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
28namespace boost {
29namespace 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 */
46template<class IntType = int, class RealType = double>
47class geometric_distribution
48{
49public:
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
200private:
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 */
225template<class IntType = int, class RealType = double>
226class geometric_distribution
227{
228public:
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
258private:
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