author | Dremov Kirill (Nokia-D-MSW/Tampere) <kirill.dremov@nokia.com> |
Tue, 02 Feb 2010 02:01:42 +0200 | |
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/* boost random/poisson_distribution.hpp header file |
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* |
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* Copyright Jens Maurer 2002 |
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* Distributed under the Boost Software License, Version 1.0. (See |
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* accompanying file LICENSE_1_0.txt or copy at |
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* http://www.boost.org/LICENSE_1_0.txt) |
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* |
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* See http://www.boost.org for most recent version including documentation. |
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* |
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* $Id: poisson_distribution.hpp,v 1.15 2005/05/21 15:57:00 dgregor Exp $ |
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* |
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*/ |
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|
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#ifndef BOOST_RANDOM_POISSON_DISTRIBUTION_HPP |
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#define BOOST_RANDOM_POISSON_DISTRIBUTION_HPP |
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#include <cmath> |
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#include <cassert> |
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#include <iostream> |
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#include <boost/limits.hpp> |
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#include <boost/static_assert.hpp> |
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namespace boost { |
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// Knuth |
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template<class IntType = int, class RealType = double> |
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class poisson_distribution |
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{ |
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public: |
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typedef RealType input_type; |
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typedef IntType result_type; |
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explicit poisson_distribution(const RealType& mean = RealType(1)) |
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: _mean(mean) |
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{ |
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#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS |
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// MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope |
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BOOST_STATIC_ASSERT(std::numeric_limits<IntType>::is_integer); |
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BOOST_STATIC_ASSERT(!std::numeric_limits<RealType>::is_integer); |
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#endif |
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assert(mean > RealType(0)); |
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init(); |
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} |
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// compiler-generated copy ctor and assignment operator are fine |
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RealType mean() const { return _mean; } |
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void reset() { } |
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template<class Engine> |
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result_type operator()(Engine& eng) |
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{ |
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// TODO: This is O(_mean), but it should be O(log(_mean)) for large _mean |
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RealType product = RealType(1); |
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for(result_type m = 0; ; ++m) { |
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product *= eng(); |
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if(product <= _exp_mean) |
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return m; |
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} |
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} |
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#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) |
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template<class CharT, class Traits> |
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friend std::basic_ostream<CharT,Traits>& |
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operator<<(std::basic_ostream<CharT,Traits>& os, const poisson_distribution& pd) |
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{ |
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os << pd._mean; |
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return os; |
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} |
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template<class CharT, class Traits> |
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friend std::basic_istream<CharT,Traits>& |
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operator>>(std::basic_istream<CharT,Traits>& is, poisson_distribution& pd) |
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{ |
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is >> std::ws >> pd._mean; |
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pd.init(); |
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return is; |
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} |
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#endif |
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private: |
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void init() |
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{ |
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#ifndef BOOST_NO_STDC_NAMESPACE |
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// allow for Koenig lookup |
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using std::exp; |
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#endif |
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_exp_mean = exp(-_mean); |
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} |
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RealType _mean; |
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// some precomputed data from the parameters |
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RealType _exp_mean; |
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}; |
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} // namespace boost |
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#endif // BOOST_RANDOM_POISSON_DISTRIBUTION_HPP |