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Reference Guide
myfit.C
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1 /// \file
2 /// \ingroup tutorial_fit
3 /// \notebook -js
4 /// Get in memory an histogram from a root file and fit a user defined function.
5 /// Note that a user defined function must always be defined
6 /// as in this example:
7 /// - first parameter: array of variables (in this example only 1-dimension)
8 /// - second parameter: array of parameters
9 /// Note also that in case of user defined functions, one must set
10 /// an initial value for each parameter.
11 ///
12 /// \macro_image
13 /// \macro_output
14 /// \macro_code
15 ///
16 /// \author Rene Brun
17 
18 Double_t fitf(Double_t *x, Double_t *par)
19 {
20  Double_t arg = 0;
21  if (par[2] != 0) arg = (x[0] - par[1])/par[2];
22 
23  Double_t fitval = par[0]*TMath::Exp(-0.5*arg*arg);
24  return fitval;
25 }
26 void myfit()
27 {
28  TString dir = gROOT->GetTutorialDir();
29  dir.Append("/hsimple.C");
30  dir.ReplaceAll("/./","/");
31  if (!gInterpreter->IsLoaded(dir.Data())) gInterpreter->LoadMacro(dir.Data());
32  TFile *hsimpleFile = (TFile*)gROOT->ProcessLineFast("hsimple(1)");
33  if (!hsimpleFile) return;
34 
35  TCanvas *c1 = new TCanvas("c1","the fit canvas",500,400);
36 
37  TH1F *hpx = (TH1F*)hsimpleFile->Get("hpx");
38 
39 // Creates a Root function based on function fitf above
40  TF1 *func = new TF1("fitf",fitf,-2,2,3);
41 
42 // Sets initial values and parameter names
43  func->SetParameters(100,0,1);
44  func->SetParNames("Constant","Mean_value","Sigma");
45 
46 // Fit histogram in range defined by function
47  hpx->Fit(func,"r");
48 
49 // Gets integral of function between fit limits
50  printf("Integral of function = %g\n",func->Integral(-2,2));
51 }
virtual void SetParameters(const Double_t *params)
Definition: TF1.h:628
virtual void SetParNames(const char *name0="p0", const char *name1="p1", const char *name2="p2", const char *name3="p3", const char *name4="p4", const char *name5="p5", const char *name6="p6", const char *name7="p7", const char *name8="p8", const char *name9="p9", const char *name10="p10")
Set up to 10 parameter names.
Definition: TF1.cxx:3368
return c1
Definition: legend1.C:41
TString & ReplaceAll(const TString &s1, const TString &s2)
Definition: TString.h:687
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format...
Definition: TFile.h:47
virtual TObject * Get(const char *namecycle)
Return pointer to object identified by namecycle.
#define gROOT
Definition: TROOT.h:410
Basic string class.
Definition: TString.h:131
1-D histogram with a float per channel (see TH1 documentation)}
Definition: TH1.h:567
#define gInterpreter
Definition: TInterpreter.h:527
virtual Double_t Integral(Double_t a, Double_t b, Double_t epsrel=1.e-12)
IntegralOneDim or analytical integral.
Definition: TF1.cxx:2409
Double_t x[n]
Definition: legend1.C:17
TString & Append(const char *cs)
Definition: TString.h:559
The Canvas class.
Definition: TCanvas.h:31
Double_t Exp(Double_t x)
Definition: TMath.h:726
double Double_t
Definition: RtypesCore.h:55
1-Dim function class
Definition: TF1.h:211
virtual TFitResultPtr Fit(const char *formula, Option_t *option="", Option_t *goption="", Double_t xmin=0, Double_t xmax=0)
Fit histogram with function fname.
Definition: TH1.cxx:3695
const char * Data() const
Definition: TString.h:364