[Ifeffit] Fitting Problems in Artemis version 0.9.26

[Scott Calvin]

Dear Huan,

Neither of those sound like a flaw in Artemis to me. 

1) Fitting with a range that goes below Rbkg means fitting to a part of the data’s Fourier transform that has been suppressed by background subtraction, even though the theory’s Fourier transform has not been similarly suppressed. That will yield a misleading fit. If the newer version of Artemis does a check to prevent this, that’s actually an improvement.

2) This could always happen—you may just not happen to have seen it before. Using abs() doesn’t make the variable you are fitting positive; it makes the result which is used in the fit (the “path parameter”) positive. So if, for example, Artemis reports ss1 = -0.002, that means it used +0.002 in the fit.

Best,
Scott Calvin

> On Jun 28, 2018, at 10:03 PM, LIU HUAN <huanliu_earth at hotmail.com> wrote:
> 
> Dear Dr. Ravel,
> 
> I want to ask you that when I use the new version "Artemis 0.9.26" I have two problems. (1) The fitting Range was reported to be a error that the Rmin should be larger than the Rkbg value. It makes that the fitting range cannot be smaller than 0.9 (the Rkbg value is 0.9). (2) When Fitting the Debye–Waller factor  (ss) and coordination number (N), although I use "abs()" to make it to be positive, but the fitting results still be negative. But I did not meet these problems in the old version in Artemis 0.8.012. I am wondering that whether could you tell me how to solve these problems. Thank you so much.
> 
> Sincerely,
> Huan
> 
> Huan Liu
> School of  Earth Sciences and Engineering 
> Nanjing University 
> 163 Xianlin Road, Nanjing, Jiangsu, 210023 
> P. R. China
> 
> Tel  86-15861809073
> Email: huanliu_earth at hotmail.com <mailto:huanliu_earth at hotmail.com>
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