Shark Machine Learning Library

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HyperGeometric.cpp

Go to the documentation of this file.

//===========================================================================
//===========================================================================


#include <cmath>
#include "Rng/HyperGeometric.h"


//========================================================================
HyperGeometric::HyperGeometric(double mean, double variance)
        : pMean(mean), pVariance(variance)
{
    setState();
}


//========================================================================
HyperGeometric::HyperGeometric(double mean, double variance, RNG& r)
        : RandomVar< double >(r), pMean(mean), pVariance(variance)
{
    setState();
}


// Calculates the probability "p", i.e. the relation of the number of
// events of type T1 to the total number of events given
// by "p = N1/N" from the stored mean value and the
// variance. "p" will always be a real number greater than or equal
// to zero. If the stored mean value is zero, then "p" will be set
// to "0.", as for the default values "mean = 0" and "variance = 1".
// Change: 2002-04-16, ra:
// If the mean value is equal to zero or the calculation
// of "p" results in a negative value then "p" will be set to "0." now.
//
void HyperGeometric::setState()
{
    if (pMean == 0) {
        pP = 0.;
        return;
    }

    double z = pVariance / (pMean * pMean);
    pP = (1 - sqrt((z - 1) / (z + 1))) / 2;

    if (pP < 0.) pP = 0.;
    return;
}



//========================================================================
void HyperGeometric::mean(double newMean)
{
    pMean = newMean;
    setState();
}


//========================================================================
void HyperGeometric::variance(double newVariance)
{
    pVariance = newVariance;
    setState();
}



//========================================================================
double HyperGeometric::operator()()
{
    return -pMean * log(rng()) / (2 *(rng() > pP ? 1 - pP : pP));
}



//========================================================================
double HyperGeometric::p(const double& x) const
{
    return 0.; // !!!
}