[Ifeffit] Log-ratio method
bravel at anl.gov
Tue Apr 11 14:19:28 CDT 2006
On Tuesday 11 April 2006 12:19, lisandro at fisica.unlp.edu.ar wrote:
> Hi, I recently realized that Athena implement the ratio method as an
> analysis tool. I have look in the ifeffit web page and Athena manual
> and can not find any manual or user guide. Does anyone know any kind of
> instructive or manual for this type of analysis with Athena?
You have found yet another example where documentation lags behind
inmplementation. Since you have brought it up, I'll try to find some
time in the next couple of weeks to write up a document page for the
In the interim, if you are familiar with how other tools in Athena
work, then you should be able to figure out how to drive the LR tool.
1. Analysis menu -> Log-ratio
2. Select one of the data groups as the Standard using the drop down
menu on the LR/PD page.
3. The unknown data is the one selected in the groups list, i.e. the
one highlighted in orange.
4. The parameters for the FT and fitting are, by default, the
parameters of the standard. But you can change them by hand on the
5. Click the fit button and the standard LR/PD fits are done as
described in Grant Bunker's paper in Nuc. Inst. and Methods 207
6. The cumulants get written to the little box below the fit button.
You may need to play around with the FT and fit parameters to get
7. There are buttons for plotting the phase and amplitude parts of the
fit. There is a button for writing out the results of the fit to a
column data file.
I should also say that this part of Athena is not particularly well
tested, so if you have any feedback, suggestions, bug reports, hate
mail ;-) -- feel free to send them along.
The ifeffit distribution (Windows) and the horae tarball both come
with a set of example data files. Included among them are a number of
scans of an copper foil at different temperatures. That seems like
good data to play around with to learn how to use the tool since you
already know the answer.
Bruce Ravel ---------------------------------------------- bravel at anl.gov
Molecular Environmental Science Group, Building 203, Room E-165
MRCAT, Sector 10, Advanced 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/exafs/
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