// Illustrates how to fit a Gaussian peak in a histogram
// using a functor.
//
// To execute this example, do
//   root > .x functorFit.C
//
//Author: Kazuyoshi Furutaka

class TTestFunctor {
 private:
  Int_t fNumPeaks;
 public:
  // Constructor & Destructor
  TTestFunctor(Int_t np) : fNumPeaks(np) {
    printf("TTestFunctor::TTestFunctor(): fNumPeaks = %d\n",fNumPeaks);}
  virtual ~TTestFunctor() {
    printf("TTestFunctor::~TTestFunctor():\n");}
  // Call operator
  Double_t operator() (Double_t *x, Double_t *par) {
    Double_t xx = x[0];
    Double_t norm  = par[0];
    Double_t mean  = par[1];
    Double_t sigma = par[2]/2.35482;  // fPar[3*p+2]: FWHM
    return norm*TMath::Gaus(xx,mean,sigma);
  }

};

void functorFit(void) {

  // Create some histograms, a profile histogram and an ntuple
  TH1F *hpx = new TH1F("hpx","This is the px distribution",100,-4,4);
  // Create a new canvas.
  TCanvas *c1 = new TCanvas("c1");
  // Fill histograms randomly
  gRandom->SetSeed();
  Float_t px,py;
  for (Int_t i = 0; i < 100000; i++) {
    gRandom->Rannor(px,py);
    hpx->Fill(px);
  }
  // Display the histogram
  hpx->Draw();

  // Instantiate a TF1 object using TTestFunctor and set its parameters
  TTestFunctor *fff = new TTestFunctor(1);
  TF1 *f = new TF1("f", fff, -4,4, 3, "TTestFunctor");
  f->SetParameters(3000.,0.,1.);
  f->SetLineColor(4);
  //f->Draw("SAME");

  // Fit the histogram using the functor TF1
  hpx->Fit("f","","SAME");

}