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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.
12/// \macro_image
13/// \macro_output
14/// \macro_code
16/// \author Rene Brun
18Double_t fitf(Double_t *x, Double_t *par)
20 Double_t arg = 0;
21 if (par[2] != 0) arg = (x[0] - par[1])/par[2];
23 Double_t fitval = par[0]*TMath::Exp(-0.5*arg*arg);
24 return fitval;
26void myfit()
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;
35 TCanvas *c1 = new TCanvas("c1","the fit canvas",500,400);
37 TH1F *hpx = (TH1F*)hsimpleFile->Get("hpx");
39// Creates a Root function based on function fitf above
40 TF1 *func = new TF1("fitf",fitf,-2,2,3);
42// Sets initial values and parameter names
43 func->SetParameters(100,0,1);
44 func->SetParNames("Constant","Mean_value","Sigma");
46// Fit histogram in range defined by function
47 hpx->Fit(func,"r");
49// Gets integral of function between fit limits
50 printf("Integral of function = %g\n",func->Integral(-2,2));
double Double_t
Definition RtypesCore.h:59
#define gInterpreter
#define gROOT
Definition TROOT.h:406
The Canvas class.
Definition TCanvas.h:23
TObject * Get(const char *namecycle) override
Return pointer to object identified by namecycle.
1-Dim function class
Definition TF1.h:213
virtual Double_t Integral(Double_t a, Double_t b, Double_t epsrel=1.e-12)
IntegralOneDim or analytical integral.
Definition TF1.cxx:2515
virtual void SetParameters(const Double_t *params)
Definition TF1.h:644
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:3475
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition TFile.h:54
1-D histogram with a float per channel (see TH1 documentation)}
Definition TH1.h:575
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:3892
Basic string class.
Definition TString.h:136
const char * Data() const
Definition TString.h:369
TString & ReplaceAll(const TString &s1, const TString &s2)
Definition TString.h:692
TString & Append(const char *cs)
Definition TString.h:564
return c1
Definition legend1.C:41
Double_t x[n]
Definition legend1.C:17
Double_t Exp(Double_t x)
Definition TMath.h:727