if (multi_gr) { // make sure it really exists
multi_gr->Draw("ap"); // draw it
gPad->Modified(); gPad->Update(); // make sure it's really (re)drawn;
multi_gr->SetMaximum(1.0);
multi_gr->SetMinimum(0.0000001);
multi_gr->GetXaxis()->SetLimits(10.0,100.0);
gPad->Modified(); gPad->Update(); // make sure it's really (re)drawn;
} else {std::cout << "Error : multi_gr == 0" << std::endl;}