Note that in general any and every smoothing operation reduces the information content of the data and its ability to reveal structure. Also, many of the smoothing algorithms change the data point values at vertices, so change the data prior to analysis.


Hence in general avoid unless you know exactly the physical cause requiring smoothing.


Best wishes


--------------------------------------------------------------------------------------
Christopher Chantler, Professor, FAIP, Fellow American Physical Society
Editor-in-Chief, Radiation Physics and Chemistry
Chair, International IUCr Commission on XAFS
President, International Radiation Physics Society
School of Physics, University of Melbourne
Parkville Victoria 3010 Australia
+61-3-83445437 FAX +61-3-93474783

From: Ifeffit <ifeffit-bounces@millenia.cars.aps.anl.gov> on behalf of ifeffit-request@millenia.cars.aps.anl.gov <ifeffit-request@millenia.cars.aps.anl.gov>
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Subject: Ifeffit Digest, Vol 170, Issue 19
 
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Today's Topics:

   1. Re: The difference of EXAFS oscillation when using Athena and
      when using Larch (Yuji Mahara)


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Message: 1
Date: Thu, 20 Apr 2017 19:47:20 +0900
From: "Yuji Mahara" <mahara.yuji@e.mbox.nagoya-u.ac.jp>
To: "'XAFS Analysis using Ifeffit'"
        <ifeffit@millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] The difference of EXAFS oscillation when using
        Athena  and when using Larch
Message-ID: <003501d2b9c3$7c75c560$75615020$@e.mbox.nagoya-u.ac.jp>
Content-Type: text/plain; charset="utf-8"

Dear Matt

 

Thank you for your reply.

I confirmed that chi (k) becomes smooth by the Savitzky-Goley method by doing the attached lar file.

 

I will try on various conditions from now.

I may also ask if there is something I do not understand.

Thank you for your help again!

 

Bests,

Yuji Mahara

 

 

From: Ifeffit [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Matt Newville
Sent: Thursday, April 20, 2017 5:26 AM
To: XAFS Analysis using Ifeffit <ifeffit@millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] The difference of EXAFS oscillation when using Athena and when using Larch

 

Hi Yuji,

The attached larch script (a modification of your script but note: not python, so you may have to add a bunch of '_larch=mylarch' arguments) to show the effects of smoothing with Savitzky-Golay and of interpolating onto a "classic XAFS energy grid".   You might want to play around with this different options.  It definitely seems that none of these methods are systematically over-smoothing the data and reducing the amplitudes of the oscillations -- one more reason to use Larch instead of Ifeffit.  But it also seems like smoothing this data with a Savitzky-Golay fitler is helpful.

Also attached are plots showing k- and R-space generated from the attached script.

 

--Matt

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