Trouble Fitting the data

[Nisha]

Hi ROOTers,

I am having trouble fitting my data with fits. I have a spectrum of multiple peaks. I am creating separate canvas for each peak and fitting them using gaus+pol1 fitting. Whenever I fit using gaus, everything works well but whenever I add a pol1 to the fit, my fit fails. I tried defining gaus and pol1 functions separately but still for some reason it fails. Here is the code -

Double_t min, max, sigma;

   TH1F *myhist[npeaksFound];

   char *histname = new char[npeaksFound];

   TCanvas *ch=new TCanvas(histname,"ch");

   ch->Print("Peaks_disk118.pdf[");

   for (int i=0;i<npeaksFound;i++) {

       sprintf(histname,"histo%d",i);

      // sigma = 5/2.5 ; // using the first peak, fwhm visually is 5 so std dev = fwhm/2.5  this only considers half the peak

       min = xpeaks[i] - 5; // just taking fwhm

       max = xpeaks[i] + 5;

       cout << "peak , xmin, xmax = " << xpeaks[i] << " " << min << " " << max << endl;

       myhist[i] = (TH1F*)hTVsC_backsub->Clone();

       TCanvas *ch=new TCanvas(histname,"ch");

       myhist[i]->GetXaxis()->SetRangeUser(min,max);

       Double_t binmaxY = myhist[i]->GetMaximumBin();

       Double_t binmaxX = myhist[i]->GetBinCenter(binmaxY);

       TF1 *gaus = new TF1("gaus", "[0]* exp(-0.5*((x-[1])/[2])^2)");

       TF1 *pol1 = new TF1("pol1", "[3] + [4] * x ");

     

       gaus->SetParameter(1,xpeaks[i]); // mean

       gaus->SetParameter(2,(max-min)/2.); // std dev ...defines the sigma

       pol1->SetParameter(4,0.1);// slope

       pol1->SetParameter(3,1.); // intercept

       //TF1* Tfit =new TF1("Tfit","gaus"); // add pol1

       //myhist[i]->Fit("gaus");

       myhist[i]->Fit("pol1");

      // myhist[i]->Fit("Tfit");

       /*TF1* Tfit =new TF1("Tfit","gaus+pol1"); // add pol1

       myhist[i]->Fit("Tfit");*/

       ch->cd();

       myhist[i]->Draw(""); // I have removed Draw("histo") to see the fit lines; Ask Dr. Meisel why this happens;

       ch->Print("Peaks_disk118.pdf");

       Double_t p1 =    gaus->GetParameter(1); //mean

       Double_t p2 =    gaus->GetParameter(2); //std dev

       cout << " Mean p1 : " << p1 << "\t sigma p2: " << p2 << endl;

       Double_t lower_limit = p1 - 3*p2;

       Double_t upper_limit = p1 + 3*p2;

     

       Double_t counts = myhist[i]->Integral(upper_limit, lower_limit);

       Double_t rms = myhist[i]->GetRMS();

       Double_t total_counts = sqrt(counts);

       Double_t uncertainty = rms/total_counts; // use getRMS command here..this is wrong

       cout << lower_limit << "=============================" << endl;

       cout << upper_limit << "=============================" << endl;

       cout << rms << "=============================" << endl;

       cout << total_counts << "=============================" << endl;

       cout << uncertainty << "=============================" << endl;

       Double_t Mean = myhist[i]->GetMean();

Can anyone help with this? Thank you for your time and help!

ROOT Version: 6.18/04
Platform: C++
Compiler: Visual Studio Code

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