Hi Marco, > Actually, I have made a class which derived from TF1 and overloaded the > Eval() and EvalPar() methods, in oredr to be able to use a fitfunction, > which a programmed myself. This is especially convenient since this > function needs input from a certain histogram, which serves as a range of > fixed parmeters. This seems to work fine, although, of course, if such a > function is attached to a histogram after fitting, it doesn't work > anymore, because it will be copied to a TF1... However, this possibility > has never been suggested in earlier discussion about the use of user > functions in a TF1 (notably also about using object member functions). > Is anyone aware of any additional (or 'hidden') problem to be expected > with this implementation?? I also derived some specialised functions from TF1. The clear advantage is that everything related to the function is grouped in one place (i.e. no user function etc.. needed). I did not experience any problems. Of course this use is not completely correct because your derived class "is" not a TF1 (which is the case for a publicly derived class), i.e. it should not have e.g. the behaviour of TFormula (defining forumla from a string etc...). But as said, it seems to work. Rutger
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