Method create_sub_index_map

cpp/dolfinx/common/IndexMap.cpp:815–853

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}
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std::pair<IndexMap, std::vector<std::int32_t>>
common::create_sub_index_map(const IndexMap& imap,
                             std::span<const std::int32_t> indices,
                             IndexMapOrder order, bool allow_owner_change)
{
  // Compute the owned, ghost, and ghost owners of submap indices.
  // NOTE: All indices are local and numbered w.r.t. the original (imap)
  // index map
  auto [submap_owned, submap_ghost, submap_ghost_owners, submap_src,
        submap_dest]
      = compute_submap_indices(imap, indices, order, allow_owner_change);

  // Compute submap offset for this rank
  std::int64_t submap_local_size = submap_owned.size();
  std::int64_t submap_offset = 0;
  int ierr = MPI_Exscan(&submap_local_size, &submap_offset, 1, MPI_INT64_T,
                        MPI_SUM, imap.comm());
  dolfinx::MPI::check_error(imap.comm(), ierr);

  // Compute the global indices (w.r.t. the submap) of the submap ghosts
  std::vector<std::int64_t> submap_ghost_global(submap_ghost.size());
  imap.local_to_global(submap_ghost, submap_ghost_global);
  std::vector<std::int64_t> submap_ghost_gidxs = compute_submap_ghost_indices(
      submap_src, submap_dest, submap_owned, submap_ghost_global,
      submap_ghost_owners, submap_offset, imap);

  // Create a map from (local) indices in the submap to the corresponding
  // (local) index in the original map
  std::vector<std::int32_t> sub_imap_to_imap;
  sub_imap_to_imap.reserve(submap_owned.size() + submap_ghost.size());
  sub_imap_to_imap.insert(sub_imap_to_imap.end(), submap_owned.begin(),
                          submap_owned.end());
  sub_imap_to_imap.insert(sub_imap_to_imap.end(), submap_ghost.begin(),
                          submap_ghost.end());

  return {IndexMap(imap.comm(), submap_local_size, {submap_src, submap_dest},
                   submap_ghost_gidxs, submap_ghost_owners),
          std::move(sub_imap_to_imap)};
}
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IndexMap::IndexMap(MPI_Comm comm, std::int32_t local_size) : _comm(comm, true)