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Reference Guide
RooSubsidiaryL Class Reference

RooSubsidiaryL calculates the sum of the -(log) likelihoods of a set of RooAbsPdf objects that represent subsidiary or constraint functions.

This class is used to gather all subsidiary PDF terms from the component PDFs of RooSumL likelihoods and calculate the composite -log(L). Such subsidiary terms can be marked using RooFit::Constrain arguments to RooAbsPdf::fitTo() or RooAbsPdf::createNLL().

Subsidiary terms are summed separately for increased numerical stability, since these terms are often small and cause numerical variances in their original PDFs, whereas by summing as one separate subsidiary collective term, it is numerically very stable.

Note
When a subsidiary PDF is part of multiple component PDFs, it will only be summed once in this class! This doesn't change the derivative of the log likelihood (which is what matters in fitting the likelihood), but does change the value of the (log-)likelihood itself.

The documentation for this class was generated from the following file: