[Ifeffit] re:fits

[Bruce Ravel]

On Wednesday 07 January 2004 02:51 pm, k-kupiecki at northwestern.edu wrote:

> I just wanted to thank Matt, Bruce and everyone involved with
> IFEFFIT/Artemis/Athena... it has been a Godsend.... I couldn't have
> stumbled on it at a better time (I'm frantically trying to analyze about
> 4 beamtimes worth of SEXAFS data for papers and my thesis and WINXAS
> wasn't really working out for me)!!!!!

Well, thank you very much, Kristine.  Email like this one of the great
rewards of working on the codes and one of things that keeps me going.
Best of luck with the thesis!

> Does anyone have any suggestions for additional literature in
> regards to better understanding the quality of fits and the
> parameters involved?....

Have you looked through all the stuff linked to on Matt's XAFS page?
   http://cars9.uchicago.edu/xafs/

> or perhaps know when we might be able to expect a updated version of the
> Artemis literature?  (What is currently there has helped me sooo much
> that I've been checking for an update every couple of weeks hoping to get
> see sections 2.2-3.2..... )

Uhhhh....  hmmmm.... okay, everyone, move along.... nothing to see
here ...


> Also.... I guess I've realized that only knowing IFEFFIT with Artemis I
> kinda take things for granted (like I didn't know that IFEFFIT was having
> problems, in certain cases since I had only been checking the "Results"
> and the error messages on the bottom of the window....) which meant I
> missed errors like this in the IFEFFIT (since I didn't notice anything
> unusual in the "Results"):
>
> .............
> # Do the fit!
>
> ## fitting difference of Cov_0_06ML_bl1435_111703.chi and one or more paths
> ... ## === data set #1 of 1
> feffit(1-8, group=data0_fit, chi=data0.chi, k=data0.k,
>        kweight=2.00,  rmin=1, rmax=4, kmin=2.5, kmax=15, dk=2,
>        kwindow=kaiser-bessel, fit_space=R, do_bkg=no,
>        data_set=1, data_total=1)
> feffit fitting   1 data sets
> fitting ...
> fitting ...
> fitting ...
> fitting ...
> fitting ...
> fitting ...
> fitting ...
> fitting ...
> no uncertainties estimated!
> fit gave a warning message:
> too many fit iterations.  try again with better
> guesses or a simpler problem.
>
> ................................................
>
>
> I guess my question is.... is there anything else I should be looking for
> in the IFEFFIT printout that I might not otherwise notice by just using
> Artemis and looking at the error messages and "Results"?

That's the most important one to keep an eye on.  Artemis is pretty
good at making sure that all the other ifeffit commands are run in a
way that will not make ifeffit unhappy.  However, the only way to know
if ifeffit is happy fitting is to run the fit.

Certainly, if Artemis every starts behaving in some way out of the
ordinary, it would be prudent to scroll through the ifeffit buffer
messages.  Ifeffit may have told you something that will help you
solve your own problem.  Or it may help you make a bug report that
will better help solve the problem.

As you no doubt recall, you and I had an exchange on this topic last
month here on the mailing list.  Here's my response:
  http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2003-December/000602.html
The suggestions I made then still seem appropriate.

I started noticing the sort of situation that leads to the error
message that you cite before I went on holiday.  Artemis really should
be looking for that error message and post a warning to the user when
it happens.  I'll put that on the list of things to do.

B


-- 
 Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
 Code 6134, Building 3, Room 222
 Naval Research Laboratory                          phone: (1) 202 767 5947
 Washington DC 20375, USA                             fax: (1) 202 767 1697

 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/