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Reference Guide
Integration.C File Reference

Detailed Description

View in nbviewer Open in SWAN Numerical integration using R passing the function from ROOT

#include<TMath.h>
#include<TRInterface.h>
#include<TF1.h>
//To integrate using R the function must be vectorized
//The idea is just to receive a vector like an argument,to evaluate
//every element saving the result in another vector
//and return the resultant vector.
std::vector<Double_t> BreitWignerVectorized(std::vector<Double_t> xx)
{
std::vector<Double_t> result(xx.size());
for(Int_t i=0;i<xx.size();i++)
{
result[i]=TMath::BreitWigner(xx[i]);
}
return result;
}
double BreitWignerWrap( double x){
return TMath::BreitWigner(x);
}
{
r["BreitWigner"]=ROOT::R::TRFunctionExport(BreitWignerVectorized);
Double_t value=r.Eval("integrate(BreitWigner, lower = -2, upper = 2)$value");
std::cout.precision(18);
std::cout<<"Integral of the BreitWigner Function in the interval [-2, 2] R = "<<value<<std::endl;
ROOT::Math::WrappedFunction<> wf(BreitWignerWrap);
value=i.Integral(-2,2);
std::cout<<"Integral of the BreitWigner Function in the interval [-2, 2] MathMore = "<<value<<std::endl;
TF1 f1("BreitWigner","BreitWignerWrap(x)");
value=f1.Integral(-2,2);
std::cout<<"Integral of the BreitWigner Function in the interval [-2, 2] TF1 = "<<value<<std::endl;
// infinite limits
value=r.Eval("integrate(BreitWigner, lower = -Inf, upper = Inf)$value");
std::cout<<"Integral of BreitWigner Function in the interval [-Inf, Inf] R = "<<value<<std::endl;
}
Author

Definition in file Integration.C.