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

[Joern Thyssen]

On Wed, Aug 20, 2003 at 02:14:22AM -0400, Christopher D. Yep wrote
> Windows XP, GUI version
> Version 0.14-devel 1.1282 030818 (build Aug 19 2003)
> 
> gnubg misinterprets the following evaluation:
> 
>     GNU Backgammon  Position ID: 27ZCFADbtgEDQA
>                     Match ID   : cAkAAAAAAAAA
>     +24-23-22-21-20-19------18-17-16-15-14-13-+  O: gnubg
>     | O  O  O  O  O  O |   | O           O  X |  0 points
>     | O  O  O  O  O    |   |                X |
>     |                  |   |                  |
>     |                  |   |                  |
>     |                  |   |                  |
>     |                  |BAR|                  |v (Cube: 1)
>     |                  |   |                  |
>     |                  |   |                  |
>     |                  |   |                  |
>     | X  X  X  X  X  X |   |                  |  On roll
>     | X  X  X  X  X  X | X |          O  O    |  0 points
>     +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: Chris
> 
> 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
> 
> [Jacoby rule used above]
> Correct cube action, based on the above numbers is actually 
> no-double/beaver.  Double/beaver is worth -.472 to X which is worse than 
> the -.389 he can get from holding the cube.

No, as gnubg writes the value of double, take is -.236. The value
reported does include the value of the cube! So the logic is correct:
this is a double, beaver.

Here is a plain evaluation of the position after the double:

        Win     W(g)    W(bg)   L(g)    L(bg)   Equity    Cubeful  
 2 ply: 0.383   0.286   0.071   0.149   0.000    -0.027    -0.107   

My version of gnubg running under windows is quite old so you don't see
the expected value of -0.236/2 = -0.118. 

Can you set up the position after the double and run Analysis->Evaluate?
You should see a cubeful equity (normed to 1) of -0.118. Hence the value
of double, take before the double is -0.236.

Jørn

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