[Ifeffit] Problem with XAS Viewer

Matt Newville newville at cars.uchicago.edu
Sun May 3 08:21:43 CDT 2020

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

Hope that helps,


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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