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Reference Guide
exampleFunctor.C
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1 /// \file
2 /// \ingroup tutorial_math
3 /// \notebook
4 /// Tutorial illustrating how creating a TF1 class using functor or class member functions
5 ///
6 /// can be run with:
7 ///
8 /// ~~~{.cpp}
9 /// root > .x exampleFunctor.C
10 /// root > .x exampleFunctor.C+ with ACLIC
11 /// ~~~
12 ///
13 /// \macro_image
14 /// \macro_code
15 ///
16 /// \author Lorenzo Moneta
17 
18 #include "TF1.h"
19 #include "TMath.h"
20 #include "TLegend.h"
21 
22 
23 double MyFunc (double *x, double *p ) {
24  return TMath::Gaus(x[0],p[0],p[1] );
25 }
26 
27 // function object (functor)
28 struct MyDerivFunc {
29  MyDerivFunc(TF1 * f): fFunc(f) {}
30  double operator() (double *x, double * ) const {
31  return fFunc->Derivative(*x);
32  }
33  TF1 * fFunc;
34 };
35 // function class with a member function
36 struct MyIntegFunc {
37  MyIntegFunc(TF1 * f): fFunc(f) {}
38  double Integral (double *x, double * ) const {
39  double a = fFunc->GetXmin();
40  return fFunc->Integral(a, *x);
41  }
42  TF1 * fFunc;
43 };
44 
45 
46 
47 void exampleFunctor() {
48 
49  double xmin = -10; double xmax = 10;
50 
51  // create TF1 using a free C function
52  TF1 * f1 = new TF1("f1",MyFunc,xmin,xmax,2);
53  f1->SetParameters(0.,1.);
54  f1->SetMaximum(3); f1->SetMinimum(-1);
55  f1->Draw();
56 
57  // Derivative function
58  // example to create TF1 using a functor
59 
60  // in order to work with interpreter the function object must be created and lived all time for all time
61  // of the TF1. In compiled mode, the function object can be passed by value (recommended) and there
62  // is also no need to specify the type of the function class. Example is as follows:
63  //
64  // `TF1 * f2 = new TF1("f2",MyDerivFunc(f1), xmin, xmax,0); // only for C++ compiled mode`
65 
66  MyDerivFunc * deriv = new MyDerivFunc(f1);
67  TF1 * f2 = new TF1("f2",deriv, xmin, xmax, 0);
68 
69  f2->SetLineColor(kBlue);
70  f2->Draw("same");
71 
72 
73  // integral function
74  // example to create a TF1 using a member function of a user class
75 
76  // in order to work with interpreter the function object must be created and lived all time for all time
77  // of the TF1. In compiled mode there is no need to specify the type of the function class and the name
78  // of the member function
79  //
80  // `TF1 * f3 = new TF1("f3",intg,&MyIntegFunc::Integral,xmin,xmax, 0); // only for C++ compiled mode`
81 
82  MyIntegFunc * intg = new MyIntegFunc(f1);
83  TF1 * f3 = new TF1("f3",intg,&MyIntegFunc::Integral, xmin, xmax, 0);
84 
85  f3->SetLineColor(kRed);
86  f3->Draw("same");
87 
88  TLegend * l = new TLegend(0.78, 0.25, 0.97 ,0.45);
89  l->AddEntry(f1, "Func");
90  l->AddEntry(f2, "Deriv.");
91  l->AddEntry(f3, "Integral");
92  l->Draw();
93 }
virtual void SetParameters(const Double_t *params)
Definition: TF1.h:628
float xmin
Definition: THbookFile.cxx:93
This class displays a legend box (TPaveText) containing several legend entries.
Definition: TLegend.h:23
Definition: Rtypes.h:59
virtual void Draw(Option_t *option="")
Draw this legend with its current attributes.
Definition: TLegend.cxx:423
#define f(i)
Definition: RSha256.hxx:104
virtual void Draw(Option_t *option="")
Draw this function with its current attributes.
Definition: TF1.cxx:1224
virtual void SetMinimum(Double_t minimum=-1111)
Set the minimum value along Y for this function In case the function is already drawn, set also the minimum in the helper histogram.
Definition: TF1.cxx:3313
TRObject operator()(const T1 &t1) const
Double_t x[n]
Definition: legend1.C:17
virtual void SetLineColor(Color_t lcolor)
Set the line color.
Definition: TAttLine.h:40
auto * a
Definition: textangle.C:12
float xmax
Definition: THbookFile.cxx:93
Double_t Gaus(Double_t x, Double_t mean=0, Double_t sigma=1, Bool_t norm=kFALSE)
Calculate a gaussian function with mean and sigma.
Definition: TMath.cxx:448
virtual void SetMaximum(Double_t maximum=-1111)
Set the maximum value along Y for this function In case the function is already drawn, set also the maximum in the helper histogram.
Definition: TF1.cxx:3300
TLegendEntry * AddEntry(const TObject *obj, const char *label="", Option_t *option="lpf")
Add a new entry to this legend.
Definition: TLegend.cxx:330
auto * l
Definition: textangle.C:4
1-Dim function class
Definition: TF1.h:211
TF1 * f1
Definition: legend1.C:11
Definition: Rtypes.h:59