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 |
268 | |