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Ifit.C
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1/// \file
2/// \ingroup tutorial_fit
3/// \notebook -nodraw
4/// Example of a program to fit non-equidistant data points
5///
6/// The fitting function fcn is a simple chisquare function
7/// The data consists of 5 data points (arrays x,y,z) + the errors in errorsz
8/// More details on the various functions or parameters for these functions
9/// can be obtained in an interactive ROOT session with:
10///
11/// ~~~{.cpp}
12/// Root > TMinuit *minuit = new TMinuit(10);
13/// ~~~
14///
15/// ~~~{.cpp}
16/// Root > minuit->mnhelp("*") to see the list of possible keywords
17/// Root > minuit->mnhelp("SET") explains most parameters
18/// ~~~
19///
20/// \macro_output
21/// \macro_code
22///
23/// \author Rene Brun
24
25#include "TMinuit.h"
26
27float z[5],x[5],y[5],errorz[5];
28
29//______________________________________________________________________________
30double func(float x,float y,double *par)
31{
32 double value=( (par[0]*par[0])/(x*x)-1)/ ( par[1]+par[2]*y-par[3]*y*y);
33 return value;
34}
35
36//______________________________________________________________________________
37void fcn(int &npar, double *gin, double &f, double *par, int iflag)
38{
39 const int nbins = 5;
40 int i;
41
42//calculate chisquare
43 double chisq = 0;
44 double delta;
45 for (i=0;i<nbins; i++) {
46 delta = (z[i]-func(x[i],y[i],par))/errorz[i];
47 chisq += delta*delta;
48 }
49 f = chisq;
50}
51
52//______________________________________________________________________________
53void Ifit()
54{
55// The z values
56 z[0]=1;
57 z[1]=0.96;
58 z[2]=0.89;
59 z[3]=0.85;
60 z[4]=0.78;
61// The errors on z values
62 float error = 0.01;
63 errorz[0]=error;
64 errorz[1]=error;
65 errorz[2]=error;
66 errorz[3]=error;
67 errorz[4]=error;
68// the x values
69 x[0]=1.5751;
70 x[1]=1.5825;
71 x[2]=1.6069;
72 x[3]=1.6339;
73 x[4]=1.6706;
74// the y values
75 y[0]=1.0642;
76 y[1]=0.97685;
77 y[2]=1.13168;
78 y[3]=1.128654;
79 y[4]=1.44016;
80
81 TMinuit *gMinuit = new TMinuit(5); //initialize TMinuit with a maximum of 5 params
82 gMinuit->SetFCN(fcn);
83
84 double arglist[10];
85 int ierflg = 0;
86
87 arglist[0] = 1;
88 gMinuit->mnexcm("SET ERR", arglist ,1,ierflg);
89
90// Set starting values and step sizes for parameters
91 static double vstart[4] = {3, 1 , 0.1 , 0.01};
92 static double step[4] = {0.1 , 0.1 , 0.01 , 0.001};
93 gMinuit->mnparm(0, "a1", vstart[0], step[0], 0,0,ierflg);
94 gMinuit->mnparm(1, "a2", vstart[1], step[1], 0,0,ierflg);
95 gMinuit->mnparm(2, "a3", vstart[2], step[2], 0,0,ierflg);
96 gMinuit->mnparm(3, "a4", vstart[3], step[3], 0,0,ierflg);
97
98// Now ready for minimization step
99 arglist[0] = 500;
100 arglist[1] = 1.;
102
103// Print results
104 double amin,edm,errdef;
105 int nvpar,nparx,icstat;
106 gMinuit->mnstat(amin,edm,errdef,nvpar,nparx,icstat);
107 //gMinuit->mnprin(3,amin);
108
109}
110
#define f(i)
Definition RSha256.hxx:104
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void value
R__EXTERN TMinuit * gMinuit
Definition TMinuit.h:271
Implementation in C++ of the Minuit package written by Fred James.
Definition TMinuit.h:27
virtual void SetFCN(void(*fcn)(Int_t &, Double_t *, Double_t &f, Double_t *, Int_t))
To set the address of the minimization function.
Definition TMinuit.cxx:919
virtual void mnexcm(const char *comand, Double_t *plist, Int_t llist, Int_t &ierflg)
Interprets a command and takes appropriate action.
Definition TMinuit.cxx:2663
virtual void mnstat(Double_t &fmin, Double_t &fedm, Double_t &errdef, Int_t &npari, Int_t &nparx, Int_t &istat)
Returns concerning the current status of the minimization.
Definition TMinuit.cxx:7637
virtual void mnparm(Int_t k, TString cnamj, Double_t uk, Double_t wk, Double_t a, Double_t b, Int_t &ierflg)
Implements one parameter definition.
Definition TMinuit.cxx:5666
Double_t y[n]
Definition legend1.C:17
Double_t x[n]
Definition legend1.C:17