Documentation RooVoigtian

Emil_R · November 18, 2022, 3:05pm

Hi,
just a quick comment to the people making the documentation of RooFit. I just had to correct a very big error that came up, because I used RooVoigtian with the Half Width half maximum for the breit Wigner part. As I think it is quite uncommon to use the standard deviation for the gaussian part but the FWHM (not the HWHM) for the breit Wigner part, it might be a good idea to write in the documentation what exactly is meant by “width” and “sigma”. Otherwise it is great, that there even is a function like a voigtian implemented.
Thanks,
Emil

jonas · November 22, 2022, 4:47pm

Hi @Emil_R,

thank you very much for letting us know about this inconvenience!

Since this is not a ROOT support question but a very reasonable improvement suggestion, can you please open a GitHub improvement issue with the same content?

I can’t implement this improvement right now, so it would be very good if an open issue exists for this so I don’t forget.

Thank you very much!
Jonas

jonas · November 24, 2022, 11:35am

Thanks for having opened this GitHub issue:

github.com/root-project/root

[RF] Documentation for the RooVoigtian

opened 07:37AM - 23 Nov 22 UTC

EmilRosanowski

improvement in:RooFit/RooStats

### Explain what you would like to see improved  The RooVoigtian uses the standard deviation sigma as the width of the gaussian part. However it uses the FWHM (Full width half maximum) as the width of the Breit-Wigner part, which is rather unusual as many sources define the Breit-Wigner profile with the HWHM (half width half maximum). This is not explained in the documentation which can easily lead to mistakes as people use the RooVoigtian with the HWHM. It would be nice, if this could be added to the documentation in order to prevent mistakes. Thanks, Emil ### Optional: share how it could be improved  ### To Reproduce  ### Setup  ### Additional context

Let’s follow up there!

jonas · December 1, 2022, 7:02am

The following PR implements the documentation update as suggested:

github.com/root-project/root

[RF] Improve RooVoigtian documentation

root-project:master ← guitargeek:issue-11757

opened 07:42AM - 25 Nov 22 UTC

guitargeek

+29 -17

The RooVoigtian uses the FWHM (Full width half maximum) as the width of the Brei…t-Wigner part, which is the usual definition from HEP text books because it corresponds to the decay width. However, other sources define the Breit-Wigner profile with the HWHM (half width half maximum), for example the Wikipedia article: https://en.wikipedia.org/wiki/Cauchy_distribution This can easily lead to mistakes if people use the RooVoigtian with the HWHM. With this commit, it is explicitly stated in the docs that the RooVoigtian takes the FWHM, both in the constructor and the overall class documentation. Furthermore, some other small improvements are made to the docs of the RooVoigtian, like converting some of the function documentations to doxygen. Closes #11757.

system · December 15, 2022, 7:02am

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