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fitcont.C File Reference

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Example illustrating how to draw the n-sigma contour of a Minuit fit.

To get the n-sigma contour the ERRDEF parameter in Minuit has to set to n^2. The fcn function has to be set before the routine is called.

WARNING!!! This test works only with TMinuit

The TGraph object is created via the interpreter. The user must cast it to a TGraph*

FCN=96.6163 FROM MIGRAD STATUS=CONVERGED 62 CALLS 63 TOTAL
EDM=2.07594e-08 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 Constant 1.43454e+02 2.29666e+00 9.00732e-03 -6.49594e-05
2 Mean 1.60911e-02 1.30402e-02 6.28520e-05 3.57224e-03
3 Sigma 9.87683e-01 9.45637e-03 1.24479e-05 2.14428e-02
#include <TCanvas.h>
#include <TGraph.h>
#include <TH1F.h>
#include <TMinuit.h>
#include <TVirtualFitter.h>
void fitcont()
{
//be sure default is Minuit since we will use gMinuit
TCanvas *c1 = new TCanvas("c1");
TH1F *h = new TH1F("h","My histogram",100,-3,3);
h->FillRandom("gaus",6000);
h->Fit("gaus");
c1->Update();
TCanvas *c2 = new TCanvas("c2","contours",10,10,600,800);
c2->Divide(1,2);
c2->cd(1);
/*get first contour for parameter 1 versus parameter 2*/
TGraph *gr12 = (TGraph*)gMinuit->Contour(40,1,2);
gr12->Draw("alp");
c2->cd(2);
/*Get contour for parameter 0 versus parameter 2 for ERRDEF=2*/
gMinuit->SetErrorDef(4); //note 4 and not 2!
TGraph *gr2 = (TGraph*)gMinuit->Contour(80,0,2);
gr2->SetFillColor(42);
gr2->Draw("alf");
/*Get contour for parameter 0 versus parameter 2 for ERRDEF=1*/
TGraph *gr1 = (TGraph*)gMinuit->Contour(80,0,2);
gr1->SetFillColor(38);
gr1->Draw("lf");
}
#define h(i)
Definition RSha256.hxx:106
R__EXTERN TMinuit * gMinuit
Definition TMinuit.h:271
virtual void SetFillColor(Color_t fcolor)
Set the fill area color.
Definition TAttFill.h:37
The Canvas class.
Definition TCanvas.h:23
A TGraph is an object made of two arrays X and Y with npoints each.
Definition TGraph.h:41
void Draw(Option_t *chopt="") override
Draw this graph with its current attributes.
Definition TGraph.cxx:809
1-D histogram with a float per channel (see TH1 documentation)}
Definition TH1.h:577
virtual Int_t SetErrorDef(Double_t up)
To get the n-sigma contour the error def parameter "up" has to set to n^2.
Definition TMinuit.cxx:907
virtual TObject * Contour(Int_t npoints=10, Int_t pa1=0, Int_t pa2=1)
Creates a TGraph object describing the n-sigma contour of a TMinuit fit.
Definition TMinuit.cxx:652
static void SetDefaultFitter(const char *name="")
static: set name of default fitter
return c1
Definition legend1.C:41
return c2
Definition legend2.C:14
Author
Rene Brun

Definition in file fitcont.C.