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// G4WeightWindowAlgorithm
// 
// Class description:
//
// Implementation of a weight window algorithm. 
// The arguments in the constructor configure the algorithm:
//   - upperLimitFactor: the factor defining the upper weight limit 
//      W_u = upperLimitFactor * W_l (W_l lower weight bound)
//   - survivalFactor: used in calculating the survival weight
//      W_s = survivalFactor * W_l
//   - maxNumberOfSplits: the maximal number of splits allowed
//     to be created in one go, and the reciprocal of the minimal
//     survival probability in case of Russian roulette
//
// In case of upperLimitFactor=survivalFactor=1 the algorithm becomes
// the expected weight algorithm of the importance sampling technique.
//
// See also G4VWeightWindowAlgorithm.

// Author: Michael Dressel (CERN), 2003
// ----------------------------------------------------------------------
#ifndef G4WEIGHTWINDOWALGORITHM_HH
#define G4WEIGHTWINDOWALGORITHM_HH

#include "G4Nsplit_Weight.hh"
#include "G4VWeightWindowAlgorithm.hh"

/**
 * @brief G4WeightWindowAlgorithm is a concrete implementation of a weight
 * window algorithm.
 */

class G4WeightWindowAlgorithm : public G4VWeightWindowAlgorithm
{
  public:
  
    /**
     * Constructor. The arguments configure the algorithm.
     * In case of upperLimitFactor=survivalFactor=1 the algorithm becomes
     * the expected weight algorithm of the importance sampling technique.
     *  @param[in] upperLimitFactor The factor defining the upper weight limit 
     *             W_u = upperLimitFactor * W_l (W_l lower weight bound).
     *  @param[in] survivalFactor uUsed in calculating the survival weight
     *             W_s = survivalFactor * W_l.
     *  @param[in] maxNumberOfSplits The maximal number of splits allowed
     *             to be created in one go, and the reciprocal of the minimal
     *             survival probability in case of Russian roulette.
     */
    G4WeightWindowAlgorithm(G4double upperLimitFactor = 5,
                            G4double survivalFactor = 3,
                            G4int maxNumberOfSplits = 5);
  
    /**
     * Default Destructor.
     */
    ~G4WeightWindowAlgorithm() override = default;

    /**
     * Calculates the number of tracks and their weight according
     * to the initial track weight and the lower energy bound.
     */
    G4Nsplit_Weight Calculate(G4double init_w,
                              G4double lowerWeightBound) const override;

  private:

    G4double fUpperLimitFactor = 0.0;
    G4double fSurvivalFactor = 0.0;
    G4int fMaxNumberOfSplits = 0;
};

#endif
