williamr@2: /* boost random/binomial_distribution.hpp header file
williamr@2:  *
williamr@2:  * Copyright Jens Maurer 2002
williamr@2:  * Distributed under the Boost Software License, Version 1.0. (See
williamr@2:  * accompanying file LICENSE_1_0.txt or copy at
williamr@2:  * http://www.boost.org/LICENSE_1_0.txt)
williamr@2:  *
williamr@2:  * See http://www.boost.org for most recent version including documentation.
williamr@2:  *
williamr@2:  * $Id: binomial_distribution.hpp,v 1.10 2005/06/24 22:13:43 jmaurer Exp $
williamr@2:  *
williamr@2:  */
williamr@2: 
williamr@2: #ifndef BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
williamr@2: #define BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
williamr@2: 
williamr@2: #include <cmath>
williamr@2: #include <cassert>
williamr@2: #include <boost/random/bernoulli_distribution.hpp>
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2: // Knuth
williamr@2: template<class IntType = int, class RealType = double>
williamr@2: class binomial_distribution
williamr@2: {
williamr@2: public:
williamr@2:   typedef typename bernoulli_distribution<RealType>::input_type input_type;
williamr@2:   typedef IntType result_type;
williamr@2: 
williamr@2:   explicit binomial_distribution(IntType t = 1,
williamr@2:                                  const RealType& p = RealType(0.5))
williamr@2:     : _bernoulli(p), _t(t)
williamr@2:   {
williamr@2:     assert(t >= 0);
williamr@2:     assert(RealType(0) <= 0 && p <= RealType(1));
williamr@2:   }
williamr@2: 
williamr@2:   // compiler-generated copy ctor and assignment operator are fine
williamr@2: 
williamr@2:   IntType t() const { return _t; }
williamr@2:   RealType p() const { return _bernoulli.p(); }
williamr@2:   void reset() { }
williamr@2: 
williamr@2:   template<class Engine>
williamr@2:   result_type operator()(Engine& eng)
williamr@2:   {
williamr@2:     // TODO: This is O(_t), but it should be O(log(_t)) for large _t
williamr@2:     result_type n = 0;
williamr@2:     for(IntType i = 0; i < _t; ++i)
williamr@2:       if(_bernoulli(eng))
williamr@2:         ++n;
williamr@2:     return n;
williamr@2:   }
williamr@2: 
williamr@2: #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
williamr@2:   template<class CharT, class Traits>
williamr@2:   friend std::basic_ostream<CharT,Traits>&
williamr@2:   operator<<(std::basic_ostream<CharT,Traits>& os, const binomial_distribution& bd)
williamr@2:   {
williamr@2:     os << bd._bernoulli << " " << bd._t;
williamr@2:     return os;
williamr@2:   }
williamr@2: 
williamr@2:   template<class CharT, class Traits>
williamr@2:   friend std::basic_istream<CharT,Traits>&
williamr@2:   operator>>(std::basic_istream<CharT,Traits>& is, binomial_distribution& bd)
williamr@2:   {
williamr@2:     is >> std::ws >> bd._bernoulli >> std::ws >> bd._t;
williamr@2:     return is;
williamr@2:   }
williamr@2: #endif
williamr@2: 
williamr@2: private:
williamr@2:   bernoulli_distribution<RealType> _bernoulli;
williamr@2:   IntType _t;
williamr@2: };
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif // BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP