ROOT Version: 6.30.02
Platform: Ubuntu 20.04
Compiler: gcc 12.3.0
Hello root experts. I have a question about the difference in the stored error values for a RooRealVar vs what is printed on the terminal when the minimization is taking place.
I am using RooFit to make a composite signal + background fit to data. The fit status seems to converge, and the covariance matrix status seems good. However, I notice a difference in the uncertainty values that are printed out next to the terminal’s output for a given fit parameter compared to the value that is stored and able to be accessed by FitParam.getError(). This isn’t a large difference, for example an error next to a parameter in the terminal output is 0.8, and the error saved with the variable is 0.9. This discrepancy also exists if I instead of use FitParam.getError(), do:
RooRealVar *param = dynamic_cast<RooRealVar*>(RooFitResult->floatParsFinal().find("paramName"));
param->getError();
I notice this difference when I am minimizing with Minuit2, but I don’t notice this when I minimize with Minuit. I have tried to look through some of the previous forum discussions but haven’t seen this topic come up. Is this a known issue (or is it really an issue?). What could be the cause of this discrepancy?
Thank you for any help!
Respectfully,
Becky