[Ifeffit] Another ATHENA error

Bruce Ravel ravel at phys.washington.edu
Wed Jan 12 13:19:41 CST 2005

On Wednesday 12 January 2005 09:38 am, Norbert Weiher wrote:
> just to throw another one in :)

The more the merrier!

> ATHENA has the following problem - I make a linear combination fit of two
> spectra and put the result in a group. Then I want to export it using the
> "save groups as..." and.... just get zero's in the file. Using the IFEFFIT
> buffer and saving the corresponding array with the write_data() command
> works fine - maybe there's a renaming bug of the corresponding array?
> Furthermore, the fit looks shifted as soon as written to an array. When I
> fit (the 3rd spectrum in the example with a LC of the first two) everything
> looks nice. The saved LC is, however, shifted compared to the one seen
> during the fit. Furthermore, I cannot change any parameter of this (LC)
> group...

You are correct on all counts.  The energy shift was due to the fact
that I applied the e0 shift of the unknown data group twice to the LCF
data group.  Oops!

I am not completely sure why it was being saved as all zeros, but
fixing other problems also solved that.

You could not change the parameters because, long ago, I had decided
to save the LCF-in-energy data as a detector group.  My thought was
that an artificial data group should not be analyzed like real data.
There really isn't a good reason why the LCF-in-energy group should
not be treated that way.  For instance, it might be interesting to
remove the background from the LCF-in-energy group to see if its
chi(k) looks like the chi(k) of the unknown data.  In any case, I
changed that so now you can treat LCF-in-energy data just like real
measured data.

All of those fixes will be in the next release.

Thanks, Norbert!

 Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
 Code 6134, Building 3, Room 405
 Naval Research Laboratory                          phone: (1) 202 767 2268
 Washington DC 20375, USA                             fax: (1) 202 767 4642

 NRL Synchrotron Radiation Consortium (NRL-SRC)
 Beamlines X11a, X11b, X23b
 National Synchrotron Light Source
 Brookhaven National Laboratory, Upton, NY 11973

 My homepage:    http://feff.phys.washington.edu/~ravel 
 EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/

More information about the Ifeffit mailing list