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

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)

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Message: 1 Date: Thu, 17 Oct 2002 09:33:37 -0400 To: ifeffit mailing list Subject: Re: [Ifeffit] using Artemis Reply-To: ravel@phys.washington.edu From: Bruce Ravel

John,

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- progress.

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.

Regards, B

-- Bruce Ravel ----------------------------------- ravel@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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