A question about TSpectrum->Search

ROOT
1

For a 1-dim spectrum, I can use TSpectrum->Search to find peaks. If the option is not “goff”, I can also draw marks on the peaks that I found. But I can only draw marks without any peak information. How can I also display the bin location of each peak on the histogram?

Another question, how can I get the histogram which is displayed in the current actively pad, no matter what is its name?

Thank you very much!

2

I think the following macro (inspired by $ROOTSYS/peaks.C) answers your question.

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 dpeaks(Int_t np=10) {
   npeaks = np;
   TH1F *h = new TH1F("h","test",500,0,1000);
   //generate n peaks at random
   Double_t par[3000];
   par[0] = 0.8;
   par[1] = -0.6/1000;
   Int_t p;
   for (p=0;p<npeaks;p++) {
      par[3*p+2] = 1;
      par[3*p+3] = 10+gRandom->Rndm()*980;
      par[3*p+4] = 3+2*gRandom->Rndm();
   }
   TF1 *f = new TF1("f",fpeaks,0,1000,2+3*npeaks);
   f->SetNpx(1000);
   f->SetParameters(par);
   TCanvas *c1 = new TCanvas("c1","c1",10,10,700,700);
   c1->cd(1);
   h->FillRandom("f",200000);
   h->Draw();
   TH1F *h2 = (TH1F*)h->Clone("h2");
   //Use TSpectrum to find the peak candidates
   TSpectrum *s = new TSpectrum(2*npeaks);
   Int_t nfound = s->Search(h,2,"");
   printf("Found %d candidate peaks to fit\n",nfound);
                                                                                
   // Draw the peaks values
   Float_t *xpeaks = s->GetPositionX();
   Float_t *ypeaks = s->GetPositionY();
   char val[20];
   TLatex l;
   l.SetTextSize(0.02);
   for (p=0;p<nfound;p++) {
      Float_t xp = xpeaks[p];
      Float_t yp = ypeaks[p];
      sprintf(val,"%g",yp);
      l.DrawLatex(xp,yp,val);
   }
}

Look at the part “Draw the peaks values”.

To answer your 2nd question I think you should use code similar to the following one:

      TH2 *h2;
      TIter next(gPad->GetListOfPrimitives());
      while ((h2 = (TH2 *)next())) {
         if (!h2->InheritsFrom(TH2::Class())) continue;
         zmin = h2->GetMinimum();
         zmax = h2->GetMaximum();
[.....]
         break;
      }

I took these few lines in THistPainter.cxx.