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Re: [Bug-gnubg] Removal of absolute fibs ratings

From: Christian Anthon
Subject: Re: [Bug-gnubg] Removal of absolute fibs ratings
Date: Tue, 5 Sep 2006 10:11:47 +0200

I agree assigning skill levels to backgammon players is a very complex
matter and what is difficult varies from player to player. As to your
position you must remember that gnubg counts close doubles and not
non-obvious cube actions. In the position the cube actions may be
non-obvious, but they certainly aren't close.


On 9/4/06, Albert Silver <address@hidden> wrote:
I think it is rather complicated. Admittedly, some doubles with such
an equity difference can seem absurd, but many will leave players very
much in doubt, especially if they are dependent on the score. Here is
an example:

 GNU Backgammon  Position ID: 7LYBAGPN3QYgIA
                 Match ID   : MAFgAAAAAAAA
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     O: GNU
 |                O |   | O  O  O  X  O  O |     0 points
 |                O |   | O  O  O  X  O    |     On roll
 |                  |   |    O  O          |
 |                  |   |                  |
 |                  |   |                  |
^|                  |BAR|                  |     3 point match (Cube: 1)
 |                  |   |                  |
 |                  |   |                  |
 |                  |   |       X          |
 |                X | X | X  X  X  X       |
 |             O  X | X | X  X  X  X     O |     0 points
 +13-14-15-16-17-18------19-20-21-22-23-24-+     X: Albert

Cube analysis
2-ply cubeless equity  +0.3741 (Money:  +0.2537)
   51.93%  29.02%   1.08% -  48.07%   8.47%   0.14%
Cubeful equities:
1. No double            +0.3045
2. Double, pass         +1.0000  ( +0.6955)
3. Double, take         +0.0365  ( -0.2681)
Proper cube action: No double, take (27.8%)

This situation occured in a game of mine, and my opponent sent the
cube. It is a blunder to send, over 0.250, and a larger one to pass. I
had no idea what to do, and analyzed quite some time before taking.
I've analyzed it and understand better, but even if it is in blunder
territory, I don't think that it is so obvious to all, despite the
potential size of the mistake.


On 9/4/06, Christian Anthon <address@hidden> wrote:
> The threshold of 0.25 seemed too large for common sense, far too many
> doubles very counted as being close, but also the function was plain
> stupid and hard to understand. For example all too-good positions were
> counted in for some reason. The threshold could be set back to 0.25
> for counting of the doubles, but it would still be difficult to guess
> the average relation between the old and current versions of the
> function.
> Christian.

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