source: NonGTP/Boost/boost/random/binomial_distribution.hpp @ 857

Revision 857, 2.2 KB checked in by igarcia, 19 years ago (diff)
RevLine 
[857]1/* boost random/binomial_distribution.hpp header file
2 *
3 * Copyright Jens Maurer 2002
4 * Distributed under the Boost Software License, Version 1.0. (See
5 * accompanying file LICENSE_1_0.txt or copy at
6 * http://www.boost.org/LICENSE_1_0.txt)
7 *
8 * See http://www.boost.org for most recent version including documentation.
9 *
10 * $Id: binomial_distribution.hpp,v 1.10 2005/06/24 22:13:43 jmaurer Exp $
11 *
12 */
13
14#ifndef BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
15#define BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
16
17#include <cmath>
18#include <cassert>
19#include <boost/random/bernoulli_distribution.hpp>
20
21namespace boost {
22
23// Knuth
24template<class IntType = int, class RealType = double>
25class binomial_distribution
26{
27public:
28  typedef typename bernoulli_distribution<RealType>::input_type input_type;
29  typedef IntType result_type;
30
31  explicit binomial_distribution(IntType t = 1,
32                                 const RealType& p = RealType(0.5))
33    : _bernoulli(p), _t(t)
34  {
35    assert(t >= 0);
36    assert(RealType(0) <= 0 && p <= RealType(1));
37  }
38
39  // compiler-generated copy ctor and assignment operator are fine
40
41  IntType t() const { return _t; }
42  RealType p() const { return _bernoulli.p(); }
43  void reset() { }
44
45  template<class Engine>
46  result_type operator()(Engine& eng)
47  {
48    // TODO: This is O(_t), but it should be O(log(_t)) for large _t
49    result_type n = 0;
50    for(IntType i = 0; i < _t; ++i)
51      if(_bernoulli(eng))
52        ++n;
53    return n;
54  }
55
56#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
57  template<class CharT, class Traits>
58  friend std::basic_ostream<CharT,Traits>&
59  operator<<(std::basic_ostream<CharT,Traits>& os, const binomial_distribution& bd)
60  {
61    os << bd._bernoulli << " " << bd._t;
62    return os;
63  }
64
65  template<class CharT, class Traits>
66  friend std::basic_istream<CharT,Traits>&
67  operator>>(std::basic_istream<CharT,Traits>& is, binomial_distribution& bd)
68  {
69    is >> std::ws >> bd._bernoulli >> std::ws >> bd._t;
70    return is;
71  }
72#endif
73
74private:
75  bernoulli_distribution<RealType> _bernoulli;
76  IntType _t;
77};
78
79} // namespace boost
80
81#endif // BOOST_RANDOM_BINOMIAL_DISTRIBUTION_HPP
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