/src/contrib/boost/random/exponential_distribution.hpp
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- /* 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