Uploaded image for project: 'ROOT'
  1. ROOT
  2. ROOT-7290

RooMinimizer::contour only does 1sigma, ignores n1,n2,... parameters

    XMLWordPrintable

Details

    • Bug
    • Status: Closed (View Workflow)
    • Medium
    • Resolution: Fixed
    • 5.34/24
    • None
    • RooFit/RooStats
    • None
    • RooFit

    Description

      RooMinimizer::contour (var1, var2, n1, n2) ignores the values specified with n1 and n2 (etc) and generates every contour as if n1=n2=1. This means the default (n1=1, n2=2) makes two identical contours.

      I think the problem is that the SetErrorDef call does not work once the initial minimisation is done. However, if SetErrorDef is called before running minimize, then the global error level can be changed.

      This problem does not occur if RooMinuit::contour is used instead.

      On a related matter, I'm also not sure whether the ErrorDef values used are appropriate for 2D contours (for RooMinimizer or RooMinuit). For 68% and 95% contours, I specified n1=sqrt(2.3) and n2=sqrt(6.0), corresponding to ROOT::Math::chisquared_quantile(0.68,2) and 0.95. The sqrt() is just because contour() uses n1*n1 etc. Would it be better if contour() used for the "n-sigma" contour: ROOT::Math::chisquared_quantile(2*ROOT::Math::gaussian_cdf(n)-1,2) (or maybe there's a simplification)?

      Attachments

        Activity

          People

            moneta Lorenzo Moneta
            adye Tim Adye
            Votes:
            0 Vote for this issue
            Watchers:
            2 Start watching this issue

            Dates

              Created:
              Updated:
              Resolved:
              Actual End: