ExponentialDiscreteDistribution.h

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//
// File: ExponentialDiscreteDistribution.h
// Created by: Julien Dutheil
// Created on: Tue Nov 13 12:37 2007
//

/*
   Copyright or © or Copr. Bio++ Development Team, (November 17, 2004)

   This software is a computer program whose purpose is to provide classes
   for numerical calculus.

   This software is governed by the CeCILL  license under French law and
   abiding by the rules of distribution of free software.  You can  use,
   modify and/ or redistribute the software under the terms of the CeCILL
   license as circulated by CEA, CNRS and INRIA at the following URL
   "http://www.cecill.info".

   As a counterpart to the access to the source code and  rights to copy,
   modify and redistribute granted by the license, users are provided only
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   economic rights,  and the successive licensors  have only  limited
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   software by the user in light of its specific status of free software,
   that may mean  that it is complicated to manipulate,  and  that  also
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 */

#ifndef _EXPONENTIALDISCRETEDISTRIBUTION_H_
#define _EXPONENTIALDISCRETEDISTRIBUTION_H_

#include "AbstractDiscreteDistribution.h"
#include "../Constraints.h"
#include "../Random/RandomTools.h"

namespace bpp
{
class ExponentialDiscreteDistribution :
  public AbstractDiscreteDistribution
{
protected:
  double lambda_;

public:
  ExponentialDiscreteDistribution(size_t n, double lambda = 1.);

  ExponentialDiscreteDistribution(const ExponentialDiscreteDistribution& dist) :
    AbstractParameterAliasable(dist),
    AbstractDiscreteDistribution(dist),
    lambda_(dist.lambda_)
  {}

  ExponentialDiscreteDistribution& operator=(const ExponentialDiscreteDistribution& dist)
  {
    AbstractParameterAliasable::operator=(dist);    
    AbstractDiscreteDistribution::operator=(dist);
    lambda_ = dist.lambda_;
    return *this;
  }

  ~ExponentialDiscreteDistribution(){};

  ExponentialDiscreteDistribution* clone() const { return new ExponentialDiscreteDistribution(*this); }

public:
  std::string getName() const {return("Exponential");}
  
  void fireParameterChanged(const ParameterList& parameters);

  double randC() const throw (Exception)
  {
    double x = RandomTools::randExponential(1. / getParameterValue("lambda"));
    while (!intMinMax_.isCorrect(x))
      x = RandomTools::randExponential(1. / getParameterValue("lambda"));

    return x;
  }

  double pProb(double x) const
  {
    return 1. - exp(-lambda_ * x);
  }

  double qProb(double x) const
  {
    return -log(1. - x) / lambda_;
  }

  double Expectation(double a) const
  {
    return 1. / lambda_ - exp(-a * lambda_) * (a + 1. / lambda_);
  }
};
} //end of namespace bpp.

#endif  //_EXPONENTIALDISCRETEDISTRIBUTION_H_