fitConvolution.C File Reference

Detailed Description

Tutorial for convolution of two functions

 
****************************************
Minimizer is Minuit2 / Migrad
Chi2                      =       298.12
NDf                       =           96
Edm                       =  1.67196e-06
NCalls                    =          448
p0                        =      7.32861   +/-   0.0370492   
p1                        =    0.0733018   +/-   0.00243973  
p2                        =     -2.26418   +/-   0.0491372   
p3                        =      1.12808   +/-   0.0628185   

 
#include <TCanvas.h>
#include <TRandom.h>
#include <TF1Convolution.h>
#include <TF1.h>
#include <TH1F.h>
 
void fitConvolution()
{
   // Construction of histogram to fit.
   TH1F *h_ExpGauss = new TH1F("h_ExpGauss", "Exponential convoluted by Gaussian", 100, 0., 5.);
   for (int i = 0; i < 1e6; i++) {
      // Gives a alpha of -0.3 in the exp.
      double x = gRandom->Exp(1. / 0.3);
      x += gRandom->Gaus(0., 3.);
      // Probability density function of the addition of two variables is the
      // convolution of two density functions.
      h_ExpGauss->Fill(x);
   }
 
   TF1Convolution *f_conv = new TF1Convolution("expo", "gaus", -1, 6, true);
   f_conv->SetRange(-1., 6.);
   f_conv->SetNofPointsFFT(1000);
   TF1 *f = new TF1("f", *f_conv, 0., 5., f_conv->GetNpar());
   f->SetParameters(1., -0.3, 0., 1.);
 
   // Fit.
   new TCanvas("c", "c", 800, 1000);
   h_ExpGauss->Fit("f");
   h_ExpGauss->Draw();
}

Author

Aurelie Flandi

Definition in file fitConvolution.C.