| /* boost random/exponential_distribution.hpp header file |
| * |
| * Copyright Jens Maurer 2000-2001 |
| * Copyright Steven Watanabe 2011 |
| * 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. |
| * |
| * $Id$ |
| * |
| * 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 <iosfwd> |
| #include <boost/assert.hpp> |
| #include <boost/limits.hpp> |
| #include <boost/random/detail/config.hpp> |
| #include <boost/random/detail/operators.hpp> |
| #include <boost/random/uniform_01.hpp> |
| |
| namespace boost { |
| namespace random { |
| |
| /** |
| * The exponential distribution is a model of \random_distribution with |
| * a single parameter lambda. |
| * |
| * It has \f$\displaystyle p(x) = \lambda e^{-\lambda x}\f$ |
| */ |
| template<class RealType = double> |
| class exponential_distribution |
| { |
| public: |
| typedef RealType input_type; |
| typedef RealType result_type; |
| |
| class param_type |
| { |
| public: |
| |
| typedef exponential_distribution distribution_type; |
| |
| /** |
| * Constructs parameters with a given lambda. |
| * |
| * Requires: lambda > 0 |
| */ |
| param_type(RealType lambda_arg = RealType(1.0)) |
| : _lambda(lambda_arg) { BOOST_ASSERT(_lambda > RealType(0)); } |
| |
| /** Returns the lambda parameter of the distribution. */ |
| RealType lambda() const { return _lambda; } |
| |
| /** Writes the parameters to a @c std::ostream. */ |
| BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, param_type, parm) |
| { |
| os << parm._lambda; |
| return os; |
| } |
| |
| /** Reads the parameters from a @c std::istream. */ |
| BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, param_type, parm) |
| { |
| is >> parm._lambda; |
| return is; |
| } |
| |
| /** Returns true if the two sets of parameters are equal. */ |
| BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(param_type, lhs, rhs) |
| { return lhs._lambda == rhs._lambda; } |
| |
| /** Returns true if the two sets of parameters are different. */ |
| BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(param_type) |
| |
| private: |
| RealType _lambda; |
| }; |
| |
| /** |
| * Constructs an exponential_distribution with a given lambda. |
| * |
| * Requires: lambda > 0 |
| */ |
| explicit exponential_distribution(RealType lambda_arg = RealType(1.0)) |
| : _lambda(lambda_arg) { BOOST_ASSERT(_lambda > RealType(0)); } |
| |
| /** |
| * Constructs an exponential_distribution from its parameters |
| */ |
| explicit exponential_distribution(const param_type& parm) |
| : _lambda(parm.lambda()) {} |
| |
| // compiler-generated copy ctor and assignment operator are fine |
| |
| /** Returns the lambda parameter of the distribution. */ |
| RealType lambda() const { return _lambda; } |
| |
| /** Returns the smallest value that the distribution can produce. */ |
| RealType min BOOST_PREVENT_MACRO_SUBSTITUTION () const |
| { return RealType(0); } |
| /** Returns the largest value that the distribution can produce. */ |
| RealType max BOOST_PREVENT_MACRO_SUBSTITUTION () const |
| { return (std::numeric_limits<RealType>::infinity)(); } |
| |
| /** Returns the parameters of the distribution. */ |
| param_type param() const { return param_type(_lambda); } |
| /** Sets the parameters of the distribution. */ |
| void param(const param_type& parm) { _lambda = parm.lambda(); } |
| |
| /** |
| * Effects: Subsequent uses of the distribution do not depend |
| * on values produced by any engine prior to invoking reset. |
| */ |
| void reset() { } |
| |
| /** |
| * Returns a random variate distributed according to the |
| * exponential distribution. |
| */ |
| template<class Engine> |
| result_type operator()(Engine& eng) const |
| { |
| using std::log; |
| return -result_type(1) / |
| _lambda * log(result_type(1)-uniform_01<RealType>()(eng)); |
| } |
| |
| /** |
| * Returns a random variate distributed according to the exponential |
| * distribution with parameters specified by param. |
| */ |
| template<class Engine> |
| result_type operator()(Engine& eng, const param_type& parm) const |
| { |
| return exponential_distribution(parm)(eng); |
| } |
| |
| /** Writes the distribution to a std::ostream. */ |
| BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, exponential_distribution, ed) |
| { |
| os << ed._lambda; |
| return os; |
| } |
| |
| /** Reads the distribution from a std::istream. */ |
| BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, exponential_distribution, ed) |
| { |
| is >> ed._lambda; |
| return is; |
| } |
| |
| /** |
| * Returns true iff the two distributions will produce identical |
| * sequences of values given equal generators. |
| */ |
| BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(exponential_distribution, lhs, rhs) |
| { return lhs._lambda == rhs._lambda; } |
| |
| /** |
| * Returns true iff the two distributions will produce different |
| * sequences of values given equal generators. |
| */ |
| BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(exponential_distribution) |
| |
| private: |
| result_type _lambda; |
| }; |
| |
| } // namespace random |
| |
| using random::exponential_distribution; |
| |
| } // namespace boost |
| |
| #endif // BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP |