fit2d¶

Example illustrating how to fit a 2-d histogram of type y=f(x)

Author: Rene Brun
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Monday, March 27, 2023 at 09:47 AM.

generate a 2-d histogram using a TCutG

In [1]:

const int n = 6;
float x[n] = {0.092,0.83,0.94,0.81,0.12,0.1};
float y[n] = {0.71,9.4,9,8,0.3,0.71};
TCutG *cut = new TCutG("cut",n,x,y);
TH2F *h2 = new TH2F("h2","h2",40,0,1,40,0,10);
float u,v;
for (int i=0;i<100000;i++) {
   u = gRandom->Rndm();
   v = 10*gRandom->Rndm();
   if (cut->IsInside(u,v)) h2->Fill(u,v);
}
TCanvas *c1 = new TCanvas("c1","show profile",600,900);
c1->Divide(1,2);
c1->cd(1);
h2->Draw();
c1->cd(2);

use a TProfile to convert the 2-d to 1-d problem

In [2]:

TProfile *prof = h2->ProfileX();
prof->Fit("pol1");

****************************************
Minimizer is Linear / Migrad
Chi2                      =      4501.58
NDf                       =           33
p0                        =     -0.47055   +/-   0.00713644  
p1                        =      10.8033   +/-   0.0124078

Draw all canvases

In [3]:

%jsroot on
gROOT->GetListOfCanvases()->Draw()