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// Copyright (C) 2022 Jorgen S. Dokken
//
// This file is part of DOLFINX_MPC
//
// SPDX-License-Identifier: MIT
#include "mpi_utils.h"
MPI_Comm
dolfinx_mpc::create_owner_to_ghost_comm(const dolfinx::common::IndexMap& map)
{
// Get source (owner of ghosts) and destination (processes that
// ghost an owned index) ranks
std::span<const int> src_ranks = map.src();
std::span<const int> dest_ranks = map.dest();
// Check that src and dest ranks are unique and sorted
assert(std::ranges::is_sorted(src_ranks));
assert(std::ranges::is_sorted(dest_ranks));
// Create communicators with directed edges owner -> ghost,
MPI_Comm comm;
MPI_Dist_graph_create_adjacent(map.comm(), (int)src_ranks.size(),
src_ranks.data(), MPI_UNWEIGHTED,
(int)dest_ranks.size(), dest_ranks.data(),
MPI_UNWEIGHTED, MPI_INFO_NULL, false, &comm);
return comm;
}
//-------------------------------------------------------------------------------
std::pair<std::vector<int>, std::vector<int>>
dolfinx_mpc::compute_neighborhood(const MPI_Comm& comm)
{
int status;
MPI_Topo_test(comm, &status);
assert(status != MPI_UNDEFINED);
// Get list of neighbors
int indegree(-1);
int outdegree(-2);
int weighted(-1);
MPI_Dist_graph_neighbors_count(comm, &indegree, &outdegree, &weighted);
std::vector<int> src_ranks(indegree);
std::vector<int> dest_ranks(outdegree);
MPI_Dist_graph_neighbors(comm, indegree, src_ranks.data(), MPI_UNWEIGHTED,
outdegree, dest_ranks.data(), MPI_UNWEIGHTED);
return {src_ranks, dest_ranks};
}
//-------------------------------------------------------------------------------
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