CylindricalVelocityProfile.hpp

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/*
 * Copyright (C) 2010-2026 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/>.
 */
 
#pragma once
 
#include "BoxGeometry.hpp"
#include "CylindricalPidProfileObservable.hpp"
#include "system/System.hpp"
#include "utils_histogram.hpp"
 
#include <utils/Histogram.hpp>
#include <utils/math/coordinate_transformation.hpp>
 
#include <cstddef>
#include <vector>
 
namespace Observables {
class CylindricalVelocityProfile : public CylindricalPidProfileObservable {
public:
  using CylindricalPidProfileObservable::CylindricalPidProfileObservable;
 
  std::vector<double>
  evaluate(boost::mpi::communicator const &comm,
           ParticleReferenceRange const &local_particles,
           const ParticleObservables::traits<Particle> &traits) const override {
    using pos_type = Utils::Vector3d;
    using vel_type = Utils::Vector3d;
    auto const &box_geo = *System::get_system().box_geo;
 
    std::vector<pos_type> local_folded_positions{};
    std::vector<vel_type> local_velocities{};
    local_folded_positions.reserve(local_particles.size());
    local_velocities.reserve(local_particles.size());
 
    for (auto const &p : local_particles) {
      auto const pos = box_geo.folded_position(traits.position(p)) -
                       transform_params->center();
      local_folded_positions.emplace_back(
          Utils::transform_coordinate_cartesian_to_cylinder(
              pos, transform_params->axis(), transform_params->orientation()));
      local_velocities.emplace_back(
          Utils::transform_vector_cartesian_to_cylinder(
              traits.velocity(p), transform_params->axis(), pos));
    }
 
    auto const [global_folded_positions, global_velocities] =
        detail::gather(comm, local_folded_positions, local_velocities);
 
    if (comm.rank() != 0) {
      return {};
    }
 
    Utils::CylindricalHistogram<double, 3> histogram(n_bins(), limits());
    detail::accumulate(histogram, global_folded_positions, global_velocities);
    return detail::normalize_by_bin_size(histogram);
  }
 
  std::vector<std::size_t> shape() const override {
    auto const b = n_bins();
    return {b[0], b[1], b[2], 3};
  }
};
 
} // Namespace Observables