Degrees of Freedom

Collaboration diagram for Degrees of Freedom:

Topics
	Constraints on degrees of freedom

Namespaces
namespace	internal::DoFHandlerImplementation
namespace	DoFRenumbering
namespace	DoFTools

Classes
class	BlockInfo
	A small class collecting the different BlockIndices involved in global, multilevel and local computations. More...
struct	internal::DoFAccessorImplementation::Inheritance< structdim, dim, spacedim >
class	DoFAccessor< structdim, dim, spacedim, level_dof_access >
class	DoFCellAccessor< dimension_, space_dimension_, level_dof_access >
class	DoFHandler< dim, spacedim >
class	internal::DoFHandlerImplementation::DoFObjects< dim >
class	AffineConstraints< number >

Detailed Description

This topic groups classes and namespaces that have to do with handling degrees of freedom. The central class of this group is the DoFHandler class: it is built on top of a triangulation and a finite element class and allocated degrees of freedom on each cell of the triangulation as required for the finite element space described by the finite element object.

DoFHandler objects are used together with objects of type FiniteElement (or hp::FECollection) to enumerate all the degrees of freedom that exist in a triangulation for this particular finite element. As such, the combination of mesh, finite element, and DoF handler object can be thought of as providing a basis of the finite element space: the mesh provides the locations at which basis functions are defined; the finite element describes what kinds of basis functions exist; and the DoF handler object provides an enumeration of the basis, i.e., it is provides a concrete structure of the space so that we can describe functions in this finite dimensional space by vectors of coefficients.

DoFHandlers extend Triangulation objects (and the other classes in the Grids and Triangulations topic) in that they, too, offer iterators that run over all cells, faces, or other geometric objects that make up a triangulation. These iterators are derived from the triangulation iterators and therefore offer the same functionality, but they also offer additional functions. For example, they allow to query the indices of the degrees of freedom associated with the present cell. Note that DoFHandler classes are not derived from Triangulation, though they use Triangulation objects; the reason is that there can be more than one DoFHandler object that works on the same Triangulation object.

In addition to the DoF handler classes, this group holds a number of auxiliary classes not commonly used in application programs, as well as three classes that are not directly associated with the data structures of the DoFHandler class. The first of these is the AffineConstraints class that stores and treats the constraints associated with hanging nodes. Secondly, the DoFRenumbering namespace offers functions that can reorder degrees of freedom; among its functions are ones that sort degrees of freedom in downstream direction, for example, and ones that sort degrees of freedom in such a way that the bandwidth of associated matrices is minimized. Finally, the DoFTools namespace offers a variety of algorithms around handling degrees of freedom.

In the grand scheme of things, the pieces of this group interact with a variety of other parts of the library: