fit1.C File Reference

Detailed Description

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

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     

 
#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);
 
   // (for more details, see 
   // <a href="hist001_TH1_fillrandom_userfunc.C.nbconvert.ipynb">filling histograms with random numbers from a function</a>)
   TFormula *form1 = new TFormula("form1", "abs(sin(x)/x)");
   TF1 *sqroot = new TF1("sqroot", "x*gaus(0) + [3]*form1", 0.0, 10.0);
   sqroot->SetLineColor(4);
   sqroot->SetLineWidth(6);
   // Set parameters to the functions "gaus" and "form1".
   sqroot->SetParameters(10.0, 4.0, 1.0, 20.0);
   sqroot->Print();
   
   TH1D *h1d = new TH1D("h1d", "Test random numbers", 200, 0.0, 10.0);
   h1d->FillRandom("sqroot", 10000);
 
   //
   // Now fit histogram h1d with the function sqroot
   //
   h1d->SetFillColor(45);
   h1d->Fit("sqroot");
 
   // We now annotate the picture by creating a PaveText object
   // and displaying the list of commands in this macro
   //
   TString dir = gROOT->GetTutorialDir();
   dir.Append("/math/fit/");
   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();
}

Author

Rene Brun

Definition in file fit1.C.