foam_kanwa.C

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// This program can be execute from the command line as folows:
//     
//      root -l foam_kanwa.C
//_____________________________________________________________________________

Int_t foam_kanwa(){
  cout<<"--- kanwa started ---"<<endl;
  gSystem->Load("libFoam.so");
  TH2D  *hst_xy = new TH2D("hst_xy" ,  "x-y plot", 50,0,1.0, 50,0,1.0);
  Double_t *MCvect =new Double_t[2]; // 2-dim vector generated in the MC run
  //
  TRandom     *PseRan   = new TRandom3();  // Create random number generator
  PseRan->SetSeed(4357);
  TFoam   *FoamX    = new TFoam("FoamX");   // Create Simulator
  FoamX->SetkDim(2);         // No. of dimensions, obligatory!
  FoamX->SetnCells(500);     // Optionally No. of cells, default=2000
  FoamX->SetRhoInt(Camel2);  // Set 2-dim distribution, included below
  FoamX->SetPseRan(PseRan);  // Set random number generator
  FoamX->Initialize();       // Initialize simulator, may take time...
  //
  // visualising generated distribution
  TCanvas *cKanwa = new TCanvas("cKanwa","Canvas for plotting",600,600);
  cKanwa->cd();
  // From now on FoamX is ready to generate events
  int nshow=5000;
  for(long loop=0; loop<100000; loop++){
    FoamX->MakeEvent();            // generate MC event
    FoamX->GetMCvect( MCvect);     // get generated vector (x,y)
    Double_t x=MCvect[0];
    Double_t y=MCvect[1];
    if(loop<10) cout<<"(x,y) =  ( "<< x <<", "<< y <<" )"<<endl;
    hst_xy->Fill(x,y);
    // live plot
    if(loop == nshow){
      nshow += 5000;
      hst_xy->Draw("lego2");
      cKanwa->Update();
    }
  }// loop
  //
  hst_xy->Draw("lego2");  // final plot
  cKanwa->Update();
  //
  Double_t MCresult, MCerror;
  FoamX->GetIntegMC( MCresult, MCerror);  // get MC integral, should be one
  cout << " MCresult= " << MCresult << " +- " << MCerror <<endl;
  cout<<"--- kanwa ended ---"<<endl;
  
  return 0;
}//kanwa

//_____________________________________________________________________________
Double_t sqr(Double_t x){return x*x;};
//_____________________________________________________________________________
Double_t Camel2(Int_t nDim, Double_t *Xarg){
// 2-dimensional distribution for Foam, normalized to one (within 1e-5)
  Double_t x=Xarg[0];
  Double_t y=Xarg[1];
  Double_t GamSq= sqr(0.100e0);
  Double_t Dist= 0;
  Dist +=exp(-(sqr(x-1./3) +sqr(y-1./3))/GamSq)/GamSq/TMath::Pi();
  Dist +=exp(-(sqr(x-2./3) +sqr(y-2./3))/GamSq)/GamSq/TMath::Pi();
  return 0.5*Dist;
}// Camel2
//_____________________________________________________________________________

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