[Ifeffit] Too many points in pre-edge

[Bruce Ravel]

On Thursday 02 December 2004 04:40 pm, Matt Newville wrote:
> I agree that the algorithm to find E0 could be improved,
> especially for noisy and XANES-only data. The ideas Bruce added to
> athena seem like good approaches. FWIW, Ifeffit's E0 finding
> strategy is mostly tuned to avoid glitches in the extended XAFS.
> Therefore, it choose the point that has the largest first
> derivative provided that the previous two points have a positive
> first derivative.

> It only looks in the first half of the energy
> array (counting by array index).

That would explain what was going on in Carlo's data.

> It's quite possible that it would miss e0 in data with an
> unexpectedly long pre-edge.

I can see the argument that ifeffit should have been able to figure
this out, but it does seem kind of silly to bin the data in the
pre-edge such that the energy steps are about 1/2 volt.  That vastly
overspecifies the pre-edge.

> Carlo wrote:
> > Grant has been using a differential evolution algorithm to take
> > case of noisy data.  Perhaps this could help?
>
> I have no idea what that is.  Does it help you and Grant?

Ditto.  I would like to see a reference.

B


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 Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
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