[Ifeffit] Athena Artemis

[Bruce Ravel]

Wow!  This is a strange one.  I don't yet understand quite why this
problem is happening, but I do have a work-around and a hand-wavy
explanation for why the work-around works.

Here's the work-around.  When you import data from an Athena project,
you click on that group in the Athena import dialog.  In the attached
picture, you would click where I have drawn the red oval to select the
4th data group.  The work-around is to click twice on the group you
want to import.  Not double-click, but click ... wait for it to
display ... click again.  Then hit the import button.

Here's my incomplete understanding of this bug.  I noticed that when
you remove the background from that data group in Athena, the
background removal requires 4 iterations in its fit to come to a
conclusion.  When you import that Athena project file into Artemis and
click once on that data group, it requires 7 iterations.  When you
click again, it requires 4 iterations.  In several other scenarios
that I have investigated, it requires 4 iterations.  So, it seems the
background removal is being done incorrectly in the one-click case --
where "incorrectly" is defined as not consistent with all other
scenarios. 

So, why does it take 7 iterations in that one case?  I don't know yet.
As most of you know, Athena and Artemis are merely fancy front-ends to
Ifeffit.  When you click a button, A&A generate ifeffit commands and
send those command off to the Ifeffit library, which is hanging out in
the background out of sight.  When you use A&A, you are relying upon
them to place Ifeffit in the same state whenever you do the same
operation.  Something about the interaction of Artemis and Ifeffit in
our scenario is done wrongly (that is, inconsistently with the other
scenarios).  This different state leads to some small numerical
difference that leads to 7 iterations and George's slightly different
data. 

That's not a very satisfying answer, but I have been poking at this
for the last 2 hours and that's my story so far.

In conclusion:

  * George found am Artemis bug leading to a numerical difference in
    his data in a certain scenario

  * The work around for now is to click twice on your data when you
    import it into Artemis from an Athena project file.

Ugh!
B



On Thursday, May 12, 2011 03:18:03 pm Bruce Ravel wrote:
> Something funny is certainly happening as your data are imported from
> Athena into Artemis.  The two data sets, which are identical in
> Athena, become slightly different when processed by Artemis.  Odd.
> 
> I don't yet understand either what is causing the discrepancy nor why
> it manifests as a differnce at the high end of the spectrum.
> 
> I'll let you know if I figure this out.
> 
> B
> 
> On Thursday, May 12, 2011 01:23:47 pm George Sterbinsky wrote:
> > Hello,
> > 
> > I've noticed an odd behavior in Athena and Artemis and I was hoping
> > someone could explain it to me.
> > 
> > I've attached an Artemis file Data3.apj and an Athena file Data4.prj.
> > 
> > First open Data3.apj. Then from the Artemis file menu choose open, then
> > open Data4.prj and import the Data4.xmu file. Now plot the data in
> > k-space you will see a slight difference between the two spectra, most
> > noticeably above 15 k, so plotting in k^3 is best to see the difference.
> > 
> > Now close Artemis and don't save. Open Data4.prj with athena and choose
> > to import only the file Data4.xmu. Save the project as something else. I
> > saved as Data4C.prj, which I have also attached.
> > 
> > Close Athena and don't save. Open Data3.apj again. Then from the Artemis
> > file menu choose open, then open Data4C.prj or whatever you may have
> > named the file and import the Data4.xmu file, which should now be the
> > only data file in the project. Now plot the data in k-space and you will
> > find that the two data sets are now the same. The differences at high k
> > are no longer present. Can anyone explain what is going on here?
> > 
> > Thank you,
> > George

-- 

 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
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