poisson.h

// Copyright 2009-2016 Sandia Corporation. Under the terms
// of Contract DE-AC04-94AL85000 with Sandia Corporation, the U.S.
// Government retains certain rights in this software.
//
// Copyright (c) 2009-2016, Sandia Corporation
// All rights reserved.
//
// This file is part of the SST software package. For license
// information, see the LICENSE file in the top level directory of the
// distribution.

#ifndef _H_SST_CORE_RNG_POISSON
#define _H_SST_CORE_RNG_POISSON

#include "math.h"

#include "distrib.h"
#include "mersenne.h"

using namespace SST::RNG;

namespace SST {
namespace RNG {

/**
        \class SSTPoissonDistribution poisson.h "sst/core/rng/poisson.h"

        Creates an Poisson distribution for use within SST. This distribution is the same across
        platforms and compilers.
*/
class SSTPoissonDistribution : public SSTRandomDistribution {

        public:
                /**
                        Creates an Poisson distribution with a specific lambda
                        \param mn The lambda of the Poisson distribution
                */
    SSTPoissonDistribution(const double mn)  :
    SSTRandomDistribution(), lambda(mn) {
        
        baseDistrib = new MersenneRNG();
        deleteDistrib = true;
    }

                /**
                        Creates an Poisson distribution with a specific lambda and a base random number generator
                        \param lambda The lambda of the Poisson distribution
                        \param baseDist The base random number generator to take the distribution from.
                */
    SSTPoissonDistribution(const double mn, SSTRandom* baseDist)  :
    SSTRandomDistribution(), lambda(mn) {
        
        baseDistrib = baseDist;
        deleteDistrib = false;
    }

                /**
                        Destroys the Poisson distribution
                */
    ~SSTPoissonDistribution()  {
        if(deleteDistrib) {
            delete baseDistrib;
        }
    }

                /**
                        Gets the next (random) double value in the distribution
                        \return The next random double from the distribution
                */
     double getNextDouble() {
        const double L = exp(-lambda);
        double p = 1.0;
        int k = 0;
        
        do {
            k++;
            p *= baseDistrib->nextUniform();
        } while(p > L);
        
        return k - 1;
    }

                /**
                        Gets the lambda with which the distribution was created
                        \return The lambda which the user created the distribution with
                */
    double getLambda()  {
        return lambda;
    }

        protected:
                /**
                        Sets the lambda of the Poisson distribution.
                */
                const double lambda;
                /**
                        Sets the base random number generator for the distribution.
                */
                SSTRandom* baseDistrib;

                /**
                        Controls whether the base distribution should be deleted when this class is destructed.
                */
                bool deleteDistrib;

};

}
}

#endif