95% confident level lines of fitting fuction

ROOT
1

Hi,
For some commercial softwares such as “Origin” can provide the function to plot 95% confident level interval (95% prediction interval) of the fitting function to estimate the quality of the fitting, I am wondering if ROOT has implemented such a function? If not, for users, there is a macros available to be a sample?

Thanks,
Zhiyi.

2

See TMinuit::Contour at
root.cern.ch/root/htmldoc//TMinu … it:Contour

with an example in the standard ROOT tutorials at
$ROOTSYS/tutorials/fitcont.C

see below

Rene

[code]void fitcont()
{
// 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*
// Author; Rene Brun

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
gMinuit->SetErrorDef(1);
TGraph gr1 = (TGraph)gMinuit->Contour(80,0,2);
gr1->SetFillColor(38);
gr1->Draw(“lf”);
}
[/code]

3

Thanks. In fact, before I posted my problem, I have read it. But TMinuit::Contour can not do what I want. I mean the confident interval of the fitting function but not of its fitting parameters. If given the confident level band of the fitting function (fiting function is inside this band), it is very easy for reader to get some idea whether the fitting is good or not.

Cheers,
Zhiyi.