[Ifeffit] xraylarch

[Paul Fons]

Hi.
  Due to the difficulties of getting demeter to work on the Apple M1 machines, I have started to use xraylarch and so far I like the interface as well as the possibility of scripting later on. I had a couple of observations and a question regarding xraylarch usage that I hope could be addressed here.

First, one can load multiple spectra into the (feff) fitting window. It seems, however, that which paths are selected are universal (the selected paths are used for all exafs spectra). Does this mean that multiple edge fitting is not possible. If multiple edge fitting is possible, how is it done?
In the fitting window, one can have several spectra loaded and one can select all or some of the spectra to be fit. The interface seems like it was designed for multiple edge fitting, but is it?

Second, it is strange that whenever a parameter is changed that the fitting variable settings (fixed, vary, constrain) are reset. For complex fits, this generates a lot of unnecessary clicking (and the corresponding mistake possibilities)

Third, when one reads in several different feff calculations, one would, in principle, like to have a different value of e0 (the origin of energy offset) for each feff calculation. By default when a feff calculation is read in the variable e0 is defined. When one defines alternative energy offset variables for the different feff calculations and deletes the original e0 value, something strange happens. Accessing the “Edit Parameters” window results in e0 reappearing (even though it has been manually deleted previously). Is this a feature? The same thing may happen for other “automatic” variables as well.

Four. This is really a feature request. When a variable is unused (lets say some additional paths are introduced in the fitting process and a new fit without them is attempted), the choices in the parameter list are (fix, vary, and constrain). There is no option to “skip” like in Artemis. Obviously, one can choose fix, but in doing so the unused variable shows up in the fit result summary and is somewhat confusing. It would be subjectively better to have the option to “skip” a variable and not have it show up in the fit summary.

Just some initial thoughts...