Re: [Bug-gnubg] Bug: Double/Beaver

[Joern Thyssen]

On Thu, Aug 21, 2003 at 09:05:54AM -0400, Christopher D. Yep wrote
> At 12:51 PM 8/21/2003 +0000, Jørn Thyssen wrote:
> >On Thu, Aug 21, 2003 at 08:35:25AM -0400, Christopher D. Yep wrote
> >
> >> Here is the output from Analyse - Evaluate:
> >>
> >>         Win     W(g)    W(bg)   L(g)    L(bg)   Equity    Cubeful
> >> static:  42.0%   34.2%    7.7%   12.8%    0.1%   -0.159    +0.032
> >>  1 ply:  42.6%   28.6%    6.2%   11.1%    0.1%   -0.148    -0.396
> >>  2 ply:  38.3%   28.2%    6.2%   14.7%    0.0%   -0.235    -0.389
> >>
> >> Cube analysis
> >> 2-ply cubeless equity  -0.038
> >>    38.3%  28.2%   6.2% -  61.7%  14.7%   0.0%
> >> Cubeful equities:
> >> 1. Double, take         -0.236
> >> 2. Double, pass         +1.000  ( +1.236)
> >> 3. No double            -0.389  ( -0.153)
> >> Proper cube action: Double, beaver
> >
> >This is _before_ the double. Try _after_ the double!
> 
> Oops, I wasn't thinking clearly.  My eyes were immediately drawn to the 
> -0.235 without looking at the column headings!
> 
> >No, the equity-column is supposed to be the cubeless equity, but I can
> >see there is a small bug in the calculation. The cubeful column is the
> >interesting one.
> 
> Right, the cubeless equities reported don't seem to match up with the 
> win/gammon/backgammon figures reported.  E.g. 2-ply cubeless equity should 
> be .383 + .282 + .062 - (1 - .383) - .147 - .000 = -.037.

The cubeless equity is calculated with the current gammon price of 0
(due to the jacoby rule). I better change that.

> 
> Here's Analyse - Evaluate after I move a 2-cube over to the other side:
> 
>         Win     W(g)    W(bg)   L(g)    L(bg)   Equity    Cubeful
> static:  42.0%   34.2%    7.7%   12.8%    0.1%   +0.131    -0.066
>  1 ply:  42.6%   29.0%    6.8%   11.2%    0.1%   +0.096    -0.083
>  2 ply:  38.3%   28.6%    7.1%   14.9%    0.0%   -0.027    -0.107
> 
> Ok, so now I match your reported numbers exactly (you wrote: "0.383 0.286 
> 0.071 0.149 0.000 -0.027 -0.107").  But that means that there's another bug 
> as -0.107 is quite different from -0.236.

No, I do expect a value around -0.1 since the value is being reported
normed to 1. In the cube analysis the "no double" equity is reported
normed to 1 and the "double, take" equity is reported normed to 2 (for
money play -- for match play we use MWCs).

The difference probably comes from "chequer play according to score".
For the cube decision gnubg plays according to the undoubled cube, but
for the evaluation after the double gnubgs plays according to the
current cube (i.e., the 2-cube). This may cause gnubg to play
differently at the intermediate plies leading to different gwc and
equities[*].

Jørn

[*] This problem is due to the forward pruning we employ, and will
hopefully be fixed in the future by Thomas Hauks implementation of the
*-minimax algorithm.

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