Changing the parameters name in a fit

Newbie
1

Hello, I have this code that performs a double gaussian fit on two close photopeaks in a gamma spectrum. It works fine but whenever I try to set different parameters names for the Gauss function, this messes up the fit and I can’t figure out why. Any explanation or suggestion? Thanks!

#include "TCanvas.h"
#include "TFile.h"
#include "TH1.h"
#include "TF1.h"
#include "TAxis.h"
#include "TStyle.h"
#include <string>
#include <iostream>

void doublefit(
    std::string filename="Co60hq0.root"
    ,std::string histoname="hq0"
    ,std::string bkgfunc="expo"
    ,int xminGFit1=1100
    ,int xmaxGFit1=1240
    ,int xminGFit2=1250
    ,int xmaxGFit2=1400
    ){
    gStyle->SetOptFit(1111);

    TCanvas* can = new TCanvas("can","my canvas",800,800);

    // retrieve the histogram from the input file
    TFile* file = TFile::Open(filename.c_str());
    if(!file){
        std::cout << "File " << filename << " not found... check the input name!" << std::endl;
        return; 
    }
    TH1D* histo = (TH1D*) file->Get(histoname.c_str());
    if(!histo){
        std::cout << "histo " << histoname << " not found... check the input name!" << std::endl;
        return; 
    }
    
    
    // Get the TTree from the file
    TTree *nt = (TTree*) file->Get("nt");

    // Create a new histogram with 500 bins in the range [0, 10000]
    TH1D *histonew = new TH1D("histonew", "hq0new", 500, 0, 10000);

    // Draw the variable "qlong" from the TTree "nt" into the histogram "histonew"
    nt->Draw("qlong>>histonew", "ch==0");
    TH1D* histo_copy = (TH1D*)histonew->Clone();
    histo_copy->SetName("histo_copy");

    // Calibration
    TH1D *histo_cal = new TH1D("histo_cal", "Calibrated Histogram", 500, 0, 3000);
    nt->Draw("-32.4+qlong*0.1942>>histo_cal", "ch==0");


    // Gaussian fit

    const double normGaus=730; // Gauss normalization
    const double meanGaus=1173.2;    // Gauss mean
    const double sigmaGaus=50;

    std::string fitfunc = "gaus(0)";
    TF1* gaussFunc = new TF1("gaussFunc",fitfunc.c_str(),xminGFit1,xmaxGFit1);

    gaussFunc->SetParName(0,"Gauss Norm.");
    gaussFunc->SetParName(1,"Gauss mean");
    gaussFunc->SetParName(2,"Gauss sigma");
    
    gaussFunc->SetParameters(normGaus, meanGaus, sigmaGaus);


    //TFile* file_output = new TFile("file_output.root","recreate");
    //can->Write();
    //histo_cal->Write();

    TF1 *bkgFunc = new TF1("bkgFunc", "expo", 0, 3000);
    bkgFunc->SetParName(0,"Exp amp");
    bkgFunc->SetParName(1,"Exp decay");
    bkgFunc->SetParameters(0, 1.0); // Exponential amplitude
    bkgFunc->SetParameters(1, -0.001); // Exponential decay constant
    
    //TF1 *fitFunc = new TF1("fitFunc", "gaussFunc + bkgFunc(3)", xminGFit1, xmaxGFit1);
    //histo_cal->Fit(fitFunc, "R");




    // Second gaussian fit
    const double normGaus2=620; 
    const double meanGaus2=1333;    
    const double sigmaGaus2=50;

    TF1* gaussFunc2 = new TF1("gaussFunc2",fitfunc.c_str(),xminGFit2,xmaxGFit2);

    gaussFunc2->SetParName(0,"Gauss Norm.2");
    gaussFunc2->SetParName(1,"Gauss mean2");
    gaussFunc2->SetParName(2,"Gauss sigma2");
    
    gaussFunc2->SetParameters(normGaus2, meanGaus2, sigmaGaus2);

    //TF1 *fitFunc2 = new TF1("fitFunc2", "gaussFunc2 + bkgFunc(3)", xminGFit2, xmaxGFit2);
    //histo_cal->Fit(fitFunc2, "R+");

    TF1 *fitFuncDouble = new TF1("fitFuncDouble", "gaussFunc + gaussFunc2 + bkgFunc(3)", xminGFit1, xmaxGFit2);
    histo_cal->Fit(fitFuncDouble, "IR0");
    histo_cal->SetTitle("Co60");
    histo_cal->GetXaxis()->SetTitle("Energy [keV]");
    histo_cal->GetYaxis()->SetTitle("Counts");
    fitFuncDouble->Draw("same");


    // Legend
    TLegend *legend = new TLegend(0.1,0.75,0.3,0.9);
    legend->SetHeader("Legend","C");
    legend->AddEntry(histo_cal,"Calibrated data","f");
    legend->AddEntry("fitFuncDouble","Double Gaussian fit","l");
    legend->SetTextSize(0.02); 
    legend->Draw("same");

  


    // Energy vs Pos graph
    TCanvas *canvas3=new TCanvas("canvas3", "canvas", 800, 800);
    TGraph *graph = new TGraph();
    for (int i = 0; i < histo->GetNbinsX(); ++i) {
        double original_value = histo->GetBinCenter(i+1);
        double calibrated_value = -32.4 + original_value * 0.1942;
        graph->SetPoint(i, original_value, calibrated_value);
    }

    graph->SetTitle("Calibration Linearity;Original Data;Calibrated Data");
    graph->SetMarkerStyle(20);
    graph->SetMarkerSize(0.1);
    graph->SetMarkerColor(kBlue);
    graph->Draw("AP");



    return;
}
2

Can you try to set the parameters before setting their names? For example:

    gaussFunc->SetParameters(normGaus, meanGaus, sigmaGaus);
    gaussFunc->SetParName(0,"Gauss Norm.");
    gaussFunc->SetParName(1,"Gauss mean");
    gaussFunc->SetParName(2,"Gauss sigma");

and so on

3

Now it works, thank you so much! :blush:

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