cart_comm.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 UTILS_MPI_CART_COMM_HPP
#define UTILS_MPI_CART_COMM_HPP
 
#include <utils/Vector.hpp>
 
#include <boost/mpi/communicator.hpp>
#include <boost/mpi/exception.hpp>
 
#include <mpi.h>
 
#include <cstddef>
#include <utility>
 
namespace Utils {
namespace Mpi {
 
/**
 * @brief Wrapper around MPI_Dims_create.
 *
 * @tparam dim Number of dimensions
 */
template <std::size_t dim> Vector<int, dim> dims_create(int nodes) {
  Vector<int, dim> dims{};
  BOOST_MPI_CHECK_RESULT(MPI_Dims_create,
                         (nodes, static_cast<int>(dim), dims.data()))
 
  return dims;
}
 
/**
 * @brief Wrapper around MPI_Cart_create.
 *
 * @tparam dim Number of dimensions
 */
template <std::size_t dim>
boost::mpi::communicator cart_create(
    boost::mpi::communicator const &comm, Vector<int, dim> const &dims,
    bool reorder = true,
    Vector<int, dim> const &periodicity = Vector<int, dim>::broadcast(1)) {
  MPI_Comm temp_comm;
  BOOST_MPI_CHECK_RESULT(MPI_Cart_create,
                         (comm, dim, dims.data(), periodicity.data(),
                          static_cast<int>(reorder), &temp_comm))
 
  return {temp_comm, boost::mpi::comm_take_ownership};
}
 
/**
 * @brief Wrapper around MPI_Cart_coords.
 *
 * @tparam dims Number of dimensions
 */
template <std::size_t dims>
Vector3i cart_coords(boost::mpi::communicator const &comm, int rank) {
  Vector3i pos;
  BOOST_MPI_CHECK_RESULT(MPI_Cart_coords, (comm, rank, dims, pos.data()))
  return pos;
}
 
/**
 * @brief Wrapper around MPI_Cart_rank.
 *
 * @tparam dims Number of dimensions
 */
template <std::size_t dims>
int cart_rank(boost::mpi::communicator const &comm,
              const Vector<int, dims> &pos) {
  int rank;
  BOOST_MPI_CHECK_RESULT(MPI_Cart_rank, (comm, pos.data(), &rank))
  return rank;
}
 
/**
 * @brief Wrapper around MPI_Cart_shift.
 *
 * @return pair of source and destination rank.
 */
inline std::pair<int, int> cart_shift(boost::mpi::communicator const &comm,
                                      int direction, int displacement) {
  int src = -1, dst = -1;
  BOOST_MPI_CHECK_RESULT(MPI_Cart_shift,
                         (comm, direction, displacement, &src, &dst))
 
  return {src, dst};
}
 
/**
 * @brief Calculates the numbers of the nearest neighbors for a node.
 *
 * @tparam dim Dimension of the communicator
 * @param comm Cartesian communicator
 *
 * @return Ranks of 2*dim neighbors
 */
template <std::size_t dim>
Utils::Vector<int, 2 * dim>
cart_neighbors(const boost::mpi::communicator &comm) {
 
  Vector<int, 2 * dim> ret;
 
  for (std::size_t i = 0; i < dim; i++) {
    ret[2 * i + 0] = std::get<1>(cart_shift(comm, static_cast<int>(i), -1));
    ret[2 * i + 1] = std::get<1>(cart_shift(comm, static_cast<int>(i), +1));
  }
 
  return ret;
}
 
/**
 * @brief Information about a cartesian communicator.
 *
 * Members correspond to the output arguments of
 * MPI_Cart_get.
 *
 * @tparam dim Number of dimensions.
 */
template <std::size_t dim> struct CartInfo {
  Utils::Vector<int, dim> dims;
  Utils::Vector<int, dim> periods;
  Utils::Vector<int, dim> coords;
};
 
/**
 * @brief Wrapper around MPI_Cart_get.
 *
 * @tparam dim Number of dimensions.
 * @param comm Communicator with cartesian topology.
 *
 * @return Struct with information about the communicator.
 */
template <std::size_t dim>
CartInfo<dim> cart_get(const boost::mpi::communicator &comm) {
  CartInfo<dim> ret{};
 
  BOOST_MPI_CHECK_RESULT(MPI_Cart_get, (comm, dim, ret.dims.data(),
                                        ret.periods.data(), ret.coords.data()));
 
  return ret;
}
 
} // namespace Mpi
} // namespace Utils
 
#endif