// This code implementation is the intellectual property of
// the RD44 GEANT4 collaboration.
//
// By copying, distributing or modifying the Program (or any work
// based on the Program) you indicate your acceptance of this statement,
// and all its terms.
//
// $Id: G4IMuPairProduction.icc,v 2.1 1998/08/23 11:50:53 urban Exp $
// GEANT4 tag $Name: geant4-00 $
//
// $Id: 
// ---------------------------------------------------------------
//      GEANT 4 class inlined methods file 
//
//      For information related to this code contact:
//      CERN, CN Division, ASD group
//      History: first implementation, based on object model of
//      2nd December 1995, G.Cosmo
//      -------- G4IMuPairProduction physics process ---------
//                by Laszlo Urban, May 1998  
// ***************************************************************
inline G4double G4IMuPairProduction::PostStepGetPhysicalInteractionLength(
                             const G4Track& track,
                             G4double   previousStepSize,
                             G4ForceCondition* condition
                            )
{// get particle,particle type,kin.energy,material,mat.index
  const G4double eps=1.e-2 ;
  const G4double Tfac=0.95,Tfac1=1.-Tfac  ;
  G4double nl,nll,nlold,range,rangeold,rangenext,
           dEdx,KineticEnergyOld,KineticEnergyNext,value;
  G4bool isOut;
  const G4DynamicParticle* particle = track.GetDynamicParticle();
  const G4ParticleDefinition* particletype = particle->GetDefinition() ;
  G4double KineticEnergy = particle->GetKineticEnergy();
  G4Material* material = track.GetMaterial();
  const G4MaterialTable* theMaterialTable =
                         G4Material::GetMaterialTable();
  G4int materialindex = material->GetIndex();

  nl = (*theNlambdaTable)[materialindex]->
                           GetValue(KineticEnergy,isOut);

 // if ( nl == 0.)
 // {
 //   value = BIGSTEP ;
 //   return value ;
 // } 

  range = G4EnergyLossTables::GetPreciseRangeFromEnergy(particletype,
                                       KineticEnergy,material) ;

  if ( (previousStepSize <=0.0) || (theNumberOfInteractionLengthLeft<=0.0)) {
    // beggining of tracking (or just after DoIt of this process)
    ResetNumberOfInteractionLengthLeft();
  } else {
    // subtract NumberOfInteractionLengthLeft
   if(previousStepSize/range < eps)
   {
    nll = (*theNlambdaTable)[materialindex]->
                             GetValue(Tfac*KineticEnergy,isOut) ;
    dEdx = G4EnergyLossTables::GetPreciseDEDX(particletype,
                                              KineticEnergy,
                                              material) ;
    nlold = nl + dEdx*previousStepSize*(nl-nll)/
                                  (Tfac1*KineticEnergy) ;
   }
   else
   {
    rangeold = range + previousStepSize ;
    KineticEnergyOld = G4EnergyLossTables::GetPreciseEnergyFromRange(
                                             particletype,
                                       rangeold,material);
    nlold = (*theNlambdaTable)[materialindex]->
                           GetValue(KineticEnergyOld,isOut);
    if(nlold < nl)
     {
     if(verboseLevel>2)
     {
      G4cout << "G4IMuPairProduction PostStepGPIL : Nlambda has been" <<
              " increased at update.Nlambda old/new :" << nlold <<
              "  " << nl << endl;
      G4cout << "(theNumberOfInteractionLengthLeft has been increased!)" << endl
;
      G4cout << " correction : Nlambda old=new ........." << endl;
     }
      //corr. of num errror
      nlold = nl ;
     }
    }

    theNumberOfInteractionLengthLeft -= nlold-nl ;

    if(theNumberOfInteractionLengthLeft<perMillion)
       theNumberOfInteractionLengthLeft=0.;
  }


 // condition is set to "Not Forced"
  *condition = NotForced;
  if(nl <= theNumberOfInteractionLengthLeft)
  {
    value = BIGSTEP ;
  }
  else
  {
   if(theNumberOfInteractionLengthLeft/nl < eps)
   {
    nll = (*theNlambdaTable)[materialindex]->
                             GetValue(Tfac*KineticEnergy,isOut) ;
    dEdx = G4EnergyLossTables::GetPreciseDEDX(particletype,
                                              KineticEnergy,
                                              material) ;

    value = theNumberOfInteractionLengthLeft*Tfac1*KineticEnergy/(dEdx*(nl-nll))
 ;
   }
   else
   {

    KineticEnergyNext = (*theInverseNlambdaTable)[materialindex]->
                        GetValue(nl-theNumberOfInteractionLengthLeft,isOut);
    rangenext = G4EnergyLossTables::GetPreciseRangeFromEnergy(particletype,
                                       KineticEnergyNext,material);

    value = range - rangenext ;

     if(range<rangenext)
    {
    if(verboseLevel>2)
    {
     G4cout << "G4IMuPairProduction PostStepGPIL: Step < 0.!, Step=" << value << endl
;
     G4cout << "range,rangenext:" << range << "  " << rangenext << endl ;
     G4cout << "correction : rangenext=range ....." << endl;
    }
     //corr. of num error
     rangenext = range ;
     value = range - rangenext ;
    }
   }
  }

  return value;
}


inline G4double G4IMuPairProduction::ComputeMeanFreePath(
                                     const G4ParticleDefinition* ParticleType,
                                           G4double KineticEnergy,
                                           const G4Material* aMaterial)
{
  const G4ElementVector* theElementVector = aMaterial->GetElementVector() ;
  const G4double* theAtomNumDensityVector = aMaterial->GetAtomicNumDensityVector();
  G4double ElectronEnergyCut = (G4Electron::GetCutsInEnergy())[aMaterial->GetIndex()];   
  G4double PositronEnergyCut = (G4Positron::GetCutsInEnergy())[aMaterial->GetIndex()];   

  const G4double BigPath= DBL_MAX;

  G4double SIGMA = 0 ;

  for ( G4int i=0 ; i < aMaterial->GetNumberOfElements() ; i++ )
      {             
            SIGMA += theAtomNumDensityVector[i] * 
                     ComputeMicroscopicCrossSection( ParticleType, KineticEnergy,
                                                     (*theElementVector)(i)->GetZ(), 
                                                     ElectronEnergyCut,PositronEnergyCut );
      }       

  return SIGMA<=0.0 ? BigPath : 1./SIGMA ;
}


inline G4bool G4IMuPairProduction::IsApplicable(
                            const G4ParticleDefinition& particle)
{
   return(   (&particle == (const G4ParticleDefinition *)theMuonMinus)
           ||(&particle == (const G4ParticleDefinition *)theMuonPlus)
         ) ;
}