void Partitioner::set_parent_processor_ids(MeshBase & mesh)
{
// Ignore the parameter when !LIBMESH_ENABLE_AMR
libmesh_ignore(mesh);
LOG_SCOPE("set_parent_processor_ids()", "Partitioner");
#ifdef LIBMESH_ENABLE_AMR
// If the mesh is serial we have access to all the elements,
// in particular all the active ones. We can therefore set
// the parent processor ids indirectly through their children, and
// set the subactive processor ids while examining their active
// ancestors.
// By convention a parent is assigned to the minimum processor
// of all its children, and a subactive is assigned to the processor
// of its active ancestor.
if (mesh.is_serial())
{
for (auto & child : mesh.active_element_ptr_range())
{
// First set descendents
std::vector<const Elem *> subactive_family;
child->total_family_tree(subactive_family);
for (std::size_t i = 0; i != subactive_family.size(); ++i)
const_cast<Elem *>(subactive_family[i])->processor_id() = child->processor_id();
// Then set ancestors
Elem * parent = child->parent();
while (parent)
{
// invalidate the parent id, otherwise the min below
// will not work if the current parent id is less
// than all the children!
parent->invalidate_processor_id();
for (auto & child : parent->child_ref_range())
{
libmesh_assert(!child.is_remote());
libmesh_assert_not_equal_to (child.processor_id(), DofObject::invalid_processor_id);
parent->processor_id() = std::min(parent->processor_id(),
child.processor_id());
}
parent = parent->parent();
}
}
}
// When the mesh is parallel we cannot guarantee that parents have access to
// all their children.
else
{
// Setting subactive processor ids is easy: we can guarantee
// that children have access to all their parents.
// Loop over all the active elements in the mesh
for (auto & child : mesh.active_element_ptr_range())
{
std::vector<const Elem *> subactive_family;
child->total_family_tree(subactive_family);
for (std::size_t i = 0; i != subactive_family.size(); ++i)
const_cast<Elem *>(subactive_family[i])->processor_id() = child->processor_id();
}
// When the mesh is parallel we cannot guarantee that parents have access to
// all their children.
// We will use a brute-force approach here. Each processor finds its parent
// elements and sets the parent pid to the minimum of its
// semilocal descendants.
// A global reduction is then performed to make sure the true minimum is found.
// As noted, this is required because we cannot guarantee that a parent has
// access to all its children on any single processor.
libmesh_parallel_only(mesh.comm());
libmesh_assert(MeshTools::n_elem(mesh.unpartitioned_elements_begin(),
mesh.unpartitioned_elements_end()) == 0);
const dof_id_type max_elem_id = mesh.max_elem_id();
std::vector<processor_id_type>
parent_processor_ids (std::min(communication_blocksize,
max_elem_id));
for (dof_id_type blk=0, last_elem_id=0; last_elem_id<max_elem_id; blk++)
{
last_elem_id =
std::min(static_cast<dof_id_type>((blk+1)*communication_blocksize),
max_elem_id);
const dof_id_type first_elem_id = blk*communication_blocksize;
std::fill (parent_processor_ids.begin(),
parent_processor_ids.end(),
DofObject::invalid_processor_id);
// first build up local contributions to parent_processor_ids
MeshBase::element_iterator not_it = mesh.ancestor_elements_begin();
const MeshBase::element_iterator not_end = mesh.ancestor_elements_end();
bool have_parent_in_block = false;
for ( ; not_it != not_end; ++not_it)
{
Elem * parent = *not_it;
const dof_id_type parent_idx = parent->id();
libmesh_assert_less (parent_idx, max_elem_id);
if ((parent_idx >= first_elem_id) &&
(parent_idx < last_elem_id))
{
have_parent_in_block = true;
processor_id_type parent_pid = DofObject::invalid_processor_id;
std::vector<const Elem *> active_family;
parent->active_family_tree(active_family);
for (std::size_t i = 0; i != active_family.size(); ++i)
parent_pid = std::min (parent_pid, active_family[i]->processor_id());
const dof_id_type packed_idx = parent_idx - first_elem_id;
libmesh_assert_less (packed_idx, parent_processor_ids.size());
parent_processor_ids[packed_idx] = parent_pid;
}
}
// then find the global minimum
mesh.comm().min (parent_processor_ids);
// and assign the ids, if we have a parent in this block.
if (have_parent_in_block)
for (not_it = mesh.ancestor_elements_begin();
not_it != not_end; ++not_it)
{
Elem * parent = *not_it;
const dof_id_type parent_idx = parent->id();
if ((parent_idx >= first_elem_id) &&
(parent_idx < last_elem_id))
{
const dof_id_type packed_idx = parent_idx - first_elem_id;
libmesh_assert_less (packed_idx, parent_processor_ids.size());
const processor_id_type parent_pid =
parent_processor_ids[packed_idx];
libmesh_assert_not_equal_to (parent_pid, DofObject::invalid_processor_id);
parent->processor_id() = parent_pid;
}
}
}
}
#endif // LIBMESH_ENABLE_AMR
}
bool MeshRefinement::flag_elements_by_nelem_target (const ErrorVector & error_per_cell)
{
parallel_object_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 dof_id_type n_active_elem = _mesh.n_active_elem();
// The maximum number of active elements to flag for coarsening
const dof_id_type max_elem_coarsen =
static_cast<dof_id_type>(_coarsen_fraction * n_active_elem) + 1;
// The maximum number of elements to flag for refinement
const dof_id_type max_elem_refine =
static_cast<dof_id_type>(_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 std::ptrdiff_t n_elem_new =
std::ptrdiff_t(_nelem_target) - std::ptrdiff_t(n_active_elem);
// Create an vector with active element errors and ids,
// sorted by highest errors first
const dof_id_type max_elem_id = _mesh.max_elem_id();
std::vector<std::pair<ErrorVectorReal, dof_id_type>> sorted_error;
sorted_error.reserve (n_active_elem);
// On a DistributedMesh, we need to communicate to know which remote ids
// correspond to active elements.
{
std::vector<bool> is_active(max_elem_id, false);
for (auto & elem : _mesh.active_local_element_ptr_range())
{
const dof_id_type eid = elem->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));
}
this->comm().max(is_active);
this->comm().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<ErrorVectorReal, dof_id_type>> 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 (std::size_t 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
dof_id_type coarsen_count = 0;
dof_id_type 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(cast_int<dof_id_type>(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(cast_int<dof_id_type>(-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 DistributedMesh, we need to communicate to know which remote ids
// correspond to refinable elements
dof_id_type successful_refine_count = 0;
{
std::vector<bool> is_refinable(max_elem_id, false);
for (std::size_t i=0; i != sorted_error.size(); ++i)
{
dof_id_type eid = sorted_error[i].second;
Elem * elem = _mesh.query_elem_ptr(eid);
if (elem && elem->level() < _max_h_level)
is_refinable[eid] = true;
}
this->comm().max(is_refinable);
if (refine_count > max_elem_refine)
refine_count = max_elem_refine;
for (std::size_t i=0; i != sorted_error.size(); ++i)
{
if (successful_refine_count >= refine_count)
break;
dof_id_type eid = sorted_error[i].second;
Elem * elem = _mesh.query_elem_ptr(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;
dof_id_type successful_coarsen_count = 0;
if (coarsen_count)
{
for (std::size_t i=0; i != sorted_parent_error.size(); ++i)
{
if (successful_coarsen_count >= coarsen_count * twotodim)
break;
dof_id_type parent_id = sorted_parent_error[i].second;
Elem * parent = _mesh.query_elem_ptr(parent_id);
// On a DistributedMesh we skip remote elements
if (!parent)
continue;
libmesh_assert(parent->has_children());
for (auto & elem : parent->child_ref_range())
{
if (&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;
}