FastSimulation/Utilities/interface/LandauFluctuationGenerator.h - master - githubmirror/cmssw

FastSimulation/Utilities/interface/LandauFluctuationGenerator.h

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24 май 2019, 00:14

24 май 2019, 00:14740c44a

#ifndef FastSimulation_Utilities_LandauFluctuationGenerator_H
#define FastSimulation_Utilities_LandauFluctuationGenerator_H

#include "FastSimulation/Utilities/interface/BaseNumericalRandomGenerator.h"

#include <cmath>

/** Numerical Random Generator for Landau Fluctuations.
 * The constructor integrates and inverses the Ersaztz for the 
 * Landau fluctuation density probability parametrization, and 
 * the method landau() randomly a number according to this 
 * density probability
 * 
 * \author Patrick Janot, CERN
 * $Date 8-Jan-2004
 */

class RandomEngineAndDistribution;

class LandauFluctuationGenerator : public BaseNumericalRandomGenerator {
public:
  /// Constructor : initialization of the Random Generator
  LandauFluctuationGenerator() : BaseNumericalRandomGenerator(-3.5, 25.) { initialize(); }

  /// Default destructor
  ~LandauFluctuationGenerator() override {}

  /// Random generator of the dE/dX spread (Landau function)
  double landau(RandomEngineAndDistribution const* random) const { return generate(random); }

  /// The probability density function implementation
  double function(double x) override { return ersatzt(x); }

private:
  /// Ersatzt for Landau Fluctuations (very good approximation)
  double ersatzt(double x) { return std::exp(-0.5 * (x + std::exp(-x))) / std::sqrt(2. * M_PI); }
};
#endif