[Ifeffit] Least Squares Fitting in Athena

Ravel, Bruce D. bravel at anl.gov
Wed May 25 13:39:37 CDT 2005

> I have a couple of comments about LSF in Athena and I would like to hear 
> other people's opinions on the matter.
> Also, it would be interesting to know: are there 
> many people who use Athena to do LSF?

> I found that there is some inconsistency with plotting after 
> the fit is done. In my case nonzero energy shifts are applied to 
> the fitted data and the standards. The resulting linear combination fit 
> doesn't look shifted in energy appropriately - visually there is a 
> mismatch between the data and the fit. On the other hand, R-factor and 
> Chi^2 are very reasonable. This looks somewhat confusing.

> Also, in my experience the obtained fractions in Athena come out slightly 
> different from those I could get using Sixpack LSF software. In my fits I 
> used the same constrains/options, same data and references and same data 
> range. What can be the cause of this?


I have recently seem similar behavior.  There are several possible causes for what you are seeing -- the most likely being an error in how the standards are interpolated onto the grid of the unknown data.  I have been working hard on the LCF features in Athena recently and have fixed several bugs and added lots of new features.  Rather than try particularly hard to address your questions now, I am going to wait and see if they persist after I release the next version of Athena (which will be soon).


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