FitMethodFunction class Interface for objective functions (like chi2 and likelihood used in the fit) In addition to normal function interface provide interface for calculating each data contrinution to the function which is required by some algorithm (like Fumili) @ingroup FitMethodFunc
method returning the data i-th contribution to the fit objective function For example the residual for the least square functions or the pdf element for the likelihood functions. Estimating eventually also the gradient of the data element if the passed pointer is not null