[Ifeffit] trying to start...

[Bruce Ravel]

On Friday 27 August 2004 09:04 am, Mauricio wrote:
> I'm in troubles when trying to work with my L3-Pb absorption data
> with Athena. I'm a beginner with the Ifeffit stuffs...  Also, sorry
> if this report is not correctly posted, but I will try to give you
> the maximum information I can...
>
> Let's go. The data were taken at the Brazilian syncrotron laboratory, and
> the "important" data are in columns 3 (energy), 4 (Io) and 6 (It). The file
> is of the following form:

Hi Mauricio,

It seems that the problem is with the first two columns, which contain
date and time information.  Athena relies upon Ifeffit's notion of
what is and is not a line of data in a file.  For Ifeffit, a line of
data is a line which contains only strings which are recognizable as 
floating point numbers.  Strings such as "04/02/04" and "12:32:51",
though obvious to the human reader, are not interpretable as numbers
by Ifeffit.  So Ifeffit reports that it could not find *any* lines
containing data in your file.  Athena should have complained about
that without issuing an error message, but apparently there remains a
problem.

The immediate solution is to edit the data file and remove the first
two columns of data.  I suspect that Ifeffit and Athena will then be
happy with your data files.

There are two more permanent solutions.

1.  Convince the person who maintains the data acquisition software at
    your beamline to use a file format that Ifeffit can read.
    Alternately, disable the recording of date and time with every
    data point.

    Frankly, it seems silly to record the date at every point.  EXAFS
    scans are typically on the order of minutes.  It should be
    sufficient to record the data once at the top of the file.  The
    same is probably true of the time, although I can imagine
    situations where the time is useful information.  In that case,
    recording the start time at the top of the file and recording a
    column of elapsed seconds serves the same purpose and would not
    confuse a program expecting floating point numbers in the data
    columns. 

2.  It may be impossible for some reason to have the data file format
    changed, but there are people doing exafs and wanting to use
    Athena.  That was the case with beamline X10C at NSLS.  There is
    special code in Athena to recognize a data file from X10C and
    rewrite it in a way that Ifeffit will handle.  I am willing to do
    the same for other beamlines, but I would need several examples of
    data to work with.

B

P.S. That was a dandy problem report.  You gave me sufficient
     information to understand the problem, which is all I ever ask
     for.  Thanks!


-- 
 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/