I am probably missing the point, but it is not immediately obvious to me why the following is equivalent in terms of improving the signal to noise: a) constant E-space increment and b) constant k-space increment combined with k-dependent integration time. In a), the data cluster at high E, but each data point in E corresponds to a different final state and thus is unique. Averaging over E-space data in the small interval Delta E, (1/Delta E)*Int [xmu(E) dE] is not equivalent to the time average of xmu(E) collected at a fixed E: (1/T)*Int [xmu(E) dt]. Thus, k^n-weighted integration time, to my mind, is the only proper way of reducing statistical noise. Anatoly -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of Carlo Segre Sent: Thu 8/25/2005 5:13 PM To: XAFS Analysis using Ifeffit Cc: Subject: Re: [Ifeffit] A basic question about data collection Matt and Scott: On Thu, 25 Aug 2005, Matt Newville wrote:
This is important for QEXAFS (which typically does sample at a very fine energy grid). I've been told by people doing QEXAFS that a simple box-car average is good enough for binnning QEXAFS data. That's what Ifeffit's rebin() function does. I'd think that a more sophisticated rolling average (convolution) would be better (and not screw up energy resolution), but apparantly it's not an issue.
I have ben playing with the athena smoothing and rebinning funcionalities and I think that I prefer the rebinning because smoothing tends to attenuate sharp peaked structure. A rolling average might be good too but I haven't tried it too much. My guess is that for gentle features such as in the EXAFS region, rebinning, rolling averages and smoothing will all give statistically indistiguishable results. I amy be wrong. Carlo -- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 Carlo.Segre@iit.edu http://www.iit.edu/~segre _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit