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///////////////////////////////////////////////////////////////////////////////
// moment.hpp
//
// Copyright 2005 Eric Niebler. 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)
#ifndef BOOST_ACCUMULATORS_STATISTICS_MOMENT_HPP_EAN_15_11_2005
#define BOOST_ACCUMULATORS_STATISTICS_MOMENT_HPP_EAN_15_11_2005
#include <boost/config/no_tr1/cmath.hpp>
#include <boost/mpl/int.hpp>
#include <boost/mpl/assert.hpp>
#include <boost/mpl/placeholders.hpp>
#include <boost/accumulators/framework/accumulator_base.hpp>
#include <boost/accumulators/framework/extractor.hpp>
#include <boost/accumulators/numeric/functional.hpp>
#include <boost/accumulators/framework/parameters/sample.hpp>
#include <boost/accumulators/framework/depends_on.hpp>
#include <boost/accumulators/statistics_fwd.hpp>
#include <boost/accumulators/statistics/count.hpp>
namespace boost { namespace numeric
{
/// INTERNAL ONLY
///
template<typename T>
T const &pow(T const &x, mpl::int_<1>)
{
return x;
}
/// INTERNAL ONLY
///
template<typename T, int N>
T pow(T const &x, mpl::int_<N>)
{
using namespace operators;
T y = numeric::pow(x, mpl::int_<N/2>());
T z = y * y;
return (N % 2) ? (z * x) : z;
}
}}
namespace boost { namespace accumulators
{
namespace impl
{
///////////////////////////////////////////////////////////////////////////////
// moment_impl
template<typename N, typename Sample>
struct moment_impl
: accumulator_base // TODO: also depends_on sum of powers
{
BOOST_MPL_ASSERT_RELATION(N::value, >, 0);
// for boost::result_of
typedef typename numeric::functional::fdiv<Sample, std::size_t>::result_type result_type;
template<typename Args>
moment_impl(Args const &args)
: sum(args[sample | Sample()])
{
}
template<typename Args>
void operator ()(Args const &args)
{
this->sum += numeric::pow(args[sample], N());
}
template<typename Args>
result_type result(Args const &args) const
{
return numeric::fdiv(this->sum, count(args));
}
private:
Sample sum;
};
} // namespace impl
///////////////////////////////////////////////////////////////////////////////
// tag::moment
//
namespace tag
{
template<int N>
struct moment
: depends_on<count>
{
/// INTERNAL ONLY
///
typedef accumulators::impl::moment_impl<mpl::int_<N>, mpl::_1> impl;
};
}
///////////////////////////////////////////////////////////////////////////////
// extract::moment
//
namespace extract
{
BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, moment, (int))
}
using extract::moment;
// So that moment<N> can be automatically substituted with
// weighted_moment<N> when the weight parameter is non-void
template<int N>
struct as_weighted_feature<tag::moment<N> >
{
typedef tag::weighted_moment<N> type;
};
template<int N>
struct feature_of<tag::weighted_moment<N> >
: feature_of<tag::moment<N> >
{
};
}} // namespace boost::accumulators
#endif
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