Likelihood Contour Plotting Error

I was using root version 6.28/04 and I use the following code to draw likelihood contours:

RooPlot* frame = minuit_hf->contour( * etap_var , * V20_var);
frame->SetTitle( "etap vs dV20" );
frame->SetAxisRange( etap_var->getValV() - 3.0 * etap_var->getError() , etap_var->getValV() + 3.0 * etap_var->getError() , "X" );
frame->SetAxisRange( V20_var->getValV() - 3.0 * V20_var->getError() , V20_var->getValV() + 3.0 * V20_var->getError() , "Y" );

It gave me the following contours, in which the 1-sigma and 2-sigma contours intersect. How do I solve this problem?
Screenshot 2023-09-23 at 13.23.10


Thanks for posting. This is not necessarily an artifact of the plot, but could be resulting from an ill-behaved fit.
Are you able to make us capable to reproduce this behaviour (knowing that we might not be able to make the fit properly converge of course) ?


Hello @delick!

Are you using Minuit2? The contour algorithm is known to be buggy with Minuit2:


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