sd_interface.cpp

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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/>.
 */
 
#include <config/config.hpp>
 
#ifdef ESPRESSO_STOKESIAN_DYNAMICS
 
#include "sd_interface.hpp"
 
#include "stokesian_dynamics/sd_cpu.hpp"
 
#include "BoxGeometry.hpp"
#include "Particle.hpp"
#include "communication.hpp"
#include "system/System.hpp"
#include "thermostat.hpp"
 
#include <utils/Vector.hpp>
#include <utils/mpi/gather_buffer.hpp>
#include <utils/mpi/scatter_buffer.hpp>
 
#include <boost/serialization/is_bitwise_serializable.hpp>
 
#include <algorithm>
#include <cmath>
#include <cstddef>
#include <iterator>
#include <stdexcept>
#include <string>
#include <utility>
#include <vector>
 
/* type for particle data transfer between nodes */
struct SD_particle_data {
  SD_particle_data() = default;
  explicit SD_particle_data(Particle const &p)
      : type(p.type()), pos(p.pos()), ext_force(p.force_and_torque()) {}
 
  int type = 0;
 
  /* particle position */
  Utils::Vector3d pos = {0., 0., 0.};
 
  /* external force */
  ParticleForce ext_force = {};
 
  template <class Archive> void serialize(Archive &ar, long int /* version */) {
    ar & type;
    ar & pos;
    ar & ext_force;
  }
};
 
BOOST_IS_BITWISE_SERIALIZABLE(SD_particle_data)
 
/** Update translational and rotational velocities of all particles. */
template <typename ParticleIterable>
static void sd_update_locally(ParticleIterable const &parts,
                              std::vector<double> const &v_sd) {
  std::size_t i = 0;
 
  // Even though on the head node, the v_sd vector is larger than
  // the (local) parts vector, this should still work. Because the local
  // particles correspond to the first 6*n entries in the head node's v_sd
  // (which holds the velocities of ALL particles).
 
  for (auto &p : parts) {
    // Copy velocities
    p.v()[0] = v_sd[6 * i + 0];
    p.v()[1] = v_sd[6 * i + 1];
    p.v()[2] = v_sd[6 * i + 2];
 
    p.omega()[0] = v_sd[6 * i + 3];
    p.omega()[1] = v_sd[6 * i + 4];
    p.omega()[2] = v_sd[6 * i + 5];
 
    ++i;
  }
}
 
StokesianDynamics::StokesianDynamics(double viscosity,
                                     std::unordered_map<int, double> radii,
                                     int flags)
    : viscosity{viscosity}, radii{radii}, flags{flags} {
  if (viscosity < 0.) {
    throw std::domain_error("Viscosity has an invalid value: " +
                            std::to_string(viscosity));
  }
  /* Check that radii are positive */
  for (auto const &[p_type, radius] : radii) {
    if (radius < 0.) {
      throw std::domain_error(
          "Particle radius for type " + std::to_string(p_type) +
          " has an invalid value: " + std::to_string(radius));
    }
  }
}
 
void StokesianDynamics::propagate_vel_pos(
    ParticleRangeStokesian const &particles,
    StokesianThermostat const &stokesian, double const time_step,
    double const kT) const {
 
  std::vector<SD_particle_data> parts_buffer{};
  parts_buffer.reserve(particles.size());
 
  for (auto const &p : particles) {
    parts_buffer.emplace_back(p);
  }
  Utils::Mpi::gather_buffer(parts_buffer, ::comm_cart, 0);
 
  /* Buffer that holds local particle data, and all particles on the head
   * node used for sending particle data to head node. */
  if (::comm_cart.rank() == 0) {
    std::size_t n_part = parts_buffer.size();
 
    x_host.resize(6 * n_part);
    f_host.resize(6 * n_part);
    a_host.resize(n_part);
 
    std::size_t i = 0;
    for (auto const &p : parts_buffer) {
      x_host[6 * i + 0] = p.pos[0];
      x_host[6 * i + 1] = p.pos[1];
      x_host[6 * i + 2] = p.pos[2];
      // Actual orientation is not needed, just need default.
      x_host[6 * i + 3] = 1;
      x_host[6 * i + 4] = 0;
      x_host[6 * i + 5] = 0;
 
      f_host[6 * i + 0] = p.ext_force.f[0];
      f_host[6 * i + 1] = p.ext_force.f[1];
      f_host[6 * i + 2] = p.ext_force.f[2];
 
      f_host[6 * i + 3] = p.ext_force.torque[0];
      f_host[6 * i + 4] = p.ext_force.torque[1];
      f_host[6 * i + 5] = p.ext_force.torque[2];
 
      a_host[i] = radii.at(p.type);
 
      ++i;
    }
 
    v_sd = sd_cpu(x_host, f_host, a_host, n_part, viscosity,
                  std::sqrt(kT / time_step),
                  static_cast<std::size_t>(stokesian.rng_counter()),
                  static_cast<std::size_t>(stokesian.rng_seed()), flags);
  } else { // if (this_node == 0)
    v_sd.resize(particles.size() * 6);
  } // if (this_node == 0) {...} else
 
  Utils::Mpi::scatter_buffer(
      v_sd.data(), static_cast<int>(particles.size() * 6), ::comm_cart, 0);
  sd_update_locally(particles, v_sd);
}
 
#endif // ESPRESSO_STOKESIAN_DYNAMICS