[Ifeffit] Linear combination fitting reports

[Jens Kruse]

Thanks for the fast answers. Attached is a screenshot. Maybe I just read 
the pages incorrectly.

cheers,
Jens


ifeffit-request at millenia.cars.aps.anl.gov schrieb:
> Send Ifeffit mailing list submissions to
> 	ifeffit at millenia.cars.aps.anl.gov
>
> To subscribe or unsubscribe via the World Wide Web, visit
> 	http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
> or, via email, send a message with subject or body 'help' to
> 	ifeffit-request at millenia.cars.aps.anl.gov
>
> You can reach the person managing the list at
> 	ifeffit-owner at millenia.cars.aps.anl.gov
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Ifeffit digest..."
>
>
> Today's Topics:
>
>    1. Linear combination fitting reports (Jens Kruse)
>    2. Re: Linear combination fitting reports (Bruce Ravel)
>    3. Re: Linear combination fitting reports (Kelly, Shelly)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 2 Sep 2009 10:13:55 +0200
> From: Jens Kruse <jens.kruse at uni-rostock.de>
> Subject: [Ifeffit] Linear combination fitting reports
> To: <ifeffit at millenia.cars.aps.anl.gov>
> Message-ID: <4A9E2943.5020408 at uni-rostock.de>
> Content-Type: text/plain; charset="ISO-8859-15"; format=flowed
>
> Hi,
>
> I have only two short questions. Is it possible that values for 
> chi-square and reduced chi-square given in the "Fit results" and the 
> "Combinatorics" page are inverted within Athena?
> In the CSV report  for all fits, which of these both columns ("chisqr", 
> "chinu" ) is chi-square and which is reduced chi-square?
>
> thanks,
> Jens
>   
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 2 Sep 2009 09:40:48 -0400
> From: Bruce Ravel <bravel at bnl.gov>
> Subject: Re: [Ifeffit] Linear combination fitting reports
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Message-ID: <200909020940.48150.bravel at bnl.gov>
> Content-Type: text/plain;  charset="iso-8859-1"
>
> On Wednesday 02 September 2009 04:13:55 am Jens Kruse wrote:
>   
>> Hi,
>>
>> I have only two short questions. Is it possible that values for
>> chi-square and reduced chi-square given in the "Fit results" and the
>> "Combinatorics" page are inverted within Athena?
>>     
>
> I tried running a combinatorial LCF series just before writing this
> email and I think these numbers are reported correctly.  If you think
> otherwise, you will need to show me an example.
>
> Of course, the values for both R-factor and reduced chi-square are
> rather peculiar in Athena's LC fitting, as explained in the manual:
>
>   http://cars9.uchicago.edu/~ravel/software/doc/Athena/html/analysis/lcf.html
>
>
>   
>> In the CSV report  for all fits, which of these both columns ("chisqr",
>> "chinu" ) is chi-square and which is reduced chi-square?
>>     
>
> I don't think these are reported wrongly.  As I discuss in the manual,
> it is hard to know how to evaluate chi-nu in a XANES fit.  I use
> epsilon=1 (for want of a better number) and I use the number of points
> in the data as the number of independent measurements.  There are
> typically of the order of 100 points in a XANES scan, so chi-nu tends
> to be about 2 orders of magnitude smaller than chi-square, which
> itself is very small due to the value of epsilon.
>
> All of this just underscores the squishiness of the statistical
> parameters in this context.  Interpreting LCF results requies the use
> of prior knowledge and a very conservative interpretation of what
> Athena reports.
>
> B
>
>
>
>   

-- 
Jens Kruse
Institute for Land Use
Faculty for Agricultural and Environmental Sciences
Rostock University
Justus-von-Liebig-Weg 6
18059 Rostock GERMANY
Phone: +49(0)381-498 3190 

-------------- next part --------------
A non-text attachment was scrubbed...
Name: Example.jpg
Type: image/jpeg
Size: 51418 bytes
Desc: not available
URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20090902/a047cc4c/attachment.jpg>