algorithms.hpp

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/*
 * Copyright (C) 2010-2022 The ESPResSo project
 *
 * This file is part of ESPResSo.
 *
 * ESPResSo is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ESPResSo is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef SRC_PARTICLE_OBSERVABLES_ALGORITHMS_HPP
#define SRC_PARTICLE_OBSERVABLES_ALGORITHMS_HPP
 
/**
 * @file
 *
 * Generic algorithms for the calculation of particle
 * property derived observables.
 */
 
#include <algorithm>
#include <numeric>
#include <utility>
#include <vector>
 
namespace ParticleObservables {
namespace detail {
struct One {
  template <class Particle> auto operator()(Particle const &p) const {
    return 1;
  }
};
 
template <class ValueOp, class WeightOp> struct WeightedSum {
  template <class ParticleRange>
  auto operator()(ParticleRange const &particles) const {
    using particle_type = typename ParticleRange::value_type;
    using value_op_type = decltype(ValueOp{}(std::declval<particle_type>()));
    using weight_op_type = decltype(WeightOp{}(std::declval<particle_type>()));
    auto func = [](auto const &sum, auto const &p) {
      auto const w = WeightOp{}(p);
      return std::make_pair(sum.first + ValueOp{}(p)*w, sum.second + w);
    };
 
    return std::accumulate(std::begin(particles), std::end(particles),
                           std::pair<value_op_type, weight_op_type>(), func);
  }
};
} // namespace detail
 
template <class ValueOp, class WeightOp> struct WeightedSum {
  template <class ParticleRange>
  auto operator()(ParticleRange const &particles) const {
    auto const ws = detail::WeightedSum<ValueOp, WeightOp>()(particles);
 
    return std::make_pair(ws.first, ws.second);
  }
 
  template <typename T> auto operator()(T const &acc, T const &val) const {
    return std::make_pair(acc.first + val.first, acc.second + val.second);
  }
};
 
template <class ValueOp> struct Sum {
  template <class ParticleRange>
  auto operator()(ParticleRange const &particles) const {
    return std::make_pair(
        detail::WeightedSum<ValueOp, detail::One>()(particles).first, 0.0);
  }
 
  template <typename T> auto operator()(T const &acc, T const &val) const {
    return WeightedSum<ValueOp, detail::One>{}.operator()(acc, val);
  }
};
 
template <class ValueOp, class WeightOp> struct WeightedAverage {
  template <class ParticleRange>
  auto operator()(ParticleRange const &particles) const {
    auto const ws = detail::WeightedSum<ValueOp, WeightOp>()(particles);
    return std::make_pair((ws.second) ? ws.first / ws.second : ws.first,
                          ws.second);
  }
 
  template <typename T> auto operator()(T const &acc, T const &val) const {
    auto const value = acc.first * acc.second + val.first * val.second;
    auto const weight = acc.second + val.second;
    return std::make_pair((weight) ? value / weight : value, weight);
  }
};
 
template <class ValueOp> struct Average {
  template <class ParticleRange>
  auto operator()(ParticleRange const &particles) const {
    return WeightedAverage<ValueOp, detail::One>()(particles);
  }
 
  template <typename T> auto operator()(T const &acc, T const &val) const {
    return WeightedAverage<ValueOp, detail::One>{}.operator()(acc, val);
  }
};
 
template <class ValueOp> struct Map {
  template <class ParticleRange>
  auto operator()(ParticleRange const &particles) const {
    using particle_type = typename ParticleRange::value_type;
    using value_op_type = decltype(ValueOp{}(std::declval<particle_type>()));
    std::vector<value_op_type> res;
    std::transform(std::begin(particles), std::end(particles),
                   std::back_inserter(res),
                   [](auto const &p) { return ValueOp{}(p); });
    return res;
  }
};
} // namespace ParticleObservables
#endif // SRC_PARTICLE_OBSERVABLES_ALGORITHMS_HPP