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路径: \\game3dprogramming\materials\GameFactory\GameFactoryDemo\references\boost_1_35_0\boost\random\gamma_distribution.hpp
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/* boost random/gamma_distribution.hpp header file * * Copyright Jens Maurer 2002 * 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: gamma_distribution.hpp 41369 2007-11-25 18:07:19Z bemandawes $ * */ #ifndef BOOST_RANDOM_GAMMA_DISTRIBUTION_HPP #define BOOST_RANDOM_GAMMA_DISTRIBUTION_HPP #include
#include
#include
#include
#include
namespace boost { // Knuth template
class gamma_distribution { public: typedef RealType input_type; typedef RealType result_type; #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS BOOST_STATIC_ASSERT(!std::numeric_limits
::is_integer); #endif explicit gamma_distribution(const result_type& alpha_arg = result_type(1)) : _exp(result_type(1)), _alpha(alpha_arg) { assert(_alpha > result_type(0)); init(); } // compiler-generated copy ctor and assignment operator are fine RealType alpha() const { return _alpha; } void reset() { _exp.reset(); } template
result_type operator()(Engine& eng) { #ifndef BOOST_NO_STDC_NAMESPACE // allow for Koenig lookup using std::tan; using std::sqrt; using std::exp; using std::log; using std::pow; #endif if(_alpha == result_type(1)) { return _exp(eng); } else if(_alpha > result_type(1)) { // Can we have a boost::mathconst please? const result_type pi = result_type(3.14159265358979323846); for(;;) { result_type y = tan(pi * eng()); result_type x = sqrt(result_type(2)*_alpha-result_type(1))*y + _alpha-result_type(1); if(x <= result_type(0)) continue; if(eng() > (result_type(1)+y*y) * exp((_alpha-result_type(1)) *log(x/(_alpha-result_type(1))) - sqrt(result_type(2)*_alpha -result_type(1))*y)) continue; return x; } } else /* alpha < 1.0 */ { for(;;) { result_type u = eng(); result_type y = _exp(eng); result_type x, q; if(u < _p) { x = exp(-y/_alpha); q = _p*exp(-x); } else { x = result_type(1)+y; q = _p + (result_type(1)-_p) * pow(x, _alpha-result_type(1)); } if(u >= q) continue; return x; } } } #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) template
friend std::basic_ostream
& operator<<(std::basic_ostream
& os, const gamma_distribution& gd) { os << gd._alpha; return os; } template
friend std::basic_istream
& operator>>(std::basic_istream
& is, gamma_distribution& gd) { is >> std::ws >> gd._alpha; gd.init(); return is; } #endif private: void init() { #ifndef BOOST_NO_STDC_NAMESPACE // allow for Koenig lookup using std::exp; #endif _p = exp(result_type(1)) / (_alpha + exp(result_type(1))); } exponential_distribution
_exp; result_type _alpha; // some data precomputed from the parameters result_type _p; }; } // namespace boost #endif // BOOST_RANDOM_GAMMA_DISTRIBUTION_HPP
gamma_distribution.hpp
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