Graphing TF1 Integral

ROOT
1

Hello,
I am having issues graphing an integral of a TF1 function I created. Below is my source code:

#include <iostream>
#include "TF1.h"
#include "TGraph.h"
#include "Math/Integrator"
using namespace std;

void main()
{
  TCanvas *c1 = new TCanvas("c1", "br");
    TF1 *f1 = new TF1("Differential Cross Section of Compton Scattering for 5MeV Photons",myfunction,0,10,3);
    f1->SetParameters(0.0794, 9.769, 5.0);
    f1->SetParNames("electron radius squared","Incident Photon Energy/Rest Mass Energy of Electron", "Incident Photon Energy");
    gPad -> SetLogy();
    f1->Draw();
    f1->GetHistogram()->GetYaxis()->SetTitle("d#sigma/dE_{k}(barns/MeV)");
    f1->GetHistogram()->GetXaxis()->SetTitle("Kinetic Energy of Ejected Electron = E_{k}(MeV)");
    c1->Modified();
    
    TGraph *g = (TGraph*)f1->DrawIntegral();
}

Double_t myfunction(Double_t *x, Double_t *par)
{
    const Double_t pi = TMath::Pi(); 
    Float_t y = x[0];
    Double_t f = (pi*par[0])/(par[1]*par[2])*(2-(2*y)/(par[1]*(par[2]-y))+(y*y)/((par[1]*par[1])*(par[2]-y)*(par[2]-y))+(y*y/(par[2]*(par[2]-y))));
  
    return f;
}

When I run this macro I get this:

Warning: template pair duplicate definition /usr/local/root/cint/cint/stl/_pair.h:31:
Warning: template reverse_iterator duplicate definition /usr/local/root/cint/cint/stl/_iterator.h:269:
Warning: template vector duplicate definition /usr/local/root/cint/cint/stl/_vector.h:44:
^C
*** Break *** keyboard interrupt main.cpp:33:
^C
*** Break *** keyboard interrupt

Thank you in advance!
Natasha

2

In the “myfunction”, you divide by 0 for “x[0] = par[2]” -> see terms in form “(par[2]-y)”.

3

Hi Wilie,
Thank you so much for your quick response. I did not think of that. Here is the back story…I am trying to account for thermal Doppler effects in Compton scattering by convolving the distribution with a Gaussian. So will it not be possible to compute the convolution integral as there is an asymptote?

Thank you so much!
Natasha