Re: [Ifeffit] amplitude parameter S02 larger than 1

On Mon, Mar 23, 2015 at 9:45 PM, Scott Calvin wrote: > Hi Anatoly, > > The method Ifeffit uses to compute uncertainties in fitted parameters is > independent of noise in the data because it, in essence, assumes the fit is > statistically good and rescales accordingly. This means that the estimate

Re: [Ifeffit] amplitude parameter S02 larger than 1

Hi Scott and Anatoly, I didn't add any noise to the calculated data. So I can understand the magnitude of chi-square and reduced chi-square are terribly large, which is OK. I see the small uncertainties in fitted parameters in the way that the generated data is very consistent with the gu

Re: [Ifeffit] amplitude parameter S02 larger than 1

Hi Anatoly, The method Ifeffit uses to compute uncertainties in fitted parameters is independent of noise in the data because it, in essence, assumes the fit is statistically good and rescales accordingly. This means that the estimated uncertainties really aren't dependable for fits that are kn

Re: [Ifeffit] amplitude parameter S02 larger than 1

Hi Yuanyun and Bruce, Your test is a very nice way to check the effect of the muffin tin radius on the fit value of the amplitude fator. Although I hadn't run your test myself I would have expected that the error bars produced by the fit of a theory to "theoretically generated data" would have

Re: [Ifeffit] amplitude parameter S02 larger than 1

Hi Bruce, Thanks for the comments. Just to make an end to this topic so far: the samples which give large amplitude are suspected to be more complicated than the normal skutterudites I showned to you last fall. Normal skutterudites data actually didn't cause me worried because its S02 is f

Re: [Ifeffit] amplitude parameter S02 larger than 1

On 03/23/2015 04:10 PM, huyan...@physics.utoronto.ca wrote: This is to follow up the *test* experiment you suggested. Attached are three Artemis files. I chose the Fe (im-3m) structure to do the test. The normal crystal structure has its first-shell distance at 2.48 angstrom. A large structure

Re: [Ifeffit] Installing demeter from source on Yosemite?

Hi Anders, Is there a reason you are trying to install from source? Have you tried to install from macports? George On Fri, Mar 20, 2015 at 5:16 PM, Anders Glans wrote: > Hi again, > > I have rebuilt things more carefully but I still have problems. > > - I built pgplot following the instructio

Re: [Ifeffit] Breaking down correlationships between parameters

Hi Bruce, Thanks for your comments and links of your lectures. I forgot to mention that I use Artemis for fitting my data. Best regards, Jatin -Original Message- From: ifeffit-boun...@millenia.cars.aps.anl.gov [mailto:ifeffit-boun...@millenia.cars.aps.anl.gov] On Behalf Of ifeffit-req

Re: [Ifeffit] Breaking down correlationships between parameters

Hi Scott, Thanks for your explanation. It means the reverse can also be true, i.e., I can guess N1 (nearest-neighbors in the first shell) and S02 by setting N2, N3 and N4 to values known from other analysis. I did a quick check by fitting the data. I conducted two fits: 1) setting S02 and guess

Re: [Ifeffit] Breaking down correlationships between parameters

On 03/23/2015 08:54 AM, Rana, Jatinkumar Kantilal wrote: The term N*S02 is fitted for each path of the FEFF calculation. So my question is, even if we know N with a great certainty for some path, how can we vary both N and S02 for other paths ? or Did I understand it wrong ? At no point in your

Re: [Ifeffit] Breaking down correlationships between parameters

Hi Jatin, The key is that S02 should be the same for all paths. For example: Suppose you are very confident path 1 has a coordination number of 6, because of prior knowledge you have about the system. Paths 2, 3, and 4 have unknown coordination numbers, however. N1 (i.e. the degeneracy of pat

Re: [Ifeffit] Breaking down correlationships between parameters

Hi Chris, The term N*S02 is fitted for each path of the FEFF calculation. So my question is, even if we know N with a great certainty for some path, how can we vary both N and S02 for other paths ? or Did I understand it wrong ? Best regards, Jatin -Original Message- From: ifeffit-boun

Re: [Ifeffit] Breaking down correlationships between parameters

I think Scott was pointing out that first neighbors may be known with high certainty and therefore you can set this value thereby removing it and slightly reducing the correlations. Chris Sent from my iPhone > On Mar 23, 2015, at 7:00 AM, Rana, Jatinkumar Kantilal > wrote: > > Hi Scott, >

Re: [Ifeffit] Breaking down correlationships between parameters

Hi Scott, Thank you for your comments. Can you please elaborate a little bit more on this "In cases like that, both N for all paths but one and S02 can be fit without 100% correlation." Best regards, Jatin -Original Message- From: ifeffit-boun...@millenia.cars.aps.anl.gov [mailto:ifef

Re: [Ifeffit] Breaking down correlationships between parameters

Hi Matt, Thank you very much for your detailed explanation. As you pointed out that this approach ignores the statistical significance of fits and assumes that all fits are "good" fits. Also, the point that this approach yields a value of the parameter which is only slightly less correlated wit