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fitCircle.C File Reference

Detailed Description

View in nbviewer Open in SWAN Generate points distributed with some errors around a circle Fit a circle through the points and draw To run the script, do, eg

root > .x fitCircle.C (10000 points by default)
root > .x fitCircle.C(100); (with only 100 points
root > .x fitCircle.C++(100000); with ACLIC
point * points
Definition X3DBuffer.c:22
Minimizer is Minuit / Migrad
MinFCN = 903.174
NDf = 0
Edm = 2.25062e-09
NCalls = 72
x0 = 0.00667777 +/- 0.0141774
y0 = 0.00536467 +/- 0.0141954
R = 3.995 +/- 0.0100048
#include "TCanvas.h"
#include "TRandom3.h"
#include "TGraph.h"
#include "TMath.h"
#include "TArc.h"
#include "Fit/Fitter.h"
#include <Math/Functor.h>
void fitCircle(Int_t n=10000) {
//generates n points around a circle and fit them
TCanvas *c1 = new TCanvas("c1","c1",600,600);
TGraph* gr = new TGraph(n);
if (n> 999) gr->SetMarkerStyle(1);
else gr->SetMarkerStyle(3);
for (Int_t i=0;i<n;i++) {
auto chi2Function = [&](const Double_t *par) {
//minimisation function computing the sum of squares of residuals
// looping at the graph points
Int_t np = gr->GetN();
Double_t f = 0;
Double_t *x = gr->GetX();
Double_t *y = gr->GetY();
for (Int_t i=0;i<np;i++) {
Double_t u = x[i] - par[0];
Double_t v = y[i] - par[1];
Double_t dr = par[2] - std::sqrt(u*u+v*v);
f += dr*dr;
return f;
// wrap chi2 function in a function object for the fit
// 3 is the number of fit parameters (size of array par)
ROOT::Math::Functor fcn(chi2Function,3);
double pStart[3] = {0,0,1};
fitter.SetFCN(fcn, pStart);
// do the fit
bool ok = fitter.FitFCN();
if (!ok) {
Error("line3Dfit","Line3D Fit failed");
const ROOT::Fit::FitResult & result = fitter.Result();
//Draw the circle on top of the points
TArc *arc = new TArc(result.Parameter(0),result.Parameter(1),result.Parameter(2));
ROOT::R::TRInterface & r
Definition Object.C:4
#define f(i)
Definition RSha256.hxx:104
int Int_t
Definition RtypesCore.h:45
double Double_t
Definition RtypesCore.h:59
@ kRed
Definition Rtypes.h:66
void Error(const char *location, const char *msgfmt,...)
Use this function in case an error occurred.
Definition TError.cxx:187
const ParameterSettings & ParSettings(unsigned int i) const
get the parameter settings for the i-th parameter (const method)
Definition FitConfig.h:76
class containg the result of the fit and all the related information (fitted parameter values,...
Definition FitResult.h:47
void Print(std::ostream &os, bool covmat=false) const
print the result and optionaly covariance matrix and correlations
double Parameter(unsigned int i) const
parameter value by index
Definition FitResult.h:181
Fitter class, entry point for performing all type of fits.
Definition Fitter.h:77
bool FitFCN(unsigned int npar, Function &fcn, const double *params=0, unsigned int dataSize=0, bool chi2fit=false)
Fit using the a generic FCN function as a C++ callable object implementing double () (const double *)...
Definition Fitter.h:610
bool SetFCN(unsigned int npar, Function &fcn, const double *params=0, unsigned int dataSize=0, bool chi2fit=false)
Set a generic FCN function as a C++ callable object implementing double () (const double *) Note that...
Definition Fitter.h:615
const FitResult & Result() const
get fit result
Definition Fitter.h:384
const FitConfig & Config() const
access to the fit configuration (const method)
Definition Fitter.h:412
void SetName(const std::string &name)
Documentation for class Functor class.
Definition Functor.h:400
Create an Arc.
Definition TArc.h:26
virtual void SetFillStyle(Style_t fstyle)
Set the fill area style.
Definition TAttFill.h:39
virtual void SetLineWidth(Width_t lwidth)
Set the line width.
Definition TAttLine.h:43
virtual void SetLineColor(Color_t lcolor)
Set the line color.
Definition TAttLine.h:40
virtual void SetMarkerStyle(Style_t mstyle=1)
Set the marker style.
Definition TAttMarker.h:40
The Canvas class.
Definition TCanvas.h:23
virtual void Draw(Option_t *option="")
Draw this ellipse with its current attributes.
Definition TEllipse.cxx:168
A TGraph is an object made of two arrays X and Y with npoints each.
Definition TGraph.h:41
virtual void SetPoint(Int_t i, Double_t x, Double_t y)
Set x and y values for point number i.
Definition TGraph.cxx:2284
Double_t * GetY() const
Definition TGraph.h:132
Int_t GetN() const
Definition TGraph.h:124
virtual void Draw(Option_t *chopt="")
Draw this graph with its current attributes.
Definition TGraph.cxx:769
Double_t * GetX() const
Definition TGraph.h:131
Random number generator class based on M.
Definition TRandom3.h:27
return c1
Definition legend1.C:41
Double_t y[n]
Definition legend1.C:17
Double_t x[n]
Definition legend1.C:17
const Int_t n
Definition legend1.C:16
TGraphErrors * gr
Definition legend1.C:25
Rene Brun

Definition in file fitCircle.C.