You really need to know the number of actual data points, which must come from the actual data. You should also know the experimental uncertainties of each point.


Most standard procedures map the actual data to a uniform grid, sometimes with smoothing of the original data. Then the information content is lost.


We are doing final testing on some general routines to address this and will make them available soon.


--------------------------------------------------------------------------------------
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 7
 
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Today's Topics:

   1. Information content from Athena for Hamilton test? (Will Bennett)
   2. Re: Information content from Athena for Hamilton test?
      (Wayne Lukens)


----------------------------------------------------------------------

Message: 1
Date: Mon, 10 Apr 2017 13:59:36 +1000
From: Will Bennett <w.bennett@griffith.edu.au>
To: ifeffit@millenia.cars.aps.anl.gov
Subject: [Ifeffit] Information content from Athena for Hamilton test?
Message-ID:
        <CAA5p-7P__WKyB6Hzf4bUkd6=+mYEEvGc967p+3hdcsqAvY8ENw@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hi everyone,

Just a quick question regarding the "Information Content" output in
Athena's LCF window. I've recently been playing around with using the
Hamilton test (as outlined in Scott Calvin's book "XAFS for Everyone") to
interrogate my combinatorics results. As many of you will know, this
requires an estimate of the number of independent measurements in the data,
in order to determine the degrees of freedom and subsequently the "a" value
for computing the Lower Incomplete Beta Function. Would Athena's value for
"Information Content" be appropriate to use as an estimate of the number of
independent measurements in this case? How is this value of "Information
Content" determined in Athena?

Thanks in advance.

Will
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Message: 2
Date: Mon, 10 Apr 2017 08:00:46 -0700
From: Wayne Lukens <wwlukens@lbl.gov>
To: XAFS Analysis using Ifeffit <ifeffit@millenia.cars.aps.anl.gov>
Subject: Re: [Ifeffit] Information content from Athena for Hamilton
        test?
Message-ID:
        <CAKMihFcRgyCH1DN4ARn=_3JYnpiY3EBD8jikFmzAHXwuev2HWQ@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

HI Will,

I am not entirely sure how this value is determined in Athena, but the
number of independent data in a XANES fit is the data range divided by the
resolution. If you have a spectrum with a strong pre-edge peak, you can
determine the resolution from its width. Otherwise, the resolution is a
convolution of the core-hole broadening and the beamline energy resolution.

Athena gives a value that is very close to the value determined directly
from the width of a preedge peak.

Sincerely,

Wayne

On Sun, Apr 9, 2017 at 8:59 PM, Will Bennett <w.bennett@griffith.edu.au>
wrote:

> Hi everyone,
>
> Just a quick question regarding the "Information Content" output in
> Athena's LCF window. I've recently been playing around with using the
> Hamilton test (as outlined in Scott Calvin's book "XAFS for Everyone") to
> interrogate my combinatorics results. As many of you will know, this
> requires an estimate of the number of independent measurements in the data,
> in order to determine the degrees of freedom and subsequently the "a" value
> for computing the Lower Incomplete Beta Function. Would Athena's value for
> "Information Content" be appropriate to use as an estimate of the number of
> independent measurements in this case? How is this value of "Information
> Content" determined in Athena?
>
> Thanks in advance.
>
> Will
>
> _______________________________________________
> Ifeffit mailing list
> Ifeffit@millenia.cars.aps.anl.gov
> https://protect-au.mimecast.com/s/EM1xBvSoXK5NsR?domain=millenia.cars.aps.anl.gov
> Unsubscribe: https://protect-au.mimecast.com/s/vxwYBDFg0Md7Iw?domain=millenia.cars.aps.anl.gov
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>


--
Wayne Lukens
Staff Scientist
Lawrence Berkeley National Lab
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