#include "Math/IParamFunction.h"
#include <iostream>
#include <vector>
#include "Fit/Chi2FCN.h"

class MyModel: public ROOT::Fit::Chi2Function::IModelFunction{
    public:
        std::vector<double>* fParameters;
        MyModel(){ 
            int npar = 2;
            fParameters = new std::vector<double>(npar);
            // std::cout << "npar " <<  NPar() << std::endl;
        };
        virtual ~MyModel(){ delete fParameters;};
        virtual MyModel * Clone() const{ return new MyModel();};
        virtual unsigned int NDim() const{ return 1;};
        virtual unsigned int NPar() const{ return fParameters->size();};
        virtual const double* Parameters() const{ return &fParameters->front();};
        virtual void SetParameters(const double* p){ 
            for(unsigned int i = 0; i < NPar();i++){
              (*fParameters)[i] = p[i];
            }
        };

    private:
        virtual double DoEvalPar(const double* x, const double* p) const{
            // just a linear function
            return p[0]+p[1]*x[0];
        };
};