Reference documentation for deal.II version Git 5109843 2018-03-21 23:56:40 +0700

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

## Public Member Functions

ComponentMask (const unsigned int n_components, const bool initializer)

void set (const unsigned int index, const bool value)

unsigned int size () const

bool operator[] (const unsigned int component_index) const

bool represents_n_components (const unsigned int n) const

unsigned int n_selected_components (const unsigned int overall_number_of_components=numbers::invalid_unsigned_int) const

unsigned int first_selected_component (const unsigned int overall_number_of_components=numbers::invalid_unsigned_int) const

std::size_t memory_consumption () const

## Static Public Member Functions

static::ExceptionBase & ExcNoComponentSelected ()

## Detailed Description

This class represents a mask that can be used to select individual vector components of a finite element (see also this glossary entry). It will typically have as many elements as the finite element has vector components, and one can use operator[] to query whether a particular component has been selected.

Note
A "mask" represents a data structure with true and false entries that is generally used to enable or disable an operation for a particular vector component. By this definition, disabled vector components still exist – they are simply not touched. As a consequence, when you apply a component mask for interpolating boundary values (to choose just one example) of a problem with $$C$$ vector components, the input argument that describes the boundary values will still have to provide $$C$$ components even if the mask says that we only want to interpolate a subset of these components onto the finite element space. In other words, a component mask does not represent a reduction operation; it represents a selection.

Objects of this kind are used in many places where one wants to restrict operations to a certain subset of components, e.g. in DoFTools::make_zero_boundary_values() or VectorTools::interpolate_boundary_values(). These objects can either be created by hand, or, simpler, by asking the finite element to generate a component mask from certain selected components using code such as this where we create a mask that only denotes the velocity components of a Stokes element (see Handling vector valued problems):

FESystem<dim> stokes_fe (FE_Q<dim>(2), dim, // Q2 element for the velocities
FE_Q<dim>(1), 1); // Q1 element for the pressure

The result is a component mask that, in 2d, would have values [false, false, true]. Similarly, using

would result in a mask [true, true, false] in 2d. Of course, in 3d, the result would be [true, true, true, false].

Date
2012

Definition at line 80 of file component_mask.h.

## Constructor & Destructor Documentation

default

Initialize a component mask. The default is that a component mask represents a set of components that are all selected, i.e., calling this constructor results in a component mask that always returns true whenever asked whether a component is selected.

inline

Initialize an object of this type with a set of selected components specified by the argument.

Parameters
 component_mask A vector of true/false entries that determine which components of a finite element are selected. If the length of the given vector is zero, then this interpreted as the case where every component is selected.

Definition at line 255 of file component_mask.h.

inline

Initialize the component mask with a number of elements that are either all true or false.

Parameters
 n_components The number of elements of this mask initializer The value each of these elements is supposed to have: either true or false.

Definition at line 262 of file component_mask.h.

## Member Function Documentation

 void ComponentMask::set ( const unsigned int index, const bool value )
inline

Set a particular entry in the mask to a value.

Definition at line 279 of file component_mask.h.

 unsigned int ComponentMask::size ( ) const
inline

If this component mask has been initialized with a mask of size greater than zero, then return the size of the mask represented by this object. On the other hand, if this mask has been initialized as an empty object that represents a mask that is true for every element (i.e., if this object would return true when calling represents_the_all_selected_mask()) then return zero since no definite size is known.

Definition at line 271 of file component_mask.h.

 bool ComponentMask::operator[] ( const unsigned int component_index ) const
inline

Return whether a particular component is selected by this mask. If this mask represents the case of an object that selects all components (e.g. if it is created using the default constructor or is converted from an empty vector of type bool) then this function returns true regardless of the given argument.

Parameters
 component_index The index for which the function should return whether the component is selected. If this object represents a mask in which all components are always selected then any index is allowed here. Otherwise, the given index needs to be between zero and the number of components that this mask represents.

Definition at line 288 of file component_mask.h.

 bool ComponentMask::represents_n_components ( const unsigned int n ) const
inline

Return whether this component mask represents a mask with exactly n components. This is true if either it was initialized with a vector with exactly n entries of type bool (in this case, n must equal the result of size()) or if it was initialized with an empty vector (or using the default constructor) in which case it can represent a mask with an arbitrary number of components and will always say that a component is selected.

Definition at line 306 of file component_mask.h.

 unsigned int ComponentMask::n_selected_components ( const unsigned int overall_number_of_components = numbers::invalid_unsigned_int ) const
inline

Return the number of components that are selected by this mask.

Since empty component masks represent a component mask that would return true for every component, this function may not know the true size of the component mask and it therefore requires an argument that denotes the overall number of components.

If the object has been initialized with a non-empty mask (i.e., if the size() function returns something greater than zero, or equivalently if represents_the_all_selected_mask() returns false) then the argument can be omitted and the result of size() is taken.

Definition at line 316 of file component_mask.h.

 unsigned int ComponentMask::first_selected_component ( const unsigned int overall_number_of_components = numbers::invalid_unsigned_int ) const
inline

Return the index of the first selected component. The argument is there for the same reason it exists with the n_selected_components() function.

The function throws an exception if no component is selected at all.

Definition at line 342 of file component_mask.h.

inline

Return true if this mask represents a default constructed mask that corresponds to one in which all components are selected. If true, then the size() function will return zero.

Definition at line 364 of file component_mask.h.

inline

Return a component mask that contains the union of the components selected by the current object and the one passed as an argument.

Definition at line 373 of file component_mask.h.

inline

Return a component mask that has only those elements set that are set both in the current object as well as the one passed as an argument.

Definition at line 397 of file component_mask.h.

inline

Return whether this object and the argument are identical.

Definition at line 421 of file component_mask.h.

inline

Return whether this object and the argument are not identical.

Definition at line 429 of file component_mask.h.

Determine an estimate for the memory consumption (in bytes) of this object.

Definition at line 47 of file component_mask.cc.

## Friends And Related Function Documentation

friend

Write a component mask to an output stream. If the component mask represents one where all components are selected without specifying a particular size of the mask, then it writes the string [all components selected] to the stream. Otherwise, it prints the component mask in a form like [true,true,true,false].

Parameters
Returns
A reference to the first argument.

Definition at line 24 of file component_mask.cc.