[Ifeffit] Reporting math expressions in scientific papers

Bruce Ravel bravel at anl.gov
Mon May 2 13:21:47 CDT 2005

On Monday 02 May 2005 12:30, MauRo wrote:
> I would like to ask you if it exist one common convention, apart the
> XAFS society one, to report IFEFFIT results when you have unusual math
> expressions.
> In particular, I have used a two-phase model (two FEFF calculations)
> to fit my sample and for the amplitude variable I have these math
> expressions:
> amp_feff1 = amp * x
> amp_feff2 = amp * y = amp * (1-x)
> In this way I can estimate the global amplitude variable and introduce
> a "percentage" of the two chemical compounds (correlation is kept
> under control).
> How to explain what I have done to a non-ifeffiter?

In this case, your parameter can be described by fairly common
language.  Here you are fitting your spectrum as a linear combination
of the two phases and your parameter x is the "mixing parameter" or
"weighting parameter" used to quantify the contributions of the

This is one of the things I like a lot about Ifeffit's very general
way of parameterizing the fit.  You are free to define parameters
which have a direct physical interpretation and then hide the
implementation details in your math expressions, which can then be as
complicated as you need them to be.  Often, it is outside the scope of
a paper to provide all the ugly details and it suffices to just talk
about these parameters and their direct physical interpretations.
This might actually make it easier to discuss your exafs results with
the non-ifeffiter or even the non-exafs person!


 Bruce Ravel  ----------------------------------- bravel at anl.gov  -or-
						  ravel at phys.washington.edu
 Environmental Research Division, Building 203, Room E-165
 Argonne National Laboratory         phone and voice mail: (1) 630 252 5033
 Argonne IL 60439, USA                                fax: (1) 630 252 9793

 My homepage:    http://feff.phys.washington.edu/~ravel 
 EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/

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