void fitGraph() {
  gStyle->SetOptFit(1111);
  // create first graph
  Int_t n1 = 10;
  Double_t x1[]  = {-0.1, 0.05, 0.25, 0.35, 0.5, 0.61,0.7,0.85,0.89,0.95};
  Double_t y1[]  = {-1,2.9,5.6,7.4,9,9.6,8.7,6.3,4.5,1};
  Double_t ex1[] = {.05,.1,.07,.07,.04,.05,.06,.07,.08,.05};
  Double_t ey1[] = {.8,.7,.6,.5,.4,.4,.5,.6,.7,.8};
  gr1 = new TGraphErrors(n1,x1,y1,ex1,ey1);
  gr1->SetMarkerColor(kBlue);
  gr1->SetMarkerStyle(21);
  gr1->Fit("gaus");
  gr1->Draw("ALP");
}