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,

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-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of ifeffit-request@millenia.cars.aps.anl.gov Sent: 23 March, 2015 10:16 To: ifeffit@millenia.cars.aps.anl.gov Subject: Ifeffit Digest, Vol 145, Issue 41

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Today's Topics:

1. Re: Breaking down correlationships between parameters (Scott Calvin) 2. Re: Breaking down correlationships between parameters (Matt Newville) 3. Re: Breaking down correlationships between parameters (Rana, Jatinkumar Kantilal)

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Message: 1 Date: Sun, 22 Mar 2015 13:44:28 -0400 From: Scott Calvin To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Breaking down correlationships between parameters Message-ID: Content-Type: text/plain; charset="utf-8"

One side-comment from me:

On Mar 22, 2015, at 12:52 PM, Matt Newville mailto:newville@cars.uchicago.edu> wrote:

N and S02 are always 100% correlated (mathematically, not merely by the finite k range).

Matt is saying that N and S02 are always 100% correlated for a single path. But in some situations you might know N for one path but not others. For example, you might know that the absorbing atom is octahedrally coordinated to oxygen but not be as certain as to next-nearest neighbors, or that there are copper atoms on the corners of a simple cubic lattice with a mixture of atoms at other positions. In cases like that, both N for all paths but one and S02 can be fit without 100% correlation.

The degeneracy of multiple-scattering paths can often be constrained in terms of the coordination numbers for direct-scattering paths, which can further reduce (not ?break?) the correlation.

In terms of the main question, I agree with Matt: I don?t think there?s much point in using the line-crossing technique nowadays; fitting using multiple k-weights simultaneously accomplishes the same thing but is a bit easier to interpret statistically.

?Scott Calvin Sarah Lawrence College