[Ifeffit] Log-ratio method

Bruce Ravel 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?
> Thanks

Hi Lisandro,

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
LR/PD utility.

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
   LR/PD page.
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
   (1983) 437-444.
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
   decent-ish fits.
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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