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fit2a.C
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1/// \file
2/// \ingroup tutorial_fit
3/// \notebook
4/// Fitting a 2-D histogram (a variant)
5/// This tutorial illustrates :
6/// - how to create a 2-d function
7/// - fill a 2-d histogram randomly from this function
8/// - fit the histogram
9/// - display the fitted function on top of the histogram (lego-plot)
10/// using a surface plot in a sub-range of the histogram.
11///
12/// This example can be executed via the interpreter or/and the compiler
13///
14/// ~~~{.cpp}
15/// root > .x fit2a.C
16/// root > .x fit2a.C++
17/// ~~~
18///
19/// \macro_image
20/// \macro_output
21/// \macro_code
22///
23/// \author Rene Brun
24
25#include "TF2.h"
26#include "TH2.h"
27#include "TCutG.h"
28#include "TMath.h"
29#include "TCanvas.h"
30#include "TStyle.h"
31
32double g2(double *x, double *par) {
33 double r1 = double((x[0]-par[1])/par[2]);
34 double r2 = double((x[1]-par[3])/par[4]);
35 return par[0]*TMath::Exp(-0.5*(r1*r1+r2*r2));
36}
37double fun2(double *x, double *par) {
38 double *p1 = &par[0];
39 double *p2 = &par[5];
40 double *p3 = &par[10];
41 double result = g2(x,p1) + g2(x,p2) + g2(x,p3);
42 return result;
43}
44
45TCanvas *fit2a() {
46 TCanvas *c = new TCanvas();
47 gStyle->SetOptStat(true);
48 gStyle->SetPalette(57);
49 const int npar = 15;
50 double f2params[npar] = {100,-3,3,-3,3,160,0,0.8,0,0.9,40,4,0.7,4,0.7};
51 auto f2 = new TF2("f2",fun2,-10,10,-10,10, npar);
52 f2->SetParameters(f2params);
53
54 //Create an histogram and fill it randomly with f2
55 auto h2 = new TH2F("h2","From f2",40,-10,10,40,-10,10);
56 int nentries = 100000;
57 h2->FillRandom("f2",nentries);
58 //Fit h2 with original function f2
59 float ratio = 4*nentries/100000;
60 f2params[ 0] *= ratio;
61 f2params[ 5] *= ratio;
62 f2params[10] *= ratio;
63 f2->SetParameters(f2params);
64 h2->Fit("f2","N");
65 auto cutg = new TCutG("cutg",5);
66 cutg->SetPoint(0,-7,-7);
67 cutg->SetPoint(1, 2,-7);
68 cutg->SetPoint(2, 2, 2);
69 cutg->SetPoint(3,-7, 2);
70 cutg->SetPoint(4,-7,-7);
71 h2->Draw("lego2 0");
72 h2->SetFillColor(38);
73 f2->SetNpx(80);
74 f2->SetNpy(80);
75 f2->Draw("surf1 same bb [cutg]");
76 return c;
77}
#define c(i)
Definition RSha256.hxx:101
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void char Point_t Rectangle_t WindowAttributes_t Float_t Float_t Float_t Int_t Int_t UInt_t UInt_t Rectangle_t result
int nentries
R__EXTERN TStyle * gStyle
Definition TStyle.h:433
The Canvas class.
Definition TCanvas.h:23
Graphical cut class.
Definition TCutG.h:20
A 2-Dim function with parameters.
Definition TF2.h:29
2-D histogram with a float per channel (see TH1 documentation)}
Definition TH2.h:258
void SetOptStat(Int_t stat=1)
The type of information printed in the histogram statistics box can be selected via the parameter mod...
Definition TStyle.cxx:1636
void SetPalette(Int_t ncolors=kBird, Int_t *colors=nullptr, Float_t alpha=1.)
See TColor::SetPalette.
Definition TStyle.cxx:1884
Double_t x[n]
Definition legend1.C:17
Double_t Exp(Double_t x)
Returns the base-e exponential function of x, which is e raised to the power x.
Definition TMath.h:709