void Re_Smear_3gauss()
{

gStyle->SetOptStat(2211);
gStyle->SetOptFit(1111);

/////////////////// Tree opening \\\\\\\\\\\\\\\

TFile *file1=TFile::Open("Analysis.root");
TTree *tree1=(TTree*)file1->Get("Analysis");

TH1D*h1 = new TH1D("h1","h1", 101.0,39.5,140.5);

//Defining a TF1Convolution
    TF1Convolution *f_conv = new TF1Convolution("[0]*exp(-((x-[1])/[2])**2) + [3]*exp(-((x-([1]-[4]))/[5])**2) + [3]*exp(-((x-([1]+[4]))/[5])**2)", "gaus", 30.,150., true);
    
    
f_conv->SetRange(30.,150.);
f_conv->SetNofPointsFFT(1000);


TF1 *f = new TF1("f", *f_conv, 40., 140., f_conv->GetNpar());
    TF1 *f_no_res = new TF1("f_no_res", "[0]*exp(-((x-[1])/[2])**2) + [3]*exp(-((x-([1]-[4]))/[5])**2) + [3]*exp(-((x-([1]+[4]))/[5])**2)", 40., 140.);
    
f->SetParameters(1e3,90.,13., 1e3 ,100.,30., 1.,0.,3.5);
    
    f->SetParNames("A_{1}","#mu_{1}","#sigma_{1}","A_{2}","#mu_shift","#sigma_{2}","Amplitude Convolution","#mu_conv","#sigma_res");

    // I set the amplitude of the 2 gaussian to be positive
    f->SetParLimits(0,0.,1e6);
    f->SetParLimits(3,0.,1e6);
    
    // I set the mean  of the 2 gaussian to be between 60 and 120
    f->SetParLimits(1,60.,120.);
    f->SetParLimits(4,0.,20.);
    
    // I set the sigma  of the 2 gaussian to be between 0 and 100
    f->SetParLimits(2,1.,40.);
    f->SetParLimits(5,1.,40.);
    
// i fix the parameters of the convoluted gaussian
    f->FixParameter(6,1./(3.5*TMath::Sqrt(2*TMath::Pi())) );
f->FixParameter(7,0.);
f->FixParameter(8,3.5);
    
    
    
TCanvas *c1 = new TCanvas("c1","Without constraint",800,600);
c1->Divide(2,2);
c1->cd(1);
tree1->Draw("M_Tot>>h1");

c1->cd(2);
h1->Draw("E1");
    h1->Fit(f,"ME");
    


    f_no_res->SetParameters(f->GetParameters());
    
auto h2 = new TH1D("h2","h2_Mass_resolution",101.0,39.5,140.5);
h2 = (TH1D*)f_no_res->GetHistogram();
    h2->SetStats(kTRUE);
c1->cd(3);
gStyle->SetOptStat(2211);
gStyle->SetOptFit(111);
h2->Draw("E1");

}