exampleFunctor.C File Reference

Detailed Description

Tutorial illustrating how to create a TF1 class using C++ functors or class member functions.

Can be run with:

root > .x exampleFunctor.C
root > .x exampleFunctor.C+ with ACLIC

 
#include "TF1.h"
#include "TMath.h"
#include "TLegend.h"
 
 
double MyFunc (double *x, double *p ) {
   return TMath::Gaus(x[0],p[0],p[1] );
}
 
// function object (functor)
struct MyDerivFunc {
   MyDerivFunc(TF1 * f): fFunc(f) {}
   double operator() (double *x, double * )  const {
      return fFunc->Derivative(*x);
   }
   TF1 * fFunc;
};
// function class with a member function
struct MyIntegFunc {
   MyIntegFunc(TF1 * f): fFunc(f) {}
   double Integral (double *x, double * ) const {
      double a = fFunc->GetXmin();
      return fFunc->Integral(a, *x);
   }
   TF1 * fFunc;
};
 
 
 
void exampleFunctor() {
 
   double xmin = -10;  double xmax = 10;
 
   // create TF1 using a free C function
   TF1 * f1 = new TF1("f1",MyFunc,xmin,xmax,2);
   f1->SetParameters(0.,1.);
   f1->SetMaximum(3);   f1->SetMinimum(-1);
   f1->Draw();
 
   // Derivative function
   // example to create TF1 using a functor
 
   // in order to work with interpreter the function object must be created and lived all time for all time
   // of the TF1. In compiled mode, the function object can be passed by value (recommended) and there
   // is also no need to specify the type of the function class. Example is as follows:
   //
   // `TF1 * f2 = new TF1("f2",MyDerivFunc(f1), xmin, xmax,0); // only for C++ compiled mode`
 
   MyDerivFunc * deriv = new MyDerivFunc(f1);
   TF1 * f2 = new TF1("f2",deriv, xmin, xmax, 0);
 
   f2->SetLineColor(kBlue);
   f2->Draw("same");
 
 
   // Integral function
   // example to create a TF1 using a member function of a user class
 
   // in order to work with interpreter the function object must be created and lived all time for all time
   // of the TF1. In compiled mode there is no need to specify the type of the function class and the name
   // of the member function
   //
   // `TF1 * f3 = new TF1("f3",intg,&MyIntegFunc::Integral,xmin,xmax, 0); // only for C++ compiled mode`
 
   MyIntegFunc * intg = new MyIntegFunc(f1);
   TF1 * f3 = new TF1("f3",intg,&MyIntegFunc::Integral, xmin, xmax, 0);
 
   f3->SetLineColor(kRed);
   f3->Draw("same");
 
   TLegend * l = new TLegend(0.78, 0.25, 0.97 ,0.45);
   l->AddEntry(f1, "Func");
   l->AddEntry(f2, "Deriv.");
   l->AddEntry(f3, "Integral");
   l->Draw();
}

Author

Lorenzo Moneta

Definition in file exampleFunctor.C.