[Ifeffit] Re: Ifeffit digest, Vol 1 #67 - 1 msg

Gustavo de Medeiros Azevedo gma109 at rsphy1.anu.edu.au
Tue Oct 22 04:34:06 CDT 2002

Dear Bruce  and Matthew,

I''ve recently started using  IFEFFIT,
and  I'm a bit confused on the way it estimates the error bars.
In the IFEFFIT Reference guide,  (page 38) you mention  the variables
epsilon_k and epsilon_r, where the measurement uncertainty is stored.
In that same page, you remark that changing the values of
  epsilon_k and epsilon_r will change chi_squared, Chi-reduced
but  won't affect R_factor and the error bars.
As far as I understand, the error bars should  given by  the diagonal elements
of the  co-variance matrix, multiplied by the square root of Chi_reduced.
  In this way, I would expect that varying epsilon_k or  epsilon_r
should affect the estimated uncertainties.

Could you, please, clarify  this point?

Best Regards,
Gustavo Azevedo

At 12:00 PM 17/10/2002 -0500, you wrote:
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>Today's Topics:
>    1. Re: using Artemis (Bruce Ravel)
>Message: 1
>Date: Thu, 17 Oct 2002 09:33:37 -0400
>To: ifeffit mailing list <ifeffit at millenia.cars.aps.anl.gov>
>Subject: Re: [Ifeffit] using Artemis
>Reply-To: ravel at phys.washington.edu
>From: Bruce Ravel <ravel at phys.washington.edu>
>I think you replied to me rather than to the list, so I am answering
>to list.
>You said:
>  jjr> It's great to have the hints on artemis usage. My friendly
>  jjr> suggestion would be to complement this with sample input/output
>  jjr> so one can follow along a worked example. The "examples" in the
>  jjr> artemis source are somewhat useful in this respect, but hacking
>  jjr> one's way wasn't completely straightford for me.
>I have been thinking about how to provide useful, interactive examples
>and documents for the programs.  It's difficult.
>The example projects for Artemis are certainly incomplete works-in-
>There is a README file in the examples directory for Athena that is
>helpful, but should, I guess, be an html file.  The project files in
>both programs' examples directories do have journal entries that help
>explain what's going on and give suggestions for other things to do.
>The journals are accessible from the Edit menu in either program and
>are a space for writing notes about the project.  The journal is saved
>in the project file along with all the data.  The idea is that you have
>a space to record note so that, in 6 months, you can recall why you
>did all the wacky things in the project.  Not using the journals?  You
>should be ;-)
>So, I agree that the examples are not all they could be.  It is
>actually hard for me to make good examples since I already know how
>the programs work.  Good examples are something the people on this
>list could put together and contribute.  That would be extremely
>welcome and an excellent, non-programmer's way of giving something
>back to Matt and I.
>  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, X24c, U4b
>  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/
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