void anil() {
   TCanvas *c1 = new TCanvas("c1","c1",600,800);
   c1->Divide(1,2);
   TRandom3 r;
   TRandom3 r2;
   double err=2;
   double x,y;
   double xmin = 0;
   double xmax = 100;
   double ymin = 0;
   double ymax = 1;
   TF1 *f1 = new TF1("f1","1/x",xmin+0.1,xmax);
   f1->SetNpx(10000);
   TH2F *h2 = new TH2F("h2","test",100,xmin,xmax,100,ymin,ymax);
   int i,j;
   for (i=0;i<10000;i++) {
      y = f1->GetRandom();
      x = r.Uniform(xmin,xmax);
      r2.Gaus(0,err);
      h2->Fill(x+r2.Gaus(0,err),0.1/y);
      h2->Fill(x+r2.Gaus(0,err),0.2/y);
      h2->Fill(x+r2.Gaus(0,err),0.3/y);
   }
   c1->cd(1);
   h2->Draw();
   c1->cd(2);
   //transform dedx vs e into e*dedx vs e
   TH2F *h2e = new TH2F("h2e","h2e",100,xmin,xmax,100,xmin*ymin,0.2*xmax*ymax);
   for (j=1;j<=100;j++) {
      y = h2->GetYaxis()->GetBinCenter(j);
      for (i=1;i<=100;i++) {
         x = h2->GetXaxis()->GetBinCenter(i);
         h2e->Fill(x,y*x,h2->GetBinContent(i,j));
      }
   }
   h2e->Draw();
   
}