Sorry, I was not quite precise.
I also use a “functor class” which defines:
Double_t operator() (const Double_t *x, const Double_t *p) { … }
Double_t operator() (const Double_t *x) { return ( operator() (x, ((const Double_t *)0)) ); }
But I use them only in cases I can also create a ROOT TFx object from it (i.e. TF1, TF2 or TF3): [url]Minimizing a functor - hand holding needed