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//
// -------------------------------------------------------------------
//      GEANT4 Class file
//
//      For information related to this code contact:
//
//      File name:     G4XnpElasticLowE
//
//      Author:        
// 
//      Creation date: 15 April 1999
//
//      Modifications: 
//      
// Neutron-Proton elastic cross section 
// Linear interpolation from data table
//
// -------------------------------------------------------------------

#include "globals.hh"
#include "G4ios.hh"
#include "G4XnpElasticLowE.hh"
#include "G4KineticTrack.hh"
#include "G4ParticleDefinition.hh"
#include "G4PhysicsVector.hh"
#include "G4PhysicsLnVector.hh"
#include "G4ParticleDefinition.hh"
#include "G4Proton.hh"
#include "G4Neutron.hh"

const G4double G4XnpElasticLowE::_lowLimit = 0.;
const G4double G4XnpElasticLowE::_highLimit = 3.*GeV;

// Low energy limit of the cross-section table (in GeV)
// Units are assigned while filling the PhysicsVector
const G4double G4XnpElasticLowE::_eMinTable = 1.8964808;
const G4double G4XnpElasticLowE::_eStepLog = 0.01;

// Cross-sections in mb
// Units are assigned while filling the PhysicsVector
const G4int G4XnpElasticLowE::_tableSize = 101;
const G4double G4XnpElasticLowE::_sigmaTable[101] = 
{ 
  1500.0,  //GF  was 0.0
  248.20, 93.38, 55.26, 44.50, 41.33, 38.48, 37.20, 35.98,
  35.02, 34.47, 32.48, 30.76, 29.46, 28.53, 27.84, 27.20,
  26.53, 25.95, 25.59, 25.46, 25.00, 24.49, 24.08, 23.86,
  23.17, 22.70, 21.88, 21.48, 20.22, 19.75, 18.97, 18.39,
  17.98, 17.63, 17.21, 16.72, 16.68, 16.58, 16.42, 16.22,
  15.98, 15.71, 15.42, 15.14, 14.87, 14.65, 14.44, 14.26,
  14.10, 13.95, 13.80, 13.64, 13.47, 13.29, 13.09, 12.89,
  12.68, 12.47, 12.27, 12.06, 11.84, 11.76, 11.69, 11.60,
  11.50, 11.41, 11.29, 11.17, 11.06, 10.93, 10.81, 10.68,
  10.56, 10.44, 10.33, 10.21, 10.12, 10.03,  9.96,  9.89,
  9.83,  9.80,  9.77,  9.75,  9.74,  9.74,  9.74,  9.76,
  9.73,  9.70,  9.68,  9.65,  9.63,  9.60,  9.57,  9.55,
  9.52,  9.49,  9.46,  9.43
};


G4XnpElasticLowE::G4XnpElasticLowE() 
{ 
  // Cross-sections are available in the range (_eMin,_eMax)

  _eMin = _eMinTable * GeV;
  _eMin = std::exp(std::log(_eMinTable)-_eStepLog)*GeV;
  _eMax = std::exp(std::log(_eMinTable) + _tableSize * _eStepLog) * GeV;

  // Protections: validity limits must be compatible with available data

  if (_eMin < _lowLimit)
    throw G4HadronicException(__FILE__, __LINE__, "G4XnpElasticLowE::G4XnpElasticLowE - Low energy limit not valid");
    
  if (_highLimit > _eMax)
    throw G4HadronicException(__FILE__, __LINE__, "G4XnpElasticLowE::G4XnpElasticLowE - High energy limit not valid");
    
  _sigma = new G4PhysicsLnVector(_eMin,_eMax,_tableSize);
  G4int i;
  for (i=0; i<_tableSize; i++)
    {
      G4double value = _sigmaTable[i] * millibarn;
      _sigma->PutValue(i,value);
    }
}


G4XnpElasticLowE::~G4XnpElasticLowE()
{
  delete _sigma;
}


G4bool G4XnpElasticLowE::operator==(const G4XnpElasticLowE &right) const
{
  return (this == (G4XnpElasticLowE *) &right);
}


G4bool G4XnpElasticLowE::operator!=(const G4XnpElasticLowE &right) const
{
  return (this != (G4XnpElasticLowE *) &right);
}


G4double G4XnpElasticLowE::CrossSection(const G4KineticTrack& trk1, const G4KineticTrack& trk2) const
{
  G4double sigma = 0.;
  G4double sqrtS = (trk1.Get4Momentum() + trk2.Get4Momentum()).mag();
  G4bool dummy = false;

  G4ParticleDefinition* proton = G4Proton::ProtonDefinition();
  G4ParticleDefinition* neutron = G4Neutron::NeutronDefinition();   

  G4ParticleDefinition* def1 = trk1.GetDefinition();
  G4ParticleDefinition* def2 = trk2.GetDefinition();
  if ( (def1 == proton && def2 == neutron) ||
       (def1 == neutron && def2 == proton) )
  {
      if (sqrtS >= _eMin && sqrtS <= _eMax)
      {
	  sigma = _sigma->GetValue(sqrtS,dummy);
      } else if ( sqrtS < _eMin )
      {
          sigma = _sigma->GetValue(_eMin,dummy);
      }
  }

  return sigma;
}

void G4XnpElasticLowE::Print() const
{
  // Dump the cross-section table
  G4cout << Name() << "Cross-section table: " << G4endl;
  G4bool dummy = false;
  G4int i;

  for (i=0; i<_tableSize; i++)
    {
      G4double e = _sigma->GetLowEdgeEnergy(i) / GeV;
      G4double sigma = _sigma->GetValue(e,dummy) / millibarn;
      G4cout << i << ") e = " << e << " GeV ---- Cross section = " << sigma << " mb " << G4endl;
    }

  G4VCrossSectionSource::Print();
}


G4String G4XnpElasticLowE::Name() const
{
  G4String name("npElasticLowE");
  return name;
}


G4bool G4XnpElasticLowE::IsValid(G4double e) const
{
  G4bool answer = InLimits(e,_lowLimit,_highLimit);

  return answer;
}