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