Reference documentation for deal.II version 9.2.0
TriaAccessor< structdim, dim, spacedim > Class Template Reference

#include <deal.II/grid/tria_accessor.h>

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

## Public Types

using AccessorData = typename TriaAccessorBase< structdim, dim, spacedim >::AccessorData

Public Types inherited from TriaAccessorBase< structdim, dim, spacedim >
using LocalData = void *

## Public Member Functions

TriaAccessor (const Triangulation< dim, spacedim > *parent=nullptr, const int level=-1, const int index=-1, const AccessorData *local_data=nullptr)

template<int structdim2, int dim2, int spacedim2>
TriaAccessor (const InvalidAccessor< structdim2, dim2, spacedim2 > &)

template<int structdim2, int dim2, int spacedim2>
TriaAccessor (const TriaAccessor< structdim2, dim2, spacedim2 > &)

void operator= (const TriaAccessor &)=delete

bool used () const

template<>
double extent_in_direction (const unsigned int axis) const

template<>
double extent_in_direction (const unsigned int axis) const

template<>
double extent_in_direction (const unsigned int axis) const

template<>
double extent_in_direction (const unsigned int axis) const

template<>
double extent_in_direction (const unsigned int axis) const

template<>
void set_all_manifold_ids (const types::manifold_id manifold_ind) const

Accessing sub-objects
TriaIterator< TriaAccessor< 0, dim, spacedim > > vertex_iterator (const unsigned int i) const

unsigned int vertex_index (const unsigned int i) const

Point< spacedim > & vertex (const unsigned int i) const

typename ::internal::TriangulationImplementation::Iterators< dim, spacedim >::line_iterator line (const unsigned int i) const

unsigned int line_index (const unsigned int i) const

unsigned int quad_index (const unsigned int i) const

Orientation of sub-objects
bool face_orientation (const unsigned int face) const

bool face_flip (const unsigned int face) const

bool face_rotation (const unsigned int face) const

bool line_orientation (const unsigned int line) const

Accessing children
bool has_children () const

unsigned int n_children () const

unsigned int number_of_children () const

unsigned int max_refinement_depth () const

TriaIterator< TriaAccessor< structdim, dim, spacedim > > child (const unsigned int i) const

unsigned int child_iterator_to_index (const TriaIterator< TriaAccessor< structdim, dim, spacedim >> &child) const

TriaIterator< TriaAccessor< structdim, dim, spacedim > > isotropic_child (const unsigned int i) const

RefinementCase< structdim > refinement_case () const

int child_index (const unsigned int i) const

int isotropic_child_index (const unsigned int i) const

Dealing with boundary indicators
types::boundary_id boundary_id () const

void set_boundary_id (const types::boundary_id) const

void set_all_boundary_ids (const types::boundary_id) const

bool at_boundary () const

const Manifold< dim, spacedim > & get_manifold () const

Dealing with manifold indicators
types::manifold_id manifold_id () const

void set_manifold_id (const types::manifold_id) const

void set_all_manifold_ids (const types::manifold_id) const

User data
bool user_flag_set () const

void set_user_flag () const

void clear_user_flag () const

void recursively_set_user_flag () const

void recursively_clear_user_flag () const

void clear_user_data () const

void set_user_pointer (void *p) const

void clear_user_pointer () const

void * user_pointer () const

void recursively_set_user_pointer (void *p) const

void recursively_clear_user_pointer () const

void set_user_index (const unsigned int p) const

void clear_user_index () const

unsigned int user_index () const

void recursively_set_user_index (const unsigned int p) const

void recursively_clear_user_index () const

double diameter () const

std::pair< Point< spacedim >, doubleenclosing_ball () const

BoundingBox< spacedim > bounding_box () const

double extent_in_direction (const unsigned int axis) const

double minimum_vertex_distance () const

Point< spacedim > intermediate_point (const Point< structdim > &coordinates) const

Point< structdim > real_to_unit_cell_affine_approximation (const Point< spacedim > &point) const

Point< spacedim > center (const bool respect_manifold=false, const bool interpolate_from_surrounding=false) const

Point< spacedim > barycenter () const

double measure () const

bool is_translation_of (const TriaIterator< TriaAccessor< structdim, dim, spacedim >> &o) const

Public Member Functions inherited from TriaAccessorBase< structdim, dim, spacedim >
void operator= (const TriaAccessorBase *)=delete

int level () const

int index () const

IteratorState::IteratorStates state () const

const Triangulation< dim, spacedim > & get_triangulation () const

## Private Member Functions

void set_boundary_id_internal (const types::boundary_id id) const

void set (const ::internal::TriangulationImplementation::TriaObject< structdim > &o) const

void set_line_orientation (const unsigned int line, const bool orientation) const

void set_face_orientation (const unsigned int face, const bool orientation) const

void set_face_flip (const unsigned int face, const bool flip) const

void set_face_rotation (const unsigned int face, const bool rotation) const

void set_used_flag () const

void clear_used_flag () const

void set_refinement_case (const RefinementCase< structdim > &ref_case) const

void clear_refinement_case () const

void set_children (const unsigned int i, const int index) const

void clear_children () const

## Friends

template<int , int >
class Triangulation

struct ::internal::TriangulationImplementation::Implementation

struct ::internal::TriaAccessorImplementation::Implementation

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

static const unsigned int dimension = dim

static const unsigned int structure_dimension = structdim

Protected Types inherited from TriaAccessorBase< structdim, dim, spacedim >
using AccessorData = void

Protected Member Functions inherited from TriaAccessorBase< structdim, dim, spacedim >
TriaAccessorBase (const Triangulation< dim, spacedim > *parent=nullptr, const int level=-1, const int index=-1, const AccessorData *=nullptr)

TriaAccessorBase (const TriaAccessorBase &)

void copy_from (const TriaAccessorBase &)

TriaAccessorBaseoperator= (const TriaAccessorBase &)

bool operator< (const TriaAccessorBase &other) const

bool operator== (const TriaAccessorBase &) const

bool operator!= (const TriaAccessorBase &) const

::internal::TriangulationImplementation::TriaObjects< ::internal::TriangulationImplementation::TriaObject< structdim > > & objects () const

void operator++ ()

void operator-- ()

Protected Attributes inherited from TriaAccessorBase< structdim, dim, spacedim >
typename ::internal::TriaAccessorImplementation::PresentLevelType< structdim, dim >::type present_level

int present_index

const Triangulation< dim, spacedim > * tria

## Detailed Description

### template<int structdim, int dim, int spacedim> class TriaAccessor< structdim, dim, spacedim >

A class that provides access to objects in a triangulation such as its vertices, sub-objects, children, geometric information, etc. This class represents objects of dimension structdim (i.e. 1 for lines, 2 for quads, 3 for hexes) in a triangulation of dimensionality dim (i.e. 1 for a triangulation of lines, 2 for a triangulation of quads, and 3 for a triangulation of hexes) that is embedded in a space of dimensionality spacedim (for spacedim==dim the triangulation represents a domain in $$R^{dim}$$, for spacedim>dim the triangulation is of a manifold embedded in a higher dimensional space).

There is a specialization of this class for the case where structdim equals zero, i.e., for vertices of a triangulation.

Definition at line 127 of file tria_accessor.h.

## ◆ AccessorData

template<int structdim, int dim, int spacedim>
 using TriaAccessor< structdim, dim, spacedim >::AccessorData = typename TriaAccessorBase::AccessorData

Propagate alias from base class to this class.

Definition at line 706 of file tria_accessor.h.

## ◆ TriaAccessor() [1/3]

template<int structdim, int dim, int spacedim>
 TriaAccessor< structdim, dim, spacedim >::TriaAccessor ( const Triangulation< dim, spacedim > * parent = nullptr, const int level = -1, const int index = -1, const AccessorData * local_data = nullptr )

Constructor.

## ◆ TriaAccessor() [2/3]

template<int structdim, int dim, int spacedim>
template<int structdim2, int dim2, int spacedim2>
 TriaAccessor< structdim, dim, spacedim >::TriaAccessor ( const InvalidAccessor< structdim2, dim2, spacedim2 > & )

Conversion constructor. This constructor exists to make certain constructs simpler to write in dimension independent code. For example, it allows assigning a face iterator to a line iterator, an operation that is useful in 2d but doesn't make any sense in 3d. The constructor here exists for the purpose of making the code conform to C++ but it will unconditionally abort; in other words, assigning a face iterator to a line iterator is better put into an if-statement that checks that the dimension is two, and assign to a quad iterator in 3d (an operator that, without this constructor would be illegal if we happen to compile for 2d).

Definition at line 3668 of file tria_accessor.h.

## ◆ TriaAccessor() [3/3]

template<int structdim, int dim, int spacedim>
template<int structdim2, int dim2, int spacedim2>
 TriaAccessor< structdim, dim, spacedim >::TriaAccessor ( const TriaAccessor< structdim2, dim2, spacedim2 > & )

Another conversion operator between objects that don't make sense, just like the previous one.

Definition at line 3698 of file tria_accessor.h.

## ◆ operator=()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::operator= ( const TriaAccessor< structdim, dim, spacedim > & )
delete

Copy operator. These operators are usually used in a context like iterator a,b; *a=*b;. Presumably, the intent here is to copy the object pointed to by b to the object pointed to by a. However, the result of dereferencing an iterator is not an object but an accessor; consequently, this operation is not useful for iterators on triangulations. Consequently, this operator is declared as deleted and can not be used.

## ◆ used()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::used ( ) const

Test for the element being used or not. The return value is true for all iterators that are either normal iterators or active iterators, only raw iterators can return false. Since raw iterators are only used in the interiors of the library, you will not usually need this function.

## ◆ vertex_iterator()

template<int structdim, int dim, int spacedim>
 TriaIterator > TriaAccessor< structdim, dim, spacedim >::vertex_iterator ( const unsigned int i ) const

Pointer to the ith vertex bounding this object. Throw an exception if dim=1.

## ◆ vertex_index()

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::vertex_index ( const unsigned int i ) const

Return the global index of i-th vertex of the current object. The convention regarding the numbering of vertices is laid down in the documentation of the GeometryInfo class.

Note that the returned value is only the index of the geometrical vertex. It has nothing to do with possible degrees of freedom associated with it. For this, see the DoFAccessor::vertex_dof_index functions.

Note
Despite the name, the index returned here is only global in the sense that it is specific to a particular Triangulation object or, in the case the triangulation is actually of type parallel::distributed::Triangulation, specific to that part of the distributed triangulation stored on the current processor.

## ◆ vertex()

template<int structdim, int dim, int spacedim>
 Point& TriaAccessor< structdim, dim, spacedim >::vertex ( const unsigned int i ) const

Return a reference to the ith vertex. The reference is not const, i.e., it is possible to call this function on the left hand side of an assignment, thereby moving the vertex of a cell within the triangulation. Of course, doing so requires that you ensure that the new location of the vertex remains useful – for example, avoiding inverted or otherwise distorted (see also this glossary entry).

Note
When a cell is refined, its children inherit the position of the vertex positions of those vertices they share with the mother cell (plus the locations of the new vertices on edges, faces, and cell interiors that are created for the new child cells). If the vertex of a cell is moved, this implies that its children will also use these new locations. On the other hand, imagine a 2d situation where you have one cell that is refined (with four children) and then you move the central vertex connecting all four children. If you coarsen these four children again to the mother cell, then the location of the moved vertex is lost and if, in a later step, you refine the mother cell again, the then again new vertex will be placed again at the same position as the first time around – i.e., not at the location you had previously moved it to.
The behavior described above is relevant if you have a parallel::distributed::Triangulation object. There, refining a mesh always involves a re-partitioning. In other words, vertices of locally owned cells (see this glossary entry) that you may have moved to a different location on one processor may be moved to a different processor upon mesh refinement (even if these particular cells were not refined) which will re-create their position based on the position of the coarse cells they previously had, not based on the position these vertices had on the processor that previously owned them. In other words, in parallel computations, you will probably have to move nodes explicitly after every mesh refinement because vertex positions may or may not be preserved across the re-partitioning that accompanies mesh refinement.

## ◆ line()

template<int structdim, int dim, int spacedim>
 typename ::internal::TriangulationImplementation:: Iterators::line_iterator TriaAccessor< structdim, dim, spacedim >::line ( const unsigned int i ) const

Pointer to the ith line bounding this object.

## ◆ line_index()

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::line_index ( const unsigned int i ) const

Line index of the ith line bounding this object.

Implemented only for structdim>1, otherwise an exception generated.

template<int structdim, int dim, int spacedim>
 typename ::internal::TriangulationImplementation:: Iterators::quad_iterator TriaAccessor< structdim, dim, spacedim >::quad ( const unsigned int i ) const

Pointer to the ith quad bounding this object.

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::quad_index ( const unsigned int i ) const

Quad index of the ith quad bounding this object.

Implemented only for structdim>2, otherwise an exception generated.

## ◆ face_orientation()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::face_orientation ( const unsigned int face ) const

Return whether the face with index face has its normal pointing in the standard direction (true) or whether it is the opposite (false). Which is the standard direction is documented with the GeometryInfo class. In 1d and 2d, this is always true, but in 3d it may be different, see the respective discussion in the documentation of the GeometryInfo class.

This function is really only for internal use in the library unless you absolutely know what this is all about.

## ◆ face_flip()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::face_flip ( const unsigned int face ) const

Return whether the face with index face is rotated by 180 degrees (true) or not (false). In 1d and 2d, this is always false, but in 3d it may be different, see the respective discussion in the documentation of the GeometryInfo class.

This function is really only for internal use in the library unless you absolutely know what this is all about.

## ◆ face_rotation()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::face_rotation ( const unsigned int face ) const

Return whether the face with index face is rotated by 90 degrees (true) or not (false). In 1d and 2d, this is always false, but in 3d it may be different, see the respective discussion in the documentation of the GeometryInfo class.

This function is really only for internal use in the library unless you absolutely know what this is all about.

## ◆ line_orientation()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::line_orientation ( const unsigned int line ) const

Return whether the line with index line is oriented in standard direction. true indicates, that the line is oriented from vertex 0 to vertex 1, whereas it is the other way around otherwise. In 1d and 2d, this is always true, but in 3d it may be different, see the respective discussion in the documentation of the GeometryInfo class.

This function is really only for internal use in the library unless you absolutely know what this is all about.

## ◆ has_children()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::has_children ( ) const

Test whether the object has children.

## ◆ n_children()

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::n_children ( ) const

Return the number of immediate children of this object. The number of children of an unrefined cell is zero.

## ◆ number_of_children()

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::number_of_children ( ) const

Compute and return the number of active descendants of this objects. For example, if all of the eight children of a hex are further refined isotropically exactly once, the returned number will be 64, not 80.

If the present cell is not refined, one is returned.

If one considers a triangulation as a forest where the root of each tree are the coarse mesh cells and nodes have descendants (the children of a cell), then this function returns the number of terminal nodes in the sub-tree originating from the current object; consequently, if the current object is not further refined, the answer is one.

## ◆ max_refinement_depth()

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::max_refinement_depth ( ) const

Return the number of times that this object is refined. Note that not all its children are refined that often (which is why we prepend max_), the returned number is rather the maximum number of refinement in any branch of children of this object.

For example, if this object is refined, and one of its children is refined exactly one more time, then max_refinement_depth should return 2.

If this object is not refined (i.e. it is active), then the return value is zero.

## ◆ child()

template<int structdim, int dim, int spacedim>
 TriaIterator > TriaAccessor< structdim, dim, spacedim >::child ( const unsigned int i ) const

Return an iterator to the ith child.

## ◆ child_iterator_to_index()

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::child_iterator_to_index ( const TriaIterator< TriaAccessor< structdim, dim, spacedim >> & child ) const

Return the child number of child on the current cell. This is the inverse function of TriaAccessor::child().

## ◆ isotropic_child()

template<int structdim, int dim, int spacedim>
 TriaIterator > TriaAccessor< structdim, dim, spacedim >::isotropic_child ( const unsigned int i ) const

Return an iterator to that object that is identical to the ith child for isotropic refinement. If the current object is refined isotropically, then the returned object is the ith child. If the current object is refined anisotropically, the returned child may in fact be a grandchild of the object, or may not exist at all (in which case an exception is generated).

## ◆ refinement_case()

template<int structdim, int dim, int spacedim>
 RefinementCase TriaAccessor< structdim, dim, spacedim >::refinement_case ( ) const

Return the RefinementCase of this cell.

## ◆ child_index()

template<int structdim, int dim, int spacedim>
 int TriaAccessor< structdim, dim, spacedim >::child_index ( const unsigned int i ) const

Index of the ith child. The level of the child is one higher than that of the present cell, if the children of a cell are accessed. The children of faces have no level. If the child does not exist, -1 is returned.

## ◆ isotropic_child_index()

template<int structdim, int dim, int spacedim>
 int TriaAccessor< structdim, dim, spacedim >::isotropic_child_index ( const unsigned int i ) const

Index of the ith isotropic child. See the isotropic_child() function for a definition of this concept. If the child does not exist, -1 is returned.

## ◆ boundary_id()

template<int structdim, int dim, int spacedim>
 types::boundary_id TriaAccessor< structdim, dim, spacedim >::boundary_id ( ) const

Return the boundary indicator of this object.

If the return value is the special value numbers::internal_face_boundary_id, then this object is in the interior of the domain.

Glossary entry on boundary indicators

## ◆ set_boundary_id()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_boundary_id ( const types::boundary_id ) const

Set the boundary indicator of the current object. The same applies as for the boundary_id() function.

This function only sets the boundary object of the current object itself, not the indicators of the ones that bound it. For example, in 3d, if this function is called on a face, then the boundary indicator of the 4 edges that bound the face remain unchanged. If you want to set the boundary indicators of face and edges at the same time, use the set_all_boundary_ids() function. You can see the result of not using the correct function in the results section of step-49.

Warning
You should never set the boundary indicator of an interior face (a face not at the boundary of the domain), or set the boundary indicator of an exterior face to numbers::internal_face_boundary_id (this value is reserved for another purpose). Algorithms may not work or produce very confusing results if boundary cells have a boundary indicator of numbers::internal_face_boundary_id or if interior cells have boundary indicators other than numbers::internal_face_boundary_id. Unfortunately, the current object has no means of finding out whether it really is at the boundary of the domain and so cannot determine whether the value you are trying to set makes sense under the current circumstances.
Glossary entry on boundary indicators

## ◆ set_all_boundary_ids()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_all_boundary_ids ( const types::boundary_id ) const

Do as set_boundary_id() but also set the boundary indicators of the objects that bound the current object. For example, in 3d, if set_boundary_id() is called on a face, then the boundary indicator of the 4 edges that bound the face remain unchanged. In contrast, if you call the current function, the boundary indicators of face and edges are all set to the given value.

This function is useful if you set boundary indicators of faces in 3d (in 2d, the function does the same as set_boundary_id()) and you do so because you want a curved boundary object to represent the part of the boundary that corresponds to the current face. In that case, the Triangulation class needs to figure out where to put new vertices upon mesh refinement, and higher order Mapping objects also need to figure out where new interpolation points for a curved boundary approximation should be. In either case, the two classes first determine where interpolation points on the edges of a boundary face should be, asking the boundary object, before asking the boundary object for the interpolation points corresponding to the interior of the boundary face. For this to work properly, it is not sufficient to have set the boundary indicator for the face alone, but you also need to set the boundary indicators of the edges that bound the face. This function does all of this at once. You can see the result of not using the correct function in the results section of step-49.

Glossary entry on boundary indicators

## ◆ at_boundary()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::at_boundary ( ) const

Return whether this object is at the boundary. Obviously, the use of this function is only possible for dim>structdim; however, for dim==structdim, an object is a cell and the CellAccessor class offers another possibility to determine whether a cell is at the boundary or not.

## ◆ get_manifold()

template<int structdim, int dim, int spacedim>
 const Manifold& TriaAccessor< structdim, dim, spacedim >::get_manifold ( ) const

Return a constant reference to the manifold object used for this object.

As explained in the Manifold description for triangulations module, the process involved in finding the appropriate manifold description involves querying both the manifold or boundary indicators. See there for more information.

## ◆ manifold_id()

template<int structdim, int dim, int spacedim>
 types::manifold_id TriaAccessor< structdim, dim, spacedim >::manifold_id ( ) const

Return the manifold indicator of this object.

If the return value is the special value numbers::flat_manifold_id, then this object is associated with a standard Cartesian Manifold Description.

Glossary entry on manifold indicators

## ◆ user_flag_set()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::user_flag_set ( ) const

## ◆ set_user_flag()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_user_flag ( ) const

## ◆ clear_user_flag()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::clear_user_flag ( ) const

## ◆ recursively_set_user_flag()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::recursively_set_user_flag ( ) const

Set the user flag for this and all descendants. See GlossUserFlags for more information.

## ◆ recursively_clear_user_flag()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::recursively_clear_user_flag ( ) const

Clear the user flag for this and all descendants. See GlossUserFlags for more information.

## ◆ clear_user_data()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::clear_user_data ( ) const

Reset the user data to zero, independent if pointer or index. See GlossUserData for more information.

## ◆ set_user_pointer()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_user_pointer ( void * p ) const

Set the user pointer to p.

Note
User pointers and user indices are mutually exclusive. Therefore, you can only use one of them, unless you call Triangulation::clear_user_data() in between.

## ◆ clear_user_pointer()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::clear_user_pointer ( ) const

Reset the user pointer to a nullptr pointer. See GlossUserData for more information.

## ◆ user_pointer()

template<int structdim, int dim, int spacedim>
 void* TriaAccessor< structdim, dim, spacedim >::user_pointer ( ) const

Access the value of the user pointer. It is in the responsibility of the user to make sure that the pointer points to something useful. You should use the new style cast operator to maintain a minimum of type safety, e.g.

Note
User pointers and user indices are mutually exclusive. Therefore, you can only use one of them, unless you call Triangulation::clear_user_data() in between. A a=static_cast<A>(cell->user_pointer());.

## ◆ recursively_set_user_pointer()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::recursively_set_user_pointer ( void * p ) const

Set the user pointer of this object and all its children to the given value. This is useful for example if all cells of a certain subdomain, or all faces of a certain part of the boundary should have user pointers pointing to objects describing this part of the domain or boundary.

Note that the user pointer is not inherited under mesh refinement, so after mesh refinement there might be cells or faces that don't have user pointers pointing to the describing object. In this case, simply loop over all the elements of the coarsest level that has this information, and use this function to recursively set the user pointer of all finer levels of the triangulation.

Note
User pointers and user indices are mutually exclusive. Therefore, you can only use one of them, unless you call Triangulation::clear_user_data() in between.

## ◆ recursively_clear_user_pointer()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::recursively_clear_user_pointer ( ) const

Clear the user pointer of this object and all of its descendants. The same holds as said for the recursively_set_user_pointer() function. See GlossUserData for more information.

## ◆ set_user_index()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_user_index ( const unsigned int p ) const

Set the user index to p.

Note
User pointers and user indices are mutually exclusive. Therefore, you can only use one of them, unless you call Triangulation::clear_user_data() in between. See GlossUserData for more information.

## ◆ clear_user_index()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::clear_user_index ( ) const

## ◆ user_index()

template<int structdim, int dim, int spacedim>
 unsigned int TriaAccessor< structdim, dim, spacedim >::user_index ( ) const

Access the value of the user index.

Note
User pointers and user indices are mutually exclusive. Therefore, you can only use one of them, unless you call Triangulation::clear_user_data() in between.

## ◆ recursively_set_user_index()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::recursively_set_user_index ( const unsigned int p ) const

Set the user index of this object and all its children.

Note that the user index is not inherited under mesh refinement, so after mesh refinement there might be cells or faces that don't have the expected user indices. In this case, simply loop over all the elements of the coarsest level that has this information, and use this function to recursively set the user index of all finer levels of the triangulation.

Note
User pointers and user indices are mutually exclusive. Therefore, you can only use one of them, unless you call Triangulation::clear_user_data() in between.

## ◆ recursively_clear_user_index()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::recursively_clear_user_index ( ) const

Clear the user index of this object and all of its descendants. The same holds as said for the recursively_set_user_index() function.

## ◆ diameter()

template<int structdim, int dim, int spacedim>
 double TriaAccessor< structdim, dim, spacedim >::diameter ( ) const

Diameter of the object.

The diameter of an object is computed to be the largest diagonal. This is not necessarily the true diameter for objects that may use higher order mappings, but completely sufficient for most computations.

## ◆ enclosing_ball()

template<int structdim, int dim, int spacedim>
 std::pair, double> TriaAccessor< structdim, dim, spacedim >::enclosing_ball ( ) const

Return a pair of Point and double corresponding to the center and the radius of a reasonably small enclosing ball of the object.

The function implements Ritter's O(n) algorithm to get a reasonably small enclosing ball around the vertices of the object. The initial guess for the enclosing ball is taken to be the ball which contains the largest diagonal of the object as its diameter. Starting from such an initial guess, the algorithm tests whether all the vertices of the object (except the vertices of the largest diagonal) are geometrically within the ball. If any vertex (v) is found to be geometrically outside the ball, a new iterate of the ball is constructed by shifting its center and increasing the radius so as to geometrically enclose both the previous ball and the vertex (v). The algorithm terminates when all the vertices are geometrically inside the ball.

If a vertex (v) is geometrically inside a particular iterate of the ball, then it will continue to be so in the subsequent iterates of the ball (this is true by construction).

Note
This function assumes d-linear mapping from the reference cell.

see this and [Ritter 1990]

## ◆ bounding_box()

template<int structdim, int dim, int spacedim>
 BoundingBox< spacedim > TriaAccessor< structdim, dim, spacedim >::bounding_box ( ) const

Return the smallest bounding box that encloses the object.

Notice that this method is not aware of any mapping you may be using to do your computations. If you are using a mapping object that modifies the position of the vertices, like MappingQEulerian, or MappingFEField, then you should call the function Mapping::get_bounding_box() instead.

Definition at line 1526 of file tria_accessor.cc.

## ◆ extent_in_direction() [1/6]

template<int structdim, int dim, int spacedim>
 double TriaAccessor< structdim, dim, spacedim >::extent_in_direction ( const unsigned int axis ) const

Length of an object in the direction of the given axis, specified in the local coordinate system. See the documentation of GeometryInfo for the meaning and enumeration of the local axes.

Note that the "length" of an object can be interpreted in a variety of ways. Here, we choose it as the maximal length of any of the edges of the object that are parallel to the chosen axis on the reference cell.

Definition at line 1548 of file tria_accessor.cc.

## ◆ minimum_vertex_distance()

template<int structdim, int dim, int spacedim>
 double TriaAccessor< structdim, dim, spacedim >::minimum_vertex_distance ( ) const

Return the minimal distance between any two vertices.

## ◆ intermediate_point()

template<int structdim, int dim, int spacedim>
 Point< spacedim > TriaAccessor< structdim, dim, spacedim >::intermediate_point ( const Point< structdim > & coordinates ) const

Return a point belonging to the Manifold<dim,spacedim> where this object lives, given its parametric coordinates on the reference structdim cell. This function queries the underlying manifold object, and can be used to obtain the exact geometrical location of arbitrary points on this object.

Notice that the argument coordinates are the coordinates on the reference cell, given in reference coordinates. In other words, the argument provides a weighting between the different vertices. For example, for lines, calling this function with argument Point<1>(.5), is equivalent to asking the line for its center.

Definition at line 1655 of file tria_accessor.cc.

## ◆ real_to_unit_cell_affine_approximation()

template<int structdim, int dim, int spacedim>
 Point< structdim > TriaAccessor< structdim, dim, spacedim >::real_to_unit_cell_affine_approximation ( const Point< spacedim > & point ) const

This function computes a fast approximate transformation from the real to the unit cell by inversion of an affine approximation of the $$d$$-linear function from the reference $$d$$-dimensional cell.

The affine approximation of the unit to real cell mapping is found by a least squares fit of an affine function to the $$2^d$$ vertices of the present object. For any valid mesh cell whose geometry is not degenerate, this operation results in a unique affine mapping. Thus, this function will return a finite result for all given input points, even in cases where the actual transformation by an actual bi-/trilinear or higher order mapping might be singular. Besides only approximating the mapping from the vertex points, this function also ignores the attached manifold descriptions. The result is only exact in case the transformation from the unit to the real cell is indeed affine, such as in one dimension or for Cartesian and affine (parallelogram) meshes in 2D/3D.

For exact transformations to the unit cell, use Mapping::transform_real_to_unit_cell().

Note
If dim<spacedim we first project p onto the plane.

Definition at line 1773 of file tria_accessor.cc.

## ◆ center()

template<int structdim, int dim, int spacedim>
 Point< spacedim > TriaAccessor< structdim, dim, spacedim >::center ( const bool respect_manifold = false, const bool interpolate_from_surrounding = false ) const

Center of the object. The center of an object is defined to be the average of the locations of the vertices, which is also where a $$Q_1$$ mapping would map the center of the reference cell. However, you can also ask this function to instead return the average of the vertices as computed by the underlying Manifold object associated with the current object, by setting to true the optional parameter respect_manifold. Manifolds would then typically pull back the coordinates of the vertices to a reference domain (not necessarily the reference cell), compute the average there, and then push forward the coordinates of the averaged point to the physical space again; the resulting point is guaranteed to lie within the manifold, even if the manifold is curved.

When the object uses a different manifold description as its surrounding, like when part of the bounding objects of this TriaAccessor use a non-flat manifold description but the object itself is flat, the result given by the TriaAccessor::center() function may not be accurate enough, even when parameter respect_manifold is set to true. If you find this to be case, than you can further refine the computation of the center by setting to true the second additional parameter interpolate_from_surrounding. This computes the location of the center by a so-called transfinite interpolation from the center of all the bounding objects. For a 2D object, it puts a weight of 1/2 on each of the four surrounding lines and a weight -1/4 on the four vertices. This corresponds to a linear interpolation between the descriptions of the four faces, subtracting the contribution of the vertices that is added twice when coming through both lines adjacent to the vertex. In 3D, the weights for faces are 1/2, the weights for lines are -1/4, and the weights for vertices are 1/8. For further information, also confer to the TransfiniteInterpolationManifold class that is able to not only apply this beneficial description to a single cell but all children of a coarse cell.

Definition at line 1801 of file tria_accessor.cc.

## ◆ barycenter()

template<int structdim, int dim, int spacedim>
 Point< spacedim > TriaAccessor< structdim, dim, spacedim >::barycenter ( ) const

Return the barycenter (also called centroid) of the object. The barycenter for an object $$K$$ of dimension $$d$$ in $$D$$ space dimensions is given by the $$D$$-dimensional vector $$\mathbf x_K$$ defined by

$\mathbf x_K = \frac{1}{|K|} \int_K \mathbf x \; \textrm{d}x$

where the measure of the object is given by

$|K| = \int_K \mathbf 1 \; \textrm{d}x.$

This function assumes that $$K$$ is mapped by a $$d$$-linear function from the reference $$d$$-dimensional cell. Then the integrals above can be pulled back to the reference cell and evaluated exactly (if through lengthy and, compared to the center() function, expensive computations).

Definition at line 1504 of file tria_accessor.cc.

## ◆ measure()

template<int structdim, int dim, int spacedim>
 double TriaAccessor< structdim, dim, spacedim >::measure ( ) const

Compute the dim-dimensional measure of the object. For a dim-dimensional cell in dim-dimensional space, this equals its volume. On the other hand, for a 2d cell in 3d space, or if the current object pointed to is a 2d face of a 3d cell in 3d space, then the function computes the area the object occupies. For a one-dimensional object, return its length.

The function only computes the measure of cells, faces or edges assumed to be represented by (bi-/tri-)linear mappings. In other words, it only takes into account the locations of the vertices that bound the current object but not how the interior of the object may actually be mapped. In most simple cases, this is exactly what you want. However, for objects that are not "straight", e.g. 2d cells embedded in 3d space as part of a triangulation of a curved domain, two-dimensional faces of 3d cells that are not just parallelograms, or for faces that are at the boundary of a domain that is not just bounded by straight line segments or planes, this function only computes the dim-dimensional measure of a (bi-/tri-)linear interpolation of the "real" object as defined by the manifold or boundary object describing the real geometry of the object in question. If you want to consider the "real" geometry, you will need to compute the measure by integrating a function equal to one over the object, which after applying quadrature equals the summing the JxW values returned by the FEValues or FEFaceValues object you will want to use for the integral.

Definition at line 1515 of file tria_accessor.cc.

## ◆ is_translation_of()

template<int structdim, int dim, int spacedim>
 bool TriaAccessor< structdim, dim, spacedim >::is_translation_of ( const TriaIterator< TriaAccessor< structdim, dim, spacedim >> & o ) const

Return true if the current object is a translation of the given argument.

Note
For the purpose of a triangulation, cells, faces, etc are only characterized by their vertices. The current function therefore only compares the locations of vertices. For many practical applications, however, it is not only the vertices that determine whether one cell is a translation of another, but also how the cell is mapped from the reference cell to its location in real space. For example, if we are using higher order mappings, then not only do the vertices have to be translations of each other, but also the points along edges. In these questions, therefore, it would be appropriate to ask the mapping, not the current function, whether two objects are translations of each other.

## ◆ set_boundary_id_internal()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_boundary_id_internal ( const types::boundary_id id ) const
private

Like set_boundary_id but without checking for internal faces or invalid ids.

## ◆ set()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set ( const ::internal::TriangulationImplementation::TriaObject< structdim > & o ) const
private

Copy the data of the given object into the internal data structures of a triangulation.

Definition at line 1493 of file tria_accessor.cc.

## ◆ set_line_orientation()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_line_orientation ( const unsigned int line, const bool orientation ) const
private

Set the flag indicating, what line_orientation() will return.

It is only possible to set the line_orientation of faces in 3d (i.e. structdim==2 && dim==3).

## ◆ set_face_orientation()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_face_orientation ( const unsigned int face, const bool orientation ) const
private

Set whether the quad with index face has its normal pointing in the standard direction (true) or whether it is the opposite (false). Which is the standard direction is documented with the GeometryInfo class.

This function is only for internal use in the library. Setting this flag to any other value than the one that the triangulation has already set is bound to bring you disaster.

## ◆ set_face_flip()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_face_flip ( const unsigned int face, const bool flip ) const
private

Set the flag indicating, what face_flip() will return.

It is only possible to set the face_orientation of cells in 3d (i.e. structdim==3 && dim==3).

## ◆ set_face_rotation()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_face_rotation ( const unsigned int face, const bool rotation ) const
private

Set the flag indicating, what face_rotation() will return.

It is only possible to set the face_orientation of cells in 3d (i.e. structdim==3 && dim==3).

## ◆ set_used_flag()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_used_flag ( ) const
private

Set the used flag. Only for internal use in the library.

## ◆ clear_used_flag()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::clear_used_flag ( ) const
private

Clear the used flag. Only for internal use in the library.

## ◆ set_refinement_case()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_refinement_case ( const RefinementCase< structdim > & ref_case ) const
private

Set the RefinementCase<dim> this TriaObject is refined with. Not defined for structdim=1 as lines are always refined resulting in 2 children lines (isotropic refinement).

You should know quite exactly what you are doing if you touch this function. It is exclusively for internal use in the library.

## ◆ clear_refinement_case()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::clear_refinement_case ( ) const
private

Clear the RefinementCase<dim> of this TriaObject, i.e. reset it to RefinementCase<dim>::no_refinement.

You should know quite exactly what you are doing if you touch this function. It is exclusively for internal use in the library.

## ◆ set_children()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::set_children ( const unsigned int i, const int index ) const
private

Set the index of the ith child. Since the children come at least in pairs, we need to store the index of only every second child, i.e. of the even numbered children. Make sure, that the index of child i=0 is set first. Calling this function for odd numbered children is not allowed.

## ◆ clear_children()

template<int structdim, int dim, int spacedim>
 void TriaAccessor< structdim, dim, spacedim >::clear_children ( ) const
private

Clear the child field, i.e. set it to a value which indicates that this cell has no children.

## ◆ extent_in_direction() [2/6]

template<>
 double TriaAccessor< 1, 1, 1 >::extent_in_direction ( const unsigned int axis ) const

Definition at line 1559 of file tria_accessor.cc.

## ◆ extent_in_direction() [3/6]

template<>
 double TriaAccessor< 1, 1, 2 >::extent_in_direction ( const unsigned int axis ) const

Definition at line 1570 of file tria_accessor.cc.

## ◆ extent_in_direction() [4/6]

template<>
 double TriaAccessor< 2, 2, 2 >::extent_in_direction ( const unsigned int axis ) const

Lines along x-axis, see GeometryInfo

Lines along y-axis

Definition at line 1581 of file tria_accessor.cc.

## ◆ extent_in_direction() [5/6]

template<>
 double TriaAccessor< 2, 2, 3 >::extent_in_direction ( const unsigned int axis ) const

Lines along x-axis, see GeometryInfo

Lines along y-axis

Definition at line 1595 of file tria_accessor.cc.

## ◆ extent_in_direction() [6/6]

template<>
 double TriaAccessor< 3, 3, 3 >::extent_in_direction ( const unsigned int axis ) const

Lines along x-axis, see GeometryInfo

Lines along y-axis

Lines along z-axis

Definition at line 1610 of file tria_accessor.cc.

## ◆ set_all_manifold_ids()

template<>
 void TriaAccessor< 3, 3, 3 >::set_all_manifold_ids ( const types::manifold_id manifold_ind ) const

Definition at line 1632 of file tria_accessor.cc.

## ◆ Triangulation

template<int structdim, int dim, int spacedim>
template<int , int >
 friend class Triangulation
friend

Using directive for backwards-compatibility.

Definition at line 1728 of file tria_accessor.h.

## ◆ ::internal::TriangulationImplementation::Implementation

template<int structdim, int dim, int spacedim>
 friend struct ::internal::TriangulationImplementation::Implementation
friend

Definition at line 1730 of file tria_accessor.h.

## ◆ ::internal::TriaAccessorImplementation::Implementation

template<int structdim, int dim, int spacedim>
 friend struct ::internal::TriaAccessorImplementation::Implementation
friend

Definition at line 1731 of file tria_accessor.h.

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