Double_t turnon(Double_t *x, Double_t *par)
{
  double halfpoint = par[0];
  double slope = par[1];
  double plateau = par[2];
    
  //double offset = par[3];
  //double plateau = 1.0;
  double offset = 0;

  double pt = TMath::Max(x[0],0.000001);

  double arg = 0;
  //cout << pt <<", "<< halfpoint <<", " << slope  <<endl;
  arg = (pt - halfpoint)/(TMath::Sqrt(pt)*slope);
  double fitval = offset+0.5*plateau*(1+TMath::Erf(arg));
  return fitval;
}

Double_t polynom2(Double_t *x, Double_t *par)
{
  double p0 = par[0];
  double p1 = par[1];
  double p2 = par[2];
    
  double pt = TMath::Max(x[0],0.000001);

  double fitval = p0+p1*pt+p2*pt*pt;
  return fitval;
  //   1  p0           7.44003e-01   6.27765e-02   3.06329e-06  -4.34913e-09
  // 2  p1           7.50543e-03   3.00214e-03   7.22142e-08   8.91693e-06
  // 3  p2          -6.55469e-05   3.53642e-05   1.62332e-09  -4.65067e-05
}


void plot_turnon(void) {
  gROOT->SetStyle("Plain");
  gROOT->ForceStyle();
  gStyle->SetOptTitle(1);
  gStyle->SetOptStat(0);

  //TH1F* sht20_CC, allem_CC;
  //sprintf(ntp,"c_%sd1_t%d_%d",s,t,i);    h1_d1[i]    = (TH1F *) f1.Get(ntp);
  //sht20_cc = (TH1F *) 
  sht20_seta->Rebin(2);
  sht20_seta->Sumw2();
  allem_seta->Rebin(2);
  allem_seta->Sumw2();
  
  TH1F *sht20_res = new TH1F("sht20_res","|#eta|<1.6, E*_SHT20",80,0.,80.);
  sht20_res->Rebin(2);
  sht20_res->Divide(sht20_seta,allem_seta,1,1,"B");

  TCanvas *c1 = new TCanvas("c1","c1",700,400);
  c1->Divide();
  sht20_res->Draw();

  TF1 *f1 = new TF1("f1",turnon,0,27,3);
  TF1 *f2 = new TF1("f2",polynom2,28,60,3);
  //TF1 *total =new TF1("total",*turnon+*polynom2,0,60);
  TF1 *total =new TF1("total","turnon(0)+polynom2(3)",28,60);

  f1->SetParameters(14.,0.9,0.9);
  f2->SetParameters(7.44003e-01,7.50543e-03,-6.55469e-05);
  
 Double_t par[6];
 sht20_res->Fit("f1","Rr");
 sht20_res->Fit("f2","R+");
 f1->GetParameters(&par[0]);
 f2->GetParameters(&par[0]);
  //cout << par[0] << endl;
 total->SetParameters(par);
 sht20_res->Fit(total,"R+");

}