fit1.C File Reference

Detailed Description

Simple fitting example (1-d histogram with an interpreted function)

 
TFile**     fillrandom.root   
 TFile*     fillrandom.root   
  KEY: TFormula   form1;1  abs(sin(x)/x)
  KEY: TF1  sqroot;1 x*gaus(0) + [3]*form1
  KEY: TH1F h1f;1 Test random numbers
Formula based function:     sqroot 
               sqroot : x*gaus(0) + [3]*form1 Ndim= 1, Npar= 4, Number= 0 
 Formula expression: 
   x*[p0]*exp(-0.5*((x-[p1])/[p2])*((x-[p1])/[p2]))+[p3]*(abs(sin(x)/x)) 
****************************************
Minimizer is Minuit2 / Migrad
Chi2                      =      198.935
NDf                       =          190
Edm                       =  1.49283e-07
NCalls                    =          149
p0                        =      33.1658   +/-   0.545703    
p1                        =      4.00667   +/-   0.0165304   
p2                        =     0.984663   +/-   0.0128238   
p3                        =      63.4464   +/-   1.33233     
fit1      : Real Time =   0.30 seconds Cpu Time =   0.29 seconds

 
#include "TCanvas.h"
#include "TFrame.h"
#include "TBenchmark.h"
#include "TString.h"
#include "TF1.h"
#include "TH1.h"
#include "TFile.h"
#include "TROOT.h"
#include "TError.h"
#include "TInterpreter.h"
#include "TSystem.h"
#include "TPaveText.h"
 
void fit1() {
   TCanvas *c1 = new TCanvas("c1_fit1","The Fit Canvas",200,10,700,500);
   c1->SetGridx();
   c1->SetGridy();
   c1->GetFrame()->SetFillColor(21);
   c1->GetFrame()->SetBorderMode(-1);
   c1->GetFrame()->SetBorderSize(5);
 
   gBenchmark->Start("fit1");
   //
   // We connect the ROOT file generated in a previous tutorial
   // (see <a href="fillrandom.C.nbconvert.ipynb">Filling histograms with random numbers from a function</a>)
   //
   TString dir = gROOT->GetTutorialDir();
   dir.Append("/fit/");
   TFile *file = nullptr;
   if (!gSystem->AccessPathName("fillrandom.root")) {
      // file exists
      file = TFile::Open("fillrandom.root");
   } else {
      gROOT->ProcessLine(Form(".x %s../hist/fillrandom.C(0)",dir.Data()));
      file = TFile::Open("fillrandom.root");
      if (!file) return;
   }
 
   //
   // The function "ls()" lists the directory contents of this file
   //
   file->ls();
 
   //
   // Get object "sqroot" from the file. Undefined objects are searched
   // for using gROOT->FindObject("xxx"), e.g.:
   // TF1 *sqroot = (TF1*) gROOT.FindObject("sqroot")
   //
   TF1 * sqroot = nullptr;
   file->GetObject("sqroot",sqroot);
   if (!sqroot){
      Error("fit1.C","Cannot find object sqroot of type TF1\n");
      return;
   }
   sqroot->Print();
 
   //
   // Now get and fit histogram h1f with the function sqroot
   //
   TH1F* h1f = nullptr;
   file->GetObject("h1f",h1f);
   if (!h1f){
      Error("fit1.C","Cannot find object h1f of type TH1F\n");
      return;
   }
   h1f->SetFillColor(45);
   h1f->Fit("sqroot");
 
   // We now annotate the picture by creating a PaveText object
   // and displaying the list of commands in this macro
   //
   TPaveText * fitlabel = new TPaveText(0.6,0.4,0.9,0.75,"NDC");
   fitlabel->SetTextAlign(12);
   fitlabel->SetFillColor(42);
   fitlabel->ReadFile(Form("%sfit1_C.txt",dir.Data()));
   fitlabel->Draw();
   c1->Update();
   gBenchmark->Show("fit1");
}

Author

Rene Brun

Definition in file fit1.C.