{
   auto c1 = new TCanvas("c1","c1",600,400);

   Double_t px1[2] = {2.,4.};
   Double_t dx1[2] = {0.1,0.1};
   Double_t py1[2] = {2.1,4.0};
   Double_t dy1[2] = {0.3,0.2};

   Double_t px2[2] = {3.,5.};
   Double_t dx2[2] = {0.1,0.1};
   Double_t py2[2] = {3.2,4.8};
   Double_t dy2[2] = {0.3,0.2};

   gStyle->SetOptFit(0001);

   auto g1 = new TGraphErrors(2,px1,py1,dx1,dy1);
   g1->SetMarkerStyle(21);
   g1->SetMarkerColor(2);

   auto g2 = new TGraphErrors(2,px2,py2,dx2,dy2);
   g2->SetMarkerStyle(22);
   g2->SetMarkerColor(3);

   auto g = new TMultiGraph();
   g->Add(g1);
   g->Add(g2);

   g->Draw("AP");

   g->Fit("pol1","FQ");
}