Eangle1DSec/Fit.cxx

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//This code is to fit graph gain vs eangle and get the slope
 
void Fit()
{
    TFile *f=new TFile("eangle.root");
    ostringstream strout;
    strout<<"ddgcalib";
    TTree *tree = f->Get(strout.str().c_str()); 
    double dedx[100],eangle[100], fitmean[100], fitmeanerr[100];
    tree->SetBranchAddress("gain",dedx);
    tree->SetBranchAddress("eangle",eangle);
    //    tree->SetBranchAddress("fitmean",fitmean);
    //    tree->SetBranchAddress("fitmeanerr",fitmeanerr);
    tree->SetBranchAddress("mean",fitmean);
    tree->SetBranchAddress("sigma",fitmeanerr);
 
    cout<<"Entries: "<<tree->GetEntries()<<endl; 
    tree->GetEntry(0);
    
    double sum=0;
    for(int i=0;i<100;i++)
    {
        sum+=dedx[i];
    }
    sum = sum/100;
    
    gStyle->SetOptFit(0111);
 
    TGraphErrors* gr = new TGraphErrors(100,eangle,fitmean,0,fitmeanerr); 
 
    gr->Draw("A*");
    gr->Fit("pol1","r");
}