QGaussOneOverR< dim > Class Template Reference

#include <deal.II/base/quadrature_lib.h>

Inheritance diagram for QGaussOneOverR< dim >:

Public Member Functions
	QGaussOneOverR (const unsigned int n, const Point< dim > singularity, const bool factor_out_singular_weight=false)
	QGaussOneOverR (const unsigned int n, const unsigned int vertex_index, const bool factor_out_singular_weight=false)
Public Member Functions inherited from Quadrature< dim >
	Quadrature (const unsigned int n_quadrature_points=0)
	Quadrature (const SubQuadrature &, const Quadrature< 1 > &)
	Quadrature (const Quadrature< dim !=1 ? 1 :0 > &quadrature_1d)
	Quadrature (const Quadrature< dim > &q)
	Quadrature (Quadrature< dim > &&) noexcept=default
	Quadrature (const std::vector< Point< dim >> &points, const std::vector< double > &weights)
	Quadrature (const std::vector< Point< dim >> &points)
	Quadrature (const Point< dim > &point)
virtual	~Quadrature () override=default
Quadrature &	operator= (const Quadrature< dim > &)
Quadrature &	operator= (Quadrature< dim > &&)=default
bool	operator== (const Quadrature< dim > &p) const
void	initialize (const std::vector< Point< dim >> &points, const std::vector< double > &weights)
unsigned int	size () const
const Point< dim > &	point (const unsigned int i) const
const std::vector< Point< dim > > &	get_points () const
double	weight (const unsigned int i) const
const std::vector< double > &	get_weights () const
std::size_t	memory_consumption () const
template<class Archive >
void	serialize (Archive &ar, const unsigned int version)
bool	is_tensor_product () const
const std::array< Quadrature< 1 >, dim > &	get_tensor_basis () const
Public Member Functions inherited from Subscriptor
	Subscriptor ()
	Subscriptor (const Subscriptor &)
	Subscriptor (Subscriptor &&) noexcept
virtual	~Subscriptor ()
Subscriptor &	operator= (const Subscriptor &)
Subscriptor &	operator= (Subscriptor &&) noexcept
void	subscribe (std::atomic< bool > *const validity, const std::string &identifier="") const
void	unsubscribe (std::atomic< bool > *const validity, const std::string &identifier="") const
unsigned int	n_subscriptions () const
template<typename StreamType >
void	list_subscribers (StreamType &stream) const
void	list_subscribers () const
template<class Archive >
void	serialize (Archive &ar, const unsigned int version)

Static Private Member Functions
static unsigned int	quad_size (const Point< dim > singularity, const unsigned int n)

Additional Inherited Members
Public Types inherited from Quadrature< dim >
using	SubQuadrature = Quadrature< dim - 1 >
Static Public Member Functions inherited from Subscriptor
static ::ExceptionBase &	ExcInUse (int arg1, std::string arg2, std::string arg3)
static ::ExceptionBase &	ExcNoSubscriber (std::string arg1, std::string arg2)
Protected Attributes inherited from Quadrature< dim >
std::vector< Point< dim > >	quadrature_points
std::vector< double >	weights
bool	is_tensor_product_flag
std::unique_ptr< std::array< Quadrature< 1 >, dim > >	tensor_basis

Detailed Description

template<int dim>
class QGaussOneOverR< dim >

A class for Gauss quadrature with \(1/R\) weighting function. This formula can be used to integrate \(1/R \ f(x)\) on the reference element \([0,1]^2\), where \(f\) is a smooth function without singularities, and \(R\) is the distance from the point \(x\) to the vertex \(\xi\), given at construction time by specifying its index. Notice that this distance is evaluated in the reference element.

This quadrature formula is obtained from two QGauss quadrature formulas, upon transforming them into polar coordinate system centered at the singularity, and then again into another reference element. This allows for the singularity to be cancelled by part of the Jacobian of the transformation, which contains \(R\). In practice the reference element is transformed into a triangle by collapsing one of the sides adjacent to the singularity. The Jacobian of this transformation contains \(R\), which is removed before scaling the original quadrature, and this process is repeated for the next half element.

Upon construction it is possible to specify whether we want the singularity removed, or not. In other words, this quadrature can be used to integrate \(g(x) = 1/R\ f(x)\), or simply \(f(x)\), with the \(1/R\) factor already included in the quadrature weights.

Definition at line 293 of file quadrature_lib.h.

Constructor & Destructor Documentation

QGaussOneOverR() [1/2]

template<int dim>

QGaussOneOverR< dim >::QGaussOneOverR	(	const unsigned int	n,
		const Point< dim >	singularity,
		const bool	factor_out_singular_weight = false
	)

This constructor takes three arguments: the order of the Gauss formula, the point of the reference element in which the singularity is located, and whether we include the weighting singular function inside the quadrature, or we leave it in the user function to be integrated.

Traditionally, quadrature formulas include their weighting function, and the last argument is set to false by default. There are cases, however, where this is undesirable (for example when you only know that your singularity has the same order of 1/R, but cannot be written exactly in this way).

In other words, you can use this function in either of the following way, obtaining the same result:

QGaussOneOverR singular_quad(order, q_point, false);
// This will produce the integral of f(x)/R
for(unsigned int i=0; i<singular_quad.size(); ++i)
  integral += f(singular_quad.point(i))*singular_quad.weight(i);

// And the same here
QGaussOneOverR singular_quad_noR(order, q_point, true);

// This also will produce the integral of f(x)/R, but 1/R has to
// be specified.
for(unsigned int i=0; i<singular_quad.size(); ++i) {
  double R = (singular_quad_noR.point(i)-cell->vertex(vertex_id)).norm();
  integral += f(singular_quad_noR.point(i))*singular_quad_noR.weight(i)/R;
}

QGaussOneOverR() [2/2]

template<int dim>

QGaussOneOverR< dim >::QGaussOneOverR	(	const unsigned int	n,
		const unsigned int	vertex_index,
		const bool	factor_out_singular_weight = false
	)

The constructor takes three arguments: the order of the Gauss formula, the index of the vertex where the singularity is located, and whether we include the weighting singular function inside the quadrature, or we leave it in the user function to be integrated. Notice that this is a specialized version of the previous constructor which works only for the vertices of the quadrilateral.

Traditionally, quadrature formulas include their weighting function, and the last argument is set to false by default. There are cases, however, where this is undesirable (for example when you only know that your singularity has the same order of 1/R, but cannot be written exactly in this way).

In other words, you can use this function in either of the following way, obtaining the same result:

QGaussOneOverR singular_quad(order, vertex_id, false);
// This will produce the integral of f(x)/R
for(unsigned int i=0; i<singular_quad.size(); ++i)
  integral += f(singular_quad.point(i))*singular_quad.weight(i);

// And the same here
QGaussOneOverR singular_quad_noR(order, vertex_id, true);

// This also will produce the integral of f(x)/R, but 1/R has to
// be specified.
for(unsigned int i=0; i<singular_quad.size(); ++i) {
  double R = (singular_quad_noR.point(i)-cell->vertex(vertex_id)).norm();
  integral += f(singular_quad_noR.point(i))*singular_quad_noR.weight(i)/R;
}

Member Function Documentation

quad_size()

template<int dim>

static unsigned int QGaussOneOverR< dim >::quad_size ( const Point< dim >  singularity, const unsigned int  n  )

staticprivate

Given a quadrature point and a degree n, this function returns the size of the singular quadrature rule, considering whether the point is inside the cell, on an edge of the cell, or on a corner of the cell.

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

• deal.II/base/quadrature_lib.h