// NonResonantFunction.h
class NonResonantFunction : public RooAbsPdf {
public:
    NonResonantFunction() {}
    NonResonantFunction(const char *name, const char *title,
			RooAbsReal& _x, RooAbsReal& _x0, RooAbsReal& _a, RooAbsReal& _c, RooAbsReal& _d);
    NonResonantFunction(const NonResonantFunction& other, const char* name=0);
    virtual TObject* clone(const char* newname) const { return new NonResonantFunction(*this,newname); }
    inline virtual ~NonResonantFunction() {}

protected:
  RooRealProxy x;
  RooRealProxy x0;
  RooRealProxy a;
  RooRealProxy c;
  RooRealProxy d;

  Double_t evaluate() const;

private:
  ClassDef(NonResonantFunction,1) // Your custom function
};