[Ifeffit] Bug report: Athena, multiple data export

Matt Newville newville at cars.uchicago.edu
Sun Oct 10 23:08:32 CDT 2021


Hi Soyoung,

On Fri, Oct 8, 2021 at 5:29 PM Soyoung Kim <soykim at lbl.gov> wrote:

> I see. Thank you for the quick reply.
>
> But would it be difficult to program it so that it will export properly,
> e.g., with multiple energy axes?
>

Sorry for the slight delay, and I have two answers here:

In general, it depends on what "export properly" means. If you save the
project file, the original, differing energy arrays will be retained.  If
you export to a simple ASCII column file (which is pretty ubiquitous in
scientific data), then each numeric row will be (or perhaps "is likely to
be") interpreted as the same "x" axis (energy or perhaps time - the
independent variable).   So, if you have multiple sets of data with
differing x/energy values, either you have missing values for some data
sets or you have data in rows without a consistent x/energy, and possibly a
different number of rows per column.  Many programs will struggle with such
data files.

But....

Because when the data is plotted as a graph, it is hard to tell whether or
> not the x-axes are the same... And if you are processing data from someone
> else, you may not know whether or not they were collected with the same
> energy step settings.
>

That's all true.

And also: it looks to me that the exported data from this project looks
like it is not interpolated as well as it could be. There is a definite
shift in energy in the EXAFS region.

If I read that project into Larch's XAS Viewer and export it as a CSV file
it also interpolates all arrays onto a single energy grid (by default, the
first data set) and it looks better to me (see attached file -- needs
development version of XAS Viewer for this level of details).

I'm not entirely sure where the problem is. It does look like one of the
data sets has two energy points that are very close together as the data
transitions from constant energy steps in the XANES region to wider steps
in the EXAFS region.  That should not cause a problem, but I think that I
do recall that there were some such problems in the past.

We've tried to make XAS Viewer a replacement for Athena and Artemis.   I am
aware of a few missing features, but there are also several features not in
Athena.  I can say that it would be easier for me to fix things with
Larch/XAS Viewer than it is for me to fix things in Athena.

I'm not sure that resolves the issue, but I hope it helps.

--Matt
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