[Ifeffit] problem with E0 (enot) parameters
Scott Calvin
SCalvin at slc.edu
Fri Jun 19 06:45:59 CDT 2009
Hi Darek,
You've got a false fit. The E0's aren't the biggest problem; look at
the delr for potassium! Your fit is scrambling all the paths in non-
physical ways.
Your initial description of the system suggests that you have a decent
guess as to the structure to start with. What happens when you run a
fit with very few free parameters? (Perhaps none, or perhaps just
floating an overall S02, E0, and maybe a couple of sigma2's.) Does it
look qualitatively right, with peaks where there should be peaks? If
so, then you probably need a tighter set of constraints. If not, then
the material is not what you think it is.
--Scott Calvin
Sarah Lawrence College
On Jun 19, 2009, at 7:30 AM, Zajac, Dariusz A. wrote:
> Hi Calvin,
> thanks for the email. I have tried to find something on mailing list
> about E0 but it seems that my "searching words" were not correct. I
> found only few posts but non of them explained (or followed) the
> problem
> with large enot.
> enot parameters are closed to eachother e.g. enot_C = 12.597(+-0.654)
> and enot_N=12.407(+-1.776); correlations e.g. enot_N and delr_N=0.744,
> enot_C and delr_C=0.605 enot_C and enot_N=-0.313
> more detail you can find in the attachment or below. I have found that
> the value of the first background variable is large (-3437(+-23034))
> when I constrain both enot's parameters I do not see huge changes in
> parameters, chi^2 enot, amp, delr and ssh are the same in the range of
> uncertainties.
> I agree with you that program can shift not the correct parameter, but
> why every time I change parameters (I shift parameters from the local
> minimum) their come back?
>
> cheers
> darek
>
>
> Independent points = 45.279296875
> Number of variables = 30.000000000
> Chi-square = 219223.767
> Reduced Chi-square = 14347.765383235
> R-factor = 0.022707172
> Measurement uncertainty (k) = 0.000102780
> Measurement uncertainty (R) = 0.000306293
> Number of data sets = 1.000000000
>
>
> Guess parameters +/- uncertainties (initial guess):
> amp = 0.8496050 +/- 0.0767160 (guessed as
> 0.849812 (0.095158))
> enot_C = 12.5967170 +/- 0.6539780 (guessed as
> 12.601228 (0.744286))
> delr_C = -0.0055260 +/- 0.0068920 (guessed as
> -0.005265 (0.007572))
> ss_C = 0.0016740 +/- 0.0008460 (guessed as
> 0.001676 (0.000991))
> enot_N = 12.4065290 +/- 1.7757010 (guessed as
> 12.895967 (2.018563))
> delr_N = 0.0358140 +/- 0.0193390 (guessed as
> 0.042607 (0.029913))
> ss_N = 0.0068930 +/- 0.0016280 (guessed as
> 0.008196 (0.002599))
> enot_K = 0.0064050 +/- 9.7412920 (guessed as
> -4.066616 (13.931541))
> delr_K = 0.9265430 +/- 0.1815320 (guessed as
> -0.018996 (0.154984))
> ss_K = 0.0074030 +/- 0.0124260 (guessed as
> 0.011457 (0.010167))
> enot_O = -8.4988040 +/- 13.7627610 (guessed as
> 0.906319 (10.059312))
> delr_O = -0.3610320 +/- 0.0975640 (guessed as
> -0.139554 (0.069016))
> ss_O = 0.0010060 +/- 0.0050660 (guessed as
> 0.001140 (0.004395))
>
> Def parameters (using "FEFF0: Path 1: [C5_1]"):
> enot_CN = 12.5016230
> delr_CN = 0.0151440
> ss_CN = 0.0042840
> enot_CNC = 12.5333210
> delr_CNC = 0.0082540
> ss_CNC = 0.0034140
> enot_NCN = 12.4699250
> delr_NCN = 0.0220340
> ss_NCN = 0.0051540
> enot_KN = 6.2064670
> delr_KN = 0.4811790
> ss_KN = 0.0071480
> enot_KC = 6.3015610
> delr_KC = 0.4605080
> ss_KC = 0.0045380
> enot_KNC = 8.3365500
> delr_KNC = 0.3189440
> ss_KNC = 0.0053230
>
> Set parameters:
> enot_H = -0.920939 (0.000000)
> delr_H = 0.103335 (0.000000)
> ss_H = 0.00749823 (0.000000)
>
> Background parameters +/- uncertainties:
> bkg01_01 = -3437.6705554 +/- 23034.7299514
> bkg01_02 = -0.0609379 +/- 1.8005458
> bkg01_03 = 0.1948870 +/- 0.1595573
> bkg01_04 = -0.0398830 +/- 0.0358870
> bkg01_05 = -0.0025572 +/- 0.0147361
> bkg01_06 = 0.0067564 +/- 0.0081250
> bkg01_07 = -0.0031386 +/- 0.0052991
> bkg01_08 = 0.0006703 +/- 0.0037900
> bkg01_09 = -0.0000756 +/- 0.0028462
> bkg01_10 = 0.0003428 +/- 0.0022025
> bkg01_11 = -0.0006552 +/- 0.0017628
> bkg01_12 = 0.0006924 +/- 0.0015077
> bkg01_13 = -0.0004210 +/- 0.0015140
> bkg01_14 = -0.0002224 +/- 0.0022632
> bkg01_15 = 0.0026167 +/- 0.0075534
> bkg01_16 = -0.0207863 +/- 0.0762094
> bkg01_17 = 48.5761922 +/- 4197.5368888
>
>
> Correlations between variables:
> enot_K and delr_K --> 0.8386
> enot_O and delr_O --> 0.8120
> enot_N and delr_N --> 0.7440
> amp and ss_C --> 0.7232
> enot_C and delr_C --> 0.6048
> amp and enot_N --> 0.5755
> enot_C and bkg01_02 --> -0.4957
> amp and bkg01_05 --> 0.4817
> amp and bkg01_04 --> -0.4376
> enot_C and bkg01_03 --> 0.4175
> enot_N and enot_O --> 0.3976
> ss_C and enot_N --> 0.3902
> amp and bkg01_06 --> -0.3779
> amp and ss_N --> 0.3767
> amp and enot_C --> -0.3652
> ss_C and delr_N --> 0.3422
> ss_N and bkg01_04 --> -0.3330
> amp and delr_N --> 0.3325
> ss_C and bkg01_15 --> -0.3311
> ss_N and bkg01_05 --> 0.3172
> enot_C and enot_N --> -0.3133
> enot_N and bkg01_02 --> 0.2957
> enot_N and delr_O --> 0.2918
> delr_C and ss_N --> -0.2832
> delr_N and enot_O --> 0.2804
> ss_C and bkg01_16 --> 0.2690
> ss_C and bkg01_05 --> 0.2663
> delr_C and delr_N --> -0.2572
> ss_C and bkg01_14 --> 0.2569
> amp and enot_O --> 0.2560
> ss_C and bkg01_04 --> -0.2528
> All other correlations are below 0.25
>
> Background parameters "bkg01_XX" belong to data set RP314a
> K4W(CN)8x2H2O
> W:L3
>> -----Original Message-----
>> From: ifeffit-bounces at millenia.cars.aps.anl.gov
>> [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf
>> Of Scott Calvin
>> Sent: Friday, June 19, 2009 12:23 PM
>> To: XAFS Analysis using Ifeffit
>> Subject: Re: [Ifeffit] problem with E0 (enot) parameters
>>
>>
>> Hi Zajac,
>>
>> What happens if you constrain all E0's to be the same? In the fit
>> where they come out large, what are the uncertainties in the E0's?
>> What are their correlations with other fitted parameters? There has
>> been some debate in this list on the past as to how useful it is to
>> allow for different E0's for different paths. It may be that Artemis
>> is shifting the E0's for those paths in lieu of some other correlated
>> parameter.
>>
>> --Scott Calvin
>> Sarah Lawrence College
>>
>> On Jun 19, 2009, at 5:33 AM, Zajac, Dariusz A. wrote:
>>
>>> Hi all,
>>> can anybody help me and send some link about problems with enot in
>>> Artemis? in google, tutorials I couldn't find any help. Of
>> course are
>>> few posts about delr or ss parameters, but enot is somehow
>> omited (or
>>> I can not find it...)
>>>
>>> the problem is with fiting K4W(CN)8*2H2O at W:L3 edge.
>>> fit and others parameters looks ok, except enot for C and N, where
>>> both
>>> are around 12 and don't want to fit to other values...
>>> thanks
>>> darek
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