Reference documentation for deal.II version Git b304a00 2017-03-22 15:49:17 -0600
Classes | Public Member Functions | Protected Member Functions | Protected Attributes | Friends | List of all members
MappingQGeneric< dim, spacedim > Class Template Reference

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

Inheritance diagram for MappingQGeneric< dim, spacedim >:
[legend]

Classes

class  InternalData
 

Public Member Functions

 MappingQGeneric (const unsigned int polynomial_degree)
 
 MappingQGeneric (const MappingQGeneric< dim, spacedim > &mapping)
 
virtual Mapping< dim, spacedim > * clone () const
 
unsigned int get_degree () const
 
virtual bool preserves_vertex_locations () const
 
Mapping points between reference and real cells
virtual Point< spacedim > transform_unit_to_real_cell (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const Point< dim > &p) const
 
virtual Point< dim > transform_real_to_unit_cell (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const Point< spacedim > &p) const
 
Functions to transform tensors from reference to real coordinates
virtual void transform (const ArrayView< const Tensor< 1, dim > > &input, const MappingType type, const typename Mapping< dim, spacedim >::InternalDataBase &internal, const ArrayView< Tensor< 1, spacedim > > &output) const
 
virtual void transform (const ArrayView< const DerivativeForm< 1, dim, spacedim > > &input, const MappingType type, const typename Mapping< dim, spacedim >::InternalDataBase &internal, const ArrayView< Tensor< 2, spacedim > > &output) const
 
virtual void transform (const ArrayView< const Tensor< 2, dim > > &input, const MappingType type, const typename Mapping< dim, spacedim >::InternalDataBase &internal, const ArrayView< Tensor< 2, spacedim > > &output) const
 
virtual void transform (const ArrayView< const DerivativeForm< 2, dim, spacedim > > &input, const MappingType type, const typename Mapping< dim, spacedim >::InternalDataBase &internal, const ArrayView< Tensor< 3, spacedim > > &output) const
 
virtual void transform (const ArrayView< const Tensor< 3, dim > > &input, const MappingType type, const typename Mapping< dim, spacedim >::InternalDataBase &internal, const ArrayView< Tensor< 3, spacedim > > &output) const
 
Interface with FEValues
virtual UpdateFlags requires_update_flags (const UpdateFlags update_flags) const
 
virtual InternalDataget_data (const UpdateFlags, const Quadrature< dim > &quadrature) const
 
virtual InternalDataget_face_data (const UpdateFlags flags, const Quadrature< dim-1 > &quadrature) const
 
virtual InternalDataget_subface_data (const UpdateFlags flags, const Quadrature< dim-1 > &quadrature) const
 
virtual CellSimilarity::Similarity fill_fe_values (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const CellSimilarity::Similarity cell_similarity, const Quadrature< dim > &quadrature, const typename Mapping< dim, spacedim >::InternalDataBase &internal_data,::internal::FEValues::MappingRelatedData< dim, spacedim > &output_data) const
 
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 typename Mapping< dim, spacedim >::InternalDataBase &internal_data,::internal::FEValues::MappingRelatedData< dim, spacedim > &output_data) const
 
virtual void fill_fe_subface_values (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const unsigned int face_no, const unsigned int subface_no, const Quadrature< dim-1 > &quadrature, const typename Mapping< dim, spacedim >::InternalDataBase &internal_data,::internal::FEValues::MappingRelatedData< dim, spacedim > &output_data) const
 
- Public Member Functions inherited from Mapping< dim, spacedim >
virtual ~Mapping ()
 
virtual std_cxx11::array< Point< spacedim >, GeometryInfo< dim >::vertices_per_cell > get_vertices (const typename Triangulation< dim, spacedim >::cell_iterator &cell) const
 
Point< dim-1 > project_real_point_to_unit_point_on_face (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const unsigned int &face_no, const Point< spacedim > &p) const
 
- Public Member Functions inherited from Subscriptor
 Subscriptor ()
 
 Subscriptor (const Subscriptor &)
 
 Subscriptor (Subscriptor &&)
 
virtual ~Subscriptor ()
 
Subscriptoroperator= (const Subscriptor &)
 
Subscriptoroperator= (Subscriptor &&)
 
void subscribe (const char *identifier=0) const
 
void unsubscribe (const char *identifier=0) const
 
unsigned int n_subscriptions () const
 
void list_subscribers () const
 
template<class Archive >
void serialize (Archive &ar, const unsigned int version)
 

Protected Member Functions

virtual std::vector< Point< spacedim > > compute_mapping_support_points (const typename Triangulation< dim, spacedim >::cell_iterator &cell) const
 
Point< dim > transform_real_to_unit_cell_internal (const typename Triangulation< dim, spacedim >::cell_iterator &cell, const Point< spacedim > &p, const Point< dim > &initial_p_unit) const
 
virtual void add_line_support_points (const typename Triangulation< dim, spacedim >::cell_iterator &cell, std::vector< Point< spacedim > > &a) const
 
virtual void add_quad_support_points (const typename Triangulation< dim, spacedim >::cell_iterator &cell, std::vector< Point< spacedim > > &a) const
 
Interface with FEValues

Protected Attributes

const unsigned int polynomial_degree
 
const std_cxx11::unique_ptr< FE_Q< dim > > fe_q
 
std::vector< Table< 2, double > > support_point_weights_perimeter_to_interior
 
Table< 2, double > support_point_weights_cell
 

Friends

template<int , int >
class MappingQ
 

Additional Inherited Members

- Static Public Member Functions inherited from Mapping< dim, spacedim >
static::ExceptionBase & ExcInvalidData ()
 
static::ExceptionBase & ExcTransformationFailed ()
 
static::ExceptionBase & ExcDistortedMappedCell (Point< spacedim > arg1, double arg2, int arg3)
 
- Static Public Member Functions inherited from Subscriptor
static::ExceptionBase & ExcInUse (int arg1, char *arg2, std::string &arg3)
 
static::ExceptionBase & ExcNoSubscriber (char *arg1, char *arg2)
 

Detailed Description

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

This class implements the functionality for polynomial mappings \(Q_p\) of polynomial degree \(p\) that will be used on all cells of the mesh. The MappingQ1 and MappingQ classes specialize this behavior slightly.

The class is poorly named. It should really have been called MappingQ because it consistently uses \(Q_p\) mappings on all cells of a triangulation. However, the name MappingQ was already taken when we rewrote the entire class hierarchy for mappings. One might argue that one should always use MappingQGeneric over the existing class MappingQ (which, unless explicitly specified during the construction of the object, only uses mappings of degree \(p\) on cells at the boundary of the domain). On the other hand, there are good reasons to use MappingQ in many situations: in many situations, curved domains are only provided with information about how exactly edges at the boundary are shaped, but we do not know anything about internal edges. Thus, in the absence of other information, we can only assume that internal edges are straight lines, and in that case internal cells may as well be treated is bilinear quadrilaterals or trilinear hexahedra. (An example of how such meshes look is shown in step-1 already, but it is also discussed in the "Results" section of step-6.) Because bi-/trilinear mappings are significantly cheaper to compute than higher order mappings, it is advantageous in such situations to use the higher order mapping only on cells at the boundary of the domain – i.e., the behavior of MappingQ. Of course, MappingQGeneric also uses bilinear mappings for interior cells as long as it has no knowledge about curvature of interior edges, but it implements this the expensive way: as a general \(Q_p\) mapping where the mapping support points just happen to be arranged along linear or bilinear edges or faces.

There are a number of special cases worth considering:

Behavior along curved boundaries and with different manifolds

As described above, one often only knows a manifold description of a surface but not the interior of the computational domain. In such a case, a StraightBoundary object will be assigned to the interior entities that describes a usual planar coordinate system where the additional points for the higher order mapping are placed exactly according to a bi-/trilinear mapping. When combined with a non-flat manifold on the boundary, for example a circle bulging into the interior of a square cell, the two manifold descriptions are in general incompatible. For example, a FlatManifold defined solely through the cell's vertices would put an interior point located at some small distance epsilon away from the boundary along a straight line and thus in general outside the concave part of a circle. If the polynomial degree of MappingQ is sufficiently high, the transformation from the reference cell to such a cell would in general contain inverted regions close to the boundary.

In order to avoid this situation, this class applies a smoothing on cells adjacent to the boundary by using so-called Laplace smoothing by default. In the algorithm that computes additional points, the compute_mapping_support_points() method, all the entities of the cells are passed through hierarchically, starting from the lines to the quads and finally hexes. Points on objects higher up in the hierarchy are obtained from the manifold associated with that object, taking into account all the points previously computed by the manifolds associated with the lower-dimensional objects, not just the vertices. If only a line is assigned a curved boundary but the adjacent quad is on a flat manifold, the flat manifold on the quad will take the points on the deformed line into account when interpolating the position of the additional points inside the quad and thus always result in a well-defined transformation.

While the smoothing approach works well for filling holes or avoiding inversions with low and medium convergence orders up to approximately three to four, there is nonetheless an inherent shortcoming when switching from a curved manifold to a flat manifold over a face (and the associated smoothing). The finite element theory (see e.g. Strang and Fix, 1973, Sections 2.2 and 3.3 and in particular Theorem 3.6) requires the transformation to be globally C^0 continuous also over several elements and to be uniform as the mesh is refined. Even though the Laplace smoothing fixes the discontinuity within one layer of cells, it cannot provide uniformity as the change is always within one layer of elements only. For example, the convergence rates for solving the Laplacian on a circle where only the boundary is deformed and the above mesh smoothing algorithm is applied will typically not exceed 3.5 (or 3 in the elements adjacent to the boundary), even for fourth or fifth degree polynomials. In such a case, the curved manifold needs to be switched to a flat manifold in a smooth way that does not depend on the mesh size and eventually covers a region of cells instead of only those that are immediately adjacent to the circular boundary.

Author
Wolfgang Bangerth, 2015, Martin Kronbichler, 2017

Definition at line 137 of file mapping_q_generic.h.

Constructor & Destructor Documentation

template<int dim, int spacedim>
MappingQGeneric< dim, spacedim >::MappingQGeneric ( const unsigned int  polynomial_degree)

Constructor. polynomial_degree denotes the polynomial degree of the polynomials that are used to map cells from the reference to the real cell.

Definition at line 1252 of file mapping_q_generic.cc.

template<int dim, int spacedim>
MappingQGeneric< dim, spacedim >::MappingQGeneric ( const MappingQGeneric< dim, spacedim > &  mapping)

Copy constructor.

Definition at line 1267 of file mapping_q_generic.cc.

Member Function Documentation

template<int dim, int spacedim>
Mapping< dim, spacedim > * MappingQGeneric< dim, spacedim >::clone ( ) const
virtual

Return a pointer to a copy of the present object. The caller of this copy then assumes ownership of it.

The function is declared abstract virtual in this base class, and derived classes will have to implement it.

This function is mainly used by the hp::MappingCollection class.

Implements Mapping< dim, spacedim >.

Reimplemented in MappingQ1Eulerian< dim, VectorType, spacedim >, and MappingQ1< dim, spacedim >.

Definition at line 1281 of file mapping_q_generic.cc.

template<int dim, int spacedim>
unsigned int MappingQGeneric< dim, spacedim >::get_degree ( ) const

Return the degree of the mapping, i.e. the value which was passed to the constructor.

Definition at line 1291 of file mapping_q_generic.cc.

template<int dim, int spacedim = dim>
virtual bool MappingQGeneric< dim, spacedim >::preserves_vertex_locations ( ) const
virtual

Always returns true because the default implementation of functions in this class preserves vertex locations.

Implements Mapping< dim, spacedim >.

Reimplemented in MappingQ1Eulerian< dim, VectorType, spacedim >.

template<int dim, int spacedim>
Point< spacedim > MappingQGeneric< dim, spacedim >::transform_unit_to_real_cell ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
const Point< dim > &  p 
) const
virtual

Maps the point p on the unit cell to the corresponding point on the real cell cell.

Parameters
cellIterator to the cell that will be used to define the mapping.
pLocation of a point on the reference cell.
Returns
The location of the reference point mapped to real space using the mapping defined by the class derived from the current one that implements the mapping, and the coordinates of the cell identified by the first argument.

Implements Mapping< dim, spacedim >.

Definition at line 1301 of file mapping_q_generic.cc.

template<int dim, int spacedim>
Point< dim > MappingQGeneric< dim, spacedim >::transform_real_to_unit_cell ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
const Point< spacedim > &  p 
) const
virtual

Maps the point p on the real cell to the corresponding point on the unit cell, and return its coordinates. This function provides the inverse of the mapping provided by transform_unit_to_real_cell().

In the codimension one case, this function returns the normal projection of the real point p on the curve or surface identified by the cell.

Note
Polynomial mappings from the reference (unit) cell coordinates to the coordinate system of a real cell are not always invertible if the point for which the inverse mapping is to be computed lies outside the cell's boundaries. In such cases, the current function may fail to compute a point on the reference cell whose image under the mapping equals the given point p. If this is the case then this function throws an exception of type Mapping::ExcTransformationFailed . Whether the given point p lies outside the cell can therefore be determined by checking whether the returned reference coordinates lie inside or outside the reference cell (e.g., using GeometryInfo::is_inside_unit_cell()) or whether the exception mentioned above has been thrown.
Parameters
cellIterator to the cell that will be used to define the mapping.
pLocation of a point on the given cell.
Returns
The reference cell location of the point that when mapped to real space equals the coordinates given by the second argument. This mapping uses the mapping defined by the class derived from the current one that implements the mapping, and the coordinates of the cell identified by the first argument.

Implements Mapping< dim, spacedim >.

Definition at line 1825 of file mapping_q_generic.cc.

template<int dim, int spacedim>
void MappingQGeneric< dim, spacedim >::transform ( const ArrayView< const Tensor< 1, dim > > &  input,
const MappingType  type,
const typename Mapping< dim, spacedim >::InternalDataBase internal,
const ArrayView< Tensor< 1, spacedim > > &  output 
) const
virtual

Transform a field of vectors or 1-differential forms according to the selected MappingType.

Note
Normally, this function is called by a finite element, filling FEValues objects. For this finite element, there should be an alias MappingType like mapping_bdm, mapping_nedelec, etc. This alias should be preferred to using the types below.

The mapping types currently implemented by derived classes are:

  • mapping_contravariant: maps a vector field on the reference cell to the physical cell through the Jacobian:

    \[ \mathbf u(\mathbf x) = J(\hat{\mathbf x})\hat{\mathbf u}(\hat{\mathbf x}). \]

    In physics, this is usually referred to as the contravariant transformation. Mathematically, it is the push forward of a vector field.

  • mapping_covariant: maps a field of one-forms on the reference cell to a field of one-forms on the physical cell. (Theoretically this would refer to a DerivativeForm<1,dim,1> but we canonically identify this type with a Tensor<1,dim>). Mathematically, it is the pull back of the differential form

    \[ \mathbf u(\mathbf x) = J(\hat{\mathbf x})(J(\hat{\mathbf x})^{T} J(\hat{\mathbf x}))^{-1}\hat{\mathbf u}(\hat{\mathbf x}). \]

    Gradients of scalar differentiable functions are transformed this way.

    In the case when dim=spacedim the previous formula reduces to

    \[ \mathbf u(\mathbf x) = J(\hat{\mathbf x})^{-T}\hat{\mathbf u}(\hat{\mathbf x}) \]

    because we assume that the mapping \(\mathbf F_K\) is always invertible, and consequently its Jacobian \(J\) is an invertible matrix.

  • mapping_piola: A field of dim-1-forms on the reference cell is also represented by a vector field, but again transforms differently, namely by the Piola transform

    \[ \mathbf u(\mathbf x) = \frac{1}{\text{det}\;J(\mathbf x)} J(\mathbf x) \hat{\mathbf u}(\mathbf x). \]

Parameters
[in]inputAn array (or part of an array) of input objects that should be mapped.
[in]typeThe kind of mapping to be applied.
[in]internalA pointer to an object of type Mapping::InternalDataBase that contains information previously stored by the mapping. The object pointed to was created by the get_data(), get_face_data(), or get_subface_data() function, and will have been updated as part of a call to fill_fe_values(), fill_fe_face_values(), or fill_fe_subface_values() for the current cell, before calling the current function. In other words, this object also represents with respect to which cell the transformation should be applied to.
[out]outputAn array (or part of an array) into which the transformed objects should be placed. (Note that the array view is const, but the tensors it points to are not.)

Implements Mapping< dim, spacedim >.

Definition at line 3433 of file mapping_q_generic.cc.

template<int dim, int spacedim>
void MappingQGeneric< dim, spacedim >::transform ( const ArrayView< const DerivativeForm< 1, dim, spacedim > > &  input,
const MappingType  type,
const typename Mapping< dim, spacedim >::InternalDataBase internal,
const ArrayView< Tensor< 2, spacedim > > &  output 
) const
virtual

Transform a field of differential forms from the reference cell to the physical cell. It is useful to think of \(\mathbf{T} = \nabla \mathbf u\) and \(\hat{\mathbf T} = \hat \nabla \hat{\mathbf u}\), with \(\mathbf u\) a vector field. The mapping types currently implemented by derived classes are:

  • mapping_covariant: maps a field of forms on the reference cell to a field of forms on the physical cell. Mathematically, it is the pull back of the differential form

    \[ \mathbf T(\mathbf x) = \hat{\mathbf T}(\hat{\mathbf x}) J(\hat{\mathbf x})(J(\hat{\mathbf x})^{T} J(\hat{\mathbf x}))^{-1}. \]

    Jacobians of spacedim-vector valued differentiable functions are transformed this way.

    In the case when dim=spacedim the previous formula reduces to

    \[ \mathbf T(\mathbf x) = \hat{\mathbf u}(\hat{\mathbf x}) J(\hat{\mathbf x})^{-1}. \]

Note
It would have been more reasonable to make this transform a template function with the rank in DerivativeForm<1, dim, rank>. Unfortunately C++ does not allow templatized virtual functions. This is why we identify DerivativeForm<1, dim, 1> with a Tensor<1,dim> when using mapping_covariant() in the function transform() above this one.
Parameters
[in]inputAn array (or part of an array) of input objects that should be mapped.
[in]typeThe kind of mapping to be applied.
[in]internalA pointer to an object of type Mapping::InternalDataBase that contains information previously stored by the mapping. The object pointed to was created by the get_data(), get_face_data(), or get_subface_data() function, and will have been updated as part of a call to fill_fe_values(), fill_fe_face_values(), or fill_fe_subface_values() for the current cell, before calling the current function. In other words, this object also represents with respect to which cell the transformation should be applied to.
[out]outputAn array (or part of an array) into which the transformed objects should be placed. (Note that the array view is const, but the tensors it points to are not.)

Implements Mapping< dim, spacedim >.

Definition at line 3446 of file mapping_q_generic.cc.

template<int dim, int spacedim>
void MappingQGeneric< dim, spacedim >::transform ( const ArrayView< const Tensor< 2, dim > > &  input,
const MappingType  type,
const typename Mapping< dim, spacedim >::InternalDataBase internal,
const ArrayView< Tensor< 2, spacedim > > &  output 
) const
virtual

Transform a tensor field from the reference cell to the physical cell. These tensors are usually the Jacobians in the reference cell of vector fields that have been pulled back from the physical cell. The mapping types currently implemented by derived classes are:

  • mapping_contravariant_gradient: it assumes \(\mathbf u(\mathbf x) = J \hat{\mathbf u}\) so that

    \[ \mathbf T(\mathbf x) = J(\hat{\mathbf x}) \hat{\mathbf T}(\hat{\mathbf x}) J(\hat{\mathbf x})^{-1}. \]

  • mapping_covariant_gradient: it assumes \(\mathbf u(\mathbf x) = J^{-T} \hat{\mathbf u}\) so that

    \[ \mathbf T(\mathbf x) = J(\hat{\mathbf x})^{-T} \hat{\mathbf T}(\hat{\mathbf x}) J(\hat{\mathbf x})^{-1}. \]

  • mapping_piola_gradient: it assumes \(\mathbf u(\mathbf x) = \frac{1}{\text{det}\;J(\mathbf x)} J(\mathbf x) \hat{\mathbf u}(\mathbf x)\) so that

    \[ \mathbf T(\mathbf x) = \frac{1}{\text{det}\;J(\mathbf x)} J(\hat{\mathbf x}) \hat{\mathbf T}(\hat{\mathbf x}) J(\hat{\mathbf x})^{-1}. \]

Todo:
The formulas for mapping_covariant_gradient, mapping_contravariant_gradient and mapping_piola_gradient are only true as stated for linear mappings. If, for example, the mapping is bilinear (or has a higher order polynomial degree) then there is a missing term associated with the derivative of \(J\).
Parameters
[in]inputAn array (or part of an array) of input objects that should be mapped.
[in]typeThe kind of mapping to be applied.
[in]internalA pointer to an object of type Mapping::InternalDataBase that contains information previously stored by the mapping. The object pointed to was created by the get_data(), get_face_data(), or get_subface_data() function, and will have been updated as part of a call to fill_fe_values(), fill_fe_face_values(), or fill_fe_subface_values() for the current cell, before calling the current function. In other words, this object also represents with respect to which cell the transformation should be applied to.
[out]outputAn array (or part of an array) into which the transformed objects should be placed. (Note that the array view is const, but the tensors it points to are not.)

Implements Mapping< dim, spacedim >.

Definition at line 3459 of file mapping_q_generic.cc.

template<int dim, int spacedim>
void MappingQGeneric< dim, spacedim >::transform ( const ArrayView< const DerivativeForm< 2, dim, spacedim > > &  input,
const MappingType  type,
const typename Mapping< dim, spacedim >::InternalDataBase internal,
const ArrayView< Tensor< 3, spacedim > > &  output 
) const
virtual

Transform a tensor field from the reference cell to the physical cell. This tensors are most of times the hessians in the reference cell of vector fields that have been pulled back from the physical cell.

The mapping types currently implemented by derived classes are:

  • mapping_covariant_gradient: maps a field of forms on the reference cell to a field of forms on the physical cell. Mathematically, it is the pull back of the differential form

    \[ \mathbf T_{ijk}(\mathbf x) = \hat{\mathbf T}_{iJK}(\hat{\mathbf x}) J_{jJ}^{\dagger} J_{kK}^{\dagger}\]

    ,

    where

    \[ J^{\dagger} = J(\hat{\mathbf x})(J(\hat{\mathbf x})^{T} J(\hat{\mathbf x}))^{-1}. \]

Hessians of spacedim-vector valued differentiable functions are transformed this way (After subtraction of the product of the derivative with the Jacobian gradient).

In the case when dim=spacedim the previous formula reduces to

\[J^{\dagger} = J^{-1}\]

Parameters
[in]inputAn array (or part of an array) of input objects that should be mapped.
[in]typeThe kind of mapping to be applied.
[in]internalA pointer to an object of type Mapping::InternalDataBase that contains information previously stored by the mapping. The object pointed to was created by the get_data(), get_face_data(), or get_subface_data() function, and will have been updated as part of a call to fill_fe_values(), fill_fe_face_values(), or fill_fe_subface_values() for the current cell, before calling the current function. In other words, this object also represents with respect to which cell the transformation should be applied to.
[out]outputAn array (or part of an array) into which the transformed objects should be placed. (Note that the array view is const, but the tensors it points to are not.)

Implements Mapping< dim, spacedim >.

Definition at line 3485 of file mapping_q_generic.cc.

template<int dim, int spacedim>
void MappingQGeneric< dim, spacedim >::transform ( const ArrayView< const Tensor< 3, dim > > &  input,
const MappingType  type,
const typename Mapping< dim, spacedim >::InternalDataBase internal,
const ArrayView< Tensor< 3, spacedim > > &  output 
) const
virtual

Transform a field of 3-differential forms from the reference cell to the physical cell. It is useful to think of \(\mathbf{T}_{ijk} = D^2_{jk} \mathbf u_i\) and \(\mathbf{\hat T}_{IJK} = \hat D^2_{JK} \mathbf{\hat u}_I\), with \(\mathbf u_i\) a vector field.

The mapping types currently implemented by derived classes are:

  • mapping_contravariant_hessian: it assumes \(\mathbf u_i(\mathbf x) = J_{iI} \hat{\mathbf u}_I\) so that

    \[ \mathbf T_{ijk}(\mathbf x) = J_{iI}(\hat{\mathbf x}) \hat{\mathbf T}_{IJK}(\hat{\mathbf x}) J_{jJ}(\hat{\mathbf x})^{-1} J_{kK}(\hat{\mathbf x})^{-1}. \]

  • mapping_covariant_hessian: it assumes \(\mathbf u_i(\mathbf x) = J_{iI}^{-T} \hat{\mathbf u}_I\) so that

    \[ \mathbf T_{ijk}(\mathbf x) = J_iI(\hat{\mathbf x})^{-1} \hat{\mathbf T}_{IJK}(\hat{\mathbf x}) J_{jJ}(\hat{\mathbf x})^{-1} J_{kK}(\hat{\mathbf x})^{-1}. \]

  • mapping_piola_hessian: it assumes \(\mathbf u_i(\mathbf x) = \frac{1}{\text{det}\;J(\mathbf x)} J_{iI}(\mathbf x) \hat{\mathbf u}(\mathbf x)\) so that

    \[ \mathbf T_{ijk}(\mathbf x) = \frac{1}{\text{det}\;J(\mathbf x)} J_{iI}(\hat{\mathbf x}) \hat{\mathbf T}_{IJK}(\hat{\mathbf x}) J_{jJ}(\hat{\mathbf x})^{-1} J_{kK}(\hat{\mathbf x})^{-1}. \]

Parameters
[in]inputAn array (or part of an array) of input objects that should be mapped.
[in]typeThe kind of mapping to be applied.
[in]internalA pointer to an object of type Mapping::InternalDataBase that contains information previously stored by the mapping. The object pointed to was created by the get_data(), get_face_data(), or get_subface_data() function, and will have been updated as part of a call to fill_fe_values(), fill_fe_face_values(), or fill_fe_subface_values() for the current cell, before calling the current function. In other words, this object also represents with respect to which cell the transformation should be applied to.
[out]outputAn array (or part of an array) into which the transformed objects should be placed.

Implements Mapping< dim, spacedim >.

Definition at line 3534 of file mapping_q_generic.cc.

template<int dim, int spacedim>
UpdateFlags MappingQGeneric< dim, spacedim >::requires_update_flags ( const UpdateFlags  update_flags) const
virtual

Given a set of update flags, compute which other quantities also need to be computed in order to satisfy the request by the given flags. Then return the combination of the original set of flags and those just computed.

As an example, if update_flags contains update_JxW_values (i.e., the product of the determinant of the Jacobian and the weights provided by the quadrature formula), a mapping may require the computation of the full Jacobian matrix in order to compute its determinant. They would then return not just update_JxW_values, but also update_jacobians. (This is not how it is actually done internally in the derived classes that compute the JxW values – they set update_contravariant_transformation instead, from which the determinant can also be computed – but this does not take away from the instructiveness of the example.)

An extensive discussion of the interaction between this function and FEValues can be found in the How Mapping, FiniteElement, and FEValues work together documentation module.

See also
UpdateFlags

Implements Mapping< dim, spacedim >.

Definition at line 1965 of file mapping_q_generic.cc.

template<int dim, int spacedim>
MappingQGeneric< dim, spacedim >::InternalData * MappingQGeneric< dim, spacedim >::get_data ( const UpdateFlags  update_flags,
const Quadrature< dim > &  quadrature 
) const
virtual

Create and return a pointer to an object into which mappings can store data that only needs to be computed once but that can then be used whenever the mapping is applied to a concrete cell (e.g., in the various transform() functions, as well as in the fill_fe_values(), fill_fe_face_values() and fill_fe_subface_values() that form the interface of mappings with the FEValues class).

Derived classes will return pointers to objects of a type derived from Mapping::InternalDataBase (see there for more information) and may pre- compute some information already (in accordance with what will be asked of the mapping in the future, as specified by the update flags) and for the given quadrature object. Subsequent calls to transform() or fill_fe_values() and friends will then receive back the object created here (with the same set of update flags and for the same quadrature object). Derived classes can therefore pre-compute some information in their get_data() function and store it in the internal data object.

The mapping classes do not keep track of the objects created by this function. Ownership will therefore rest with the caller.

An extensive discussion of the interaction between this function and FEValues can be found in the How Mapping, FiniteElement, and FEValues work together documentation module.

Parameters
update_flagsA set of flags that define what is expected of the mapping class in future calls to transform() or the fill_fe_values() group of functions. This set of flags may contain flags that mappings do not know how to deal with (e.g., for information that is in fact computed by the finite element classes, such as UpdateFlags::update_values). Derived classes will need to store these flags, or at least that subset of flags that will require the mapping to perform any actions in fill_fe_values(), in InternalDataBase::update_each.
quadratureThe quadrature object for which mapping information will have to be computed. This includes the locations and weights of quadrature points.
Returns
A pointer to a newly created object of type InternalDataBase (or a derived class). Ownership of this object passes to the calling function.
Note
C++ allows that virtual functions in derived classes may return pointers to objects not of type InternalDataBase but in fact pointers to objects of classes derived from InternalDataBase. (This feature is called "covariant return types".) This is useful in some contexts where the calling is within the derived class and will immediately make use of the returned object, knowing its real (derived) type.

Implements Mapping< dim, spacedim >.

Definition at line 2025 of file mapping_q_generic.cc.

template<int dim, int spacedim>
MappingQGeneric< dim, spacedim >::InternalData * MappingQGeneric< dim, spacedim >::get_face_data ( const UpdateFlags  update_flags,
const Quadrature< dim-1 > &  quadrature 
) const
virtual

Like get_data(), but in preparation for later calls to transform() or fill_fe_face_values() that will need information about mappings from the reference face to a face of a concrete cell.

Parameters
update_flagsA set of flags that define what is expected of the mapping class in future calls to transform() or the fill_fe_values() group of functions. This set of flags may contain flags that mappings do not know how to deal with (e.g., for information that is in fact computed by the finite element classes, such as UpdateFlags::update_values). Derived classes will need to store these flags, or at least that subset of flags that will require the mapping to perform any actions in fill_fe_values(), in InternalDataBase::update_each.
quadratureThe quadrature object for which mapping information will have to be computed. This includes the locations and weights of quadrature points.
Returns
A pointer to a newly created object of type InternalDataBase (or a derived class). Ownership of this object passes to the calling function.
Note
C++ allows that virtual functions in derived classes may return pointers to objects not of type InternalDataBase but in fact pointers to objects of classes derived from InternalDataBase. (This feature is called "covariant return types".) This is useful in some contexts where the calling is within the derived class and will immediately make use of the returned object, knowing its real (derived) type.

Implements Mapping< dim, spacedim >.

Definition at line 2038 of file mapping_q_generic.cc.

template<int dim, int spacedim>
MappingQGeneric< dim, spacedim >::InternalData * MappingQGeneric< dim, spacedim >::get_subface_data ( const UpdateFlags  update_flags,
const Quadrature< dim-1 > &  quadrature 
) const
virtual

Like get_data() and get_face_data(), but in preparation for later calls to transform() or fill_fe_subface_values() that will need information about mappings from the reference face to a child of a face (i.e., subface) of a concrete cell.

Parameters
update_flagsA set of flags that define what is expected of the mapping class in future calls to transform() or the fill_fe_values() group of functions. This set of flags may contain flags that mappings do not know how to deal with (e.g., for information that is in fact computed by the finite element classes, such as UpdateFlags::update_values). Derived classes will need to store these flags, or at least that subset of flags that will require the mapping to perform any actions in fill_fe_values(), in InternalDataBase::update_each.
quadratureThe quadrature object for which mapping information will have to be computed. This includes the locations and weights of quadrature points.
Returns
A pointer to a newly created object of type InternalDataBase (or a derived class). Ownership of this object passes to the calling function.
Note
C++ allows that virtual functions in derived classes may return pointers to objects not of type InternalDataBase but in fact pointers to objects of classes derived from InternalDataBase. (This feature is called "covariant return types".) This is useful in some contexts where the calling is within the derived class and will immediately make use of the returned object, knowing its real (derived) type.

Implements Mapping< dim, spacedim >.

Definition at line 2053 of file mapping_q_generic.cc.

template<int dim, int spacedim = dim>
CellSimilarity::Similarity MappingQGeneric< dim, spacedim >::fill_fe_values ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
const CellSimilarity::Similarity  cell_similarity,
const Quadrature< dim > &  quadrature,
const typename Mapping< dim, spacedim >::InternalDataBase internal_data,
::internal::FEValues::MappingRelatedData< dim, spacedim > &  output_data 
) const
virtual

Compute information about the mapping from the reference cell to the real cell indicated by the first argument to this function. Derived classes will have to implement this function based on the kind of mapping they represent. It is called by FEValues::reinit().

Conceptually, this function's represents the application of the mapping \(\mathbf x=\mathbf F_K(\hat {\mathbf x})\) from reference coordinates \(\mathbf\in [0,1]^d\) to real space coordinates \(\mathbf x\) for a given cell \(K\). Its purpose is to compute the following kinds of data:

  • Data that results from the application of the mapping itself, e.g., computing the location \(\mathbf x_q = \mathbf F_K(\hat{\mathbf x}_q)\) of quadrature points on the real cell, and that is directly useful to users of FEValues, for example during assembly.
  • Data that is necessary for finite element implementations to compute their shape functions on the real cell. To this end, the FEValues::reinit() function calls FiniteElement::fill_fe_values() after the current function, and the output of this function serves as input to FiniteElement::fill_fe_values(). Examples of information that needs to be computed here for use by the finite element classes is the Jacobian of the mapping, \(\hat\nabla \mathbf F_K(\hat{\mathbf x})\) or its inverse, for example to transform the gradients of shape functions on the reference cell to the gradients of shape functions on the real cell.

The information computed by this function is used to fill the various member variables of the output argument of this function. Which of the member variables of that structure should be filled is determined by the update flags stored in the Mapping::InternalDataBase object passed to this function.

An extensive discussion of the interaction between this function and FEValues can be found in the How Mapping, FiniteElement, and FEValues work together documentation module.

Parameters
[in]cellThe cell of the triangulation for which this function is to compute a mapping from the reference cell to.
[in]cell_similarityWhether or not the cell given as first argument is simply a translation, rotation, etc of the cell for which this function was called the most recent time. This information is computed simply by matching the vertices (as stored by the Triangulation) between the previous and the current cell. The value passed here may be modified by implementations of this function and should then be returned (see the discussion of the return value of this function).
[in]quadratureA reference to the quadrature formula in use for the current evaluation. This quadrature object is the same as the one used when creating the internal_data object. The object is used both to map the location of quadrature points, as well as to compute the JxW values for each quadrature point (which involves the quadrature weights).
[in]internal_dataA reference to an object previously created by get_data() and that may be used to store information the mapping can compute once on the reference cell. See the documentation of the Mapping::InternalDataBase class for an extensive description of the purpose of these objects.
[out]output_dataA reference to an object whose member variables should be computed. Not all of the members of this argument need to be filled; which ones need to be filled is determined by the update flags stored inside the internal_data object.
Returns
An updated value of the cell_similarity argument to this function. The returned value will be used for the corresponding argument when FEValues::reinit() calls FiniteElement::fill_fe_values(). In most cases, derived classes will simply want to return the value passed for cell_similarity. However, implementations of this function may downgrade the level of cell similarity. This is, for example, the case for classes that take not only into account the locations of the vertices of a cell (as reported by the Triangulation), but also other information specific to the mapping. The purpose is that FEValues::reinit() can compute whether a cell is similar to the previous one only based on the cell's vertices, whereas the mapping may also consider displacement fields (e.g., in the MappingQ1Eulerian and MappingFEField classes). In such cases, the mapping may conclude that the previously computed cell similarity is too optimistic, and invalidate it for subsequent use in FiniteElement::fill_fe_values() by returning a less optimistic cell similarity value.
Note
FEValues ensures that this function is always called with the same pair of internal_data and output_data objects. In other words, if an implementation of this function knows that it has written a piece of data into the output argument in a previous call, then there is no need to copy it there again in a later call if the implementation knows that this is the same value.

Implements Mapping< dim, spacedim >.

Definition at line 2614 of file mapping_q_generic.cc.

template<int dim, int spacedim = dim>
void MappingQGeneric< dim, spacedim >::fill_fe_face_values ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
const unsigned int  face_no,
const Quadrature< dim-1 > &  quadrature,
const typename Mapping< dim, spacedim >::InternalDataBase internal_data,
::internal::FEValues::MappingRelatedData< dim, spacedim > &  output_data 
) const
virtual

This function is the equivalent to Mapping::fill_fe_values(), but for faces of cells. See there for an extensive discussion of its purpose. It is called by FEFaceValues::reinit().

Parameters
[in]cellThe cell of the triangulation for which this function is to compute a mapping from the reference cell to.
[in]face_noThe number of the face of the given cell for which information is requested.
[in]quadratureA reference to the quadrature formula in use for the current evaluation. This quadrature object is the same as the one used when creating the internal_data object. The object is used both to map the location of quadrature points, as well as to compute the JxW values for each quadrature point (which involves the quadrature weights).
[in]internal_dataA reference to an object previously created by get_data() and that may be used to store information the mapping can compute once on the reference cell. See the documentation of the Mapping::InternalDataBase class for an extensive description of the purpose of these objects.
[out]output_dataA reference to an object whose member variables should be computed. Not all of the members of this argument need to be filled; which ones need to be filled is determined by the update flags stored inside the internal_data object.

Implements Mapping< dim, spacedim >.

Definition at line 3022 of file mapping_q_generic.cc.

template<int dim, int spacedim = dim>
void MappingQGeneric< dim, spacedim >::fill_fe_subface_values ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
const unsigned int  face_no,
const unsigned int  subface_no,
const Quadrature< dim-1 > &  quadrature,
const typename Mapping< dim, spacedim >::InternalDataBase internal_data,
::internal::FEValues::MappingRelatedData< dim, spacedim > &  output_data 
) const
virtual

This function is the equivalent to Mapping::fill_fe_values(), but for subfaces (i.e., children of faces) of cells. See there for an extensive discussion of its purpose. It is called by FESubfaceValues::reinit().

Parameters
[in]cellThe cell of the triangulation for which this function is to compute a mapping from the reference cell to.
[in]face_noThe number of the face of the given cell for which information is requested.
[in]subface_noThe number of the child of a face of the given cell for which information is requested.
[in]quadratureA reference to the quadrature formula in use for the current evaluation. This quadrature object is the same as the one used when creating the internal_data object. The object is used both to map the location of quadrature points, as well as to compute the JxW values for each quadrature point (which involves the quadrature weights).
[in]internal_dataA reference to an object previously created by get_data() and that may be used to store information the mapping can compute once on the reference cell. See the documentation of the Mapping::InternalDataBase class for an extensive description of the purpose of these objects.
[out]output_dataA reference to an object whose member variables should be computed. Not all of the members of this argument need to be filled; which ones need to be filled is determined by the update flags stored inside the internal_data object.

Implements Mapping< dim, spacedim >.

Definition at line 3066 of file mapping_q_generic.cc.

template<int dim, int spacedim>
std::vector< Point< spacedim > > MappingQGeneric< dim, spacedim >::compute_mapping_support_points ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell) const
protectedvirtual

Return the locations of support points for the mapping. For example, for \(Q_1\) mappings these are the vertices, and for higher order polynomial mappings they are the vertices plus interior points on edges, faces, and the cell interior that are placed in consultation with the Manifold description of the domain and its boundary. However, other classes may override this function differently. In particular, the MappingQ1Eulerian class does exactly this by not computing the support points from the geometry of the current cell but instead evaluating an externally given displacement field in addition to the geometry of the cell.

The default implementation of this function is appropriate for most cases. It takes the locations of support points on the boundary of the cell from the underlying manifold. Interior support points (ie. support points in quads for 2d, in hexes for 3d) are then computed using the solution of a Laplace equation with the position of the outer support points as boundary values, in order to make the transformation as smooth as possible.

The function works its way from the vertices (which it takes from the given cell) via the support points on the line (for which it calls the add_line_support_points() function) and the support points on the quad faces (in 3d, for which it calls the add_quad_support_points() function). It then adds interior support points that are either computed by interpolation from the surrounding points using weights computed by solving a Laplace equation, or if dim<spacedim, it asks the underlying manifold for the locations of interior points.

Reimplemented in MappingQEulerian< dim, VectorType, spacedim >::MappingQEulerianGeneric, and MappingQ1Eulerian< dim, VectorType, spacedim >.

Definition at line 3783 of file mapping_q_generic.cc.

template<int dim, int spacedim>
Point< dim > MappingQGeneric< dim, spacedim >::transform_real_to_unit_cell_internal ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
const Point< spacedim > &  p,
const Point< dim > &  initial_p_unit 
) const
protected

Transforms the point p on the real cell to the corresponding point on the unit cell cell by a Newton iteration.

Definition at line 1669 of file mapping_q_generic.cc.

template<int dim, int spacedim>
void MappingQGeneric< dim, spacedim >::add_line_support_points ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
std::vector< Point< spacedim > > &  a 
) const
protectedvirtual

For dim=2,3. Append the support points of all shape functions located on bounding lines of the given cell to the vector a. Points located on the vertices of a line are not included.

Needed by the compute_support_points() function. For dim=1 this function is empty. The function uses the underlying manifold object of the line (or, if none is set, of the cell) for the location of the requested points.

This function is made virtual in order to allow derived classes to choose shape function support points differently than the present class, which chooses the points as interpolation points on the boundary.

Definition at line 3578 of file mapping_q_generic.cc.

template<int dim, int spacedim>
void MappingQGeneric< dim, spacedim >::add_quad_support_points ( const typename Triangulation< dim, spacedim >::cell_iterator &  cell,
std::vector< Point< spacedim > > &  a 
) const
protectedvirtual

For dim=3. Append the support points of all shape functions located on bounding faces (quads in 3d) of the given cell to the vector a. Points located on the vertices or lines of a quad are not included.

Needed by the compute_support_points() function. For dim=1 and dim=2 this function is empty. The function uses the underlying manifold object of the quad (or, if none is set, of the cell) for the location of the requested points.

This function is made virtual in order to allow derived classes to choose shape function support points differently than the present class, which chooses the points as interpolation points on the boundary.

Definition at line 3772 of file mapping_q_generic.cc.

Friends And Related Function Documentation

template<int dim, int spacedim = dim>
template<int , int >
friend class MappingQ
friend

Make MappingQ a friend since it needs to call the fill_fe_values() functions on its MappingQGeneric(1) sub-object.

Definition at line 693 of file mapping_q_generic.h.

Member Data Documentation

template<int dim, int spacedim = dim>
const unsigned int MappingQGeneric< dim, spacedim >::polynomial_degree
protected

The degree of the polynomials used as shape functions for the mapping of cells.

Definition at line 555 of file mapping_q_generic.h.

template<int dim, int spacedim = dim>
const std_cxx11::unique_ptr<FE_Q<dim> > MappingQGeneric< dim, spacedim >::fe_q
protected

An FE_Q object which is only needed in 3D, since it knows how to reorder shape functions/DoFs on non-standard faces. This is used to reorder support points in the same way.

Definition at line 573 of file mapping_q_generic.h.

template<int dim, int spacedim = dim>
std::vector<Table<2,double> > MappingQGeneric< dim, spacedim >::support_point_weights_perimeter_to_interior
protected

A vector of tables of weights by which we multiply the locations of the support points on the perimeter of an object (line, quad, hex) to get the location of interior support points.

Access into this table is by [structdim-1], i.e., use 0 to access the support point weights on a line (i.e., the interior points of the GaussLobatto quadrature), use 1 to access the support point weights from to perimeter to the interior of a quad, and use 2 to access the support point weights from the perimeter to the interior of a hex.

The table itself contains as many columns as there are surrounding points to a particular object (2 for a line, 4 + 4*(degree-1) for a quad, 8 + 12*(degree-1) + 6*(degree-1)*(degree-1) for a hex) and as many rows as there are strictly interior points.

For the definition of this table see equation (8) of the `mapping' report.

Definition at line 594 of file mapping_q_generic.h.

template<int dim, int spacedim = dim>
Table<2,double> MappingQGeneric< dim, spacedim >::support_point_weights_cell
protected

A table of weights by which we multiply the locations of the vertex points of the cell to get the location of all additional support points, both on lines, quads, and hexes (as appropriate). This data structure is used when we fill all support points at once, which is the case if the same manifold is attached to all sub-entities of a cell. This way, we can avoid some of the overhead in transforming data for mappings.

The table has as many rows as there are vertices to the cell (2 in 1D, 4 in 2D, 8 in 3D), and as many rows as there are additional support points in the mapping, i.e., (degree+1)^dim - 2^dim.

Definition at line 608 of file mapping_q_generic.h.


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