#include <deal.II/fe/fe_q_iso_q1.h>

Inheritance diagram for FE_Q_iso_Q1< dim, spacedim >:

Public Member Functions
	FE_Q_iso_Q1 (const unsigned int n_subdivisions)

virtual std::string	get_name () const

virtual std::unique_ptr< FiniteElement< dim, spacedim > >	clone () const

virtual void	convert_generalized_support_point_values_to_dof_values (const std::vector< Vector< double > > &support_point_values, std::vector< double > &nodal_values) const

Functions to support hp
virtual FiniteElementDomination::Domination	compare_for_face_domination (const FiniteElement< dim, spacedim > &fe_other) const

Public Member Functions inherited from FE_Q_Base< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >
	FE_Q_Base (const TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > > &poly_space, const FiniteElementData< dim > &fe_data, const std::vector< bool > &restriction_is_additive_flags)

virtual void	get_interpolation_matrix (const FiniteElement< dim, spacedim > &source, FullMatrix< double > &matrix) const

virtual void	get_face_interpolation_matrix (const FiniteElement< dim, spacedim > &source, FullMatrix< double > &matrix) const

virtual void	get_subface_interpolation_matrix (const FiniteElement< dim, spacedim > &source, const unsigned int subface, FullMatrix< double > &matrix) const

virtual bool	has_support_on_face (const unsigned int shape_index, const unsigned int face_index) const

virtual const FullMatrix< double > &	get_restriction_matrix (const unsigned int child, const RefinementCase< dim > &refinement_case=RefinementCase< dim >::isotropic_refinement) const

virtual const FullMatrix< double > &	get_prolongation_matrix (const unsigned int child, const RefinementCase< dim > &refinement_case=RefinementCase< dim >::isotropic_refinement) const

virtual unsigned int	face_to_cell_index (const unsigned int face_dof_index, const unsigned int face, const bool face_orientation=true, const bool face_flip=false, const bool face_rotation=false) const

virtual std::pair< Table< 2, bool >, std::vector< unsigned int > >	get_constant_modes () const

virtual bool	hp_constraints_are_implemented () const

virtual std::vector< std::pair< unsigned int, unsigned int > >	hp_vertex_dof_identities (const FiniteElement< dim, spacedim > &fe_other) const

virtual std::vector< std::pair< unsigned int, unsigned int > >	hp_line_dof_identities (const FiniteElement< dim, spacedim > &fe_other) const

virtual std::vector< std::pair< unsigned int, unsigned int > >	hp_quad_dof_identities (const FiniteElement< dim, spacedim > &fe_other) const

Public Member Functions inherited from FE_Poly< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >
	FE_Poly (const TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > > &poly_space, const FiniteElementData< dim > &fe_data, const std::vector< bool > &restriction_is_additive_flags, const std::vector< ComponentMask > &nonzero_components)

unsigned int	get_degree () const

std::vector< unsigned int >	get_poly_space_numbering () const

std::vector< unsigned int >	get_poly_space_numbering_inverse () const

virtual double	shape_value (const unsigned int i, const Point< dim > &p) const

virtual double	shape_value_component (const unsigned int i, const Point< dim > &p, const unsigned int component) const

virtual Tensor< 1, dim >	shape_grad (const unsigned int i, const Point< dim > &p) const

virtual Tensor< 1, dim >	shape_grad_component (const unsigned int i, const Point< dim > &p, const unsigned int component) const

virtual Tensor< 2, dim >	shape_grad_grad (const unsigned int i, const Point< dim > &p) const

virtual Tensor< 2, dim >	shape_grad_grad_component (const unsigned int i, const Point< dim > &p, const unsigned int component) const

virtual Tensor< 3, dim >	shape_3rd_derivative (const unsigned int i, const Point< dim > &p) const

virtual Tensor< 3, dim >	shape_3rd_derivative_component (const unsigned int i, const Point< dim > &p, const unsigned int component) const

virtual Tensor< 4, dim >	shape_4th_derivative (const unsigned int i, const Point< dim > &p) const

virtual Tensor< 4, dim >	shape_4th_derivative_component (const unsigned int i, const Point< dim > &p, const unsigned int component) const

Public Member Functions inherited from FiniteElement< dim, spacedim >
	FiniteElement (const FiniteElementData< dim > &fe_data, const std::vector< bool > &restriction_is_additive_flags, const std::vector< ComponentMask > &nonzero_components)

	FiniteElement (FiniteElement< dim, spacedim > &&)=default

	FiniteElement (const FiniteElement< dim, spacedim > &)=default

virtual	~FiniteElement ()=default

std::pair< std::unique_ptr< FiniteElement< dim, spacedim > >, unsigned int >	operator^ (const unsigned int multiplicity) const

const FiniteElement< dim, spacedim > &	operator[] (const unsigned int fe_index) const

virtual bool	operator== (const FiniteElement< dim, spacedim > &fe) const

bool	operator!= (const FiniteElement< dim, spacedim > &) const

virtual std::size_t	memory_consumption () const

bool	prolongation_is_implemented () const

bool	isotropic_prolongation_is_implemented () const

bool	restriction_is_implemented () const

bool	isotropic_restriction_is_implemented () const

bool	restriction_is_additive (const unsigned int index) const

const FullMatrix< double > &	constraints (const ::internal::SubfaceCase< dim > &subface_case=::internal::SubfaceCase< dim >::case_isotropic) const

bool	constraints_are_implemented (const ::internal::SubfaceCase< dim > &subface_case=::internal::SubfaceCase< dim >::case_isotropic) const

std::pair< unsigned int, unsigned int >	system_to_component_index (const unsigned int index) const

unsigned int	component_to_system_index (const unsigned int component, const unsigned int index) const

std::pair< unsigned int, unsigned int >	face_system_to_component_index (const unsigned int index) const

unsigned int	adjust_quad_dof_index_for_face_orientation (const unsigned int index, const bool face_orientation, const bool face_flip, const bool face_rotation) const

unsigned int	adjust_line_dof_index_for_line_orientation (const unsigned int index, const bool line_orientation) const

const ComponentMask &	get_nonzero_components (const unsigned int i) const

unsigned int	n_nonzero_components (const unsigned int i) const

bool	is_primitive () const

bool	is_primitive (const unsigned int i) const

unsigned int	n_base_elements () const

virtual const FiniteElement< dim, spacedim > &	base_element (const unsigned int index) const

unsigned int	element_multiplicity (const unsigned int index) const

const FiniteElement< dim, spacedim > &	get_sub_fe (const ComponentMask &mask) const

virtual const FiniteElement< dim, spacedim > &	get_sub_fe (const unsigned int first_component, const unsigned int n_selected_components) const

std::pair< std::pair< unsigned int, unsigned int >, unsigned int >	system_to_base_index (const unsigned int index) const

std::pair< std::pair< unsigned int, unsigned int >, unsigned int >	face_system_to_base_index (const unsigned int index) const

types::global_dof_index	first_block_of_base (const unsigned int b) const

std::pair< unsigned int, unsigned int >	component_to_base_index (const unsigned int component) const

std::pair< unsigned int, unsigned int >	block_to_base_index (const unsigned int block) const

std::pair< unsigned int, types::global_dof_index >	system_to_block_index (const unsigned int component) const

unsigned int	component_to_block_index (const unsigned int component) const

ComponentMask	component_mask (const FEValuesExtractors::Scalar &scalar) const

ComponentMask	component_mask (const FEValuesExtractors::Vector &vector) const

ComponentMask	component_mask (const FEValuesExtractors::SymmetricTensor< 2 > &sym_tensor) const

ComponentMask	component_mask (const BlockMask &block_mask) const

BlockMask	block_mask (const FEValuesExtractors::Scalar &scalar) const

BlockMask	block_mask (const FEValuesExtractors::Vector &vector) const

BlockMask	block_mask (const FEValuesExtractors::SymmetricTensor< 2 > &sym_tensor) const

BlockMask	block_mask (const ComponentMask &component_mask) const

const std::vector< Point< dim > > &	get_unit_support_points () const

bool	has_support_points () const

virtual Point< dim >	unit_support_point (const unsigned int index) const

const std::vector< Point< dim-1 > > &	get_unit_face_support_points () const

bool	has_face_support_points () const

virtual Point< dim-1 >	unit_face_support_point (const unsigned int index) const

const std::vector< Point< dim > > &	get_generalized_support_points () const

bool	has_generalized_support_points () const

const std::vector< Point< dim-1 > > &	get_generalized_face_support_points () const

bool	has_generalized_face_support_points () const

GeometryPrimitive	get_associated_geometry_primitive (const unsigned int cell_dof_index) const

Public Member Functions inherited from Subscriptor
	Subscriptor ()

	Subscriptor (const Subscriptor &)

	Subscriptor (Subscriptor &&) noexcept

virtual	~Subscriptor ()

Subscriptor &	operator= (const Subscriptor &)

Subscriptor &	operator= (Subscriptor &&) noexcept

void	subscribe (const char *identifier=nullptr) const

void	unsubscribe (const char *identifier=nullptr) const

unsigned int	n_subscriptions () const

void	list_subscribers () const

template<class Archive >
void	serialize (Archive &ar, const unsigned int version)

Public Member Functions inherited from FiniteElementData< dim >
	FiniteElementData (const std::vector< unsigned int > &dofs_per_object, const unsigned int n_components, const unsigned int degree, const Conformity conformity=unknown, const BlockIndices &block_indices=BlockIndices())

unsigned int	n_dofs_per_vertex () const

unsigned int	n_dofs_per_line () const

unsigned int	n_dofs_per_quad () const

unsigned int	n_dofs_per_hex () const

unsigned int	n_dofs_per_face () const

unsigned int	n_dofs_per_cell () const

template<int structdim>
unsigned int	n_dofs_per_object () const

unsigned int	n_components () const

unsigned int	n_blocks () const

const BlockIndices &	block_indices () const

unsigned int	tensor_degree () const

bool	conforms (const Conformity) const

bool	operator== (const FiniteElementData &) const

Additional Inherited Members
Public Types inherited from FiniteElementData< dim >
enum	Conformity { unknown = 0x00, L2 = 0x01, Hcurl = 0x02, Hdiv = 0x04, H1 = Hcurl \| Hdiv, H2 = 0x0e }

Static Public Member Functions inherited from FE_Q_Base< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >
static ::ExceptionBase &	ExcFEQCannotHaveDegree0 ()

Static Public Member Functions inherited from FiniteElement< dim, spacedim >
static ::ExceptionBase &	ExcShapeFunctionNotPrimitive (int arg1)

static ::ExceptionBase &	ExcFENotPrimitive ()

static ::ExceptionBase &	ExcUnitShapeValuesDoNotExist ()

static ::ExceptionBase &	ExcFEHasNoSupportPoints ()

static ::ExceptionBase &	ExcEmbeddingVoid ()

static ::ExceptionBase &	ExcProjectionVoid ()

static ::ExceptionBase &	ExcWrongInterfaceMatrixSize (int arg1, int arg2)

static ::ExceptionBase &	ExcInterpolationNotImplemented ()

Static Public Member Functions inherited from Subscriptor
static ::ExceptionBase &	ExcInUse (int arg1, std::string arg2, std::string arg3)

static ::ExceptionBase &	ExcNoSubscriber (std::string arg1, std::string arg2)

Public Attributes inherited from FiniteElementData< dim >
const unsigned int	dofs_per_vertex

const unsigned int	dofs_per_line

const unsigned int	dofs_per_quad

const unsigned int	dofs_per_hex

const unsigned int	first_line_index

const unsigned int	first_quad_index

const unsigned int	first_hex_index

const unsigned int	first_face_line_index

const unsigned int	first_face_quad_index

const unsigned int	dofs_per_face

const unsigned int	dofs_per_cell

const unsigned int	components

const unsigned int	degree

const Conformity	conforming_space

const BlockIndices	block_indices_data

Static Public Attributes inherited from FiniteElement< dim, spacedim >
static const unsigned int	space_dimension = spacedim

Static Public Attributes inherited from FiniteElementData< dim >
static const unsigned int	dimension = dim

Protected Member Functions inherited from FE_Q_Base< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >
void	initialize (const std::vector< Point< 1 > > &support_points_1d)

void	initialize_constraints (const std::vector< Point< 1 > > &points)

void	initialize_unit_support_points (const std::vector< Point< 1 > > &points)

void	initialize_unit_face_support_points (const std::vector< Point< 1 > > &points)

void	initialize_quad_dof_index_permutation ()

Protected Member Functions inherited from FE_Poly< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >
void	correct_third_derivatives (internal::FEValuesImplementation::FiniteElementRelatedData< dim, spacedim > &output_data, const internal::FEValuesImplementation::MappingRelatedData< dim, spacedim > &mapping_data, const unsigned int n_q_points, const unsigned int dof) const

Protected Member Functions inherited from FiniteElement< dim, spacedim >
void	reinit_restriction_and_prolongation_matrices (const bool isotropic_restriction_only=false, const bool isotropic_prolongation_only=false)

TableIndices< 2 >	interface_constraints_size () const

virtual std::unique_ptr< InternalDataBase >	get_face_data (const UpdateFlags update_flags, const Mapping< dim, spacedim > &mapping, const Quadrature< dim-1 > &quadrature, ::internal::FEValuesImplementation::FiniteElementRelatedData< dim, spacedim > &output_data) const

virtual std::unique_ptr< InternalDataBase >	get_subface_data (const UpdateFlags update_flags, const Mapping< dim, spacedim > &mapping, const Quadrature< dim-1 > &quadrature, ::internal::FEValuesImplementation::FiniteElementRelatedData< dim, spacedim > &output_data) const

virtual void	fill_fe_values (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const CellSimilarity::Similarity cell_similarity, const Quadrature< dim > &quadrature, const Mapping< dim, spacedim > &mapping, const typename Mapping< dim, spacedim >::InternalDataBase &mapping_internal, const ::internal::FEValuesImplementation::MappingRelatedData< dim, spacedim > &mapping_data, const InternalDataBase &fe_internal, ::internal::FEValuesImplementation::FiniteElementRelatedData< dim, spacedim > &output_data) const =0

virtual void	fill_fe_face_values (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const unsigned int face_no, const Quadrature< dim-1 > &quadrature, const Mapping< dim, spacedim > &mapping, const typename Mapping< dim, spacedim >::InternalDataBase &mapping_internal, const ::internal::FEValuesImplementation::MappingRelatedData< dim, spacedim > &mapping_data, const InternalDataBase &fe_internal, ::internal::FEValuesImplementation::FiniteElementRelatedData< dim, spacedim > &output_data) const =0

virtual void	fill_fe_subface_values (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const unsigned int face_no, const unsigned int sub_no, const Quadrature< dim-1 > &quadrature, const Mapping< dim, spacedim > &mapping, const typename Mapping< dim, spacedim >::InternalDataBase &mapping_internal, const ::internal::FEValuesImplementation::MappingRelatedData< dim, spacedim > &mapping_data, const InternalDataBase &fe_internal, ::internal::FEValuesImplementation::FiniteElementRelatedData< dim, spacedim > &output_data) const =0

Static Protected Member Functions inherited from FE_Q_Base< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >
static std::vector< unsigned int >	get_dpo_vector (const unsigned int degree)

Static Protected Member Functions inherited from FiniteElement< dim, spacedim >
static std::vector< unsigned int >	compute_n_nonzero_components (const std::vector< ComponentMask > &nonzero_components)

Protected Attributes inherited from FE_Poly< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >
TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >	poly_space

Protected Attributes inherited from FiniteElement< dim, spacedim >
std::vector< std::vector< FullMatrix< double > > >	restriction

std::vector< std::vector< FullMatrix< double > > >	prolongation

FullMatrix< double >	interface_constraints

std::vector< Point< dim > >	unit_support_points

std::vector< Point< dim-1 > >	unit_face_support_points

std::vector< Point< dim > >	generalized_support_points

std::vector< Point< dim-1 > >	generalized_face_support_points

Table< 2, int >	adjust_quad_dof_index_for_face_orientation_table

std::vector< int >	adjust_line_dof_index_for_line_orientation_table

std::vector< std::pair< unsigned int, unsigned int > >	system_to_component_table

std::vector< std::pair< unsigned int, unsigned int > >	face_system_to_component_table

std::vector< std::pair< std::pair< unsigned int, unsigned int >, unsigned int > >	system_to_base_table

std::vector< std::pair< std::pair< unsigned int, unsigned int >, unsigned int > >	face_system_to_base_table

BlockIndices	base_to_block_indices

std::vector< std::pair< std::pair< unsigned int, unsigned int >, unsigned int > >	component_to_base_table

const std::vector< bool >	restriction_is_additive_flags

const std::vector< ComponentMask >	nonzero_components

const std::vector< unsigned int >	n_nonzero_components_table

const bool	cached_primitivity

Detailed Description

template<int dim, int spacedim = dim>
class FE_Q_iso_Q1< dim, spacedim >

Implementation of a scalar Lagrange finite element Qp-iso-Q1 that defines the finite element space of continuous, piecewise linear elements with p subdivisions in each coordinate direction. It yields an element with the same number of degrees of freedom as the Qp elements but using linear interpolation instead of higher order one. This type of element is also called macro element in the literature as it really consists of several smaller elements, namely p^dim such sub-cells.

The numbering of degrees of freedom is done in exactly the same way as in FE_Q of degree p. See there for a detailed description on how degrees of freedom are numbered within one element.

This element represents a Q-linear finite element space on a reduced mesh size h/p. Its effect is equivalent to using FE_Q of degree one on a finer mesh by a factor p if an equivalent quadrature is used. However, this element reduces the flexibility in the choice of (adaptive) mesh size by exactly this factor p, which typically reduces efficiency. On the other hand, comparing this element with p subdivisions to the FE_Q element of degree p on the same mesh shows that the convergence is typically much worse for smooth problems. In particular, Qp elements achieve interpolation orders of h^p+1 in the L2 norm, whereas these elements reach only (h/p)². For these two reasons, this element is usually not very useful as a standalone. In addition, any evaluation of face terms on the boundaries within the elements becomes impossible with this element because deal.II does not have the equivalent of FEFaceValues for lower-dimensional integrals in the interior of cells.

Nonetheless, there are a few use cases where this element actually is useful:

Systems of PDEs where certain variables demand for higher resolutions than the others and the additional degrees of freedom should be spent on increasing the resolution of linears instead of higher order polynomials, and you do not want to use two different meshes for the different components. This can be the case when irregularities (shocks) appear in the solution and stabilization techniques are used that work for linears but not higher order elements.
Stokes/Navier Stokes systems such as the one discussed in step-22 could be solved with Q2-iso-Q1 elements for velocities instead of Q2 elements. Combined with Q1 pressures they give a stable mixed element pair. However, they perform worse than the standard (Taylor-Hood \(Q_2\times Q_1\)) approach in most situations.
Preconditioning systems of FE_Q systems of higher order p with a preconditioner based on Qp-iso-Q1 elements: Some preconditioners like algebraic multigrid perform much better with linear elements than with higher order elements because they often implicitly assume a sparse connectivity between entries. Then, creating a preconditioner matrix based on these elements yields the same number of degrees of freedom (and a spectrally equivalent linear system), which can be combined with a (high order) system matrix in an iterative solver like CG.

Appropriate integration

Due to the nature of these elements as a concatenation of linears, care must be taken when selecting quadrature formulas for this element. The standard choice for an element of p subelements is a formula QIterated<dim>(QGauss<1>(2), p), which corresponds to the formula that would be used for integrating functions on a finer mesh. This is in contrast with FE_Q(p) where QGauss<dim>(p+1) is the default choice. In particular, care must be taken to not use a quadrature formula that evaluates the basis functions (and their derivatives) on sub-element boundaries as the gradients of piecewiese functions on internal boundaries are set to zero. No checks are performed internally to ensure that this is not the case - it is the user's responsibility to avoid these situations.

Also note that the usual deal.II routines for setting up sparsity patterns and assembling matrices do not make use of the increased sparsity in this element compared to FE_Q. This is because DoFTools::make_sparsity_pattern assumes coupling between all degrees of freedom within the element, whereas FE_Q_iso_Q1 with more than one subdivision does have less coupling.

Author: Martin Kronbichler, 2013

Definition at line 111 of file fe_q_iso_q1.h.

Constructor & Destructor Documentation

◆ FE_Q_iso_Q1()

template<int dim, int spacedim>

FE_Q_iso_Q1< dim, spacedim >::FE_Q_iso_Q1 ( const unsigned int n_subdivisions )

Construct a FE_Q_iso_Q1 element with a given number of subdivisions. The number of subdivision is similar to the degree in FE_Q in the sense that both elements produce the same number of degrees of freedom.

Definition at line 33 of file fe_q_iso_q1.cc.

Member Function Documentation

◆ get_name()

template<int dim, int spacedim>

std::string FE_Q_iso_Q1< dim, spacedim >::get_name ( ) const

virtual

Return a string that uniquely identifies a finite element. This class returns FE_Q_iso_q1<dim>(equivalent_degree), with dim and equivalent_degree replaced by appropriate values.

Implements FiniteElement< dim, spacedim >.

Definition at line 57 of file fe_q_iso_q1.cc.

◆ clone()

template<int dim, int spacedim>

std::unique_ptr< FiniteElement< dim, spacedim > > FE_Q_iso_Q1< dim, spacedim >::clone ( ) const

virtual

A sort of virtual copy constructor, this function returns a copy of the finite element object. Derived classes need to override the function here in this base class and return an object of the same type as the derived class.

Some places in the library, for example the constructors of FESystem as well as the hp::FECollection class, need to make copies of finite elements without knowing their exact type. They do so through this function.

Implements FiniteElement< dim, spacedim >.

Definition at line 97 of file fe_q_iso_q1.cc.

◆ convert_generalized_support_point_values_to_dof_values()

template<int dim, int spacedim>

void FE_Q_iso_Q1< dim, spacedim >::convert_generalized_support_point_values_to_dof_values	(	const std::vector< Vector< double > > &	support_point_values,
		std::vector< double > &	nodal_values
	)		const

virtual

Implementation of the corresponding function in the FiniteElement class. Since the current element is interpolatory, the nodal values are exactly the support point values. Furthermore, since the current element is scalar, the support point values need to be vectors of length 1.

Reimplemented from FiniteElement< dim, spacedim >.

Definition at line 75 of file fe_q_iso_q1.cc.

◆ compare_for_face_domination()

template<int dim, int spacedim>

FiniteElementDomination::Domination FE_Q_iso_Q1< dim, spacedim >::compare_for_face_domination ( const FiniteElement< dim, spacedim > & fe_other ) const

virtual

Return whether this element dominates the one given as argument when they meet at a common face, whether it is the other way around, whether neither dominates, or if either could dominate.

For a definition of domination, see FiniteElementDomination::Domination and in particular the hp paper.

Reimplemented from FE_Q_Base< TensorProductPolynomials< dim, Polynomials::PiecewisePolynomial< double > >, dim, spacedim >.

Definition at line 107 of file fe_q_iso_q1.cc.

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

deal.II/fe/fe_q_iso_q1.h
source/fe/fe_q_iso_q1.cc

Public Member Functions

Additional Inherited Members

Detailed Description

template<int dim, int spacedim = dim> class FE_Q_iso_Q1< dim, spacedim >

Appropriate integration

Constructor & Destructor Documentation

◆ FE_Q_iso_Q1()

Member Function Documentation

◆ get_name()

◆ clone()

◆ convert_generalized_support_point_values_to_dof_values()

◆ compare_for_face_domination()

template<int dim, int spacedim = dim>
class FE_Q_iso_Q1< dim, spacedim >