boost/histogram/accumulators/mean.hpp
// Copyright 2015-2018 Hans Dembinski
//
// 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_HISTOGRAM_ACCUMULATORS_MEAN_HPP
#define BOOST_HISTOGRAM_ACCUMULATORS_MEAN_HPP
#include <boost/assert.hpp>
#include <boost/core/nvp.hpp>
#include <boost/histogram/fwd.hpp> // for mean<>
#include <boost/throw_exception.hpp>
#include <stdexcept>
#include <type_traits>
namespace boost {
namespace histogram {
namespace accumulators {
/** Calculates mean and variance of sample.
Uses Welfords's incremental algorithm to improve the numerical
stability of mean and variance computation.
*/
template <class RealType>
class mean {
public:
mean() = default;
mean(const RealType& n, const RealType& mean, const RealType& variance) noexcept
: sum_(n), mean_(mean), sum_of_deltas_squared_(variance * (n - 1)) {}
void operator()(const RealType& x) noexcept {
sum_ += static_cast<RealType>(1);
const auto delta = x - mean_;
mean_ += delta / sum_;
sum_of_deltas_squared_ += delta * (x - mean_);
}
void operator()(const weight_type<RealType>& w, const RealType& x) noexcept {
sum_ += w.value;
const auto delta = x - mean_;
mean_ += w.value * delta / sum_;
sum_of_deltas_squared_ += w.value * delta * (x - mean_);
}
template <class T>
mean& operator+=(const mean<T>& rhs) noexcept {
if (sum_ != 0 || rhs.sum_ != 0) {
const auto tmp = mean_ * sum_ + static_cast<RealType>(rhs.mean_ * rhs.sum_);
sum_ += rhs.sum_;
mean_ = tmp / sum_;
}
sum_of_deltas_squared_ += static_cast<RealType>(rhs.sum_of_deltas_squared_);
return *this;
}
mean& operator*=(const RealType& s) noexcept {
mean_ *= s;
sum_of_deltas_squared_ *= s * s;
return *this;
}
template <class T>
bool operator==(const mean<T>& rhs) const noexcept {
return sum_ == rhs.sum_ && mean_ == rhs.mean_ &&
sum_of_deltas_squared_ == rhs.sum_of_deltas_squared_;
}
template <class T>
bool operator!=(const mean<T>& rhs) const noexcept {
return !operator==(rhs);
}
const RealType& count() const noexcept { return sum_; }
const RealType& value() const noexcept { return mean_; }
RealType variance() const noexcept { return sum_of_deltas_squared_ / (sum_ - 1); }
template <class Archive>
void serialize(Archive& ar, unsigned version) {
if (version == 0) {
// read only
std::size_t sum;
ar& make_nvp("sum", sum);
sum_ = static_cast<RealType>(sum);
} else {
ar& make_nvp("sum", sum_);
}
ar& make_nvp("mean", mean_);
ar& make_nvp("sum_of_deltas_squared", sum_of_deltas_squared_);
}
private:
RealType sum_ = 0, mean_ = 0, sum_of_deltas_squared_ = 0;
};
} // namespace accumulators
} // namespace histogram
} // namespace boost
#ifndef BOOST_HISTOGRAM_DOXYGEN_INVOKED
namespace boost {
namespace serialization {
template <class T>
struct version;
// version 1 for boost::histogram::accumulators::mean<RealType>
template <class RealType>
struct version<boost::histogram::accumulators::mean<RealType>>
: std::integral_constant<int, 1> {};
} // namespace serialization
} // namespace boost
namespace std {
template <class T, class U>
/// Specialization for boost::histogram::accumulators::mean.
struct common_type<boost::histogram::accumulators::mean<T>,
boost::histogram::accumulators::mean<U>> {
using type = boost::histogram::accumulators::mean<common_type_t<T, U>>;
};
} // namespace std
#endif
#endif