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

Public Member Functions
	InternalDataBase ()

	InternalDataBase (const InternalDataBase &)=delete

virtual	~InternalDataBase ()=default

virtual std::size_t	memory_consumption () const

Public Attributes
UpdateFlags	update_each

Detailed Description

template<int dim, int spacedim = dim>
class Mapping< dim, spacedim >::InternalDataBase

Base class for internal data of mapping objects. The internal mechanism is that upon construction of a FEValues object, it asks the mapping and finite element classes that are to be used to allocate memory for their own purpose in which they may store data that only needs to be computed once. For example, most finite elements will store the values of the shape functions at the quadrature points in this object, since they do not change from cell to cell and only need to be computed once. The same may be true for Mapping classes that want to only evaluate the shape functions used for mapping once at the quadrature points.

Since different FEValues objects using different quadrature rules might access the same mapping object at the same time, it is necessary to create one such object per FEValues object. FEValues does this by calling Mapping::get_data(), or in reality the implementation of the corresponding function in derived classes. Ownership of the object created by Mapping::get_data() is then transferred to the FEValues object, but a reference to this object is passed to the mapping object every time it is asked to compute information on a concrete cell. This happens when FEValues::reinit() (or the corresponding classes in FEFaceValues and FESubfaceValues) call Mapping::fill_fe_values() (and similarly via Mapping::fill_fe_face_values() and Mapping::fill_fe_subface_values()).

The purpose of this class is for mapping objects to store information that can be computed once at the beginning, on the reference cell, and to access it later when computing information on a concrete cell. As such, the object handed to Mapping::fill_fe_values() is marked as const, because the assumption is that at the time this information is used, it will not need to modified again. However, classes derived from Mapping can also use such objects for two other purposes:

To provide scratch space for computations that are done in Mapping::fill_fe_values() and similar functions. Some of the derived classes would like to use scratch arrays and it would be a waste of time to allocate these arrays every time this function is called, just to de- allocate it again at the end of the function. Rather, one could allocate this memory once as a member variable of the current class, and simply use it in Mapping::fill_fe_values().
After calling Mapping::fill_fe_values(), FEValues::reinit() calls FiniteElement::fill_fe_values() where the finite element computes values, gradients, etc of the shape functions using both information computed once at the beginning using a mechanism similar to the one described here (see FiniteElement::InternalDataBase) as well as the data already computed by Mapping::fill_fe_values(). As part of its work, some implementations of FiniteElement::fill_fe_values() need to transform shape function data, and they do so by calling Mapping::transform(). The call to the latter function also receives a reference to the Mapping::InternalDataBase object. Since Mapping::transform() may be called many times on each cell, it is sometimes worth for derived classes to compute some information only once in Mapping::fill_fe_values() and reuse it in Mapping::transform(). This information can also be stored in the classes that derived mapping classes derive from InternalDataBase.

In both of these cases, the InternalDataBase object being passed around is "morally const", i.e., no external observer can tell whether a scratch array or some intermediate data for Mapping::transform() is being modified by Mapping::fill_fe_values() or not. Consequently, the InternalDataBase objects are always passed around as const objects. Derived classes that would like to make use of the two additional uses outlined above therefore need to mark the member variables they want to use for these purposes as mutable to allow for their modification despite the fact that the surrounding object is marked as const.

Definition at line 619 of file mapping.h.