/**************************************************************************
 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
 *                                                                        *
 * Author: The ALICE Off-line Project.                                    *
 * Contributors are mentioned in the code where appropriate.              *
 *                                                                        *
 * Permission to use, copy, modify and distribute this software and its   *
 * documentation strictly for non-commercial purposes is hereby granted   *
 * without fee, provided that the above copyright notice appears in all   *
 * copies and that both the copyright notice and this permission notice   *
 * appear in the supporting documentation. The authors make no claims     *
 * about the suitability of this software for any purpose. It is          *
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/

/* $Id$ */

// Class to generate correlated Heavy Flavor hadron pairs (one or several pairs
// per event) using paramtrized kinematics of quark pairs from some generator
// and quark fragmentation functions.
// Is a generalisation of AliGenParam class for correlated pairs of hadrons.
// In this version quark pairs and fragmentation functions are obtained from
// Pythia6.124 using 100K events generated with kCharmppMNRwmi&kBeautyppMNRwmi 
// in pp collisions at 14 TeV.
// Decays are performed by Pythia. Used AliRoot version: v4-04-Release
// Author: S. Grigoryan, LPC Clermont-Fd & YerPhI, Smbat.Grigoryan@cern.ch
// July 07: added quarks in the stack (B. Vulpescu)
//-------------------------------------------------------------------------
// How it works (for the given flavor):
//
// 1) Reads QQbar kinematical grid from the Input file and generates
// quark pairs according to the weights of the cells.
// It is a 5D grid in y1,y2,pt1,pt2 and deltaphi, with occupancy weights
// of the cells obtained from Pythia (see details in GetQuarkPair).
// 2) Reads "soft" and "hard" fragmentation functions (12 2D-histograms each,
// for 12 pt bins) from the Input file, applies to quarks and produces hadrons
// (only lower states, with proportions of species obtained from Pythia).
// Fragmentation functions are the same for all hadron species and depend
// on 2 variables - light cone energy-momentum fractions:
//     z1=(E_H + Pz_H)/(E_Q + Pz_Q),  z2=(E_H - Pz_H)/(E_Q - Pz_Q).
// "soft" & "hard" FFs correspond to "slower" & "faster" quark of a pair 
// (see details in GetHadronPair).
// 3) Decays the hadrons and saves all the particles in the event stack in the
// following order: HF hadron from Q, then its decay products, then HF hadron
// from Qbar, then its decay productes, then next HF hadon pair (if any) 
// in the same way, etc... 
// 4) It is fast, e.g., generates the same number of events with a beauty pair 
//  ~15 times faster than AliGenPythia with kBeautyppMNRwmi (w/o tracking)
//
// An Input file for each quark flavor is included in EVGEN/dataCorrHF/
// One can use also user-defined Input files.
//
// More details could be found in my presentation at DiMuonNet Workshop, Dec 2006: 
// http://www-dapnia.cea.fr/Sphn/Alice/DiMuonNet
// and will be published in an Internal Note. 
//
//-------------------------------------------------------------------------
// How to use it:
//
// add the following typical lines in Config.C
/*
  if (!strcmp(option,"corr")) {
    // Example for correlated charm or beauty hadron pair production 

    // AliGenCorrHF *gener = new AliGenCorrHF(1, 4);  // for charm, 1 pair per event
    AliGenCorrHF *gener = new AliGenCorrHF(1, 5);  // for beauty, 1 pair per event

    gener->SetMomentumRange(0,9999);
    gener->SetCutOnChild(0);        // 1/0 means cuts on children enable/disable
    gener->SetChildThetaRange(171.0,178.0);
    gener->SetOrigin(0,0,0);          //vertex position    
    gener->SetSigma(0,0,0);           //Sigma in (X,Y,Z) (cm) on IP position
    gener->SetForceDecay(kSemiMuonic);
    gener->SetTrackingFlag(0);
    gener->Init();
}
*/
// and in aliroot do e.g. gAlice->Run(10,"Config.C") to produce 10 events.
// One can include AliGenCorrHF in an AliGenCocktail generator.
//--------------------------------------------------------------------------

#include <Riostream.h>
#include <TCanvas.h>
#include <TClonesArray.h>
#include <TDatabasePDG.h>
#include <TFile.h>
#include <TH2F.h>
#include <TLorentzVector.h>
#include <TMath.h>
#include <TParticle.h>
#include <TParticlePDG.h>
#include <TROOT.h>
#include <TRandom.h>
#include <TTree.h>
#include <TVirtualMC.h>
#include <TVector3.h>

#include "AliGenCorrHF.h"
#include "AliLog.h"
#include "AliConst.h"
#include "AliDecayer.h"
#include "AliMC.h"
#include "AliRun.h"
#include "AliGenEventHeader.h"

ClassImp(AliGenCorrHF)

  //Begin_Html
  /*
    <img src="picts/AliGenCorrHF.gif">
  */
  //End_Html

Double_t AliGenCorrHF::fgdph[19] = {0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180};
Double_t AliGenCorrHF::fgy[31] = {-10,-7, -6.5, -6, -5.5, -5, -4.5, -4, -3.5, -3, -2.5, -2,- 1.5, -1, -0.5, 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 10};
Double_t AliGenCorrHF::fgpt[33] = {0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.6, 7.2, 7.8, 8.4, 9, 9.6, 10.3, 11.1, 12, 13.1, 14.3, 15.6, 17.1, 19, 21, 24, 28, 35, 50, 100};
Int_t AliGenCorrHF::fgnptbins = 12;
Double_t AliGenCorrHF::fgptbmin[12] = {0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 9};
Double_t AliGenCorrHF::fgptbmax[12] = {0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 9, 100};

Double_t* AliGenCorrHF::fgIntegral = 0;

//____________________________________________________________
    AliGenCorrHF::AliGenCorrHF():
	fFileName(0),
	fFile(0),
	fQuark(0),
	fBias(0.),
	fTrials(0),
	fDecayer(0)
{
// Default constructor
}

//____________________________________________________________
AliGenCorrHF::AliGenCorrHF(Int_t npart, Int_t param):
    AliGenMC(npart),
    fFileName(0),
    fFile(0),
    fQuark(param),
    fBias(0.),
    fTrials(0),
    //    fDecayer(new AliDecayerPythia())
    fDecayer(0)
{
// Constructor using number of particles, quark type & default InputFile
//
    if (fQuark != 5) fQuark = 4;
    fFileName = "$ALICE_ROOT/EVGEN/dataCorrHF/CharmppMNRwmiCorr100K.root";
    if (fQuark == 5) fFileName = "$ALICE_ROOT/EVGEN/dataCorrHF/BeautyppMNRwmiCorr100K.root";

    fName = "Default";
    fTitle= "Generator for correlated pairs of HF hadrons";
      
    fChildSelect.Set(5);
    for (Int_t i=0; i<5; i++) fChildSelect[i]=0;
    SetForceDecay();
    SetCutOnChild();
    SetChildMomentumRange();
    SetChildPtRange();
    SetChildPhiRange();
    SetChildThetaRange(); 
}

//___________________________________________________________________
AliGenCorrHF::AliGenCorrHF(char* tname, Int_t npart, Int_t param):
    AliGenMC(npart),
    fFileName(tname),
    fFile(0),
    fQuark(param),
    fBias(0.),
    fTrials(0),
    //    fDecayer(new AliDecayerPythia())
    fDecayer(0)
{
// Constructor using number of particles, quark type & user-defined InputFile
//
    if (fQuark != 5) fQuark = 4;
    fName = "UserDefined";
    fTitle= "Generator for correlated pairs of HF hadrons";
      
    fChildSelect.Set(5);
    for (Int_t i=0; i<5; i++) fChildSelect[i]=0;
    SetForceDecay();
    SetCutOnChild();
    SetChildMomentumRange();
    SetChildPtRange();
    SetChildPhiRange();
    SetChildThetaRange(); 
}

//____________________________________________________________
AliGenCorrHF::~AliGenCorrHF()
{
// Destructor
  delete fFile;
}

//____________________________________________________________
void AliGenCorrHF::Init()
{
// Initialisation

  AliInfo(Form(" QQbar kinematics and fragm. functions from:  %s",fFileName.Data() )); 
    fFile = TFile::Open(fFileName.Data());
    if(!fFile->IsOpen()){
      AliError(Form("Could not open file %s",fFileName.Data() ));
    }

    ComputeIntegral(fFile);
    
    fParentWeight = 1./fNpart;   // fNpart is number of HF-hadron pairs

// particle decay related initialization

    if (gMC) fDecayer = gMC->GetDecayer();
    fDecayer->SetForceDecay(fForceDecay);
    fDecayer->Init();

//
    AliGenMC::Init();
}
//____________________________________________________________
void AliGenCorrHF::Generate()
{
//
// Generate fNpart of correlated HF hadron pairs per event
// in the the desired theta and momentum windows (phi = 0 - 2pi).
//

//  Reinitialize decayer

  fDecayer->SetForceDecay(fForceDecay);
  fDecayer->Init();
  
  //
  Float_t polar[3]= {0,0,0};  // Polarisation of the parent particle (for GEANT tracking)
  Float_t origin0[3];         // Origin of the generated parent particle (for GEANT tracking)
  Float_t pt, pl, ptot;       // Transverse, logitudinal and total momenta of the parent particle
  Float_t phi, theta;         // Phi and theta spherical angles of the parent particle momentum
  Float_t p[3], pc[3], och[3];// Momentum, polarisation and origin of the children particles from lujet
  Int_t nt, i, j, ipa, ihadron[2], iquark[2];
  Float_t  wgtp, wgtch, random[6];
  Float_t pq[2][3];           // Momenta of the two quarks
  Int_t ntq[2] = {-1, -1};
  Double_t tanhy2, qm = 0;

  Double_t dphi=0, ptq[2], yq[2], pth[2], plh[2], ph[2], phih[2], phiq[2];
  for (i=0; i<2; i++) { 
    ptq[i]     =0; 
    yq[i]      =0; 
    pth[i]     =0; 
    plh[i]     =0;
    phih[i]    =0; 
    phiq[i]    =0;
    ihadron[i] =0; 
    iquark[i]  =0;
  }

  // same quarks mass as in the fragmentation functions
  if (fQuark == 4) qm = 1.20;
  else             qm = 4.75;

  static TClonesArray *particles;
  //
  if(!particles) particles = new TClonesArray("TParticle",1000);
  
  TDatabasePDG *pDataBase = TDatabasePDG::Instance();
  //
  
  // Calculating vertex position per event
  for (j=0;j<3;j++) origin0[j]=fOrigin[j];
  if(fVertexSmear==kPerEvent) {
    Vertex();
    for (j=0;j<3;j++) origin0[j]=fVertex[j];
  }
  
  ipa=0;
  
  // Generating fNpart particles
  fNprimaries = 0;
  
  while (ipa<2*fNpart) {
    
    GetQuarkPair(fFile, fgIntegral, yq[0], yq[1], ptq[0], ptq[1], dphi);
    
    GetHadronPair(fFile, fQuark, yq[0], yq[1], ptq[0], ptq[1], ihadron[0], ihadron[1], plh[0], plh[1], pth[0], pth[1]);
    
    // Cuts from AliGenerator
    
    // Cut on theta
    theta=TMath::ATan2(pth[0],plh[0]);
    if(theta<fThetaMin || theta>fThetaMax) continue;
    theta=TMath::ATan2(pth[1],plh[1]);
    if(theta<fThetaMin || theta>fThetaMax) continue;
    
    // Cut on momentum
    ph[0]=TMath::Sqrt(pth[0]*pth[0]+plh[0]*plh[0]);
    if (ph[0]<fPMin || ph[0]>fPMax) continue;
    ph[1]=TMath::Sqrt(pth[1]*pth[1]+plh[1]*plh[1]);
    if (ph[1]<fPMin || ph[1]>fPMax) continue;
    
    // Add the quarks in the stack
    
    phiq[0] = Rndm()*k2PI;
    if (Rndm() < 0.5) {
      phiq[1] = phiq[0] + dphi*kDegrad; 
    } else {
      phiq[1] = phiq[0] - dphi*kDegrad; 
    }    
    if (phiq[1] > k2PI) phiq[1] -= k2PI;
    if (phiq[1] < 0   ) phiq[1] += k2PI;
    
    // quarks pdg
    iquark[0] = +fQuark;
    iquark[1] = -fQuark;

    // px and py
    TVector2 qvect1 = TVector2();
    TVector2 qvect2 = TVector2();
    qvect1.SetMagPhi(ptq[0],phiq[0]);
    qvect2.SetMagPhi(ptq[1],phiq[1]);
    pq[0][0] = qvect1.Px();
    pq[0][1] = qvect1.Py();
    pq[1][0] = qvect2.Px();
    pq[1][1] = qvect2.Py();

    // pz
    tanhy2 = TMath::TanH(yq[0]);
    tanhy2 *= tanhy2;
    pq[0][2] = TMath::Sqrt((ptq[0]*ptq[0]+qm*qm)*tanhy2/(1-tanhy2));
    pq[0][2] = TMath::Sign((Double_t)pq[0][2],yq[0]);
    tanhy2 = TMath::TanH(yq[1]);
    tanhy2 *= tanhy2;
    pq[1][2] = TMath::Sqrt((ptq[1]*ptq[1]+qm*qm)*tanhy2/(1-tanhy2));
    pq[1][2] = TMath::Sign((Double_t)pq[1][2],yq[1]);

    // Here we assume that  |phi_H1 - phi_H2| = |phi_Q1 - phi_Q2| = dphi
    // which is a good approximation for heavy flavors in Pythia
    // ... moreover, same phi angles as for the quarks ...
    
    phih[0] = phiq[0];    
    phih[1] = phiq[1];    

    for (Int_t ihad = 0; ihad < 2; ihad++) {
    while(1) {
      //
      // particle type 
      Int_t iPart = ihadron[ihad];
      fChildWeight=(fDecayer->GetPartialBranchingRatio(iPart))*fParentWeight;
      wgtp=fParentWeight;
      wgtch=fChildWeight;
      TParticlePDG *particle = pDataBase->GetParticle(iPart);
      Float_t am = particle->Mass();
      phi = phih[ihad];
      pt  = pth[ihad];
      pl  = plh[ihad];
      ptot=TMath::Sqrt(pt*pt+pl*pl);

      p[0]=pt*TMath::Cos(phi);
      p[1]=pt*TMath::Sin(phi);
      p[2]=pl;

      if(fVertexSmear==kPerTrack) {
	Rndm(random,6);
	for (j=0;j<3;j++) {
	  origin0[j]=
	    fOrigin[j]+fOsigma[j]*TMath::Cos(2*random[2*j]*TMath::Pi())*
	    TMath::Sqrt(-2*TMath::Log(random[2*j+1]));
	}
      }
      
      // Looking at fForceDecay : 
      // if fForceDecay != none Primary particle decays using 
      // AliPythia and children are tracked by GEANT
      //
      // if fForceDecay == none Primary particle is tracked by GEANT 
      // (In the latest, make sure that GEANT actually does all the decays you want)	  
      //
      
      if (fForceDecay != kNoDecay) {
	// Using lujet to decay particle
	Float_t energy=TMath::Sqrt(ptot*ptot+am*am);
	TLorentzVector pmom(p[0], p[1], p[2], energy);
	fDecayer->Decay(iPart,&pmom);
	//
	// select decay particles
	Int_t np=fDecayer->ImportParticles(particles);
	
	//  Selecting  GeometryAcceptance for particles fPdgCodeParticleforAcceptanceCut;
	if (fGeometryAcceptance) 
	  if (!CheckAcceptanceGeometry(np,particles)) continue;
	Int_t ncsel=0;
	Int_t* pFlag      = new Int_t[np];
	Int_t* pParent    = new Int_t[np];
	Int_t* pSelected  = new Int_t[np];
	Int_t* trackIt    = new Int_t[np];
	
	for (i=0; i<np; i++) {
	  pFlag[i]     =  0;
	  pSelected[i] =  0;
	  pParent[i]   = -1;
	}
	
	if (np >1) {
	  TParticle* iparticle =  (TParticle *) particles->At(0);
	  Int_t ipF, ipL;
	  for (i = 1; i<np ; i++) {
	    trackIt[i] = 1;
	    iparticle = (TParticle *) particles->At(i);
	    Int_t kf = iparticle->GetPdgCode();
	    Int_t ks = iparticle->GetStatusCode();
	    // flagged particle
	    
	    if (pFlag[i] == 1) {
	      ipF = iparticle->GetFirstDaughter();
	      ipL = iparticle->GetLastDaughter();	
	      if (ipF > 0) for (j=ipF-1; j<ipL; j++) pFlag[j]=1;
	      continue;
	    }
	    
	    // flag decay products of particles with long life-time (c tau > .3 mum)		      
	    
	    if (ks != 1) { 
	      //TParticlePDG *particle = pDataBase->GetParticle(kf);
	      
	      Double_t lifeTime = fDecayer->GetLifetime(kf);
	      //Double_t mass     = particle->Mass();
	      //Double_t width    = particle->Width();
	      if (lifeTime > (Double_t) fMaxLifeTime) {
		ipF = iparticle->GetFirstDaughter();
		ipL = iparticle->GetLastDaughter();	
		if (ipF > 0) for (j=ipF-1; j<ipL; j++) pFlag[j]=1;
	      } else{
		trackIt[i]     = 0;
		pSelected[i]   = 1;
	      }
	    } // ks==1 ?
	    //
	    // children
	    
	    if (ChildSelected(TMath::Abs(kf)) || fForceDecay == kAll && trackIt[i])
	      {
		if (fCutOnChild) {
		  pc[0]=iparticle->Px();
		  pc[1]=iparticle->Py();
		  pc[2]=iparticle->Pz();
		  Bool_t  childok = KinematicSelection(iparticle, 1);
		  if(childok) {
		    pSelected[i]  = 1;
		    ncsel++;
		  } else {
		    ncsel=-1;
		    break;
		  } // child kine cuts
		} else {
		  pSelected[i]  = 1;
		  ncsel++;
		} // if child selection
	      } // select muon
	  } // decay particle loop
	} // if decay products
	
	Int_t iparent;
	if ((fCutOnChild && ncsel >0) || !fCutOnChild){
	  ipa++;
	  //
	  // Parent
	  // quark
	  PushTrack(0, -1, iquark[ihad], pq[ihad], origin0, polar, 0, kPPrimary, nt, wgtp);
	  KeepTrack(nt);
	  ntq[ihad] = nt;
	  // hadron
	  PushTrack(0, ntq[ihad], iPart, p, origin0, polar, 0, kPDecay, nt, wgtp);
	  pParent[0] = nt;
	  KeepTrack(nt); 
	  fNprimaries++;
	  
	  //
	  // Decay Products
	  //		  
	  for (i = 1; i < np; i++) {
	    if (pSelected[i]) {
	      TParticle* iparticle = (TParticle *) particles->At(i);
	      Int_t kf  = iparticle->GetPdgCode();
	      Int_t ipa = iparticle->GetFirstMother()-1;
	      
	      och[0] = origin0[0]+iparticle->Vx()/10;
	      och[1] = origin0[1]+iparticle->Vy()/10;
	      och[2] = origin0[2]+iparticle->Vz()/10;
	      pc[0]  = iparticle->Px();
	      pc[1]  = iparticle->Py();
	      pc[2]  = iparticle->Pz();
	      
	      if (ipa > -1) {
		iparent = pParent[ipa];
	      } else {
		iparent = -1;
	      }
	      
	      PushTrack(fTrackIt*trackIt[i], iparent, kf,
			pc, och, polar,
			0, kPDecay, nt, wgtch);
	      pParent[i] = nt;
	      KeepTrack(nt); 
	      fNprimaries++;
	    } // Selected
	  } // Particle loop 
	}  // Decays by Lujet
	particles->Clear();
	if (pFlag)      delete[] pFlag;
	if (pParent)    delete[] pParent;
	if (pSelected)  delete[] pSelected;	   
	if (trackIt)    delete[] trackIt;
      } // kinematic selection
      else  // nodecay option, so parent will be tracked by GEANT (pions, kaons, eta, omegas, baryons)
	{
	  gAlice->GetMCApp()->
	    PushTrack(fTrackIt,-1,iPart,p,origin0,polar,0,kPPrimary,nt,wgtp);
	  ipa++; 
	  fNprimaries++;
	}
      break;
    } // while(1)
    } // hadron pair loop
  } // event loop
  
  SetHighWaterMark(nt);
  
  AliGenEventHeader* header = new AliGenEventHeader("CorrHF");
  header->SetPrimaryVertex(fVertex);
  header->SetNProduced(fNprimaries);
  AddHeader(header);

}
//____________________________________________________________________________________
Int_t AliGenCorrHF::IpCharm(TRandom* ran)
{  
// Composition of lower state charm hadrons, containing a c-quark
    Float_t random;
    Int_t ip;            // +- 411,421,431,4122,4132,4232,4332
    random = ran->Rndm();
//  Rates from Pythia6.214 using 100Kevents with kPyCharmppMNRwmi at 14 TeV.   
  
    if (random < 0.6027) {                       
        ip=421;
    } else if (random < 0.7962) {
        ip=411;
    } else if (random < 0.9127) {
        ip=431;        
    } else if (random < 0.9899) {
        ip=4122;        
    } else if (random < 0.9948) {
        ip=4132;        
    } else if (random < 0.9999) {
        ip=4232;        
    } else {
        ip=4332;
    }
    
    return ip;
}

Int_t AliGenCorrHF::IpBeauty(TRandom* ran)
{  
// Composition of lower state beauty hadrons, containing a b-quark
    Float_t random;
    Int_t ip;            // +- 511,521,531,5122,5132,5232,5332
    random = ran->Rndm(); 
//  Rates from Pythia6.214 using 100Kevents with kPyBeautyppMNRwmi at 14 TeV.   
                        // B-Bbar mixing will be done by Pythia at the decay point
 if (random < 0.3965) {                       
        ip=-511;
    } else if (random < 0.7930) {
        ip=-521;
    } else if (random < 0.9112) {
        ip=-531;        
    } else if (random < 0.9887) {
        ip=5122;        
    } else if (random < 0.9943) {
        ip=5132;        
    } else if (random < 0.9999) {
        ip=5232;        
    } else {
        ip=5332;
    }
    
  return ip;
}

//____________________________________________________________________________________
Double_t AliGenCorrHF::ComputeIntegral(TFile* fG)       // needed by GetQuarkPair
{
   // Read QQbar kinematical 5D grid's cell occupancy weights
   Int_t cell[6];           // cell[6]={wght,iy1,iy2,ipt1,ipt2,idph}
   TTree* tG = (TTree*) fG->Get("tGqq");
   tG->GetBranch("cell")->SetAddress(&cell);
   Int_t nbins = tG->GetEntries();

   //   delete previously computed integral (if any)
   if(fgIntegral) delete [] fgIntegral;

   fgIntegral = new Double_t[nbins+1];
   fgIntegral[0] = 0;
   Int_t bin;
   for(bin=0;bin<nbins;bin++) {
     tG->GetEvent(bin);
     fgIntegral[bin+1] = fgIntegral[bin] + cell[0];
   }
   //   Normalize integral to 1
   if (fgIntegral[nbins] == 0 ) {
      return 0;
   }
   for (bin=1;bin<=nbins;bin++)  fgIntegral[bin] /= fgIntegral[nbins];

   return fgIntegral[nbins];
}

//____________________________________________________________________________________
void AliGenCorrHF::GetQuarkPair(TFile* fG, Double_t* fInt, Double_t &y1, Double_t &y2, Double_t &pt1, Double_t &pt2, Double_t &dphi)              
                                 // modification of ROOT's TH3::GetRandom3 for 5D
{
   // Read QQbar kinematical 5D grid's cell coordinates
   Int_t cell[6];           // cell[6]={wght,iy1,iy2,ipt1,ipt2,idph}
   TTree* tG = (TTree*) fG->Get("tGqq");
   tG->GetBranch("cell")->SetAddress(&cell);
   Int_t nbins = tG->GetEntries();
   Double_t rand[6];
   gRandom->RndmArray(6,rand);
   Int_t ibin = TMath::BinarySearch(nbins,fInt,rand[0]);
   tG->GetEvent(ibin);
   y1   = fgy[cell[1]]  + (fgy[cell[1]+1]-fgy[cell[1]])*rand[1];
   y2   = fgy[cell[2]]  + (fgy[cell[2]+1]-fgy[cell[2]])*rand[2];
   pt1  = fgpt[cell[3]] + (fgpt[cell[3]+1]-fgpt[cell[3]])*rand[3];
   pt2  = fgpt[cell[4]] + (fgpt[cell[4]+1]-fgpt[cell[4]])*rand[4];
   dphi = fgdph[cell[5]]+ (fgdph[cell[5]+1]-fgdph[cell[5]])*rand[5];
}

//____________________________________________________________________________________
void AliGenCorrHF::GetHadronPair(TFile* fG, Int_t idq, Double_t y1, Double_t y2, Double_t pt1, Double_t pt2, Int_t &id3, Int_t &id4, Double_t &pz3, Double_t &pz4, Double_t &pt3, Double_t &pt4) 
{
    // Generate a hadron pair
    Int_t (*fIpParaFunc )(TRandom*);//Pointer to particle type parametrisation function
    fIpParaFunc = IpCharm;
    Double_t mq = 1.2;              // c & b quark masses (used in AliPythia)
    if (idq == 5) {
      fIpParaFunc = IpBeauty;
      mq = 4.75;
    }
    Double_t z11, z12, z21, z22, pz1, pz2, e1, e2, mh, ptemp, rand[2];
    char tag[100]; 
    TH2F *h2h[12], *h2s[12];      // hard & soft Fragmentation Functions
    for (Int_t ipt = 0; ipt<fgnptbins; ipt++) { 
      sprintf(tag,"h2h_pt%d",ipt); 
      h2h[ipt] = (TH2F*) fG->Get(tag); 
      sprintf(tag,"h2s_pt%d",ipt); 
      h2s[ipt] = (TH2F*) fG->Get(tag); 
    }

       if (y1*y2 < 0) {
	 for (Int_t ipt = 0; ipt<fgnptbins; ipt++) { 
	   if(pt1 >= fgptbmin[ipt] && pt1 < fgptbmax[ipt]) 
      	     h2h[ipt]->GetRandom2(z11, z21);
	   if(pt2 >= fgptbmin[ipt] && pt2 < fgptbmax[ipt]) 
      	     h2h[ipt]->GetRandom2(z12, z22); 
	 }
       }
       else {
	 if (TMath::Abs(y1) > TMath::Abs(y2)) {
	   for (Int_t ipt = 0; ipt<fgnptbins; ipt++) { 
	     if(pt1 >= fgptbmin[ipt] && pt1 < fgptbmax[ipt]) 
	       h2h[ipt]->GetRandom2(z11, z21);
	     if(pt2 >= fgptbmin[ipt] && pt2 < fgptbmax[ipt]) 
	       h2s[ipt]->GetRandom2(z12, z22); 
	   }
	 }
	 else {
	   for (Int_t ipt = 0; ipt<fgnptbins; ipt++) { 
	     if(pt1 >= fgptbmin[ipt] && pt1 < fgptbmax[ipt]) 
	       h2s[ipt]->GetRandom2(z11, z21);
	     if(pt2 >= fgptbmin[ipt] && pt2 < fgptbmax[ipt]) 
	       h2h[ipt]->GetRandom2(z12, z22); 
	   }
	 }
       }
      gRandom->RndmArray(2,rand);
      ptemp = TMath::Sqrt(pt1*pt1 + mq*mq);
      pz1   = ptemp*TMath::SinH(y1); 
      e1    = ptemp*TMath::CosH(y1); 
      ptemp = TMath::Sqrt(pt2*pt2 + mq*mq);
      pz2   = ptemp*TMath::SinH(y2); 
      e2    = ptemp*TMath::CosH(y2); 

      id3   = fIpParaFunc(gRandom);
      mh    = TDatabasePDG::Instance()->GetParticle(id3)->Mass();
      ptemp = z11*z21*(e1*e1-pz1*pz1) - mh*mh;
      pt3   = (idq-3)*rand[0];                // some smearing at low pt, try better
      if (ptemp > 0) pt3 = TMath::Sqrt(ptemp);
      if (pz1 > 0)   pz3 = (z11*(e1 + pz1) - z21*(e1 - pz1)) / 2;
      else           pz3 = (z21*(e1 + pz1) - z11*(e1 - pz1)) / 2;
      e1 = TMath::Sqrt(pz3*pz3 + pt3*pt3 + mh*mh);

      id4   = - fIpParaFunc(gRandom);
      mh    = TDatabasePDG::Instance()->GetParticle(id4)->Mass();
      ptemp = z12*z22*(e2*e2-pz2*pz2) - mh*mh;
      pt4   = (idq-3)*rand[1];                // some smearing at low pt, try better
      if (ptemp > 0) pt4 = TMath::Sqrt(ptemp);
      if (pz2 > 0)   pz4 = (z12*(e2 + pz2) - z22*(e2 - pz2)) / 2;
      else           pz4 = (z22*(e2 + pz2) - z12*(e2 - pz2)) / 2;
      e2 = TMath::Sqrt(pz4*pz4 + pt4*pt4 + mh*mh);

      // small corr. instead of using Frag. Func. depending on yQ (in addition to ptQ)
      Float_t ycorr = 0.2, y3, y4;
      gRandom->RndmArray(2,rand);
      y3 = 0.5 * TMath::Log((e1 + pz3 + 1.e-13)/(e1 - pz3 + 1.e-13));
      y4 = 0.5 * TMath::Log((e2 + pz4 + 1.e-13)/(e2 - pz4 + 1.e-13));
      if(TMath::Abs(y3)<ycorr && TMath::Abs(y4)<ycorr && rand[0]>0.5) {
	ptemp = TMath::Sqrt(e1*e1 - pz3*pz3);
	y3  = 4*(1 - 2*rand[1]);
	pz3 = ptemp*TMath::SinH(y3);
	pz4 = pz3;
      }
}