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/* boost random/geometric_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: geometric_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_GEOMETRIC_DISTRIBUTION_HPP
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#define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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#include <cmath> // std::log
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#include <cassert>
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#include <iostream>
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#include <boost/random/uniform_01.hpp>
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namespace boost {
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#if defined(__GNUC__) && (__GNUC__ < 3)
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// Special gcc workaround: gcc 2.95.x ignores using-declarations
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// in template classes (confirmed by gcc author Martin v. Loewis)
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using std::log;
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#endif
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// geometric distribution: p(i) = (1-p) * pow(p, i-1) (integer)
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template<class IntType = int, class RealType = double>
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class geometric_distribution
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{
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public:
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typedef RealType input_type;
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typedef IntType result_type;
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explicit geometric_distribution(const RealType& p = RealType(0.5))
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: _p(p)
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{
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assert(RealType(0) < p && p < RealType(1));
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init();
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}
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// compiler-generated copy ctor and assignment operator are fine
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RealType p() const { return _p; }
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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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using std::floor;
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#endif
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return IntType(floor(log(RealType(1)-eng()) / _log_p)) + IntType(1);
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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 geometric_distribution& gd)
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{
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os << gd._p;
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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, geometric_distribution& gd)
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{
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is >> std::ws >> gd._p;
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gd.init();
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return is;
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}
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#endif
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private:
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void init()
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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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_log_p = log(_p);
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}
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RealType _p;
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RealType _log_p;
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};
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} // namespace boost
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#endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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