[Ifeffit] How is the path data exported?

[Matt Newville]

Hi Gerrit,

> I just started to use Artemis again and at the moment I am a
> bit confused about the results. In one Artemis experiment I
> just select two FEFF-paths and choose a "sum of paths" which
> produces the result shown in the appended picture
> (SumOfPaths2). Shouldn't the fit be more or less look like the
> sum of the two paths?

In the R-space plots you show, you're plotting the magnitude of
chi(R), which don't add together simply.  Plotting chi(k) or the
real / imaginary parts of chi(R) should show the sum more simply.
 
> I also exported both paths as chi(k)-data and manually added
> them which produced the same result as the chi(k) of the fit.
> But when I use more paths I get a different result: the
> manually summed chi has a greater amplitude (see chi.png).
> Could that be related to the fact that the fit parameters are
> applied to the sum of path but not to the exported paths?

The fit and path parameters are definitely applied to the
individual paths.  I think they should be applied to the chi(k)
as well, but it might depend on how you exported the data.

--Matt