macro4.C

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// Create, Draw and fit a TGraph2DErrors
void macro4(){
   gStyle->SetPalette(kBird);
   const double e = 0.3;
   const int nd = 500;
 
   TRandom3 my_random_generator;
   TF2 f2("f2",
          "1000*(([0]*sin(x)/x)*([1]*sin(y)/y))+200",
          -6,6,-6,6);
   f2.SetParameters(1,1);
   TGraph2DErrors dte(nd);
   // Fill the 2D graph
   double rnd, x, y, z, ex, ey, ez;
   for (Int_t i=0; i<nd; i++) {
      f2.GetRandom2(x,y);
      // A random number in [-e,e]
      rnd = my_random_generator.Uniform(-e,e);
      z = f2.Eval(x,y)*(1+rnd);
      dte.SetPoint(i,x,y,z);
      ex = 0.05*my_random_generator.Uniform();
      ey = 0.05*my_random_generator.Uniform();
      ez = fabs(z*rnd);
      dte.SetPointError(i,ex,ey,ez);
   }
   // Fit function to generated data
   f2.SetParameters(0.7,1.5);  // set initial values for fit
   f2.SetTitle("Fitted 2D function");
   dte.Fit(&f2);
   // Plot the result
   auto c1 = new TCanvas();
   f2.SetLineWidth(1);
   f2.SetLineColor(kBlue-5);
   TF2   *f2c = (TF2*)f2.DrawClone("Surf1");
   TAxis *Xaxis = f2c->GetXaxis();
   TAxis *Yaxis = f2c->GetYaxis();
   TAxis *Zaxis = f2c->GetZaxis();
   Xaxis->SetTitle("X Title"); Xaxis->SetTitleOffset(1.5);
   Yaxis->SetTitle("Y Title"); Yaxis->SetTitleOffset(1.5);
   Zaxis->SetTitle("Z Title"); Zaxis->SetTitleOffset(1.5);
   dte.DrawClone("P0 Same");
   // Make the x and y projections
   auto c_p= new TCanvas("ProjCan",
                         "The Projections",1000,400);
   c_p->Divide(2,1);
   c_p->cd(1);
   dte.Project("x")->Draw();
   c_p->cd(2);
   dte.Project("y")->Draw();
}