[Ifeffit] Fitting multiple spectra simultaneously with Larch

[Matt Newville]

Hi Casey,


Sorry for the late reply - I see that you asked this question 2 weeks ago
- I think I got the same question from someone else by private email the
same day....  I have had this question several times this summer.  Anyway,
sorry for missing this.

Larch can definitely fit multiple spectra at one time, co-refining
parameters.   An example of fitting 3 datasets (Cu K edge at 3
temperatures) is at

https://github.com/xraypy/xraylarch/blob/master/examples/feffit/doc_feffit3.lar

That is, you create several "Feffit datasets".  Each of these has a group
for the chi(k) data, a "transform" that gives the Fourier (or Wavelet)
Transform configuration and the fitting ranges, and a list of Feff Paths.

Different data sets can use the same transform and reuse Feff Paths. You
will also have a Parameter Group with all the variables and other
Parameters used to calculate the Path Parameters for each Feff Path.
Anyway, yes, Larch can definitely fit multiple datasets.

But: The XAS Viewer GUI does not currently (yet?) support this -- it helps
build a model, do the fit, and inspect the results for one dataset.  It
also helps write out the larch script to do the fit.  One approach could be
to use that:  use the GUI for "simple stuff" and interactive data
exploration, but use a script for more complicated and involved analyses.

I'm not opposed to adding fitting of multiple data sets in the XAS Viewer
GUI, but implementing it in the current GUI framework seems challenging (it
was definitely challenging for Artemis too).   I've heard some good
suggestions, but I'd be curious to hear (either here or via private email)
what others would like to see or suggest.

I guess that question really extends to other aspects of Larch and XAS
Viewer: if there are features, analysis approaches, or GUI tools that you
think could be better, let me know.

On Mon, Sep 12, 2022 at 11:30 AM Van Stappen, Casey M <
casey.vanstappen at austin.utexas.edu> wrote:

> Dear Ifeffit team,
>
>
>
> I’d like to fit multiple EXAFS spectra simultaneously in Larch using
> several common parameters/relative restraints, but have not found a way to
> do so (yet). I’ve gone through Dr. Matt Newville’s youtube tutorials
> (generally very helpful), but this topic doesn’t seem to have been covered.
> Any suggestions? Thanks!
>
>
>
> Best,
>
>
>
> Casey Van Stappen
>
>
>
> ------------------------------------------------------------------------
>
> Dr. Casey Van Stappen
>
> University of Texas at Austin
>
> Robert A. Welch Hall, 4.318
>
> 2350 Speedway
>
> Austin, TX 78705
>
> USA
>
>
>
> Phone: +1 (512) 775-2658
>
> E-mail: casey.vanstappen at austin.utexas.edu
>
>
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-- 
--Matt Newville <newville at cars.uchicago.edu> 630-327-7411
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