{
  // Creazione di una canvas con griglia:
  gROOT->Reset();
  c1 = new TCanvas("c1", "Fit dei dati con errori su x e y", 200, 10, 700, 500);
  c1->SetGrid();
  Int_t n = 16;
  // Inizializzazione di 4 vettori:
  // x[] e ex[] sono le misure in ascissa x_i e i loro errori
  Float_t x[n]  = {0.0,1.9,3.8,6.0,9.2,12.9,14.9,19.3,24.2,29.3,35.7,42.6,52.9,67.9,90.6,158.3};
  Float_t ex[n] = {0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01};
  // y[] e ey[] sono le misure in ordinata y_i e i loro errori
  Float_t y[n]  = {0.041,0.038,0.036,0.033,0.03,0.027,0.025,0.022,0.019,0.016,0.013,0.01,0.007,0.004,0.002,0.0002};
  Float_t ey[n] = {0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0};
  // Creazione di un grafico x-y con errori
  gr = new TGraphErrors(n,x,y,ex,ey);
  gr->SetTitle("Fit della funzione");
  gr->SetMarkerColor(4);
  gr->SetMarkerStyle(21);
  gr->Draw("AP");
  gStyle->SetOptFit(1111);
  // Fit dei dati del grafico con una funzione esponenziale
  gr->Fit("expo");
  c1->Update();
}