pdfgui and Rw calculation

[peral...@gmail.com]

Dear colleagues,

I am assuming that Rw that pdfgui calculates when fitting the pdf is using the standard deviations of the PDF data as weights, am I correct? Or is it using 1/sqrt(Gexp(ri)) as weight?
Also, in case that there is no standard deviation in the data (data only contains two columns, r and G(r)), the weight is 1.0. Is this correct?

Thanks very much in advance,

Inma

[Pavol Juhas]

Hi Inma,

Yes, that is correct. The Rw formula uses standard deviations as per

Rw = sqrt(A / B)
A = sum_i { [Gobs_i - Gcalc_i)/dG_i]**2 }
B = sum_i { [Gobs_i/dG_i]**2 }

[formula (A.49) in the old pdffit manual at
http://www.diffpy.org/doc/pdffit/pdf_man.pdf]

When dG values are not available in the data, they are all assumed 1.0.

Best,
Pavol

--
Dr. Pavol Juhas
Condensed Matter Physics and Materials Science Department
Brookhaven National Laboratory
P.O. Box 5000
Upton, NY 11973-5000

[Inma Peral]

Dear Pavol,

Thanks a lot!

Inma

On 10/16/2014 05:08 PM, Pavol Juhas wrote:
> Hi Inma,
>
> Yes, that is correct. The Rw formula uses standard deviations as per
>
> Rw = sqrt(A / B)
> A = sum_i { [Gobs_i - Gcalc_i)/dG_i]**2 }
> B = sum_i { [Gobs_i/dG_i]**2 }
>
> [formula (A.49) in the old pdffit manual at
> http://www.diffpy.org/doc/pdffit/pdf_man.pdf]
>
> When dG values are not available in the data, they are all assumed 1.0.
>
> Best,
> Pavol
>


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