// Create, Draw and fit a TGraph2DErrors
void macro4(){
gStyle->SetPalette(1);
const double e = 0.3;
const int nd = 500;
TRandom3 my_random_generator;
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 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 = TMath::Abs(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
TCanvas *c1 = new TCanvas();
f2->Draw("Surf1");
dte->Draw("P0 Same");
// Make the x and y projections
TCanvas* 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();
}