[Ifeffit] energy resolution

[Bruce Ravel]

On 04/20/2015 12:01 PM, Lisa Bovenkamp wrote:
> Now here is question 1:
> What is the combination of the two profiles in the Athena peak fitting routine for the Pseudo-Voigt?

Hi Lisa,

Athena uses Ifeffit for this.  Ifeffit's pseudo-Voight function is 
implemented here:

  https://github.com/newville/ifeffit/blob/master/src/lib/conv_lor.f#L314

(Larch's is explained here: 
http://xraypy.github.io/xraylarch/fitting/lineshapes.html)

In Athena, gamma is the mixing parameter for the pseudo-Voight.

That said, this might not be doing quite what you are looking for. 
Ifeffit's implementation uses the same width for both functions (as does 
Larch), which does not seem to be what you are asking for.

I suppose you could try using two lineshapes, one Gaussian and one 
Lorentzian, which share a value for the centroid.  That is possible in 
Athena as long as you don't float the centroids.  While floating a 
common centroid is possible in both Ifeffit and Larch, there is no way 
to indicate that in Athena.  I'm not sure off the top of my head how to 
interpret the amplitudes in that situation to extract a value equivalent 
to gamma.

Perhaps Athena isn't the right tool for the job?  Or perhaps you can 
figure out something that does what you want using either Ifeffit or 
(preferably!) Larch?  In that case, let me know and I'll see about 
including it in Athena.

B

-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
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