Add a Tutorial for IntegratorMultiDim

[ynikitenko]

Explain what you would like to see improved

There is a class for multidimensional integration, IntegratorMultiDim. From that it's very hard to understand how to use that (in particular, what function should be passed to that and how).

Optional: share how it could be improved

Please add examples how to use that. In its class description and probably to tutorials (they don't contain any code with that class).

Additional context

There was a discussion on the ROOT Forum with a ready good example. It was promised that people are working on the documentation, but it seems to be forgotten since then.

[couet]

What about including this in the reference guide on this page ?

@lmoneta what do you think ?

[lmoneta]

Hi, There is some documentation in the ROOT Users guide, see https://root.cern.ch/root/htmldoc/guides/users-guide/ROOTUsersGuide.html#numerical-integration

Maybe it is not too visible, and I agree @couet we should probably include in the DOxygen description of the Integration classes. We are also missing a tutorial on the INtegratorMultiDim and we should add one before closing this issue

[atolosadelgado]

Hi @lmoneta @couet

I checked the current documentation, and the point 15.8.3.1 Using ROOT::Math::IntegratorMultiDim actually shows an example of the IntegratorMultiDim and the usage of different algorithms.

There is a typo, probably caused by copypasting: Here is a code example on how to use the ROOT::Math::IntegratorOneDim class, actually it is an example of IntegratorMultiDim