On Wednesday 14 December 2005 10:21, Stefano Ciurli wrote:
Here is an example. We find with IFEFFIT (we use Dk= 10 (from 2 to 12), DR=5 (from 1 to 6).
chi^2 = 87.1 reduced chi^2 = 3.7 parameters: E0, three distances and three sigma^2 we set S0^2 fixed to 1 R-factor: 1.15%
The ratio between chi^2 and reduced chi^2 is 23.54, which is not an integer number as we would expect. Plus, this number does not correspond to Ninp -Nvar (31.83 - 5 = 26.83)
According to what you said above, Nvar = 7, so nu=24.83, which is much closer to 23.54. That still seems bigger than rounding errors, though. Here is my understanding of Ifeffit, but I am sure Matt can elaborate. Background removal uses the integer part of dk*dr*2/pi+1 to determine the number of knots. Fitting uses dk*dr*2/pi as a real number to determine Nidp. In any case, that's what Artemis reports when you ask it how many independent points in a project. My memory is that I checked it against Ifeffit's report of Nidp. B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advance Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/