[Ifeffit] Ifeffit Question

[Matt Newville]

Hi Nicholas,

On Wed, Oct 7, 2020 at 10:02 PM Nicholas Weingartz <
nicholasweingartz2024 at u.northwestern.edu> wrote:

> Hello List,
>
> I'm having a strange problem with my EXAFS fits in Artemis in which they
> seem to fly off at higher k.  I was having trouble with background fitting
> a particularly messy data set and I wanted more control over this so I used
> the program PySpline to fit the background after I did the rest of the
> preprocessing in Athena.  I then imported the data into Athena and loaded
> the project into Artemis.  Interestingly, when I only include a single path
> in the fit and plot both the single path and the overall fit, the single
> path does not fly off but the overall fit does.  I have attached an image
> of the issue.  When I use the spline fitting built into athena, I do not
> encounter this issue.  Has anyone ever experienced this issue before?
>
>
Sorry, but I'm not sure I understand what the issue is from that plot.  You
said "the single path does not fly off but the overall fit does" but I sort
of don't see that in the image you show.   Is something flying off there?

The k-range you show appears to be pretty limited to me, roughly k=3 to 9
Ang^-1.   For a single path, I can certainly believe that actually is the
"best fit" even if it not "very good".  But it's hard to say from only one
view of the fit.

If you suspect (or well, "made") the splines be different, I might suggest
looking at the mu0(E) arrays themselves, or perhaps plotting the k^2*chi(k)
for the two background subtraction.


--Matt

Thanks for your help!
>
> Nicholas Weingartz
>
> Ph.D Student
> Department of Chemistry
> Northwestern University
>
> [image: image.png]
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