Evaluates a RooAbsReal object in other ways than recursive graph traversal.
Currently, it is being used for evaluating a RooAbsReal object and supplying the value to the minimizer, during a fit. The class scans the dependencies and schedules the computations in a secure and efficient way. The computations take place in the RooBatchCompute library and can be carried off by either the CPU or a CUDA-supporting GPU. The Evaluator class takes care of data transfers. An instance of this class is created every time RooAbsPdf::fitTo() is called and gets destroyed when the fitting ends.