[Ifeffit] Meaning of linear combination fit reports

Jens Kruse 4.meinereiner at gmx.de
Mon Aug 18 09:12:08 CDT 2014


Hi everyone,

I doing LCF on my XANES data. I wonder if someone can tell me the 
meaning of the values in parentheses following the weight value in the 
Fit results window?. I looked into the respective document section of 
the Manuel but could not find the answer, yet.

I am asking because I did a Fitting with over 20 standards (STD) to find 
all combination of max 4 standards which describe my unknown sample 
spectra. This results in a lot of combination with similar 
chi-square(reduced) and R-values. I know a relative changes between 
these values are more probably meaningful than absolute values.
A lot of the possible combinations provided by after the fit yieled 
combinations with at lest on STD having a weight of 0.000. (Fit 1). I 
thought that this would mean, that 3 standards are sufficient to 
describe the system. However, repeating the fit with only the three 
standards with weight > 0.0 yielded a complete different proportions 
(Fit 2).  How can this be explain and how should I deal with 
combinations or standards having  a weight of 0.000?

Thanks a lot for your thoughts and suggesting,

Cheers Paul

*Results **Fit  1:*

   3: STD3           0.324(0.025)
   7: STD7             0.686(0.021)
   20:  STD2O       0.127(0.016)
   27: STD27         0.000(0.036)

vs.

*Results Fit 2:*
   3: STD3           0.473(0.019)
   7: STD7             0.620(0.023)
   20:  STD20       0.000(0.030)
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