[Ifeffit] Re: your mail

[Matt Newville]

Hi Jacob,

Jacob Shokes (jshokes at chem.uga.edu) wrote:

> I had a question I was hoping you could help me with.  I have imported a
> bunch of ASCII type files into Athena and averaged them all together.  The
> ASCII files contain the Energy, detector file, I0, I1, and I2.  After I
> average the files together, I want to save the file and export it as an
> ASCII file.  I understand how to do this, but when I do it I only obtain
> the Energy, [detector/IO], and background in column three (like it states
> in the manual).  Now what I want to do, is extract the averaged I0 column
> from the process.  Is there anyway to do this or will I just have to
> average I0 in another software.  Any help with this would be appreciated.

Sorry for the delay - I was away at the EXAFS conference, and am
still catching up on email.  I hope it's OK that I forward this
question to the ifeffit mailing list, as others might have similar
questions, and Bruce Ravel might have a better answer.

I believe you'd have to average all the I0 values yourself, and that
athena cannot do this easily.  Bruce might correct me on this....  
It would be possible to do this using the Ifeffit commands directly
(including in the athena command window), something like this:

  read_data(mydat.001, group=a001, label='energy if i0')
  read_data(mydat.002, group=a002, label='energy if i0')
  read_data(mydat.003, group=a003, label='energy if i0')
  ave.energy = (a001.energy + a002.energy + a003.energy ) / 3
  ave.if     = (a001.if + a002.if + a003.if ) / 3
  ave.i0     = (a001.i0 + a002.i0 + a003.i0 ) / 3
  write_data(file= ave.dat, ave.energy, ave.if, ave.i0)

In most cases I don't think you really want to do this, or use an
averaged I0 signal.  For EXAFS data in transmission or fluorescence
(or electron yield), log(I0/I1) or IF/I0 can be averaged and merged,
but averaging I0 may not be meaningful. On the other hand, you might
be looking for typical I0 count rates, and the variations in I0, in
which case such averages might be useful.

Hope that helps,

--Matt