fit1.C File Reference

Detailed Description

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

Processing /builddir/build/BUILD/root-6.10.00/tutorials/fit/fit1.C...
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)) 
 FCN=196.97 FROM MIGRAD    STATUS=CONVERGED     149 CALLS         150 TOTAL
                     EDM=9.31789e-07    STRATEGY= 1      ERROR MATRIX ACCURATE 
  EXT PARAMETER                                   STEP         FIRST   
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE 
   1  p0           3.40357e+01   5.43457e-01   3.03491e-03   5.03126e-04
   2  p1           4.00280e+00   1.65511e-02   9.26156e-05   8.91532e-02
   3  p2           9.75144e-01   1.21536e-02   5.70335e-05   1.16949e-01
   4  p3           6.14778e+01   1.30772e+00   8.58822e-03  -2.25710e-04
fit1      : Real Time =   1.03 seconds Cpu Time =   1.02 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 = TFile::Open("fillrandom.root");
   if (!file) {
      gROOT->ProcessLine(Form(".x %s../hist/fillrandom.C",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 = 0;
   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 = 0;
   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.