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

Revision 857, 2.2 KB checked in by igarcia, 19 years ago (diff)
RevLine 
[857]1/* boost random/exponential_distribution.hpp header file
2 *
3 * Copyright Jens Maurer 2000-2001
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: exponential_distribution.hpp,v 1.16 2004/07/27 03:43:32 dgregor Exp $
11 *
12 * Revision history
13 *  2001-02-18  moved to individual header files
14 */
15
16#ifndef BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP
17#define BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP
18
19#include <cmath>
20#include <cassert>
21#include <iostream>
22#include <boost/limits.hpp>
23#include <boost/static_assert.hpp>
24
25namespace boost {
26
27// exponential distribution: p(x) = lambda * exp(-lambda * x)
28template<class RealType = double>
29class exponential_distribution
30{
31public:
32  typedef RealType input_type;
33  typedef RealType result_type;
34
35#if !defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) && !(defined(BOOST_MSVC) && BOOST_MSVC <= 1300)
36  BOOST_STATIC_ASSERT(!std::numeric_limits<RealType>::is_integer);
37#endif
38
39  explicit exponential_distribution(result_type lambda = result_type(1))
40    : _lambda(lambda) { assert(lambda > result_type(0)); }
41
42  // compiler-generated copy ctor and assignment operator are fine
43
44  result_type lambda() const { return _lambda; }
45
46  void reset() { }
47
48  template<class Engine>
49  result_type operator()(Engine& eng)
50  {
51#ifndef BOOST_NO_STDC_NAMESPACE
52    using std::log;
53#endif
54    return -result_type(1) / _lambda * log(result_type(1)-eng());
55  }
56
57#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
58  template<class CharT, class Traits>
59  friend std::basic_ostream<CharT,Traits>&
60  operator<<(std::basic_ostream<CharT,Traits>& os, const exponential_distribution& ed)
61  {
62    os << ed._lambda;
63    return os;
64  }
65
66  template<class CharT, class Traits>
67  friend std::basic_istream<CharT,Traits>&
68  operator>>(std::basic_istream<CharT,Traits>& is, exponential_distribution& ed)
69  {
70    is >> std::ws >> ed._lambda;
71    return is;
72  }
73#endif
74
75private:
76  result_type _lambda;
77};
78
79} // namespace boost
80
81#endif // BOOST_RANDOM_EXPONENTIAL_DISTRIBUTION_HPP
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