| virtual void | SetNFitPoints(unsigned int n) const |
| virtual double | DoDerivative(const double* x, unsigned int icoord) const |
| virtual double | DoEval(const double* x) const |

effective points used in the fit (exclude the rejected one)
{ return fNEffPoints; }set number of fit points (need to be called in const methods, make it const)
{ fNEffPoints = n; }