boost/random/exponential_distribution.hpp
/* boost random/exponential_distribution.hpp header file * * Copyright Jens Maurer 2000-2001 * Permission to use, copy, modify, sell, and distribute this software * is hereby granted without fee provided that the above copyright notice * appears in all copies and that both that copyright notice and this * permission notice appear in supporting documentation, * * Jens Maurer makes no representations about the suitability of this * software for any purpose. It is provided "as is" without express or * implied warranty. * * See http://www.boost.org for most recent version including documentation. * * $Id: exponential_distribution.hpp,v 1.14.2.1 2004/01/25 21:26:45 jmaurer Exp $ * * Revision history * 2001-02-18 moved to individual header files */ #ifndef BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP #define BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP #include <cmath> #include <cassert> #include <iostream> #include <boost/limits.hpp> #include <boost/static_assert.hpp> namespace boost { // exponential distribution: p(x) = lambda * exp(-lambda * x) 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 = result_type(1)) : _lambda(lambda) { 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()); } #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) 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