RooFit Problems with Acceptance Functions in ROOT v5.18


I am having the exact same problem as was described in this post last month:

And was wondering whether anyone knows what is causing this behaviour.

To recap, the problem is that when you attempt to do a fit in ROOT v5.18.00 using RooFit, the fit doesn’t work if the fitting PDF has an acceptance function in it.

I attach the output of my fit using v5.16.00, and v5.18.00. The red line is the PDF before the fit, and the blue dotted line is the PDF after the fit. Visually it is clear that the v5.16 fit is working, while the v5.18 fit seems to be ignoring the data and just doing its own thing.

Both of these fits should be identical, I used the same seed for the toy data generation and eveything. I have ran many fits to toy data using both ROOT versions and the pattern is clear -ROOT v5.16 works and ROOT 5.18 does not. If I make the PDF without the acceptance function in it, the fit works for both ROOT versions.

If anyone knows how to fix this problem I would appreciate hearing from them.


Laurence (1.79 MB) (1.79 MB)


I’ll be looking at #6248 shortly. Once that is fixed I’ll let you know and you should try again to see if that solves your problem too.