Get likelihood values from a plot drawn by a class "LikelihoodIntervalPlot"

Dear experts,

Hello, I have a question in profile likelihood analysis by roostats.
As a practice, I used “StandardProfileLikelihoodDemo.C” in $ROOTSYS/tutorial/roostats/.

I can show the log-likelihood parabola using above macro, so now I’d like to extract this curve as a function.
I just would like to know the parameter of this calculated parabolic function.
Or I’d like to extract each likelihood value and x-axis value as a ASCII style.
Is it possible?

This is because I’m planing to combine some log-likelihood curves after I get curves.
So I need to reconstruct the shape of calculated parabola.

Thank you so much for your support in advance.

best regards,


If you use the option “tf1” for drawing the likelihood, LikelihoodIntervalPlot::Draw("tf1") ,
the plotted object is actually an histogram, a TH1 and you can retrieve it using
LikelihoodIntervalPlot::GetPlottedObject(), then you can retrieve the corresponding likelihood values as bin content of the histogram. Example:

LikelihoodIntervalPlot plot(interval);
plot.SetNPoints(nScanPoints);   // nScanPoints will be the number of histogram bins
plot.SetRange(xmin, xmax);
auto h = (TH1*) plot.GetPlottedObjet(); 
for (int i = 1; i <= h->GetNbinsX(); ++i) 
   std::cout << " x = " << h->GetBinCenter(i) << " Liikelihood(x) = " << h->GetBinContent(i) << std::endl;


Thank you so much for your quick reply!!
And I succeeded to do it following your suggestion.

Thank you so much again.

best regards,

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