void Background_decr()
{
   Int_t i;
   const Int_t nbins = 1024;
   Double_t xmin = 0;
   Double_t xmax = nbins;
   Double_t source[nbins];
   gROOT->ForceStyle();

   TH1F *d = new TH1F("d", "", nbins, xmin, xmax);

   TString dir = gROOT->GetTutorialDir();
   TString file = dir + "/legacy/spectrum/TSpectrum.root";
   TFile *f = new TFile(file.Data());
   TH1F *back = (TH1F *)f->Get("back1");
   back->SetTitle("Estimation of background with decreasing window");
   back->GetXaxis()->SetRange(1, nbins);
   back->Draw("L");

   TSpectrum *s = new TSpectrum();

   for (i = 0; i < nbins; i++)
      source[i] = back->GetBinContent(i + 1);

   // Estimate the background
   s->Background(source, nbins, 6, TSpectrum::kBackDecreasingWindow, TSpectrum::kBackOrder2, kFALSE,
                 TSpectrum::kBackSmoothing3, kFALSE);

   // Draw the estimated background
   for (i = 0; i < nbins; i++)
      d->SetBinContent(i + 1, source[i]);
   d->SetLineColor(kRed);
   d->Draw("SAME L");
}