[Ifeffit] Problem with XAS Viewer

Xinyue Wang xyw0719 at gmail.com
Mon May 4 12:54:01 CDT 2020

Hi Matt,

I am trying to fit the main peak. So, to do the general peak fitting,
should I use the pre-edge peak tab in XAS viewer or other tab?
Thanks for your help.


On Sun, May 3, 2020 at 6:22 AM Matt Newville <newville at cars.uchicago.edu>

> On Sat, May 2, 2020 at 3:18 PM Xinyue Wang <xyw0719 at gmail.com> wrote:
>> Hi Matt,
>> Thanks for your detailed instructions. I am just trying to follow the
>> steps and see how it works. I am not trying to do complicated things.
>> My issue is I would expect the grey vertical lines after press the "Fit
>> Baseline" button, but nothing shows up. I tried to select a
>> larger region(which was not pre-peak), also nothing happened. So I am
>> confused.
> From what I saw of your screenshot (not much to go on, really), it was not
> obvious that your data has much (possibly "any") pre-edge data.  It also
> shows as "scaled y" vs "x", which suggests that the data wasn't even read
> in as XAS data.
> Besides, can I use the XAS Viewer to do main peak fitting?
> Well, I guess another way to put that is: yes, you probably can use XAS
> Viewer to do general-purpose peak-fitting.  It is not really designed for
> that, but you might be able to make that work.  If that is what you want to
> do.   Is that what you are trying to do?
> I know that Larch has its own language based on python. I am wondering can
>> I use larch function, like fitting peaks in Jupiter Notebook?
> You can use larch as a Python library, or use the lmfit Python library to
> do the fitting.   Some Larch functionality, notably the plotting and GUI
> aspects, may not work well from a Jupyter notebook.
> If you're using Python or Jupyter notebook, you probably don't really need
> to use the Larch language for most XAS processing and analysis
> functionality.
> Hope that helps,
> --Matt
> PS:  I should say that if one is really doing Feff-based fitting with
> `feffit()`,  it is still really, really helpful to create a
> `larch.Interpreter()` and pass that around to all of the corresponding
> functions.   Over the past year or so, this requirement has been removed
> from most of the Larch functions but the functions for doing Feff-based
> fitting are more intertwined and so keep some "state information" within a
> "session".  But that seems separate from the question here.
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