/usr/include/boost/random/poisson_distribution.hpp is in libboost1.46-dev 1.46.1-7ubuntu3.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 | /* boost random/poisson_distribution.hpp header file
*
* Copyright Jens Maurer 2002
* Distributed under the Boost Software License, Version 1.0. (See
* accompanying file LICENSE_1_0.txt or copy at
* http://www.boost.org/LICENSE_1_0.txt)
*
* See http://www.boost.org for most recent version including documentation.
*
* $Id: poisson_distribution.hpp 60755 2010-03-22 00:45:06Z steven_watanabe $
*
*/
#ifndef BOOST_RANDOM_POISSON_DISTRIBUTION_HPP
#define BOOST_RANDOM_POISSON_DISTRIBUTION_HPP
#include <boost/config/no_tr1/cmath.hpp>
#include <cassert>
#include <iostream>
#include <boost/limits.hpp>
#include <boost/static_assert.hpp>
#include <boost/random/detail/config.hpp>
namespace boost {
// Knuth
/**
* An instantiation of the class template @c poisson_distribution is a
* model of \random_distribution. The poisson distribution has
* \f$p(i) = \frac{e^{-\lambda}\lambda^i}{i!}\f$
*/
template<class IntType = int, class RealType = double>
class poisson_distribution
{
public:
typedef RealType input_type;
typedef IntType result_type;
/**
* Constructs a @c poisson_distribution with the parameter @c mean.
*
* Requires: mean > 0
*/
explicit poisson_distribution(const RealType& mean_arg = RealType(1))
: _mean(mean_arg)
{
#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
// MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope
BOOST_STATIC_ASSERT(std::numeric_limits<IntType>::is_integer);
BOOST_STATIC_ASSERT(!std::numeric_limits<RealType>::is_integer);
#endif
assert(_mean > RealType(0));
init();
}
// compiler-generated copy ctor and assignment operator are fine
/**
* Returns: the "mean" parameter of the distribution.
*/
RealType mean() const { return _mean; }
void reset() { }
template<class Engine>
result_type operator()(Engine& eng)
{
// TODO: This is O(_mean), but it should be O(log(_mean)) for large _mean
RealType product = RealType(1);
for(result_type m = 0; ; ++m) {
product *= eng();
if(product <= _exp_mean)
return m;
}
}
#ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
template<class CharT, class Traits>
friend std::basic_ostream<CharT,Traits>&
operator<<(std::basic_ostream<CharT,Traits>& os, const poisson_distribution& pd)
{
os << pd._mean;
return os;
}
template<class CharT, class Traits>
friend std::basic_istream<CharT,Traits>&
operator>>(std::basic_istream<CharT,Traits>& is, poisson_distribution& pd)
{
is >> std::ws >> pd._mean;
pd.init();
return is;
}
#endif
private:
/// \cond hide_private_members
void init()
{
#ifndef BOOST_NO_STDC_NAMESPACE
// allow for Koenig lookup
using std::exp;
#endif
_exp_mean = exp(-_mean);
}
/// \endcond
RealType _mean;
// some precomputed data from the parameters
RealType _exp_mean;
};
} // namespace boost
#endif // BOOST_RANDOM_POISSON_DISTRIBUTION_HPP
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