[Ifeffit] linear combination fitting

Matt Newville newville at cars.uchicago.edu
Wed Aug 7 06:55:15 CDT 2013

Dear Shaofeng,

On Wed, Aug 7, 2013 at 6:36 AM, Shaofeng Wang <wangshaofeng at iae.ac.cn> wrote:
> Dear Bruce,
> I am using Dathena to do some linear combination fitting. In your program,
> you give three methods for fitting, nomal, derivate and chi(k). I got three
> different results using these methods. My question is which one is better to
> obtain more reasonable result or what the purpose of each method is.

Yes, it is.  The other ones are definitely worse.

Now, slightly more seriously (yes, that was a joke),  how different
are the results?  how different are fit ranges for these three fits?
How good are the data and standards used over these ranges?   As you
might expect, a linear combination for chi(k) is generally intended
for EXAFS, and so emphasizes distances  of the nearest neighbors while
"norm" and "derivative" is generally for the XANES portion of the
spectra, and so emphasizes chemical state.



PS: Have you read the postings on this mailing list in the past couple
months and weeks?   Next time, please try to not exasperate Bruce (and
the rest of us), and ask a question that can possibly be answered.
Concrete examples and questions are much, much better than abstract
questions.   Please avoid asking "why is the blue curve always lower
than the red curve"?

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