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[Bug-gnubg] Absolute FIBS rating formula

From: Philippe Michel
Subject: [Bug-gnubg] Absolute FIBS rating formula
Date: Sun, 27 Jul 2014 22:26:07 +0200 (CEST)
User-agent: Alpine 2.11 (BSF 23 2013-08-11)

On Sat, 26 Jul 2014, Michael Petch wrote:

I will be building the next release of GNUbg (1.03.000) next Sunday
evening. So any changes that one may have should be put in as soon as
possible so testing can occur.

I have redone the simulations from Kees van den Doel that led to the "Error based abs. FIBS rating" in match statistics :

This number became quite inaccurate years ago when the definition of a "close cube decision" changed. The cube errors rating loss is underestimated by a lot. On the other hand the offset used to get the absolute rating is 2050 when the rating of the bots based on gnubg 2ply is more like 2150.

The old formula is :

R = a2(N)*EPM+b(N)*EPC,
a2(N) = 8798 + 25526/N,
b(N) = 863 - 519/N.

and what I got is :

a2(N) = 11877 + 32191/N,
b(N) = 4766 - 5285/N.

As you can see, the grading is tougher and the higher base rating of gnubg may or may not compensate for it depending on the level of play.

I'd be interested if someone who has a fair database of FIBS matches (I don't) could check if these new values are realistic. I'm not familiar with the Python API, but I suppose it should be possible to write a short script that loads an already analyzed match and shows the FIBS rating from both formulas.

I'd be interested by more accurate data from people running bots on FIBS, preferably if they use the 1.0 weights file : what is their average rating for various levels of play ? And are they cheated by droppers in a significant way ?

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