is shown together with the W(g), W(bg) etc when you
> > click the 'hint' button.
> > The winning chance refers to the chance of just winning the game, so
> > it should be the same for moneygame and matchplay. Or at least in
> > cubeless bearoffs it should, because there are no gammons to save and
> > all that.
> >
> > Misja
> Keep in mind that cubeless evaluations depend on cubeless/cubeful
> setting since the moves may depend on the score and cube value. So can
> you show me the output without the 2 sided db and without cubeful
> evaluation.

I think it's simpler than that: 

- open the money position, ask for a hint at 0/1/2/3ply: the GWC will not 
change, as they always come from the 2s bearoff db. 

- open the match position, ask for a hint at 0/1/2/3ply: the GWC will 
change each time. I suspect this comes from the fact that gnubg takes 
0ply GWC (for positions N plies ahead, if we are a N-ply) from the 2s 
db and then apply 1/2/3 ply on top. I think gnubg does this because he 
does the same for cubeful equities. It would probably be better/more 
logical to take cubeless GWC for the current position from the dB, 
without any ply applied on top. 

In other words, for match play: for a 2ply eval (cubeful and cubeless) 
gnubg needs 1ply eval of subsequent positions which needs 0ply eval of 
"subsequent subsequent" positions. I think 0ply cubeless GWCs of 
"subsequent subsequent" positions come from the dB, but then they are 
plied to get 2ply cubeless of the original position (just like 0ply 
cubeful, obtained via janowski'd formula, are then plied to get 2ply 
cubeful of the original position). 

Side question (purely theoretical): is it true that cubeless GWC 
(including g and bg %) for a given position are the same no matter the 
score (including money play) ? 

This is somehow similar to supposing that the gammon ratio or percentage 
is the same across the whole MET ... 


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