268 lines
7.4 KiB
C++
268 lines
7.4 KiB
C++
/* boost random/geometric_distribution.hpp header file
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*
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* Copyright Jens Maurer 2000-2001
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* Copyright Steven Watanabe 2011
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* Distributed under the Boost Software License, Version 1.0. (See
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* accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org for most recent version including documentation.
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*
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* $Id$
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*
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* Revision history
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* 2001-02-18 moved to individual header files
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*/
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#ifndef BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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#define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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#include <boost/config/no_tr1/cmath.hpp> // std::log
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#include <iosfwd>
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#include <ios>
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#include <boost/assert.hpp>
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#include <boost/random/detail/config.hpp>
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#include <boost/random/detail/operators.hpp>
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#include <boost/random/uniform_01.hpp>
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namespace boost {
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namespace random {
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/**
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* An instantiation of the class template @c geometric_distribution models
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* a \random_distribution. The distribution produces positive
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* integers which are the number of bernoulli trials
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* with probability @c p required to get one that fails.
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*
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* For the geometric distribution, \f$p(i) = p(1-p)^{i}\f$.
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*
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* @xmlwarning
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* This distribution has been updated to match the C++ standard.
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* Its behavior has changed from the original
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* boost::geometric_distribution. A backwards compatible
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* wrapper is provided in namespace boost.
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* @endxmlwarning
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*/
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template<class IntType = int, class RealType = double>
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class geometric_distribution
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{
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public:
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typedef RealType input_type;
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typedef IntType result_type;
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class param_type
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{
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public:
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typedef geometric_distribution distribution_type;
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/** Constructs the parameters with p. */
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explicit param_type(RealType p_arg = RealType(0.5))
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: _p(p_arg)
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{
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BOOST_ASSERT(RealType(0) < _p && _p < RealType(1));
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}
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/** Returns the p parameter of the distribution. */
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RealType p() const { return _p; }
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/** Writes the parameters to a std::ostream. */
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BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, param_type, parm)
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{
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os << parm._p;
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return os;
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}
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/** Reads the parameters from a std::istream. */
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BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, param_type, parm)
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{
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double p_in;
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if(is >> p_in) {
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if(p_in > RealType(0) && p_in < RealType(1)) {
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parm._p = p_in;
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} else {
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is.setstate(std::ios_base::failbit);
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}
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}
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return is;
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}
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/** Returns true if the two sets of parameters are equal. */
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BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(param_type, lhs, rhs)
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{ return lhs._p == rhs._p; }
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/** Returns true if the two sets of parameters are different. */
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BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(param_type)
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private:
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RealType _p;
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};
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/**
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* Contructs a new geometric_distribution with the paramter @c p.
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*
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* Requires: 0 < p < 1
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*/
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explicit geometric_distribution(const RealType& p_arg = RealType(0.5))
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: _p(p_arg)
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{
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BOOST_ASSERT(RealType(0) < _p && _p < RealType(1));
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init();
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}
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/** Constructs a new geometric_distribution from its parameters. */
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explicit geometric_distribution(const param_type& parm)
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: _p(parm.p())
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{
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init();
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}
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// compiler-generated copy ctor and assignment operator are fine
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/** Returns: the distribution parameter @c p */
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RealType p() const { return _p; }
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/** Returns the smallest value that the distribution can produce. */
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IntType min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return IntType(0); }
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/** Returns the largest value that the distribution can produce. */
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IntType max BOOST_PREVENT_MACRO_SUBSTITUTION () const
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{ return (std::numeric_limits<IntType>::max)(); }
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/** Returns the parameters of the distribution. */
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param_type param() const { return param_type(_p); }
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/** Sets the parameters of the distribution. */
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void param(const param_type& parm)
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{
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_p = parm.p();
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init();
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}
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/**
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* Effects: Subsequent uses of the distribution do not depend
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* on values produced by any engine prior to invoking reset.
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*/
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void reset() { }
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/**
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* Returns a random variate distributed according to the
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* geometric_distribution.
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*/
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template<class Engine>
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result_type operator()(Engine& eng) const
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{
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using std::log;
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using std::floor;
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RealType x = RealType(1) - boost::uniform_01<RealType>()(eng);
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return IntType(floor(log(x) / _log_1mp));
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}
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/**
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* Returns a random variate distributed according to the
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* geometric distribution with parameters specified by param.
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*/
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template<class Engine>
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result_type operator()(Engine& eng, const param_type& parm) const
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{ return geometric_distribution(parm)(eng); }
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/** Writes the distribution to a @c std::ostream. */
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BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, geometric_distribution, gd)
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{
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os << gd._p;
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return os;
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}
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/** Reads the distribution from a @c std::istream. */
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BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, geometric_distribution, gd)
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{
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param_type parm;
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if(is >> parm) {
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gd.param(parm);
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}
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return is;
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}
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/**
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* Returns true if the two distributions will produce identical
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* sequences of values given equal generators.
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*/
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BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(geometric_distribution, lhs, rhs)
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{ return lhs._p == rhs._p; }
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/**
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* Returns true if the two distributions may produce different
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* sequences of values given equal generators.
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*/
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BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(geometric_distribution)
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private:
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/// \cond show_private
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void init()
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{
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using std::log;
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_log_1mp = log(1 - _p);
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}
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RealType _p;
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RealType _log_1mp;
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/// \endcond
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};
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} // namespace random
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/// \cond show_deprecated
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/**
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* Provided for backwards compatibility. This class is
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* deprecated. It provides the old behavior of geometric_distribution
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* with \f$p(i) = (1-p) p^{i-1}\f$.
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*/
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template<class IntType = int, class RealType = double>
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class geometric_distribution
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{
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public:
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typedef RealType input_type;
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typedef IntType result_type;
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explicit geometric_distribution(RealType p_arg = RealType(0.5))
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: _impl(1 - p_arg) {}
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RealType p() const { return 1 - _impl.p(); }
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void reset() {}
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template<class Engine>
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IntType operator()(Engine& eng) const { return _impl(eng) + IntType(1); }
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BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, geometric_distribution, gd)
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{
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os << gd.p();
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return os;
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}
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BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, geometric_distribution, gd)
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{
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RealType val;
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if(is >> val) {
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typename impl_type::param_type impl_param(1 - val);
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gd._impl.param(impl_param);
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}
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return is;
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}
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private:
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typedef random::geometric_distribution<IntType, RealType> impl_type;
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impl_type _impl;
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};
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/// \endcond
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} // namespace boost
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#endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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