On Tuesday 08 July 2003 02:02 pm, Grant Bunker wrote:
I think the easiest thing to implement in feffit however would be simply to do a series of minimizations with (say, 1000) random starting points in the parameter space. This would just entail wrapping the minimization in a loop, and adding a way to summarize the results.
Minimizations starting at differentpoints may end up in the same or different "attractors". If those corresponded to bad fits, throw them out. If they are adequate fits, keep them. Quite possibly more than one attractor could fit the data adequately. A cluster analysis of the results should indicate whether different solutions are equivalent (belong to the same attractor) or not.
If Norbert or anyone else is interested in playing around with what Grant suggests (or even one of the admitedly less-clever raster schemes that I suggested), I have a suggestion. One thing that Artemis will do for you is to write a script of ifeffit commands for doing a fit using the data and feff calculation currently imported. See the second item in the Edit menu. This script can be saved to a file and used as the basis for, say, a perl or python script to do any of the explorations of parameter space that have been discussed today. Here are some excellent notes from Matt explaining how to call ifeffit from perl, python, or C: http://cars9.uchicago.edu/ifeffit/refman/node106.html This is exactly what Sam and I do in our programs. And please do report back to this list. We'd love to know what you find! B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 222 Naval Research Laboratory phone: (1) 202 767 5947 Washington DC 20375, USA fax: (1) 202 767 1697 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b, X24c, U4b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/