Re: [Bug-gnubg] Gap in guestimated ratings?

[Joern Thyssen]

On Sat, Jan 25, 2003 at 10:24:34AM -0500, James F. Kibler wrote
> 
> 
> Joern Thyssen wrote:
> > 
> > On Fri, Jan 24, 2003 at 01:13:21PM -0500, James F. Kibler wrote
> 
[snip]
> I see that the gap is caused by the slight error in the exponential
> interpolation for error rates above 0.030.  If you remove the factor of
> 10.0 on the rating, the gap will disappear.

The formulae should be:

return 500.0f + 1000.0f * exp ( 0.30f - 10.0 * r );

The factor of 10 is introduced to decay faster towards 500. With a
factor of 1 an error rate of -1 (which is almost impossible to obtain)
will give you an rating of 867. With a factor of 10 you'll get a rating
of 500.

However, it's still guestimates :-)

> One might wonder why you resort to exponential interpolation since
> presumably the error rate per decision cannot exceed 1.  

The error rate per decision can easily exceed 1 (for example, if you
cube decisions are really lousy).

> The lower bound of the linear interpolation could have been set to 1
> and just  do linear interpolation throughout the range?
> 
> As an aside, the error rates are reported in the match statistics as a
> negative number.  The sign must be changed before the rating function is
> called?  

Yes, although is the other way around: gnubg changes the sign when
writing the match statistics.

> What is the second argument (n) to the rating function?

The match length. The current interpolation scheme does not use it.

> Even with this correction, the ratings seem to be biased high relative
> to FIBS.  I'll continue to collect some data to improve the guestimate,
> but it will take me a while to reach a gazillion samples.

:-)

Jørn