parallel::CellWeights< dim, spacedim > Class Template Reference

#include <deal.II/distributed/cell_weights.h>

Public Types
using	WeightingFunction

Public Member Functions
	CellWeights ()=default
	CellWeights (const DoFHandler< dim, spacedim > &dof_handler, const WeightingFunction &weighting_function)
	~CellWeights ()
void	reinit (const DoFHandler< dim, spacedim > &dof_handler, const WeightingFunction &weighting_function)

Static Public Member Functions
static std::function< unsigned int(const typename ::Triangulation< dim, spacedim >::cell_iterator &cell, const CellStatus status)>	make_weighting_callback (const DoFHandler< dim, spacedim > &dof_handler, const WeightingFunction &weighting_function)
Selection of weighting functions
static WeightingFunction	constant_weighting (const unsigned int factor=1)
static WeightingFunction	ndofs_weighting (const std::pair< float, float > &coefficients)
static WeightingFunction	ndofs_weighting (const std::vector< std::pair< float, float > > &coefficients)

Static Private Member Functions
static unsigned int	weighting_callback (const typename ::Triangulation< dim, spacedim >::cell_iterator &cell, const CellStatus status, const DoFHandler< dim, spacedim > &dof_handler, const parallel::TriangulationBase< dim, spacedim > &triangulation, const WeightingFunction &weighting_function)

Private Attributes
boost::signals2::connection	connection

Detailed Description

template<int dim, int spacedim = dim>
class parallel::CellWeights< dim, spacedim >

Anytime a parallel::TriangulationBase is repartitioned, either upon request or by refinement/coarsening, cells will be distributed amongst all subdomains to achieve an equally balanced workload. By default, if you don't do anything specific, the workload is assumed to be the same for every cell of the triangulation, and in that case a well-balanced mesh will have about the same number of cells on each process. But, if the workload per cell varies, which is in general the case for DoFHandler objects that hp-capabilities (i.e., where you use different finite elements on different cells), we can take that into account by introducing individual weights for different cells.

This class allows computing these weights for load balancing by consulting the FiniteElement that is associated with each cell of a DoFHandler. One can choose from predefined weighting algorithms provided by this class or provide a custom one.

If the associated DoFHandler has not been initialized yet, i.e., its hp::FECollection is empty, all cell weights will be evaluated as zero.

This class offers two different ways of connecting the chosen weighting function to the corresponding signal of the linked parallel::TriangulationBase. The recommended way involves creating an object of this class which will automatically take care of registering the weighting function upon creation and de-registering it once destroyed. An object of this class needs to exist for every DoFHandler associated with the Triangulation we work on to achieve satisfying work balancing results. The connected weighting function may be changed anytime using the CellWeights::reinit() function. The following code snippet demonstrates how to achieve each cell being weighted by its current number of degrees of freedom.

parallel::CellWeights<dim, spacedim> cell_weights(
  hp_dof_handler,
  parallel::CellWeights<dim, spacedim>::ndofs_weighting({1, 1}));

On the other hand, you are also able to take care of handling the signal connection manually by using the static member function of this class. In this case, an analogous code example looks as follows.

boost::signals2::connection connection =
  hp_dof_handler.get_triangulation().signals.weight.connect(
    parallel::CellWeights<dim, spacedim>::make_weighting_callback(
      hp_dof_handler,
      parallel::CellWeights<dim, spacedim>::ndofs_weighting({1, 1}));

The use of this class is demonstrated in step-75.

Note

See Triangulation::Signals::weight for more information on weighting and load balancing.

Be aware that this class connects the weight function to the Triangulation during this class's constructor. If the Triangulation associated with the DoFHandler changes during the lifetime of the latter via DoFHandler::reinit(), an assertion will be triggered in the weight_callback() function. Use CellWeights::reinit() to deregister the weighting function on the old Triangulation and connect it to the new one.

A hp::FECollection needs to be attached to your DoFHandler object via DoFHandler::distribute_dofs() before the Triangulation::Signals::weight signal will be triggered. Otherwise, your DoFHandler does not know many degrees of freedom your cells have. In other words, you need to call DoFHandler::distribute_dofs() once before you call parallel::distributed::Triangulation::execute_coarsening_and_refinement(), parallel::distributed::Triangulation::refine_global(), parallel::distributed::Triangulation::repartition(), or GridTools::partition_triangulation() for the very first time.

Definition at line 103 of file cell_weights.h.

Member Typedef Documentation

WeightingFunction

template<int dim, int spacedim = dim>

using parallel::CellWeights< dim, spacedim >::WeightingFunction

Initial value:

 std::function<
      unsigned int(const typename DoFHandler<dim, spacedim>::cell_iterator &,
                   const FiniteElement<dim, spacedim> &)>

An alias that defines the characteristics of a function that can be used for weighting cells during load balancing.

Such weighting functions take as arguments an iterator to a cell and the future finite element that will be assigned to it after repartitioning. They return an unsigned integer which is interpreted as the cell's weight or, in other words, the additional computational load associated with it.

Definition at line 116 of file cell_weights.h.

Constructor & Destructor Documentation

CellWeights() [1/2]

template<int dim, int spacedim = dim>

parallel::CellWeights< dim, spacedim >::CellWeights ( )

default

Constructor.

No weighting function will be connected yet. Please call reinit().

CellWeights() [2/2]

template<int dim, int spacedim>

parallel::CellWeights< dim, spacedim >::CellWeights	(	const DoFHandler< dim, spacedim > &	dof_handler,
		const WeightingFunction &	weighting_function )

Constructor.

Parameters

[in]	dof_handler	The DoFHandler which will be used to determine each cell's finite element.
[in]	weighting_function	The function that determines each cell's weight during load balancing.

Definition at line 28 of file cell_weights.cc.

~CellWeights()

template<int dim, int spacedim>

parallel::CellWeights< dim, spacedim >::~CellWeights

(

)

Destructor.

Disconnects the function previously connected to the weighting signal.

Definition at line 38 of file cell_weights.cc.

Member Function Documentation

reinit()

template<int dim, int spacedim = dim>

void parallel::CellWeights< dim, spacedim >::reinit	(	const DoFHandler< dim, spacedim > &	dof_handler,
		const WeightingFunction &	weighting_function )

Connect a different weighting_function to the Triangulation associated with the dof_handler.

Disconnects the function previously connected to the weighting signal.

Definition at line 47 of file cell_weights.cc.

make_weighting_callback()

template<int dim, int spacedim = dim>

std::function< unsigned int(const typename::Triangulation< dim, spacedim >::cell_iterator &cell, const CellStatus status)> parallel::CellWeights< dim, spacedim >::make_weighting_callback ( const DoFHandler< dim, spacedim > & dof_handler, const WeightingFunction & weighting_function )

static

Converts a weighting_function to a different type that qualifies as a callback function, which can be connected to a weighting signal of a Triangulation.

This function does not connect the converted function to the Triangulation associated with the dof_handler.

Definition at line 131 of file cell_weights.cc.

constant_weighting()

template<int dim, int spacedim>

CellWeights< dim, spacedim >::WeightingFunction parallel::CellWeights< dim, spacedim >::constant_weighting ( const unsigned int factor = 1 )

static

Choose a constant weight factor on each cell.

Definition at line 65 of file cell_weights.cc.

ndofs_weighting() [1/2]

template<int dim, int spacedim>

CellWeights< dim, spacedim >::WeightingFunction parallel::CellWeights< dim, spacedim >::ndofs_weighting ( const std::pair< float, float > & coefficients )

static

The pair of floating point numbers \((a,b)\) provided via coefficients determines the weight \(w_K\) of each cell \(K\) with \(n_K\) degrees of freedom in the following way:

\[ w_K = a \, n_K^b \]

The right hand side will be rounded to the nearest integer since cell weights are required to be integers.

Definition at line 77 of file cell_weights.cc.

ndofs_weighting() [2/2]

template<int dim, int spacedim>

CellWeights< dim, spacedim >::WeightingFunction parallel::CellWeights< dim, spacedim >::ndofs_weighting ( const std::vector< std::pair< float, float > > & coefficients )

static

The container coefficients provides pairs of floating point numbers \((a_i, b_i)\) that determine the weight \(w_K\) of each cell \(K\) with \(n_K\) degrees of freedom in the following way:

\[ w_K = \sum_i a_i \, n_K^{b_i} \]

The right hand side will be rounded to the nearest integer since cell weights are required to be integers.

Definition at line 101 of file cell_weights.cc.

weighting_callback()

template<int dim, int spacedim = dim>

unsigned int parallel::CellWeights< dim, spacedim >::weighting_callback ( const typename ::Triangulation< dim, spacedim >::cell_iterator & cell, const CellStatus status, const DoFHandler< dim, spacedim > & dof_handler, const parallel::TriangulationBase< dim, spacedim > & triangulation, const WeightingFunction & weighting_function )

staticprivate

A callback function that will be connected to the weight signal of the triangulation, to which the dof_handler is attached. Ultimately returns the weight for each cell, determined by the weighting_function provided as a parameter. Returns zero if dof_handler has not been initialized yet.

Definition at line 162 of file cell_weights.cc.

Member Data Documentation

connection

template<int dim, int spacedim = dim>

boost::signals2::connection parallel::CellWeights< dim, spacedim >::connection

private

A connection to the corresponding weight signal of the Triangulation which is attached to the DoFHandler.

Definition at line 213 of file cell_weights.h.

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The documentation for this class was generated from the following files:

• include/deal.II/distributed/cell_weights.h
• source/distributed/cell_weights.cc