[Ifeffit] polarization in Artemis

Matt Newville newville at cars.uchicago.edu
Sun May 24 16:03:23 CDT 2015

On Sun, May 24, 2015 at 1:50 PM, Bruce Ravel <bravel at bnl.gov> wrote:

> Hi,
> Everything in the discussion between Eugenio and Matt is stuff I agree
> with, except ...
> When I rewrote Artemis, one of the motivations was that I wanted to write
> my own pathfinder rather than to continue using the one in Feff. My main
> motivation was fuzzy degeneracy (
> http://bruceravel.github.io/demeter/artug/extended/fuzzy.html) plus I
> wanted to correct a few other things I saw as shortcomings.
> When I was writing it years ago, I didn't immediately see an easy way to
> consider polarization correctly while also doing fuzzy degeneracy
> correctly.  I have since figured that out, but years went by and only one
> person ever asked me about polarized feff calculations in Artemis. So I
> never implemented it.
> It's a funny thing, when you wait for a bus, none comes, then two show up
> at once.  A month ago, I was asked about polarization in Artemis, and now
> Eugenio brings it up!
> Polarization works (although it needs testing) in the very latest code in
> github.  But I did that work since the last time I built a Windows
> installer.  Ellipticity does not yet work (in Artemis -- it works just fine
> in Feff, but Artemis does not deliver the ellipticity-dependent calculation
> to the user).
You mean Artemis wasn't creating a POLARIZATION card?   But one can just go
in and add that the the Feff.inp anyway, no?   The feff.inp file is
editable before running Feff with Artemis all the time, right?  That should
be independent of pathfinder.  Or do you mean something else?

> Anyway, I will try to find a few hours this week to build a new Windows
> installer, which will included the ability to consider linear polarization.
> > Artemis used to make this very easy (sum paths without fitting),  but
> > I don't recall how to do this in the latest version.
> Still is easy.  Well, I think it is.  YMMV :)
> http://bruceravel.github.io/demeter/artug/plot/vpaths.html
I understand VPaths, I think.    But I meant simply "sum these paths
applying the current parameters, without fitting".      That used to be
very, very simple and I always find it useful and instructive for exploring
the contributions from different paths.  Now it seems I have to set all
values to "set", then change them to "guess" to really do a fit.   Am I
missing something?

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