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1 | /* boost random/geometric_distribution.hpp header file |
2 | * | |
3 | * Copyright Jens Maurer 2000-2001 | |
4 | * Copyright Steven Watanabe 2011 | |
5 | * Distributed under the Boost Software License, Version 1.0. (See | |
6 | * accompanying file LICENSE_1_0.txt or copy at | |
7 | * http://www.boost.org/LICENSE_1_0.txt) | |
8 | * | |
9 | * See http://www.boost.org for most recent version including documentation. | |
10 | * | |
11 | * $Id$ | |
12 | * | |
13 | * Revision history | |
14 | * 2001-02-18 moved to individual header files | |
15 | */ | |
16 | ||
17 | #ifndef BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP | |
18 | #define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP | |
19 | ||
20 | #include <boost/config/no_tr1/cmath.hpp> // std::log | |
21 | #include <iosfwd> | |
22 | #include <ios> | |
23 | #include <boost/assert.hpp> | |
24 | #include <boost/random/detail/config.hpp> | |
25 | #include <boost/random/detail/operators.hpp> | |
26 | #include <boost/random/uniform_01.hpp> | |
27 | ||
28 | namespace boost { | |
29 | namespace random { | |
30 | ||
31 | /** | |
32 | * An instantiation of the class template @c geometric_distribution models | |
33 | * a \random_distribution. The distribution produces positive | |
34 | * integers which are the number of bernoulli trials | |
35 | * with probability @c p required to get one that fails. | |
36 | * | |
37 | * For the geometric distribution, \f$p(i) = p(1-p)^{i}\f$. | |
38 | * | |
39 | * @xmlwarning | |
40 | * This distribution has been updated to match the C++ standard. | |
41 | * Its behavior has changed from the original | |
42 | * boost::geometric_distribution. A backwards compatible | |
43 | * wrapper is provided in namespace boost. | |
44 | * @endxmlwarning | |
45 | */ | |
46 | template<class IntType = int, class RealType = double> | |
47 | class geometric_distribution | |
48 | { | |
49 | public: | |
50 | typedef RealType input_type; | |
51 | typedef IntType result_type; | |
52 | ||
53 | class param_type | |
54 | { | |
55 | public: | |
56 | ||
57 | typedef geometric_distribution distribution_type; | |
58 | ||
59 | /** Constructs the parameters with p. */ | |
60 | explicit param_type(RealType p_arg = RealType(0.5)) | |
61 | : _p(p_arg) | |
62 | { | |
63 | BOOST_ASSERT(RealType(0) < _p && _p < RealType(1)); | |
64 | } | |
65 | ||
66 | /** Returns the p parameter of the distribution. */ | |
67 | RealType p() const { return _p; } | |
68 | ||
69 | /** Writes the parameters to a std::ostream. */ | |
70 | BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, param_type, parm) | |
71 | { | |
72 | os << parm._p; | |
73 | return os; | |
74 | } | |
75 | ||
76 | /** Reads the parameters from a std::istream. */ | |
77 | BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, param_type, parm) | |
78 | { | |
79 | double p_in; | |
80 | if(is >> p_in) { | |
81 | if(p_in > RealType(0) && p_in < RealType(1)) { | |
82 | parm._p = p_in; | |
83 | } else { | |
84 | is.setstate(std::ios_base::failbit); | |
85 | } | |
86 | } | |
87 | return is; | |
88 | } | |
89 | ||
90 | /** Returns true if the two sets of parameters are equal. */ | |
91 | BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(param_type, lhs, rhs) | |
92 | { return lhs._p == rhs._p; } | |
93 | ||
94 | /** Returns true if the two sets of parameters are different. */ | |
95 | BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(param_type) | |
96 | ||
97 | ||
98 | private: | |
99 | RealType _p; | |
100 | }; | |
101 | ||
102 | /** | |
103 | * Contructs a new geometric_distribution with the paramter @c p. | |
104 | * | |
105 | * Requires: 0 < p < 1 | |
106 | */ | |
107 | explicit geometric_distribution(const RealType& p_arg = RealType(0.5)) | |
108 | : _p(p_arg) | |
109 | { | |
110 | BOOST_ASSERT(RealType(0) < _p && _p < RealType(1)); | |
111 | init(); | |
112 | } | |
113 | ||
114 | /** Constructs a new geometric_distribution from its parameters. */ | |
115 | explicit geometric_distribution(const param_type& parm) | |
116 | : _p(parm.p()) | |
117 | { | |
118 | init(); | |
119 | } | |
120 | ||
121 | // compiler-generated copy ctor and assignment operator are fine | |
122 | ||
123 | /** Returns: the distribution parameter @c p */ | |
124 | RealType p() const { return _p; } | |
125 | ||
126 | /** Returns the smallest value that the distribution can produce. */ | |
127 | IntType min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return IntType(0); } | |
128 | ||
129 | /** Returns the largest value that the distribution can produce. */ | |
130 | IntType max BOOST_PREVENT_MACRO_SUBSTITUTION () const | |
131 | { return (std::numeric_limits<IntType>::max)(); } | |
132 | ||
133 | /** Returns the parameters of the distribution. */ | |
134 | param_type param() const { return param_type(_p); } | |
135 | ||
136 | /** Sets the parameters of the distribution. */ | |
137 | void param(const param_type& parm) | |
138 | { | |
139 | _p = parm.p(); | |
140 | init(); | |
141 | } | |
142 | ||
143 | /** | |
144 | * Effects: Subsequent uses of the distribution do not depend | |
145 | * on values produced by any engine prior to invoking reset. | |
146 | */ | |
147 | void reset() { } | |
148 | ||
149 | /** | |
150 | * Returns a random variate distributed according to the | |
151 | * geometric_distribution. | |
152 | */ | |
153 | template<class Engine> | |
154 | result_type operator()(Engine& eng) const | |
155 | { | |
156 | using std::log; | |
157 | using std::floor; | |
158 | RealType x = RealType(1) - boost::uniform_01<RealType>()(eng); | |
159 | return IntType(floor(log(x) / _log_1mp)); | |
160 | } | |
161 | ||
162 | /** | |
163 | * Returns a random variate distributed according to the | |
164 | * geometric distribution with parameters specified by param. | |
165 | */ | |
166 | template<class Engine> | |
167 | result_type operator()(Engine& eng, const param_type& parm) const | |
168 | { return geometric_distribution(parm)(eng); } | |
169 | ||
170 | /** Writes the distribution to a @c std::ostream. */ | |
171 | BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, geometric_distribution, gd) | |
172 | { | |
173 | os << gd._p; | |
174 | return os; | |
175 | } | |
176 | ||
177 | /** Reads the distribution from a @c std::istream. */ | |
178 | BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, geometric_distribution, gd) | |
179 | { | |
180 | param_type parm; | |
181 | if(is >> parm) { | |
182 | gd.param(parm); | |
183 | } | |
184 | return is; | |
185 | } | |
186 | ||
187 | /** | |
188 | * Returns true if the two distributions will produce identical | |
189 | * sequences of values given equal generators. | |
190 | */ | |
191 | BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(geometric_distribution, lhs, rhs) | |
192 | { return lhs._p == rhs._p; } | |
193 | ||
194 | /** | |
195 | * Returns true if the two distributions may produce different | |
196 | * sequences of values given equal generators. | |
197 | */ | |
198 | BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(geometric_distribution) | |
199 | ||
200 | private: | |
201 | ||
202 | /// \cond show_private | |
203 | ||
204 | void init() | |
205 | { | |
206 | using std::log; | |
207 | _log_1mp = log(1 - _p); | |
208 | } | |
209 | ||
210 | RealType _p; | |
211 | RealType _log_1mp; | |
212 | ||
213 | /// \endcond | |
214 | }; | |
215 | ||
216 | } // namespace random | |
217 | ||
218 | /// \cond show_deprecated | |
219 | ||
220 | /** | |
221 | * Provided for backwards compatibility. This class is | |
222 | * deprecated. It provides the old behavior of geometric_distribution | |
223 | * with \f$p(i) = (1-p) p^{i-1}\f$. | |
224 | */ | |
225 | template<class IntType = int, class RealType = double> | |
226 | class geometric_distribution | |
227 | { | |
228 | public: | |
229 | typedef RealType input_type; | |
230 | typedef IntType result_type; | |
231 | ||
232 | explicit geometric_distribution(RealType p_arg = RealType(0.5)) | |
233 | : _impl(1 - p_arg) {} | |
234 | ||
235 | RealType p() const { return 1 - _impl.p(); } | |
236 | ||
237 | void reset() {} | |
238 | ||
239 | template<class Engine> | |
240 | IntType operator()(Engine& eng) const { return _impl(eng) + IntType(1); } | |
241 | ||
242 | BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, geometric_distribution, gd) | |
243 | { | |
244 | os << gd.p(); | |
245 | return os; | |
246 | } | |
247 | ||
248 | BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, geometric_distribution, gd) | |
249 | { | |
250 | RealType val; | |
251 | if(is >> val) { | |
252 | typename impl_type::param_type impl_param(1 - val); | |
253 | gd._impl.param(impl_param); | |
254 | } | |
255 | return is; | |
256 | } | |
257 | ||
258 | private: | |
259 | typedef random::geometric_distribution<IntType, RealType> impl_type; | |
260 | impl_type _impl; | |
261 | }; | |
262 | ||
263 | /// \endcond | |
264 | ||
265 | } // namespace boost | |
266 | ||
267 | #endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP |