Hi Ahkil,

On Tue, Feb 26, 2019 at 3:51 AM Tayal, Akhil <akhil.tayal@desy.de> wrote:

Hello Matt,

I could not be able to perform LCA using the lincomb_fit function in the
Larch software. I am getting the error message from line number 80 in
the lincombo_fitting.py script. I expect the function has some bug with
reading the group values. It could not be even able to read the default
array 'norm' nither any user-provided 'arrayname' such as 'flat or fpp.'
Can you suggest any solution for it? Please find the data files and
larch script I am using for this purpose.

There are a couple of things wrong -- some with your script but also a bug in lincombo_fit() that I had not seen until this morning.

First, you should just use the group symbols, not the names of the groups, so replace

lincombo_fit(group='g3',components='g1 g2', ....

with

lincombo_fit(group=g3, components=[g1, g2], ....

Second, you should also keep the result (somewhat unusually for Larch, it does not currently get written into the main group -- perhaps this should be fixed), so

result = lincomb_fit(group=g3, ....)

Third, the 'xmin' and 'xmax' parameters you have appear to be intended to be "relative to e0", but lincombo_fit() wants absolute x values (and e0 is not defined anyway). So you probably want something like

result = lincombo_fit(group=g3, components=[g1, g2], arrayname='flat', xmin=22070, xmax=22170, sum_to_one=True)

But: this still won't work with Larch 0.9.41 because of a typo in lincombo_fit(). I have a fix pushed to github, and I'm working on a release for 0.9.42 today anyway (mostly fixing other bugs in XAS Viewer), and this will be included in that.

Anyway, until you can upgrade to Larch 0.9.42, you will need to supply starting weights (they do not have to be accurate, just not `None`).

So, in summary, you should use:

result = lincombo_fit(group=g3, components=[g1, g2], arrayname='flat', xmin=22070, xmax=22170, weights=[0.8. 0.2], sum_to_one=True)

Cheers,

--Matt