# [Ifeffit] Reporting the fitting data (uncertainty associated with N)

pushkar shejwalkar pshejwalkar2004 at gmail.com
Wed Nov 5 01:46:45 CST 2014

```Dear Matt,
Thank you very much for the quick and illustrative solution.
That helped
Pushkar

On Tue, Nov 4, 2014 at 9:24 PM, Matt Newville <newville at cars.uchicago.edu>
wrote:

> The amplitude parameter is N*S02, so that S02 and N are completely
> correlated.   If you
>
>     set  N = 2
>     guess S02 = 0.8
>
> and the fit returns
>
>    S02 = 0.75 +/- 0.05
>
> Then the correct interpretation is that
>
>   N*S02 = 2*(0.75 +/- 0.05) = 1.5 +/- 0.10
>
> If you had asserted that S02 = 0.75 and vary N, then you should get
>
>   N = (1.5 +/- 0.10) /  0.75 =  2 +/- 0.13333
>
> The uncertainty in S02 and N cannot be separated for a single
> spectrum.   The most common approach is to assert that S02 depends on
> X-ray energy resolution (beamline setup) and absorbing atom, and use a
> constant value for S02 derived from spectra from samples with a
> well-known coordination environment (a "standard").
>
> --Matt
>
>
> On Tue, Nov 4, 2014 at 3:22 AM, pushkar shejwalkar
> <pshejwalkar2004 at gmail.com> wrote:
> > Dear All,
> >           I have seen and also been told by few professors that when you
> > report the fitting you must report the uncertainty associated with the
> > measurement as evaluated by the program used for the fitting.
> > Now, When I do the fitting I typically get the +/- values for E0, delR,
> ss
> > and SO2. However, the N value we always put either 1,2 or such whole
> > integers. Is there any way to find out the uncertainty associated with
> the
> > coordination number (N used in XAFS equation)?
> > If so how to find such uncertainty? can we see this in the log file
> > generated after the fitting is over?
> > Thank you very much for the help
> >
> > Best Regards,
> > Pushkar Shejwalkar.
> > Post-doctoral -Researcher,JSPS Fellow
> > Hokkaido University,
> > Sapporo,
> > Japan
> >
> >
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> >
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--
Best Regards,
Pushkar Shejwalkar.
Post-doctoral -Researcher,JSPS Fellow
Hokkaido University,
Sapporo,
Japan
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