boost/random/binomial_distribution.hpp
/* boost random/binomial_distribution.hpp header file
*
* Copyright Jens Maurer 2002
* Permission to use, copy, modify, sell, and distribute this software
* is hereby granted without fee provided that the above copyright notice
* appears in all copies and that both that copyright notice and this
* permission notice appear in supporting documentation,
*
* Jens Maurer makes no representations about the suitability of this
* software for any purpose. It is provided "as is" without express or
* implied warranty.
*
* See http://www.boost.org for most recent version including documentation.
*
* $Id: binomial_distribution.hpp,v 1.8 2003/07/06 21:53:42 jmaurer Exp $
*
*/
#ifndef BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
#define BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
#include <cmath>
#include <cassert>
#include <boost/random/bernoulli_distribution.hpp>
namespace boost {
// Knuth
template<class IntType = int, class RealType = double>
class binomial_distribution
{
public:
typedef typename bernoulli_distribution<RealType>::input_type input_type;
typedef IntType result_type;
explicit binomial_distribution(IntType t = 1,
const RealType& p = RealType(0.5))
: _t(t)
{
assert(t >= 0);
assert(RealType(0) <= 0 && p <= RealType(1));
}
// compiler-generated copy ctor and assignment operator are fine
IntType t() const { return _t; }
RealType p() const { return _bernoulli.p(); }
void reset() { }
template<class Engine>
result_type operator()(Engine& eng)
{
// TODO: This is O(_t), but it should be O(log(_t)) for large _t
result_type n = 0;
for(IntType i = 0; i < _t; ++i)
if(_bernoulli(eng))
++n;
return n;
}
#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
template<class CharT, class Traits>
friend std::basic_ostream<CharT,Traits>&
operator<<(std::basic_ostream<CharT,Traits>& os, const binomial_distribution& bd)
{
os << bd._bernoulli << " " << bd._t;
return os;
}
template<class CharT, class Traits>
friend std::basic_istream<CharT,Traits>&
operator>>(std::basic_istream<CharT,Traits>& is, binomial_distribution& bd)
{
is >> std::ws >> bd._bernoulli >> std::ws >> bd._t;
return is;
}
#endif
private:
bernoulli_distribution<RealType> _bernoulli;
IntType _t;
};
} // namespace boost
#endif // BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP