/* boost random/poisson_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: poisson_distribution.hpp 41369 2007-11-25 18:07:19Z bemandawes $ * */ #ifndef BOOST_RANDOM_POISSON_DISTRIBUTION_HPP #define BOOST_RANDOM_POISSON_DISTRIBUTION_HPP #include #include #include #include #include namespace boost { // Knuth template class poisson_distribution { public: typedef RealType input_type; typedef IntType result_type; explicit poisson_distribution(const RealType& mean_arg = RealType(1)) : _mean(mean_arg) { #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS // MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope BOOST_STATIC_ASSERT(std::numeric_limits::is_integer); BOOST_STATIC_ASSERT(!std::numeric_limits::is_integer); #endif assert(_mean > RealType(0)); init(); } // compiler-generated copy ctor and assignment operator are fine RealType mean() const { return _mean; } void reset() { } template result_type operator()(Engine& eng) { // TODO: This is O(_mean), but it should be O(log(_mean)) for large _mean RealType product = RealType(1); for(result_type m = 0; ; ++m) { product *= eng(); if(product <= _exp_mean) return m; } } #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) template friend std::basic_ostream& operator<<(std::basic_ostream& os, const poisson_distribution& pd) { os << pd._mean; return os; } template friend std::basic_istream& operator>>(std::basic_istream& is, poisson_distribution& pd) { is >> std::ws >> pd._mean; pd.init(); return is; } #endif private: void init() { #ifndef BOOST_NO_STDC_NAMESPACE // allow for Koenig lookup using std::exp; #endif _exp_mean = exp(-_mean); } RealType _mean; // some precomputed data from the parameters RealType _exp_mean; }; } // namespace boost #endif // BOOST_RANDOM_POISSON_DISTRIBUTION_HPP