void SiPM(){

  const Int_t n = 5;

  Float_t SiPM_x[n] = {0.0756, 0.1235, 0.1605, 0.2004, 0.254};
  Float_t SiPM_y[n] = {0.00001764,0.00003136,0.00004225,0.00005329,0.000064};

  TGraph *SiPM_g = new TGraph(n,SiPM_x,SiPM_y);

  SiPM_g->Draw("*pa");

  TF1 *SiPM_f2 = new TF1("SiPM_f2","[0]+x*[1]");
  SiPM_f2->SetLineColor(kCyan);
  SiPM_g->Fit("SiPM_f2");

  c1->SaveAs("post.pdf");

}