On Thursday 02 December 2004 04:40 pm, Matt Newville wrote:
I agree that the algorithm to find E0 could be improved, especially for noisy and XANES-only data. The ideas Bruce added to athena seem like good approaches. FWIW, Ifeffit's E0 finding strategy is mostly tuned to avoid glitches in the extended XAFS. Therefore, it choose the point that has the largest first derivative provided that the previous two points have a positive first derivative.
It only looks in the first half of the energy array (counting by array index).
That would explain what was going on in Carlo's data.
It's quite possible that it would miss e0 in data with an unexpectedly long pre-edge.
I can see the argument that ifeffit should have been able to figure this out, but it does seem kind of silly to bin the data in the pre-edge such that the energy steps are about 1/2 volt. That vastly overspecifies the pre-edge.
Carlo wrote:
Grant has been using a differential evolution algorithm to take case of noisy data. Perhaps this could help?
I have no idea what that is. Does it help you and Grant?
Ditto. I would like to see a reference. B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 405 Naval Research Laboratory phone: (1) 202 767 2268 Washington DC 20375, USA fax: (1) 202 767 4642 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b 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/