* class, see the general
* documentation of this class
* for more information.
+ *
+ * However, if this object refers
+ * to an FEFaceValues of
+ * FESubfaceValues object, then
+ * the JxW_values correspond to
+ * the Jacobian of the
+ * transformation of the face,
+ * not the cell, i.e. the
+ * dimensionality is that of a
+ * surface measure, not of a
+ * volume measure. In this case,
+ * it is computed from the
+ * boundary forms, rather than
+ * the Jacobian matrix.
*/
std::vector<double> JxW_values;
const std::vector<Point<dim> > & get_quadrature_points () const;
/**
- * Mapped quadrature weight. This
- * is the Jacobi determinant
- * times the weight of the
- *<tt>i</tt>th unit quadrature point.
+ * Mapped quadrature weight. If
+ * this object refers to a volume
+ * evaluation (i.e. the derived
+ * class is of type FEValues),
+ * then this is the Jacobi
+ * determinant times the weight
+ * of the *<tt>i</tt>th unit
+ * quadrature point.
*
- * On faces, this is the mapped
- * surface element.
+ * For surface evaluations
+ * (i.e. classes FEFaceValues or
+ * FESubfaceValues), is the
+ * mapped surface element times
+ * the weight of the quadrature
+ * point.
*/
double JxW (const unsigned int quadrature_point) const;
/**
* Pointer to the array holding
- * the Jacobi determinant times the
- * quadrature weight at the different
- * quadrature points.
+ * the values returned by JxW().
*/
const std::vector<double> & get_JxW_values () const;
/**
- * Extend the interface of FEValuesBase by surface values.
+ * Extend the interface of FEValuesBase to values that only make sense
+ * when evaluating something on the surface of a cell. All the data
+ * that is available in the interior of cells is also available here.
*
* On surfaces of mesh cells, normal vectors and boundary forms are
* additional values that can be computed. This class provides the
* interface to access those. Implementations are in derived classes
* FEFaceValues and FESubfaceValues.
*
+ * The boundary form is the cross product of the images of the unit
+ * tangential vectors. Therefore, it is the unit normal vector
+ * multiplied with the surface element. Since it may be cheaper to
+ * compute the boundary form immediately, use this value to integrate
+ * <tt>n.ds</tt>.
+ *
* See FEValuesBase
*
* @author Wolfgang Bangerth, 1998, Guido Kanschat, 2000, 2001