Hi Matt, Thank you for the explanation. This makes sense now. Sincerely, Wayne On May 2, 2004, at 8:21 PM, Matt Newville wrote:
Hi Wayne,
The R-factor is being calculated with both the real and imaginary parts. If you're looking at the source code, the R-factor is calculated in fitfun.f (in src/lib). There, the sum is over the elements of the arrays thifit and chifit. For R-space fits, thifit contain alternating real,imaginary elements of Delta chi(R) (theory-data) within the fit range and chifit contains alternating real, imaginary elements of chi(R) for the data. For k-space fits, thifit contain the elements of the k-weighted Delta chi(k) (theory-data) and chifit contais k-weighted chi(k) for the data.
But I also believe that it doesn't matter much, and that due to the nature of doing FT for a purely real function, an R-value calculated for the Real part only should be equal to one calculated for the Imaginary part only and should be very close to the total R-factor.
Hope that helps,
--Matt
On Sat, 1 May 2004, Bruce Ravel wrote:
On Friday 30 April 2004 06:33 pm, Wayne Lukens wrote:
First, thank you for the great software! I am a former EXAFSPAK user and have been really impressed by Artemis/ifeffit. It's easier to use, more flexible, and gives more reasonable errors for the fit parameters.
Well, welcome to the "family" and thanks for the kind words!
My question is about the value of the R_factor for R-space fitting. This seems to be the R_factor for the real component of the Fourier transform only although the fitting is performed on both the real and imaginary components. Is there a reason that the contribution of the imaginary component to the R_factor is not included?
A quick perusal of Matt's source code does not suggest that what you say is true. Could you be more specific as to why you think that the R-factor is computed incorrectly?
B
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