/usr/include/shark/Rng/NegExponential.h is in libshark-dev 3.0.1+ds1-2ubuntu1.
This file is owned by root:root, with mode 0o644.
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*
*
* \brief Implements the negative exponential distribution
*
*
*
* \author O. Krause
* \date 2010-01-01
*
*
* \par Copyright 1995-2015 Shark Development Team
*
* <BR><HR>
* This file is part of Shark.
* <http://image.diku.dk/shark/>
*
* Shark is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Shark is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with Shark. If not, see <http://www.gnu.org/licenses/>.
*
*/
#ifndef SHARK_RNG_NEGEXPONENTIAL_H
#define SHARK_RNG_NEGEXPONENTIAL_H
#include <boost/random/exponential_distribution.hpp>
#include <cmath>
namespace shark{
///\brief Implements the Negative exponential distribution.
///
/// It's propability distribution is defined as
/// \f[ p(x) = e^{-\lambda x}\f]
/// Instead of lambda, we define the exponential distribution using the mean
/// \f[ \mu = 1.0/\lambda \f]
template<typename RngType = shark::DefaultRngType>
class NegExponential:public boost::variate_generator<RngType*,boost::exponential_distribution<> >
{
private:
typedef boost::variate_generator<RngType*,boost::exponential_distribution<> > Base;
public:
NegExponential( RngType & rng, double mean = 0 )
:Base(&rng,boost::exponential_distribution<>(1.0/mean))
{}
using Base::operator();
///\brief Draws a random number from the negative exponential distribution with the mean defined in the argument
///
///\param mean: the mean of the distribution from which the number is drawn
double operator()(double mean)
{
boost::exponential_distribution<> dist(1.0/mean);
return dist(Base::engine());
}
///\brief Returns the mean of the negative exponential distribution
double mean()const
{
return 1.0/Base::distribution().lambda();
}
///\brief Sets the mean of the negative exponential distribution
///
///\param newMean the new Mean value
void mean(double newMean)
{
Base::distribution()=boost::exponential_distribution<>(1.0/newMean);
}
double p(double x)
{
return x >= 0 ? Base::distribution().lambda() * exp(- Base::distribution().lambda() * x) : 0.;
}
};
}
#endif
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