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/* boost random/exponential_distribution.hpp header file
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*
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* Copyright Jens Maurer 2000-2001
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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: exponential_distribution.hpp,v 1.16 2004/07/27 03:43:32 dgregor Exp $
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*
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* Revision history
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* 2001-02-18 moved to individual header files
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*/
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#ifndef BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP
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#define BOOST_RANDOM_EXPONENTIAL_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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// exponential distribution: p(x) = lambda * exp(-lambda * x)
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template<class RealType = double>
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class exponential_distribution
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{
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public:
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typedef RealType input_type;
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typedef RealType result_type;
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#if !defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) && !(defined(BOOST_MSVC) && BOOST_MSVC <= 1300)
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BOOST_STATIC_ASSERT(!std::numeric_limits<RealType>::is_integer);
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#endif
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explicit exponential_distribution(result_type lambda = result_type(1))
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: _lambda(lambda) { assert(lambda > result_type(0)); }
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// compiler-generated copy ctor and assignment operator are fine
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result_type lambda() const { return _lambda; }
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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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#ifndef BOOST_NO_STDC_NAMESPACE
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using std::log;
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#endif
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return -result_type(1) / _lambda * log(result_type(1)-eng());
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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 exponential_distribution& ed)
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{
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os << ed._lambda;
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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, exponential_distribution& ed)
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{
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is >> std::ws >> ed._lambda;
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return is;
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}
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#endif
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private:
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result_type _lambda;
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};
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} // namespace boost
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#endif // BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP
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