ROOT::Math::Functor( &member_function( const *double ), nDim )

[p73]

I have a class GKF in which member function I want to use Functor in the following way:

class GKF {

protected:
  
  vector<GKP*> Photons;

public:

  ...
  double Chi2_plus_Constraints( const double* );
  int Perform_Minimization( const char*, const char* );
  ...

and definitions:

  ...
  double GKF::Chi2_plus_Constraints( const double* x ){
    //some operations with x[];
    return Chi2 + Constraints;
  }
  int GKF::Perform_Minimization( const char* name, const char* algo ){
    ROOT::Math::MInimizer *minimizer = 
          ROOT::Math::Factory::CreateMinimizer( name, algo );
  ...
  // I want to have something like this 
  ROOT::Math::Functor functor( &GKF::Chi2_plus_Constraints, NDF );
  ...
  minimizer->SetFunction( functor );
  }

Is it possible? NOTE: I want objective function to be a member function of class in which I use Math::Functor.

Thanks in advance.

[behrenhoff]

Pointers to member functions need to be associated with a specific object. Basically the compiler needs to know what this variable to pass to the member function. So looking at the documentation at https://root.cern.ch/root/html/src/ROOT__Math__Functor.h.html#374 it looks like the Functor has a constructor taking object, pointer to member function and dimension. So that should probably work. (Disclaimer: I don’t know anything about the ROOT::Math::Minimizer.)

[p73]

Should I write that in the following way:

ROOT::Math::Functor functor( this, Chi2_plus_Constraints, nDim );
 

or in this way?

ROOT::Math::Functor functor( this, GKF::Chi2_plus_Constraints, nDim );

or something different?

[p73]

So far it is working ( I say working but in real life it has been just compiled without errors of compilation ) in this way:

ROOT::Math::Functor( this, &GKF::Chi2_plus_Constraints, nDim );