[math] Contour method has some problems with Minuit2

[guitargeek]

I the RooFit interactive Minuit tutorial, there is this line here:

   // The contour algorithm in Minuit2 does not work for this tutorial
   m.setMinimizerType("Minuit");

The implementation of CONTOUR in Minuit2 should be fixed such that this is not necessary. The problem has something to do with the contours hitting the parameter boundaries.

If one tries to get different contours inside the boundary by changing the contour() to for example:

   RooPlot *frame = m.contour(frac, sigma_g2, 1, 1.4, 1.7);

the plot looks still a bit screwed up with out-of-place lines:

Also this problem should be fixed.

[dpiparo]

A comment in #13918 suggests this is fixed: is this true?

[dpiparo]

@guitargeek @lmoneta just checking: can this be closed?

[dpiparo]

Closing as per discussion with @lmoneta

[guitargeek]

Nice. I also checked if the reproducer works now, and it's working fine.