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ROOT Version: 6.14
Platform: Not Provided
Compiler: Not Provided

```
TF1 *fpol;
Int_t npol;
const Int_t npeaks = 5;
Double_t fpeaks(Double_t *x, Double_t *par) {
Double_t result = fpol->EvalPar(x,par);
for (Int_t p=0;p<npeaks;p++) {
Double_t norm = par[3*p+npol];
Double_t mean = par[3*p+npol+1];
Double_t sigma = par[3*p+npol+2];
result += norm*TMath::Gaus(x[0],mean,sigma);
}
return result;
}
void fitg() {
TTree *t = new TTree("t", "my tree");
t->ReadFile("test.txt", "x/D");
TH1D *h = new TH1D("h", "Histo", , ., .);
//fit background with a polynomial
fpol = new TF1("fpol","pol3",60,550);
npol = fpol->GetNpar();
h->Fit("fpol","0");
Double_t xpeak[npeaks] = {200, , , , };
Double_t sigma[npeaks] = {2, , , , };
Double_t amp[npeaks] = {100,100,100,100,100};
Double_t par[100];
for (Int_t ip=0;ip<npol;ip++) par[ip] = fpol->GetParameter(ip);
TF1 *fp = new TF1("fp",fpeaks,60,550,npol+3*npeaks);
for (Int_t i=0;i<npeaks;i++) {
fp->SetParameter(3*i+npol,1000*amp[i]);
fp->SetParameter(3*i+npol+1, xpeak[i]);
fp->SetParLimits(3*i+npol+1, xpeak[i]-5,xpeak[i]+5);
fp->SetParameter(3*i+npol+2, sigma[i]);
fp->SetParLimits(3*i+npol+2, 0.5,3*sigma[i]);
}
fp->SetNpx(5000);
TVirtualFitter::SetMaxIterations(10000);
h->Fit(fp,"rw");
}
```

Dilicus
December 24, 2019, 7:06pm
#2
Hi,
you can give a look to TSpectrum class.

After declaring

```
TSpectrum *spectrum= new TSpectrum();
spectrum->Search(h);
```

Then you can use the method TSpectrum::GetNPeaks() and TSpectrum::GetPositionX() to have the number of peaks and vector with the peak position.

Then your code should work fine using the informations get from TSpectrum.

Cheers,
S

Thanks, but i already tried with the following code (modified from > tutorial>Tspectrum>peaks.C) which didn’t work.

```
#include "TCanvas.h"
#include "TMath.h"
#include "TH1.h"
#include "TF1.h"
#include "TRandom.h"
#include "TSpectrum.h"
#include "TVirtualFitter.h"
Int_t npeaks = 30;
Double_t fpeaks(Double_t *x, Double_t *par) {
Double_t result = par[0] + par[1]*x[0];
for (Int_t p=0;p<npeaks;p++) {
Double_t norm = par[3*p+2];
Double_t mean = par[3*p+3];
Double_t sigma = par[3*p+4];
result += norm*TMath::Gaus(x[0],mean,sigma);
}
return result;
}
void peaks(Int_t np=5)
{
TTree *t = new TTree("t", "my tree");
t->ReadFile("a.txt", "x/D");
// creating a histogram ...
TH1D *h = new TH1D("h", "my histo", 200, 100., 350.);
// fill histo ...
t->Project("h", "x");
TF1 *f = new TF1("f",fpeaks,0,1000,2+3*npeaks);
f->SetNpx(1000);
f->SetParameters(par);
TCanvas *c1 = new TCanvas("c1","c1",10,10,1000,900);
c1->cd(1);
h->Draw();
//Use TSpectrum to find the peak candidates
TSpectrum *s = new TSpectrum(2*npeaks);
Int_t nfound = s->Search(h,2,"",0.10);
printf("Found %d candidate peaks to fit\n",nfound);
//Estimate background using TSpectrum::Background
TH1 *hb = s->Background(h,20,"same");
if (hb) c1->Update();
if (np <0) return;
}
```

eteremi
December 26, 2019, 11:32am
#4
Hi,
Can you show your histogram in a post please ?
You say it is not working. Do you have an error message ? What is not exactly working ?
Cheers,
R

It behaves abnormally, sometimes I get the error stating “par” and other undeclared identifiers and sometimes it runs giving the attached result.

This is what I want to do, as in this example (the only difference is that 1. I have .tex file, not the root file and 2. no. of peaks are not known, they need to be automatically detected. ) I’m attaching my sample histo

whose Gaussian peak fitting is planned.

I have a histogram where I’d like to fit multiple Gaussians over a quadratic background, and draw it over the existing histogram. I have 8 Gaussian, each of which I want to constrain both the centroid and the FWHM (2nd and 3rd parameters), input manually in my script. Attached is the file containing the histogram.
Thanks
hist.root (29.5 KB)

Maybe you can help, hopefully !!

Hi, Do you know how to perform this ? It’s quit urgent.