#include <string>
Double_t myfunction(Double_t *x, Double_t *par)
{
    //     par(0) -> asymptotic efficiency
    //     par(1) -> HV of 50% of asymptotic efficiency 
    //     par(2) -> HV of 90% - HV of 10% of asymptotic efficiency 
    Double_t plat=par[0]/( 1.+ 81.**( (par[1]-x[0])/par[2] ) );
    return plat;
}
 
void fitcalibra(Double_t xlow, Double_t xup)
{
      gROOT->Reset();
   //c1 = new TCanvas("c1","Efficiency plateau",200,10,700,500);
   TCanvas *c1 = new TCanvas("c1","Retta di calibrazione");


   gPad->SetFillColor(0);
   gPad->SetGrid();
   gPad->GetFrame()->SetFillColor(21);
   gPad->GetFrame()->SetBorderSize(12);

   gStyle->SetOptFit(1112);


   string fileNameString = "../dati/camac/fit.txt";
   char* fileName = fileNameString.c_str();
   cout<<" *************** reading from file "<<fileName<<endl;
   ifstream inputFile;
   inputFile.open(fileName);
   Int_t nP = 0;
   Float_t x[100];
   Float_t dx[100];
   Float_t y[100];
   Float_t dy[100];
   
   while (1) {
       Float_t  chan = 0; Float_t time = 0.; Float_t sigmachan = 0; Float_t deltatime = 0.;
       inputFile >> chan >> sigmachan >> time >> deltatime;
       if (!inputFile.good()) break;
       // trasformo l'errore massimo in errore statistico ipotizzando una
       // distribuzione uniforme (ma i risultati del fit sono identici son sigma o con delta)
       Float_t sigmatime = deltatime/(sqrt(3.));
       cout<<nP<<" time " <<time<<" +/- "<<sigmatime<<" channel "<<chan<<" +/- "<<sigmachan <<endl;
       x[nP]      = time;
       dx[nP]     = sigmatime;  
       y[nP]  = chan;
       dy[nP] = sigmachan;
       nP++;
   }

   gr = new TGraphErrors(nP,x,y,dx,dy);
   string MyTitle = "Retta di calibrazione";
   gr->SetTitle(MyTitle.c_str());
   gr->SetMarkerColor(4);
   gr->SetMarkerStyle(21);
   gr->GetXaxis()->SetTitle(" microseconds ");
   gr->GetYaxis()->SetTitle("ADC channel");
   //gr->Draw("ALP");
   gr->Draw("AP");
   //fitto con una retta il cui coefficiente angolare sara' il fattore di conversione
   // canali ADC->tempi
   TF1 *f1 = new TF1 ("linear", "pol1", xlow, xup);
   gr->Fit("linear","R");
   //gr->Fit("pol3","");
   c1->Update();
}