On 03/23/2015 08:54 AM, Rana, Jatinkumar Kantilal wrote:
The term N*S02 is fitted for each path of the FEFF calculation. So my question is, even if we know N with a great certainty for some path, how can we vary both N and S02 for other paths ? or Did I understand it wrong ?
At no point in your emails did you say that you are using Artemis to do your fitting. The comment I am about to make may not, therefore, be relevant to you. In Ifeffit and Larch -- and therefore in Artemis -- we DO NOT fit N*SO2. Fits in Ifeffit, Larch, and Artemis use a set of user-defined parameters as the variables of the fit. As part of the fitting model, the user relates the variables of the fit to the parameters of the EXAFS equation using math expression. This benefit of the generality of the fitting model allows the user to easily encode prior knowledge into a fit. The cost is that the parameters have to be interpreted in some kind of physical context. To answer you question specifically, Artemis allows you to set or float parameters for N and S02 and to define the amplitude term of the EXAFS equation for each path in any way that you see fit. In that way, you can implement all the suggestions that Matt, Scott, and Chris have made. I discuss this in some detail starting at page 35 of this presentation. https://speakerdeck.com/bruceravel/advanced-topics-in-exafs-analysis Among the lectures at http://www.diamond.ac.uk/Beamlines/Spectroscopy/Techniques/XAS.html, this is the one called "Fit Evaluation and Fitting multiple structures". HTH, B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/