| /* boost random/exponential_distribution.hpp header file |
| * |
| * Copyright Jens Maurer 2000-2001 |
| * 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: exponential_distribution.hpp 60755 2010-03-22 00:45:06Z steven_watanabe $ |
| * |
| * Revision history |
| * 2001-02-18 moved to individual header files |
| */ |
| |
| #ifndef BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP |
| #define BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP |
| |
| #include <boost/config/no_tr1/cmath.hpp> |
| #include <cassert> |
| #include <iostream> |
| #include <boost/limits.hpp> |
| #include <boost/static_assert.hpp> |
| #include <boost/random/detail/config.hpp> |
| |
| namespace boost { |
| |
| /** |
| * The exponential distribution has a single parameter lambda. |
| * |
| * It has \f$p(x) = \lambda e^{-\lambda x}\f$ |
| */ |
| template<class RealType = double> |
| class exponential_distribution |
| { |
| public: |
| typedef RealType input_type; |
| typedef RealType result_type; |
| |
| #if !defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) && !(defined(BOOST_MSVC) && BOOST_MSVC <= 1300) |
| BOOST_STATIC_ASSERT(!std::numeric_limits<RealType>::is_integer); |
| #endif |
| |
| explicit exponential_distribution(result_type lambda_arg = result_type(1)) |
| : _lambda(lambda_arg) { assert(_lambda > result_type(0)); } |
| |
| // compiler-generated copy ctor and assignment operator are fine |
| |
| result_type lambda() const { return _lambda; } |
| |
| void reset() { } |
| |
| template<class Engine> |
| result_type operator()(Engine& eng) |
| { |
| #ifndef BOOST_NO_STDC_NAMESPACE |
| using std::log; |
| #endif |
| return -result_type(1) / _lambda * log(result_type(1)-eng()); |
| } |
| |
| #ifndef BOOST_RANDOM_NO_STREAM_OPERATORS |
| template<class CharT, class Traits> |
| friend std::basic_ostream<CharT,Traits>& |
| operator<<(std::basic_ostream<CharT,Traits>& os, const exponential_distribution& ed) |
| { |
| os << ed._lambda; |
| return os; |
| } |
| |
| template<class CharT, class Traits> |
| friend std::basic_istream<CharT,Traits>& |
| operator>>(std::basic_istream<CharT,Traits>& is, exponential_distribution& ed) |
| { |
| is >> std::ws >> ed._lambda; |
| return is; |
| } |
| #endif |
| |
| private: |
| result_type _lambda; |
| }; |
| |
| } // namespace boost |
| |
| #endif // BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP |