[Ifeffit] Modelling texture in Artemis

Joselaine Cáceres gonzalez joselainecaceres at gmail.com
Sun Aug 19 20:01:19 CDT 2018


Dear Matt,

Thank you very much, your answer has been very helpful. Please, apologize
me for not opening a separate topic, I was not sure how this work, I´ll be
more careful in the future.
Best regards
Joselaine

El mié., 15 ago. 2018 a las 12:49, Matt Newville (<
newville at cars.uchicago.edu>) escribió:

> Hi Joselaine,
>
> On Tue, Aug 14, 2018 at 10:21 AM Joselaine Cáceres gonzalez <
> joselainecaceres at gmail.com> wrote:
>
>> Dear all,
>>
>> I am new in this group so I don't know if this is the right place to ask
>> about it, but I´d like to know about LCF performed with Athena in XANES
>> data. I had some difficulties in founding information about errors reported
>> by the program.
>> I am working with different techniques and in some cases I have to
>> calculate uncertainty in results reported. In LCF results reported by
>> Athena I don't know how to interpret the errors reported between
>> parenthesis along with each model spectra.
>> In my reports I carefully define if I am reporting the standard deviation
>> of the mean, a combined standard uncertainty,etc. depending each case, the
>> coverage probability, etc. So I need to understand the information Athena
>> is reporting as errors in LCF.
>>
>
> The reported uncertainties are the 1-sigma standard errors.  However, the
> uncertainties in the data are necessary to get the scale of the standard
> errors correctly, and these uncertainties in the data are (almost always)
> not supplied for the analysis, so the program has to guess what those
> uncertainties should be.
>
> To do this it follows a common if not-quite-rigorous approach of first
> asserting that the fit is "good" (otherwise you probably wouldn't care
> about the detailed scale of the uncertainties) so that reduced chi-square
> should be 1.   That is, it effectively rescales the uncertainty in the
> data, epsilon, so that reduced chi-square is 1, and uses that to scale the
> reported uncertainties. Another way to look at this is that the reported
> uncertainties increase the reported chi-square by reported reduced
> chi-square, without regard to the value of epsilon used.
>
> Hope that helps.  Please try to use a separate topic thread in the future,
> as this question has little or nothing to do with the subject line...
>
> --Matt
>
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