On Thursday, April 05, 2012 12:59:55 am John Farell wrote:
Hi..
Can you please explain me how to report the errors of EXAFS parameters like bond length, Co - ordination number, disorder etc. (Or how to obtain those errors ??)
This topic is discussed at length in the standard online resources for EXAFS and for our software. Ifeffit's error reporting is reasonably well explained in its documentation. See http://cars9.uchicago.edu/ifeffit/Documentation Artemis reports all of Ifeffit's error reporting in the log file of each fit. Ifeffit uses a Levenberg-Marquardt, non-linear, least-squares minimization. Error bars and correlations are taken in the standard manner form the covariance matirx, with the caveat that the error bars are scaled assuming that the fit was good and that the measurement uncertainty, epsilon, was incorrectly evaluated. Thus, if you actually like the fit, the error bars are scaled to the correct size. I talk about all this at some length in my "Advanced Topics in EXAFS Analysis" talk, atea.pdf at https://github.com/bruceravel/XAS-Education/downloads I am not really certain what you mean by "how to report" them. I usually say something like "<best fit> +/- <uncertainty>" for any number I report. If you use a lot of constraints in a fit, you will need to do error propagation by hand -- neither Ifeffit nor Artemis attempt to do error propagation. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/ifeffit/Demeter