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 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

...

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

On Tue, Nov 4, 2014 at 3:22 AM, pushkar shejwalkar wrote: 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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-- Best Regards, Pushkar Shejwalkar. Post-doctoral -Researcher,JSPS Fellow Hokkaido University, Sapporo, Japan