graph2derrorsfit.C File Reference

Detailed Description

Draw and fit a TGraph2DErrors

 
#include <TMath.h>
#include <TGraph2DErrors.h>
#include <TRandom.h>
#include <TStyle.h>
#include <TCanvas.h>
#include <TF2.h>
 
void graph2derrorsfit()
{
   TCanvas *c1 = new TCanvas("c1");
 
   Double_t rnd, x, y, z, ex, ey, ez;
   Double_t e = 0.3;
   Int_t nd = 500;
 
   TRandom r;
   TF2 *f2 = new TF2("f2", "1000*(([0]*sin(x)/x)*([1]*sin(y)/y))+200", -6, 6, -6, 6);
   f2->SetParameters(1, 1);
   TGraph2DErrors *dte = new TGraph2DErrors(nd);
 
   // Fill the 2D graph
   Double_t zmax = 0;
   for (Int_t i = 0; i < nd; i++) {
      f2->GetRandom2(x, y);
      rnd = r.Uniform(-e, e); // Generate a random number in [-e,e]
      z = f2->Eval(x, y) * (1 + rnd);
      if (z > zmax)
         zmax = z;
      dte->SetPoint(i, x, y, z);
      ex = 0.05 * r.Rndm();
      ey = 0.05 * r.Rndm();
      ez = TMath::Abs(z * rnd);
      dte->SetPointError(i, ex, ey, ez);
   }
 
   f2->SetParameters(0.5, 1.5);
   dte->Fit(f2);
   TF2 *fit2 = (TF2 *)dte->FindObject("f2");
   fit2->SetTitle("Minuit fit result on the Graph2DErrors points");
   fit2->SetMaximum(zmax);
   gStyle->SetHistTopMargin(0);
   fit2->SetLineColor(1);
   fit2->SetLineWidth(1);
   fit2->Draw("surf1");
   dte->Draw("same p0");
}

Author

Olivier Couet

Definition in file graph2derrorsfit.C.