fit2dHist.C File Reference

Detailed Description

Example to fit two histograms at the same time via the Fitter class

To execute this tutorial, you can do:

root > .x fit2dHist.C  (executing via cling, slow)

or

root > .x fit2dHist.C+     (executing via ACLIC , fast, with Minuit)
root > .x fit2dHist.C+(2)  (executing via ACLIC , fast, with Minuit2)

or using the option to fit independently the 2 histos

root > .x fit2dHist.C+(10) (via ACLIC, fast, independent fits with Minuit)
root > .x fit2dHist.C+(12) (via ACLIC, fast, independent fits with Minuit2)

Note that you can also execute this script in batch with eg,

root -b -q "fit2dHist.C+(12)"

or execute interactively from the shell

root fit2dHist.C+
root "fit2dHist.C+(12)"

 
****************************************
Minimizer is Minuit2 / Migrad
Chi2                      =      2613.61
NDf                       =         2478
Edm                       =  2.04928e-05
NCalls                    =         1133
p0                        =      534.106   +/-   2.22027     
p1                        =      6.00013   +/-   0.00562856  
p2                        =      1.98723   +/-   0.00361514  
p3                        =      7.02975   +/-   0.0260609   
p4                        =       2.9968   +/-   0.0137019   
p5                        =      519.282   +/-   50.0512     
p6                        =      11.5486   +/-   0.456627    
p7                        =      2.72866   +/-   0.245596    
p8                        =      11.1983   +/-   0.233757    
p9                        =      2.08449   +/-   0.0982633   
****************************************
Minimizer is Minuit2 / Migrad
Chi2                      =      2220.46
NDf                       =         2231
Edm                       =  2.08188e-06
NCalls                    =          311
p0                        =      530.876   +/-   1.55657     
p1                        =       6.0121   +/-   0.00596885  
p2                        =      1.99427   +/-   0.0055483   
p3                        =      6.98634   +/-   0.0177191   
p4                        =      2.98763   +/-   0.0113697   
p5                        =       532.75   +/-   1.15393     
p6                        =      11.9894   +/-   0.00876067  
p7                        =      2.99537   +/-   0.00613849  
p8                        =      10.9975   +/-   0.00338646  
p9                        =      1.98879   +/-   0.00240993  
(int) 0

 
#include "TH2D.h"
#include "TF2.h"
#include "TCanvas.h"
#include "TStyle.h"
#include "TRandom3.h"
#include "Fit/Fitter.h"
#include "TList.h"
 
#include <iostream>
 
double gauss2D(double *x, double *par) {
   double z1 = double((x[0]-par[1])/par[2]);
   double z2 = double((x[1]-par[3])/par[4]);
   return par[0]*exp(-0.5*(z1*z1+z2*z2));
}
double my2Dfunc(double *x, double *par) {
   return gauss2D(x,&par[0]) + gauss2D(x,&par[5]);
}
 
 
 
class MyFcn {
 public:
   TH2D *h1 = nullptr;
   TH2D *h2 = nullptr;
   int npfits = 0;
 
   MyFcn(TH2D * _h1, TH2D * _h2) :
    h1(_h1), h2(_h2) {}
 
   double operator()(const double *p) {
 
   TAxis *xaxis1  = h1->GetXaxis();
   TAxis *yaxis1  = h1->GetYaxis();
   TAxis *xaxis2  = h2->GetXaxis();
   TAxis *yaxis2  = h2->GetYaxis();
 
   int nbinX1 = h1->GetNbinsX();
   int nbinY1 = h1->GetNbinsY();
   int nbinX2 = h2->GetNbinsX();
   int nbinY2 = h2->GetNbinsY();
 
   double chi2 = 0;
   double x[2];
   double tmp;
   npfits = 0;
   for (int ix = 1; ix <= nbinX1; ++ix) {
      x[0] = xaxis1->GetBinCenter(ix);
      for (int iy = 1; iy <= nbinY1; ++iy) {
         if ( h1->GetBinError(ix,iy) > 0 ) {
         x[1] = yaxis1->GetBinCenter(iy);
         tmp = (h1->GetBinContent(ix,iy) - my2Dfunc(x,(double*) p))/h1->GetBinError(ix,iy);
         chi2 += tmp*tmp;
         npfits++;
         }
      }
   }
   for (int ix = 1; ix <= nbinX2; ++ix) {
      x[0] = xaxis2->GetBinCenter(ix);
      for (int iy = 1; iy <= nbinY2; ++iy) {
         if ( h2->GetBinError(ix,iy) > 0 ) {
         x[1] = yaxis2->GetBinCenter(iy);
         tmp = (h2->GetBinContent(ix,iy) - my2Dfunc(x,(double *) p))/h2->GetBinError(ix,iy);
         chi2 += tmp*tmp;
         npfits++;
         }
      }
   }
   return chi2;
}
};
 
void FillHisto(TH2D * h, int n, double * p) {
 
 
   const double mx1 = p[1];
   const double my1 = p[3];
   const double sx1 = p[2];
   const double sy1 = p[4];
   const double mx2 = p[6];
   const double my2 = p[8];
   const double sx2 = p[7];
   const double sy2 = p[9];
   //const double w1 = p[0]*sx1*sy1/(p[5]*sx2*sy2);
   const double w1 = 0.5;
 
   double x, y;
   for (int i = 0; i < n; ++i) {
      // generate randoms with larger Gaussians
      gRandom->Rannor(x,y);
 
      double r = gRandom->Rndm(1);
      if (r < w1) {
         x = x*sx1 + mx1;
         y = y*sy1 + my1;
      }
      else {
         x = x*sx2 + mx2;
         y = y*sy2 + my2;
      }
      h->Fill(x,y);
 
   }
}
 
 
 
 
int fit2dHist(int option=1) {
 
   // create two histograms
 
   int nbx1 = 50;
   int nby1 = 50;
   int nbx2 = 50;
   int nby2 = 50;
   double xlow1 = 0.;
   double ylow1 = 0.;
   double xup1 = 10.;
   double yup1 = 10.;
   double xlow2 = 5.;
   double ylow2 = 5.;
   double xup2 = 20.;
   double yup2 = 20.;
 
   auto h1 = new TH2D("h1","core",nbx1,xlow1,xup1,nby1,ylow1,yup1);
   auto h2 = new TH2D("h2","tails",nbx2,xlow2,xup2,nby2,ylow2,yup2);
 
   double iniParams[10] = { 100, 6., 2., 7., 3, 100, 12., 3., 11., 2. };
   // create fit function
   TF2 * func = new TF2("func",my2Dfunc,xlow2,xup2,ylow2,yup2, 10);
   func->SetParameters(iniParams);
 
   // fill Histos
   int n1 = 1000000;
   int n2 = 1000000;
   FillHisto(h1,n1,iniParams);
   FillHisto(h2,n2,iniParams);
 
   // scale histograms to same heights (for fitting)
   double dx1 = (xup1-xlow1)/double(nbx1);
   double dy1 = (yup1-ylow1)/double(nby1);
   double dx2 = (xup2-xlow2)/double(nbx2);
   double dy2 = (yup2-ylow2)/double(nby2);
   // scale histo 2 to scale of 1
   h2->Sumw2();
   h2->Scale(  ( double(n1) * dx1 * dy1 )  / ( double(n2) * dx2 * dy2 ) );
 
   bool global = false;
   if (option > 10) global = true;
   // do global combined fit
   if (global) {
      // fill data structure for fit (coordinates + values + errors)
      std::cout << "Do global fit" << std::endl;
      // fit now all the function together
 
      ROOT::Fit::Fitter fitter;
      //The default minimizer is Minuit, you can also try Minuit2
 
      MyFcn myFcn(h1,h2);
      fitter.SetFCN(10, myFcn);
      if (option%10 == 2) fitter.Config().SetMinimizer("Minuit2");
 
      // set parameter initial value, name and step size
      for (int i = 0; i < 10; ++i) {
         fitter.Config().ParSettings(i) = ROOT::Fit::ParameterSettings(func->GetParName(i), func->GetParameter(i), 0.01);
      }
 
      bool ret = fitter.FitFCN();
      if (!ret) {
         Error("fit2DHist","Fit Failed to converge");
         return -1;
      }
 
      //get result
      double minParams[10];
      double parErrors[10];
      for (int i = 0; i < 10; ++i) {
         minParams[i] = fitter.Result().Parameter(i);
         parErrors[i] = fitter.Result().Error(i);
      }
      double chi2 = fitter.Result().MinFcnValue();
      double edm = fitter.Result().Edm();
      int npfits = myFcn.npfits;
 
      func->SetParameters(minParams);
      func->SetParErrors(parErrors);
      func->SetChisquare(chi2);
      int ndf = npfits - fitter.Result().NFreeParameters();
      func->SetNDF(ndf);
 
      // add to list of functions
      h1->GetListOfFunctions()->Add(func);
      h2->GetListOfFunctions()->Add(func);
   }
   else {
      // fit independently
      h1->Fit(func, "0");
      h2->Fit(func, "0");
   }
 
   // Create a new canvas.
   TCanvas * c1 = new TCanvas("c1","Two HIstogram Fit example",100,10,900,800);
   c1->Divide(2,2);
   gStyle->SetOptFit();
   gStyle->SetStatY(0.6);
 
   c1->cd(1);
   h1->Draw();
   func->SetRange(xlow1,ylow1,xup1,yup1);
   func->DrawCopy("cont3 same");
   c1->cd(2);
   h1->Draw("lego");
   func->DrawCopy("surf1 same");
   c1->cd(3);
   func->SetRange(xlow2,ylow2,xup2,yup2);
   h2->Draw();
   func->DrawCopy("cont3 same");
   c1->cd(4);
   h2->Draw("lego");
   gPad->SetLogz();
   func->Draw("surf1 same");
 
   return 0;
}

Authors

: Lorenzo Moneta, Rene Brun 18/01/2006

Definition in file fit2dHist.C.