How to use Minuit2Minimizer

I am trying to use the Minuit2Minimizer example code in this page :

#include "Minuit2/Minuit2Minimizer.h"
#include "Math/Functor.h"
double RosenBrock(const double *xx )
  const Double_t x = xx[0];
  const Double_t y = xx[1];
  const Double_t tmp1 = y-x*x;
  const Double_t tmp2 = 1-x;
  return 100*tmp1*tmp1+tmp2*tmp2;
int NumericalMinimization()
   // Choose method upon creation between:
   // kMigrad, kSimplex, kCombined, 
   // kScan, kFumili
   ROOT::Minuit2::Minuit2Minimizer min ( ROOT::Minuit2::kMigrad );
   ROOT::Math::Functor f(&RosenBrock,2); 
   double step[2] = {0.01,0.01};
   double variable[2] = { -1.,1.2};
   // Set the free variables to be minimized!
   min.SetVariable(0,"x",variable[0], step[0]);
   min.SetVariable(1,"y",variable[1], step[1]);
   const double *xs = min.X();
   cout << "Minimum: f(" << xs[0] << "," << xs[1] << "): " 
        << RosenBrock(xs) << endl;
   return 0;

This code is used to calculate the global minimum of the Rosenbrock function:OluAtHd

In this example code, it explicitly assigned a to be equal to 1 and b to be equal 100.

I would like to modify this code and include into a main program that asks the user for input a and b instead of pre-assigning them.

I first tried to modify the arguments of the RosenBrock function:

double RosenBrock(const double *xx, int user_input_a, int user_input_b)

without changing any other part of the example code.

When I tried to compile, I get the error s

 /cvmfs/ error: too few arguments to function call, expected 3, have 1
      return fFunc(x);
             ~~~~~  ^
/cvmfs/ note: in instantiation of member function
      'ROOT::Math::FunctorHandler<ROOT::Math::Functor, double (*)(const double
      *, int, int)>::DoEval' requested here
   FunctorHandler(unsigned int dim, const Func & fun ) :
/cvmfs/ note: in instantiation of member function
      'ROOT::Math::FunctorHandler<ROOT::Math::Functor, double (*)(const double
      *, int, int)>::FunctorHandler' requested here
      fImpl(new FunctorHandler<Functor,Func>(dim,f) )
/afs/ note: in instantiation of function template specialization
      'ROOT::Math::Functor::Functor<double (*)(const double *, int, int)>'
      requested here
   ROOT::Math::Functor f(&RosenBrock,2);

What is the correct way to modify the example code so that I can define the variables a and b when the program is running instead of defining them at compile time?

can anyone help me on this?

NumericalMinimization.C (3.2 KB)

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