[Ifeffit] Question about the R_factor in artemis/ifeffit

[Wayne Lukens]

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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