constexpr Double_t Pi()
{
   return 3.14159265358979323846;
} 

Double_t fit_firstder_one(Double_t *x1_one, Double_t *par1_one)
 {
    Double_t arg1_one   = 0;
    Double_t arg1_0_one = 0;
    if (par1_one[2] != 0) 
    {
       arg1_one   = (x1_one[0] - par1_one[1])/par1_one[2];
       arg1_0_one = (x1_one[0] - par1_one[1])/(par1_one[2]*par1_one[2]); 
    }
 
    Double_t fitval1_one= -par1_one[0]*TMath::Exp(-0.5*arg1_one*arg1_one)*arg1_0_one;
    return fitval1_one;
 }

void Demo()
{
gStyle->SetOptStat(2211);
gStyle->SetOptFit(1111);

// DEFINING CANVAS
TCanvas *c1 = new TCanvas("c1","Without constraint",700,1000);
c1->Divide(1,3);

TH1D*h2 = new TH1D("h2","set bin center", 100,40,140); 
TH1D*h3 = new TH1D("h3","set bin center:error", 100,40,140);



Double_t LowerLimit_Mass_one = 44;
Double_t UpperLimit_Mass_one  = 132;

Int_t no_par_one = 3;


TFile *file1=new TFile("Tot.root");
TH1D *h1 = (TH1D*)file1->Get("Tot");
c1->cd(1);

h1->Draw("HIST E1");




Double_t error_A;
Double_t A = h1->IntegralAndError(1, h1->GetNbinsX(), error_A, "");
std::cout << "Int_A (excluding underflow and overflow bins) = " << A<< " +- " <<error_A << std::endl;

cout<<"Estimated Integral : "<<"\t"<< A<<"\n";

Double_t error_A1;
Double_t A1 = h1->IntegralAndError(0, (h1->GetNbinsX() + 1), error_A1, ""); // "" or "width"
std::cout << "Int_A (including underflow and overflow bins) = " << A1<< " +- " <<error_A1 << std::endl;

TPaveText *pt_h1 = new TPaveText(0.4,0.6,0.7,0.7,"brNDC");
pt_h1->SetTextSize(0.04);
pt_h1->SetFillColor(0);
pt_h1->SetTextAlign(12);
pt_h1->AddText(Form("Integral =""%f""+/-""%f", A , error_A));
pt_h1->Draw();

//--------------- Fitting first derivative with 1 gauss -----------------------

   TF1 *f12_firstder_one_root = new TF1("fit_firstder_one_root",fit_firstder_one ,LowerLimit_Mass_one,UpperLimit_Mass_one,no_par_one);
   f12_firstder_one_root ->SetLineColor(2);

   f12_firstder_one_root ->SetParameter(0,1000);
   f12_firstder_one_root ->SetParLimits(0,1.5,1e8);

   f12_firstder_one_root->FixParameter(1, 88);

   f12_firstder_one_root ->SetParameter(2, 13);
   f12_firstder_one_root ->SetParLimits(2,1,30);


Int_t nbins = h1->GetNbinsX();

for(Int_t i=0;i<nbins;i++)
{

double a=h1->GetBinContent(i);
double a_cent=h1->GetBinCenter(i);
double a_err=h1->GetBinError(i);

double h=h1->GetBinContent(i+6);
double h_cent=h1->GetBinCenter(i+6);
double h_err=h1->GetBinError(i+6);



 //7 bins
double d_7_gauss = (h-a)/(h_cent-a_cent);
double d_mid_7_gauss = (h_cent+a_cent)/2;
double d_mid_7_gauss_err = (1/(h_cent-a_cent))*TMath::Sqrt(pow(h_err,2)+pow(a_err,2));


h2->SetBinContent(i+3,d_7_gauss);

h3->Fill(d_mid_7_gauss,d_7_gauss);

}

c1->cd(2);
         h2->SetMarkerStyle(24);
         h2->SetMarkerColor(1);
         h2->SetLineColor(6);
         h2->SetMarkerSize(0.4);
h2->Draw("HIST");
h2->Fit("fit_firstder_one_root");
f12_firstder_one_root->Draw("same");

TPaveText *pt_h15 = new TPaveText(0.4,0.6,0.7,0.75,"brNDC");
pt_h15->SetTextSize(0.04);
pt_h15->SetFillColor(0);
pt_h15->SetTextAlign(12);
pt_h15->AddText(Form("Integral =""%i""+/-""%f",TMath::Nint(TMath :: Sqrt(2*Pi())*f12_firstder_one_root->GetParameter(0)*f12_firstder_one_root->GetParameter(2)), (TMath:: Sqrt(2*Pi()*(pow(f12_firstder_one_root->GetParameter(2),2)*pow(f12_firstder_one_root->GetParError(0),2) + pow(f12_firstder_one_root->GetParameter(0),2)*pow(f12_firstder_one_root->GetParError(2),2))   )    )));

pt_h15->AddText(Form("Area =""%f""+/-""%f", ((TMath :: Sqrt(2*Pi())*f12_firstder_one_root->GetParameter(0)*f12_firstder_one_root->GetParameter(2))/A)*100 , (TMath:: Sqrt(2*Pi()*(pow(f12_firstder_one_root->GetParameter(2),2)*pow(f12_firstder_one_root->GetParError(0),2) + pow(f12_firstder_one_root->GetParameter(0),2)*pow(f12_firstder_one_root->GetParError(2),2))   )/A)*100 ));
pt_h15->Draw();

c1->cd(3);
         h3->SetMarkerStyle(24);
         h3->SetMarkerColor(1);
         h3->SetLineColor(1);
         h3->SetMarkerSize(0.4);
h3->Draw("HIST");
h3->Fit("fit_firstder_one_root");
f12_firstder_one_root->Draw("same");

TPaveText *pt_h16 = new TPaveText(0.4,0.6,0.7,0.75,"brNDC");
pt_h16->SetTextSize(0.04);
pt_h16->SetFillColor(0);
pt_h16->SetTextAlign(12);
pt_h16->AddText(Form("Integral =""%i""+/-""%f",TMath::Nint(TMath :: Sqrt(2*Pi())*f12_firstder_one_root->GetParameter(0)*f12_firstder_one_root->GetParameter(2)), (TMath:: Sqrt(2*Pi()*(pow(f12_firstder_one_root->GetParameter(2),2)*pow(f12_firstder_one_root->GetParError(0),2) + pow(f12_firstder_one_root->GetParameter(0),2)*pow(f12_firstder_one_root->GetParError(2),2))   )    )));
pt_h16->AddText(Form("Area =""%f""+/-""%f", ((TMath :: Sqrt(2*Pi())*f12_firstder_one_root->GetParameter(0)*f12_firstder_one_root->GetParameter(2))/A)*100 , (TMath:: Sqrt(2*Pi()*(pow(f12_firstder_one_root->GetParameter(2),2)*pow(f12_firstder_one_root->GetParError(0),2) + pow(f12_firstder_one_root->GetParameter(0),2)*pow(f12_firstder_one_root->GetParError(2),2))   )/A)*100 ));
pt_h16->Draw();



}