[Ifeffit] Number of independent points: Artemis & Feffit

[Matt Newville]

Hi Mauro,

> In my case the difference (+2 value) is with the command line program "feffit". I mean,
> giving a feffit.inp file to feffit I obtain a  different result than using Ifeffit/Artemis with the
> same paths/variables.
>
> To be more precise, my question should be: why differs the minimization feffit() function
> in Ifeffit  with the "feffit" command line program?

Yes, the calculation of the number of independent points changed
between Feffit and Ifeffit.   It was decided to be more conservative
and to avoid the potential abuses of the '+2' issue.   With the older
calculation, it is "allowed" to fit 2 parameters with Delta k = 0.1
and Delta R = 0.1.  That might give the impression that one can use
EXAFS tp determine distance and coordination number without any data. 
EXAFS analysis often has a bad reputation, so I hope you'll forgive me
for not wanting to give that impression.

For backward compatibility, and the benefit of the few Feffit users
(most of whom are assumed to know about these issues and act
responsibly to avoid them) Feffit was not changed..

--Matt