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//
// $Id$
//
#ifndef G4NeutronHPSimpleEvapSpectrum_h
#define G4NeutronHPSimpleEvapSpectrum_h 1

#include <fstream>
#include <CLHEP/Units/SystemOfUnits.h>

#include "globals.hh"
#include "G4ios.hh"
#include "Randomize.hh"
#include "G4NeutronHPVector.hh"
#include "G4VNeutronHPEDis.hh"

// we will need a List of these .... one per term.

class G4NeutronHPSimpleEvapSpectrum : public G4VNeutronHPEDis
{
  public:
  G4NeutronHPSimpleEvapSpectrum()
  {
    expm1 = std::exp(-1.);
  }
  ~G4NeutronHPSimpleEvapSpectrum()
  {
  }
  
  inline void Init(std::ifstream & aDataFile)
  {
    theFractionalProb.Init(aDataFile, CLHEP::eV);
    theThetaDist.Init(aDataFile, CLHEP::eV);
  }
  
  inline G4double GetFractionalProbability(G4double anEnergy)
  {
    return theFractionalProb.GetY(anEnergy);
  }
  
  inline G4double Sample(G4double anEnergy) 
  {
    G4double theta = theThetaDist.GetY(anEnergy)*CLHEP::eV;
    G4double random, cut, max, result;
    max = 10.*theta;
    do
    {
      random = G4UniformRand();
      result = -theta*std::log(random); 
      cut = G4UniformRand();
    }
    while(cut>result/max); 
    return result;
  }
  
  private:
  
  inline G4double Evapo(G4double anEnergy, G4double theta)
  {
    G4double result = (anEnergy*CLHEP::eV)*std::exp(-anEnergy*CLHEP::eV/theta);
    return result;
  }
  
  private:
  
  G4double expm1;
  
  G4NeutronHPVector theFractionalProb;
  
  G4NeutronHPVector theThetaDist;
  
};

#endif