Draw RooFit pdfs

[sciencecw]

I have a fitted RooFit pdf that I want to overlay on a stacked histogram. Is there anyway to draw pdf outside of RooFit frames? Alternatively can a frame accept a stacked histogram and plot it without changing its style?

Thanks!

[StephanH]

Hi @sciencecw

try
https://root.cern.ch/doc/master/classRooAbsReal.html#a6659d2c301e5cd65b83ee8c9422c2553

You can then always Draw(“same”) the histogram.

Cheers,
Stephan

[sciencecw]

Hi,

I guess the solution is 1) make histogram from pdf as you suggest
2) Draw using option “L” or “C” so it draws a line through bin centers instead of zig-zag

Thanks

[StephanH]

Seeing that a function seems to be better for you case, there is also asTF. See here:
https://root.cern.ch/doc/master/classRooAbsReal.html#a5b1ad5b6d761c664adc2434689ef8f99

[sciencecw]

This doesn’t have the right normalization. I wonder if this information is in the pdf at all? How does the RooFit frame work out the normalization?

[StephanH]

All PDFs are normalised to unity. That’s, in fact, the definition of a PDF.

When you start to draw a PDF and the histogram contains a dataset, RooFit automatically scales the PDF to the number of data events in the histogram. See here:
https://root.cern.ch/doc/master/classRooAbsReal.html#a32073d896314ad08535328f556379780

You indeed would have to scale the TF1 to the number of data events in your frame.