112 lines
3.2 KiB
C++
112 lines
3.2 KiB
C++
/* boost random/binomial_distribution.hpp header file
|
|
*
|
|
* Copyright Jens Maurer 2002
|
|
* Distributed under the Boost Software License, Version 1.0. (See
|
|
* accompanying file LICENSE_1_0.txt or copy at
|
|
* http://www.boost.org/LICENSE_1_0.txt)
|
|
*
|
|
* See http://www.boost.org for most recent version including documentation.
|
|
*
|
|
* $Id: binomial_distribution.hpp 60755 2010-03-22 00:45:06Z steven_watanabe $
|
|
*
|
|
*/
|
|
|
|
#ifndef BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
|
|
#define BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
|
|
|
|
#include <boost/config/no_tr1/cmath.hpp>
|
|
#include <cassert>
|
|
#include <boost/random/detail/config.hpp>
|
|
#include <boost/random/bernoulli_distribution.hpp>
|
|
|
|
namespace boost {
|
|
|
|
/**
|
|
* The binomial distribution is an integer valued distribution with
|
|
* two parameters, @c t and @c p. The values of the distribution
|
|
* are within the range [0,t].
|
|
*
|
|
* The probability that the distribution produces a value k is
|
|
* \f${t \choose k}p^k(1-p)^{t-k}\f$.
|
|
*/
|
|
template<class IntType = int, class RealType = double>
|
|
class binomial_distribution
|
|
{
|
|
public:
|
|
typedef typename bernoulli_distribution<RealType>::input_type input_type;
|
|
typedef IntType result_type;
|
|
|
|
/**
|
|
* Construct an @c binomial_distribution object. @c t and @c p
|
|
* are the parameters of the distribution.
|
|
*
|
|
* Requires: t >=0 && 0 <= p <= 1
|
|
*/
|
|
explicit binomial_distribution(IntType t = 1,
|
|
const RealType& p = RealType(0.5))
|
|
: _bernoulli(p), _t(t)
|
|
{
|
|
assert(_t >= 0);
|
|
assert(RealType(0) <= p && p <= RealType(1));
|
|
}
|
|
|
|
// compiler-generated copy ctor and assignment operator are fine
|
|
|
|
/** Returns: the @c t parameter of the distribution */
|
|
IntType t() const { return _t; }
|
|
/** Returns: the @c p parameter of the distribution */
|
|
RealType p() const { return _bernoulli.p(); }
|
|
/**
|
|
* Effects: Subsequent uses of the distribution do not depend
|
|
* on values produced by any engine prior to invoking reset.
|
|
*/
|
|
void reset() { }
|
|
|
|
/**
|
|
* Returns: a random variate distributed according to the
|
|
* binomial distribution.
|
|
*/
|
|
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;
|
|
}
|
|
|
|
#ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
|
|
/**
|
|
* Writes the parameters of the distribution to a @c std::ostream.
|
|
*/
|
|
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;
|
|
}
|
|
|
|
/**
|
|
* Reads the parameters of the distribution from a @c std::istream.
|
|
*/
|
|
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
|