Пример #1
0
void UnstructuredMesh::find_neighbors (const bool reset_remote_elements,
                                       const bool reset_current_list)
{
  // We might actually want to run this on an empty mesh
  // (e.g. the boundary mesh for a nonexistant bcid!)
  // libmesh_assert_not_equal_to (this->n_nodes(), 0);
  // libmesh_assert_not_equal_to (this->n_elem(), 0);

  // This function must be run on all processors at once
  parallel_object_only();

  LOG_SCOPE("find_neighbors()", "Mesh");

  const element_iterator el_end = this->elements_end();

  //TODO:[BSK] This should be removed later?!
  if (reset_current_list)
    for (element_iterator el = this->elements_begin(); el != el_end; ++el)
      {
        Elem * e = *el;
        for (unsigned int s=0; s<e->n_neighbors(); s++)
          if (e->neighbor_ptr(s) != remote_elem ||
              reset_remote_elements)
            e->set_neighbor(s, libmesh_nullptr);
      }

  // Find neighboring elements by first finding elements
  // with identical side keys and then check to see if they
  // are neighbors
  {
    // data structures -- Use the hash_multimap if available
    typedef unsigned int                    key_type;
    typedef std::pair<Elem *, unsigned char> val_type;
    typedef std::pair<key_type, val_type>   key_val_pair;

    typedef LIBMESH_BEST_UNORDERED_MULTIMAP<key_type, val_type> map_type;

    // A map from side keys to corresponding elements & side numbers
    map_type side_to_elem_map;



    for (element_iterator el = this->elements_begin(); el != el_end; ++el)
      {
        Elem * element = *el;

        for (unsigned char ms=0; ms<element->n_neighbors(); ms++)
          {
          next_side:
            // If we haven't yet found a neighbor on this side, try.
            // Even if we think our neighbor is remote, that
            // information may be out of date.
            if (element->neighbor_ptr(ms) == libmesh_nullptr ||
                element->neighbor_ptr(ms) == remote_elem)
              {
                // Get the key for the side of this element
                const unsigned int key = element->key(ms);

                // Look for elements that have an identical side key
                std::pair <map_type::iterator, map_type::iterator>
                  bounds = side_to_elem_map.equal_range(key);

                // May be multiple keys, check all the possible
                // elements which _might_ be neighbors.
                if (bounds.first != bounds.second)
                  {
                    // Get the side for this element
                    const UniquePtr<Elem> my_side(element->side_ptr(ms));

                    // Look at all the entries with an equivalent key
                    while (bounds.first != bounds.second)
                      {
                        // Get the potential element
                        Elem * neighbor = bounds.first->second.first;

                        // Get the side for the neighboring element
                        const unsigned int ns = bounds.first->second.second;
                        const UniquePtr<Elem> their_side(neighbor->side_ptr(ns));
                        //libmesh_assert(my_side.get());
                        //libmesh_assert(their_side.get());

                        // If found a match with my side
                        //
                        // We need special tests here for 1D:
                        // since parents and children have an equal
                        // side (i.e. a node), we need to check
                        // ns != ms, and we also check level() to
                        // avoid setting our neighbor pointer to
                        // any of our neighbor's descendants
                        if( (*my_side == *their_side) &&
                            (element->level() == neighbor->level()) &&
                            ((element->dim() != 1) || (ns != ms)) )
                          {
                            // So share a side.  Is this a mixed pair
                            // of subactive and active/ancestor
                            // elements?
                            // If not, then we're neighbors.
                            // If so, then the subactive's neighbor is

                            if (element->subactive() ==
                                neighbor->subactive())
                              {
                                // an element is only subactive if it has
                                // been coarsened but not deleted
                                element->set_neighbor (ms,neighbor);
                                neighbor->set_neighbor(ns,element);
                              }
                            else if (element->subactive())
                              {
                                element->set_neighbor(ms,neighbor);
                              }
                            else if (neighbor->subactive())
                              {
                                neighbor->set_neighbor(ns,element);
                              }
                            side_to_elem_map.erase (bounds.first);

                            // get out of this nested crap
                            goto next_side;
                          }

                        ++bounds.first;
                      }
                  }

                // didn't find a match...
                // Build the map entry for this element
                key_val_pair kvp;

                kvp.first         = key;
                kvp.second.first  = element;
                kvp.second.second = ms;

                // use the lower bound as a hint for
                // where to put it.
#if defined(LIBMESH_HAVE_UNORDERED_MAP) || defined(LIBMESH_HAVE_TR1_UNORDERED_MAP) || defined(LIBMESH_HAVE_HASH_MAP) || defined(LIBMESH_HAVE_EXT_HASH_MAP)
                side_to_elem_map.insert (kvp);
#else
                side_to_elem_map.insert (bounds.first,kvp);
#endif
              }
          }
      }
  }

#ifdef LIBMESH_ENABLE_AMR

  /**
   * Here we look at all of the child elements which
   * don't already have valid neighbors.
   *
   * If a child element has a NULL neighbor it is
   * either because it is on the boundary or because
   * its neighbor is at a different level.  In the
   * latter case we must get the neighbor from the
   * parent.
   *
   * If a child element has a remote_elem neighbor
   * on a boundary it shares with its parent, that
   * info may have become out-dated through coarsening
   * of the neighbor's parent.  In this case, if the
   * parent's neighbor is active then the child should
   * share it.
   *
   * Furthermore, that neighbor better be active,
   * otherwise we missed a child somewhere.
   *
   *
   * We also need to look through children ordered by increasing
   * refinement level in order to add new interior_parent() links in
   * boundary elements which have just been generated by refinement,
   * and fix links in boundary elements whose previous
   * interior_parent() has just been coarsened away.
   */
  const unsigned int n_levels = MeshTools::n_levels(*this);
  for (unsigned int level = 1; level < n_levels; ++level)
    {
      element_iterator end = this->level_elements_end(level);
      for (element_iterator el = this->level_elements_begin(level);
           el != end; ++el)
        {
          Elem * current_elem = *el;
          libmesh_assert(current_elem);
          Elem * parent = current_elem->parent();
          libmesh_assert(parent);
          const unsigned int my_child_num = parent->which_child_am_i(current_elem);

          for (unsigned int s=0; s < current_elem->n_neighbors(); s++)
            {
              if (current_elem->neighbor_ptr(s) == libmesh_nullptr ||
                  (current_elem->neighbor_ptr(s) == remote_elem &&
                   parent->is_child_on_side(my_child_num, s)))
                {
                  Elem * neigh = parent->neighbor_ptr(s);

                  // If neigh was refined and had non-subactive children
                  // made remote earlier, then a non-subactive elem should
                  // actually have one of those remote children as a
                  // neighbor
                  if (neigh && (neigh->ancestor()) && (!current_elem->subactive()))
                    {
#ifdef DEBUG
                      // Let's make sure that "had children made remote"
                      // situation is actually the case
                      libmesh_assert(neigh->has_children());
                      bool neigh_has_remote_children = false;
                      for (unsigned int c = 0; c != neigh->n_children(); ++c)
                        {
                          if (neigh->child_ptr(c) == remote_elem)
                            neigh_has_remote_children = true;
                        }
                      libmesh_assert(neigh_has_remote_children);

                      // And let's double-check that we don't have
                      // a remote_elem neighboring a local element
                      libmesh_assert_not_equal_to (current_elem->processor_id(),
                                                   this->processor_id());
#endif // DEBUG
                      neigh = const_cast<RemoteElem *>(remote_elem);
                    }

                  if (!current_elem->subactive())
                    current_elem->set_neighbor(s, neigh);
#ifdef DEBUG
                  if (neigh != libmesh_nullptr && neigh != remote_elem)
                    // We ignore subactive elements here because
                    // we don't care about neighbors of subactive element.
                    if ((!neigh->active()) && (!current_elem->subactive()))
                      {
                        libMesh::err << "On processor " << this->processor_id()
                                     << std::endl;
                        libMesh::err << "Bad element ID = " << current_elem->id()
                                     << ", Side " << s << ", Bad neighbor ID = " << neigh->id() << std::endl;
                        libMesh::err << "Bad element proc_ID = " << current_elem->processor_id()
                                     << ", Bad neighbor proc_ID = " << neigh->processor_id() << std::endl;
                        libMesh::err << "Bad element size = " << current_elem->hmin()
                                     << ", Bad neighbor size = " << neigh->hmin() << std::endl;
                        libMesh::err << "Bad element center = " << current_elem->centroid()
                                     << ", Bad neighbor center = " << neigh->centroid() << std::endl;
                        libMesh::err << "ERROR: "
                                     << (current_elem->active()?"Active":"Ancestor")
                                     << " Element at level "
                                     << current_elem->level() << std::endl;
                        libMesh::err << "with "
                                     << (parent->active()?"active":
                                         (parent->subactive()?"subactive":"ancestor"))
                                     << " parent share "
                                     << (neigh->subactive()?"subactive":"ancestor")
                                     << " neighbor at level " << neigh->level()
                                     << std::endl;
                        NameBasedIO(*this).write ("bad_mesh.gmv");
                        libmesh_error_msg("Problematic mesh written to bad_mesh.gmv.");
                      }
#endif // DEBUG
                }
            }

          // We can skip to the next element if we're full-dimension
          // and therefore don't have any interior parents
          if (current_elem->dim() >= LIBMESH_DIM)
            continue;

          // We have no interior parents unless we can find one later
          current_elem->set_interior_parent(libmesh_nullptr);

          Elem * pip = parent->interior_parent();

          if (!pip)
            continue;

          // If there's no interior_parent children, whether due to a
          // remote element or a non-conformity, then there's no
          // children to search.
          if (pip == remote_elem || pip->active())
            {
              current_elem->set_interior_parent(pip);
              continue;
            }

          // For node comparisons we'll need a sensible tolerance
          Real node_tolerance = current_elem->hmin() * TOLERANCE;

          // Otherwise our interior_parent should be a child of our
          // parent's interior_parent.
          for (unsigned int c=0; c != pip->n_children(); ++c)
            {
              Elem * child = pip->child_ptr(c);

              // If we have a remote_elem, that might be our
              // interior_parent.  We'll set it provisionally now and
              // keep trying to find something better.
              if (child == remote_elem)
                {
                  current_elem->set_interior_parent
                    (const_cast<RemoteElem *>(remote_elem));
                  continue;
                }

              bool child_contains_our_nodes = true;
              for (unsigned int n=0; n != current_elem->n_nodes();
                   ++n)
                {
                  bool child_contains_this_node = false;
                  for (unsigned int cn=0; cn != child->n_nodes();
                       ++cn)
                    if (child->point(cn).absolute_fuzzy_equals
                        (current_elem->point(n), node_tolerance))
                      {
                        child_contains_this_node = true;
                        break;
                      }
                  if (!child_contains_this_node)
                    {
                      child_contains_our_nodes = false;
                      break;
                    }
                }
              if (child_contains_our_nodes)
                {
                  current_elem->set_interior_parent(child);
                  break;
                }
            }

          // We should have found *some* interior_parent at this
          // point, whether semilocal or remote.
          libmesh_assert(current_elem->interior_parent());
        }
    }

#endif // AMR


#ifdef DEBUG
  MeshTools::libmesh_assert_valid_neighbors(*this,
                                            !reset_remote_elements);
  MeshTools::libmesh_assert_valid_amr_interior_parents(*this);
#endif
}
bool MeshRefinement::flag_elements_by_nelem_target (const ErrorVector& error_per_cell)
{
  parallel_only();

  // Check for valid fractions..
  // The fraction values must be in [0,1]
  libmesh_assert_greater_equal (_refine_fraction, 0);
  libmesh_assert_less_equal (_refine_fraction, 1);
  libmesh_assert_greater_equal (_coarsen_fraction, 0);
  libmesh_assert_less_equal (_coarsen_fraction, 1);

  // This function is currently only coded to work when coarsening by
  // parents - it's too hard to guess how many coarsenings will be
  // performed otherwise.
  libmesh_assert (_coarsen_by_parents);

  // The number of active elements in the mesh - hopefully less than
  // 2 billion on 32 bit machines
  const unsigned int n_active_elem  = _mesh.n_active_elem();

  // The maximum number of active elements to flag for coarsening
  const unsigned int max_elem_coarsen =
    static_cast<unsigned int>(_coarsen_fraction * n_active_elem) + 1;

  // The maximum number of elements to flag for refinement
  const unsigned int max_elem_refine  =
    static_cast<unsigned int>(_refine_fraction  * n_active_elem) + 1;

  // Clean up the refinement flags.  These could be left
  // over from previous refinement steps.
  this->clean_refinement_flags();

  // The target number of elements to add or remove
  const int n_elem_new = _nelem_target - n_active_elem;

  // Create an vector with active element errors and ids,
  // sorted by highest errors first
  const unsigned int max_elem_id = _mesh.max_elem_id();
  std::vector<std::pair<float, unsigned int> > sorted_error;

  sorted_error.reserve (n_active_elem);

  // On a ParallelMesh, we need to communicate to know which remote ids
  // correspond to active elements.
  {
    std::vector<bool> is_active(max_elem_id, false);

    MeshBase::element_iterator       elem_it  = _mesh.active_local_elements_begin();
    const MeshBase::element_iterator elem_end = _mesh.active_local_elements_end();
    for (; elem_it != elem_end; ++elem_it)
      {
        const unsigned int eid = (*elem_it)->id();
        is_active[eid] = true;
        libmesh_assert_less (eid, error_per_cell.size());
        sorted_error.push_back
          (std::make_pair(error_per_cell[eid], eid));
      }

    CommWorld.max(is_active);

    CommWorld.allgather(sorted_error);
  }

  // Default sort works since pairs are sorted lexicographically
  std::sort (sorted_error.begin(), sorted_error.end());
  std::reverse (sorted_error.begin(), sorted_error.end());

  // Create a sorted error vector with coarsenable parent elements
  // only, sorted by lowest errors first
  ErrorVector error_per_parent;
  std::vector<std::pair<float, unsigned int> > sorted_parent_error;
  Real parent_error_min, parent_error_max;

  create_parent_error_vector(error_per_cell,
                             error_per_parent,
                             parent_error_min,
                             parent_error_max);

  // create_parent_error_vector sets values for non-parents and
  // non-coarsenable parents to -1.  Get rid of them.
  for (unsigned int i=0; i != error_per_parent.size(); ++i)
    if (error_per_parent[i] != -1)
      sorted_parent_error.push_back(std::make_pair(error_per_parent[i], i));

  std::sort (sorted_parent_error.begin(), sorted_parent_error.end());

  // Keep track of how many elements we plan to coarsen & refine
  unsigned int coarsen_count = 0;
  unsigned int refine_count = 0;

  const unsigned int dim = _mesh.mesh_dimension();
  unsigned int twotodim = 1;
  for (unsigned int i=0; i!=dim; ++i)
    twotodim *= 2;

  // First, let's try to get our element count to target_nelem
  if (n_elem_new >= 0)
  {
    // Every element refinement creates at least
    // 2^dim-1 new elements
    refine_count =
      std::min(static_cast<unsigned int>(n_elem_new / (twotodim-1)),
	       max_elem_refine);
  }
  else
  {
    // Every successful element coarsening is likely to destroy
    // 2^dim-1 net elements.
    coarsen_count =
      std::min(static_cast<unsigned int>(-n_elem_new / (twotodim-1)),
	       max_elem_coarsen);
  }

  // Next, let's see if we can trade any refinement for coarsening
  while (coarsen_count < max_elem_coarsen &&
         refine_count < max_elem_refine &&
         coarsen_count < sorted_parent_error.size() &&
         refine_count < sorted_error.size() &&
         sorted_error[refine_count].first >
	 sorted_parent_error[coarsen_count].first * _coarsen_threshold)
  {
    coarsen_count++;
    refine_count++;
  }

  // On a ParallelMesh, we need to communicate to know which remote ids
  // correspond to refinable elements
  unsigned int successful_refine_count = 0;
  {
    std::vector<bool> is_refinable(max_elem_id, false);

    for (unsigned int i=0; i != sorted_error.size(); ++i)
      {
        unsigned int eid = sorted_error[i].second;
        Elem *elem = _mesh.query_elem(eid);
        if (elem && elem->level() < _max_h_level)
	  is_refinable[eid] = true;
      }
    CommWorld.max(is_refinable);

    if (refine_count > max_elem_refine)
      refine_count = max_elem_refine;
    for (unsigned int i=0; i != sorted_error.size(); ++i)
      {
        if (successful_refine_count >= refine_count)
          break;

        unsigned int eid = sorted_error[i].second;
        Elem *elem = _mesh.query_elem(eid);
        if (is_refinable[eid])
          {
            if (elem)
	      elem->set_refinement_flag(Elem::REFINE);
	    successful_refine_count++;
          }
      }
  }

  // If we couldn't refine enough elements, don't coarsen too many
  // either
  if (coarsen_count < (refine_count - successful_refine_count))
    coarsen_count = 0;
  else
    coarsen_count -= (refine_count - successful_refine_count);

  if (coarsen_count > max_elem_coarsen)
    coarsen_count = max_elem_coarsen;

  unsigned int successful_coarsen_count = 0;
  if (coarsen_count)
    {
      for (unsigned int i=0; i != sorted_parent_error.size(); ++i)
        {
          if (successful_coarsen_count >= coarsen_count * twotodim)
            break;

          unsigned int parent_id = sorted_parent_error[i].second;
          Elem *parent = _mesh.query_elem(parent_id);

          // On a ParallelMesh we skip remote elements
          if (!parent)
            continue;

          libmesh_assert(parent->has_children());
          for (unsigned int c=0; c != parent->n_children(); ++c)
            {
              Elem *elem = parent->child(c);
              if (elem && elem != remote_elem)
                {
                  libmesh_assert(elem->active());
                  elem->set_refinement_flag(Elem::COARSEN);
                  successful_coarsen_count++;
                }
            }
        }
    }

  // Return true if we've done all the AMR/C we can
  if (!successful_coarsen_count &&
      !successful_refine_count)
    return true;
  // And false if there may still be more to do.
  return false;
}
Пример #3
0
Elem *
Packing<Elem *>::unpack (std::vector<largest_id_type>::const_iterator in,
                         MeshBase * mesh)
{
#ifndef NDEBUG
  const std::vector<largest_id_type>::const_iterator original_in = in;

  const largest_id_type incoming_header = *in++;
  libmesh_assert_equal_to (incoming_header, elem_magic_header);
#endif

  // int 0: level
  const unsigned int level =
    cast_int<unsigned int>(*in++);

#ifdef LIBMESH_ENABLE_AMR
  // int 1: p level
  const unsigned int p_level =
    cast_int<unsigned int>(*in++);

  // int 2: refinement flag and encoded has_children
  const int rflag = cast_int<int>(*in++);
  const int invalid_rflag =
    cast_int<int>(Elem::INVALID_REFINEMENTSTATE);
  libmesh_assert_greater_equal (rflag, 0);

  libmesh_assert_less (rflag, invalid_rflag*2+1);

  const bool has_children = (rflag > invalid_rflag);

  const Elem::RefinementState refinement_flag = has_children ?
    cast_int<Elem::RefinementState>(rflag - invalid_rflag - 1) :
    cast_int<Elem::RefinementState>(rflag);

  // int 3: p refinement flag
  const int pflag = cast_int<int>(*in++);
  libmesh_assert_greater_equal (pflag, 0);
  libmesh_assert_less (pflag, Elem::INVALID_REFINEMENTSTATE);
  const Elem::RefinementState p_refinement_flag =
    cast_int<Elem::RefinementState>(pflag);
#else
  in += 3;
#endif // LIBMESH_ENABLE_AMR

  // int 4: element type
  const int typeint = cast_int<int>(*in++);
  libmesh_assert_greater_equal (typeint, 0);
  libmesh_assert_less (typeint, INVALID_ELEM);
  const ElemType type =
    cast_int<ElemType>(typeint);

  const unsigned int n_nodes =
    Elem::type_to_n_nodes_map[type];

  // int 5: processor id
  const processor_id_type processor_id =
    cast_int<processor_id_type>(*in++);
  libmesh_assert (processor_id < mesh->n_processors() ||
                  processor_id == DofObject::invalid_processor_id);

  // int 6: subdomain id
  const subdomain_id_type subdomain_id =
    cast_int<subdomain_id_type>(*in++);

  // int 7: dof object id
  const dof_id_type id =
    cast_int<dof_id_type>(*in++);
  libmesh_assert_not_equal_to (id, DofObject::invalid_id);

#ifdef LIBMESH_ENABLE_UNIQUE_ID
  // int 8: dof object unique id
  const unique_id_type unique_id =
    cast_int<unique_id_type>(*in++);
#endif

#ifdef LIBMESH_ENABLE_AMR
  // int 9: parent dof object id.
  // Note: If level==0, then (*in) == invalid_id.  In
  // this case, the equality check in cast_int<unsigned>(*in) will
  // never succeed.  Therefore, we should only attempt the more
  // rigorous cast verification in cases where level != 0.
  const dof_id_type parent_id =
    (level == 0)
    ? static_cast<dof_id_type>(*in++)
    : cast_int<dof_id_type>(*in++);
  libmesh_assert (level == 0 || parent_id != DofObject::invalid_id);
  libmesh_assert (level != 0 || parent_id == DofObject::invalid_id);

  // int 10: local child id
  // Note: If level==0, then which_child_am_i is not valid, so don't
  // do the more rigorous cast verification.
  const unsigned int which_child_am_i =
    (level == 0)
    ? static_cast<unsigned int>(*in++)
    : cast_int<unsigned int>(*in++);
#else
  in += 2;
#endif // LIBMESH_ENABLE_AMR

  const dof_id_type interior_parent_id =
    static_cast<dof_id_type>(*in++);

  // Make sure we don't miscount above when adding the "magic" header
  // plus the real data header
  libmesh_assert_equal_to (in - original_in, header_size + 1);

  Elem * elem = mesh->query_elem_ptr(id);

  // if we already have this element, make sure its
  // properties match, and update any missing neighbor
  // links, but then go on
  if (elem)
    {
      libmesh_assert_equal_to (elem->level(), level);
      libmesh_assert_equal_to (elem->id(), id);
      //#ifdef LIBMESH_ENABLE_UNIQUE_ID
      // No check for unique id sanity
      //#endif
      libmesh_assert_equal_to (elem->processor_id(), processor_id);
      libmesh_assert_equal_to (elem->subdomain_id(), subdomain_id);
      libmesh_assert_equal_to (elem->type(), type);
      libmesh_assert_equal_to (elem->n_nodes(), n_nodes);

#ifndef NDEBUG
      // All our nodes should be correct
      for (unsigned int i=0; i != n_nodes; ++i)
        libmesh_assert(elem->node_id(i) ==
                       cast_int<dof_id_type>(*in++));
#else
      in += n_nodes;
#endif

#ifdef LIBMESH_ENABLE_AMR
      libmesh_assert_equal_to (elem->refinement_flag(), refinement_flag);
      libmesh_assert_equal_to (elem->has_children(), has_children);

#ifdef DEBUG
      if (elem->active())
        {
          libmesh_assert_equal_to (elem->p_level(), p_level);
          libmesh_assert_equal_to (elem->p_refinement_flag(), p_refinement_flag);
        }
#endif

      libmesh_assert (!level || elem->parent() != libmesh_nullptr);
      libmesh_assert (!level || elem->parent()->id() == parent_id);
      libmesh_assert (!level || elem->parent()->child_ptr(which_child_am_i) == elem);
#endif
      // Our interior_parent link should be "close to" correct - we
      // may have to update it, but we can check for some
      // inconsistencies.
      {
        // If the sending processor sees no interior_parent here, we'd
        // better agree.
        if (interior_parent_id == DofObject::invalid_id)
          {
            if (elem->dim() < LIBMESH_DIM)
              libmesh_assert (!(elem->interior_parent()));
          }

        // If the sending processor has a remote_elem interior_parent,
        // then all we know is that we'd better have *some*
        // interior_parent
        else if (interior_parent_id == remote_elem->id())
          {
            libmesh_assert(elem->interior_parent());
          }
        else
          {
            Elem * ip = mesh->query_elem_ptr(interior_parent_id);

            // The sending processor sees an interior parent here, so
            // if we don't have that interior element, then we'd
            // better have a remote_elem signifying that fact.
            if (!ip)
              libmesh_assert_equal_to (elem->interior_parent(), remote_elem);
            else
              {
                // The sending processor has an interior_parent here,
                // and we have that element, but that does *NOT* mean
                // we're already linking to it.  Perhaps we initially
                // received elem from a processor on which the
                // interior_parent link was remote?
                libmesh_assert(elem->interior_parent() == ip ||
                               elem->interior_parent() == remote_elem);

                // If the link was originally remote, update it
                if (elem->interior_parent() == remote_elem)
                  {
                    elem->set_interior_parent(ip);
                  }
              }
          }
      }

      // Our neighbor links should be "close to" correct - we may have
      // to update a remote_elem link, and we can check for possible
      // inconsistencies along the way.
      //
      // For subactive elements, we don't bother keeping neighbor
      // links in good shape, so there's nothing we need to set or can
      // safely assert here.
      if (!elem->subactive())
        for (auto n : elem->side_index_range())
          {
            const dof_id_type neighbor_id =
              cast_int<dof_id_type>(*in++);

            // If the sending processor sees a domain boundary here,
            // we'd better agree.
            if (neighbor_id == DofObject::invalid_id)
              {
                libmesh_assert (!(elem->neighbor_ptr(n)));
                continue;
              }

            // If the sending processor has a remote_elem neighbor here,
            // then all we know is that we'd better *not* have a domain
            // boundary.
            if (neighbor_id == remote_elem->id())
              {
                libmesh_assert(elem->neighbor_ptr(n));
                continue;
              }

            Elem * neigh = mesh->query_elem_ptr(neighbor_id);

            // The sending processor sees a neighbor here, so if we
            // don't have that neighboring element, then we'd better
            // have a remote_elem signifying that fact.
            if (!neigh)
              {
                libmesh_assert_equal_to (elem->neighbor_ptr(n), remote_elem);
                continue;
              }

            // The sending processor has a neighbor here, and we have
            // that element, but that does *NOT* mean we're already
            // linking to it.  Perhaps we initially received both elem
            // and neigh from processors on which their mutual link was
            // remote?
            libmesh_assert(elem->neighbor_ptr(n) == neigh ||
                           elem->neighbor_ptr(n) == remote_elem);

            // If the link was originally remote, we should update it,
            // and make sure the appropriate parts of its family link
            // back to us.
            if (elem->neighbor_ptr(n) == remote_elem)
              {
                elem->set_neighbor(n, neigh);

                elem->make_links_to_me_local(n);
              }
          }

      // Our p level and refinement flags should be "close to" correct
      // if we're not an active element - we might have a p level
      // increased or decreased by changes in remote_elem children.
      //
      // But if we have remote_elem children, then we shouldn't be
      // doing a projection on this inactive element on this
      // processor, so we won't need correct p settings.  Couldn't
      // hurt to update, though.
#ifdef LIBMESH_ENABLE_AMR
      if (elem->processor_id() != mesh->processor_id())
        {
          elem->hack_p_level(p_level);
          elem->set_p_refinement_flag(p_refinement_flag);
        }
#endif // LIBMESH_ENABLE_AMR

      // FIXME: We should add some debug mode tests to ensure that the
      // encoded indexing and boundary conditions are consistent.
    }
  else
    {
      // We don't already have the element, so we need to create it.

      // Find the parent if necessary
      Elem * parent = libmesh_nullptr;
#ifdef LIBMESH_ENABLE_AMR
      // Find a child element's parent
      if (level > 0)
        {
          // Note that we must be very careful to construct the send
          // connectivity so that parents are encountered before
          // children.  If we get here and can't find the parent that
          // is a fatal error.
          parent = mesh->elem_ptr(parent_id);
        }
      // Or assert that the sending processor sees no parent
      else
        libmesh_assert_equal_to (parent_id, DofObject::invalid_id);
#else
      // No non-level-0 elements without AMR
      libmesh_assert_equal_to (level, 0);
#endif

      elem = Elem::build(type,parent).release();
      libmesh_assert (elem);

#ifdef LIBMESH_ENABLE_AMR
      if (level != 0)
        {
          // Since this is a newly created element, the parent must
          // have previously thought of this child as a remote element.
          libmesh_assert_equal_to (parent->child_ptr(which_child_am_i), remote_elem);

          parent->add_child(elem, which_child_am_i);
        }

      // Assign the refinement flags and levels
      elem->set_p_level(p_level);
      elem->set_refinement_flag(refinement_flag);
      elem->set_p_refinement_flag(p_refinement_flag);
      libmesh_assert_equal_to (elem->level(), level);

      // If this element should have children, assign remote_elem to
      // all of them for now, for consistency.  Later unpacked
      // elements may overwrite that.
      if (has_children)
        {
          const unsigned int nc = elem->n_children();
          for (unsigned int c=0; c != nc; ++c)
            elem->add_child(const_cast<RemoteElem *>(remote_elem), c);
        }

#endif // LIBMESH_ENABLE_AMR

      // Assign the IDs
      elem->subdomain_id()  = subdomain_id;
      elem->processor_id()  = processor_id;
      elem->set_id()        = id;
#ifdef LIBMESH_ENABLE_UNIQUE_ID
      elem->set_unique_id() = unique_id;
#endif

      // Assign the connectivity
      libmesh_assert_equal_to (elem->n_nodes(), n_nodes);

      for (unsigned int n=0; n != n_nodes; n++)
        elem->set_node(n) =
          mesh->node_ptr
          (cast_int<dof_id_type>(*in++));

      // Set interior_parent if found
      {
        // We may be unpacking an element that was a ghost element on the
        // sender, in which case the element's interior_parent may not be
        // known by the packed element.  We'll have to set such
        // interior_parents to remote_elem ourselves and wait for a
        // later packed element to give us better information.
        if (interior_parent_id == remote_elem->id())
          {
            elem->set_interior_parent
              (const_cast<RemoteElem *>(remote_elem));
          }
        else if (interior_parent_id != DofObject::invalid_id)
          {
            // If we don't have the interior parent element, then it's
            // a remote_elem until we get it.
            Elem * ip = mesh->query_elem_ptr(interior_parent_id);
            if (!ip )
              elem->set_interior_parent
                (const_cast<RemoteElem *>(remote_elem));
            else
              elem->set_interior_parent(ip);
          }
      }

      for (auto n : elem->side_index_range())
        {
          const dof_id_type neighbor_id =
            cast_int<dof_id_type>(*in++);

          if (neighbor_id == DofObject::invalid_id)
            continue;

          // We may be unpacking an element that was a ghost element on the
          // sender, in which case the element's neighbors may not all be
          // known by the packed element.  We'll have to set such
          // neighbors to remote_elem ourselves and wait for a later
          // packed element to give us better information.
          if (neighbor_id == remote_elem->id())
            {
              elem->set_neighbor(n, const_cast<RemoteElem *>(remote_elem));
              continue;
            }

          // If we don't have the neighbor element, then it's a
          // remote_elem until we get it.
          Elem * neigh = mesh->query_elem_ptr(neighbor_id);
          if (!neigh)
            {
              elem->set_neighbor(n, const_cast<RemoteElem *>(remote_elem));
              continue;
            }

          // If we have the neighbor element, then link to it, and
          // make sure the appropriate parts of its family link back
          // to us.
          elem->set_neighbor(n, neigh);

          elem->make_links_to_me_local(n);
        }

      elem->unpack_indexing(in);
    }

  in += elem->packed_indexing_size();

  // If this is a coarse element,
  // add any element side or edge boundary condition ids
  if (level == 0)
    {
      for (auto s : elem->side_index_range())
        {
          const boundary_id_type num_bcs =
            cast_int<boundary_id_type>(*in++);

          for (boundary_id_type bc_it=0; bc_it < num_bcs; bc_it++)
            mesh->get_boundary_info().add_side
              (elem, s, cast_int<boundary_id_type>(*in++));
        }

      for (auto e : elem->edge_index_range())
        {
          const boundary_id_type num_bcs =
            cast_int<boundary_id_type>(*in++);

          for (boundary_id_type bc_it=0; bc_it < num_bcs; bc_it++)
            mesh->get_boundary_info().add_edge
              (elem, e, cast_int<boundary_id_type>(*in++));
        }

      for (unsigned short sf=0; sf != 2; ++sf)
        {
          const boundary_id_type num_bcs =
            cast_int<boundary_id_type>(*in++);

          for (boundary_id_type bc_it=0; bc_it < num_bcs; bc_it++)
            mesh->get_boundary_info().add_shellface
              (elem, sf, cast_int<boundary_id_type>(*in++));
        }
    }

  // Return the new element
  return elem;
}