[doxy] upgrade to Mathjax3

[ferdymercury]

Explain what you would like to see improved

Mathjax2 is used by documentation.

Optional: share how it could be improved

Mathjax3 brings some performance improvements.

Maybe it can be even downloaded on the fly, rather than storing it as part of the ROOT source code?

To Reproduce

https://root.cern.ch/doc/master/

Setup

   ------------------------------------------------------------------
  | Welcome to ROOT 6.27/01                        https://root.cern |
  | (c) 1995-2021, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for linuxx8664gcc on Jan 12 2022, 10:17:19                 |
  | From heads/master@v6-25-01-2870-gdac9b6398d                      |
  | With c++ (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0                     |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q'       |
   ------------------------------------------------------------------

Additional context

doxygen/doxygen#9185 (comment)

[couet]

I will look at it. I prefer to have a self consistent doc. Having it with the doc reduces the dependencies in case the remote website is down.

[couet]

By chance do you know where to download it from ? it does not seem obvious.

[ferdymercury]

By chance do you know where to download it from ? it does not seem obvious.

I think from Git: https://docs.mathjax.org/en/latest/web/hosting.html#getting-mathjax-via-git

The other way is to put directly an URL in the Doxyfile, this way it is automatic:
MATHJAX_RELPATH = https://cdn.jsdelivr.net/npm/mathjax@3

[ferdymercury]

I will look at it. I prefer to have a self consistent doc. Having it with the doc reduces the dependencies in case the remote website is down.

I see. In that case, I would suggest to use a git submodule. This way it is self-consistent and it would work without Internet.

[ferdymercury]

pinging @albert-github in case he has a better idea. (thanks!)

[albert-github]

No really another idea (I never tried to prune the MathJax version 3)
An alternative place might be: https://github.com/mathjax/MathJax/releases/

[couet]

An alternative place might be: https://github.com/mathjax/MathJax/releases/

The file provided there for download does not work. It is not the equivalent of the mathjax.tar.gz file we have in the root repository. Formulae are not interpreted if I replace the original file but this one.

I will now try the URL way.

[albert-github]

@couet Did you update the Doxyfile for the MathJax version 3 (default for MATHJAX_VERSION is MathJax_2 but you need MathJax_3)

[couet]

No, I just see it now at the same time you point it. I will try again. Sorry for the noise.

[couet]

even with:

 MATHJAX_VERSION        = MathJax_3

The file downloaded from the URL previously mentioned, does not work.