From da4e5f393ef7587e39084249f92e563bef20a4b8 Mon Sep 17 00:00:00 2001 From: wolf Date: Wed, 1 Jun 2005 14:48:40 +0000 Subject: [PATCH] Update a number of comments. git-svn-id: https://svn.dealii.org/trunk@10808 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/deal.II/include/fe/fe_values.h | 48 ++++++++++++++++++++------ 1 file changed, 38 insertions(+), 10 deletions(-) diff --git a/deal.II/deal.II/include/fe/fe_values.h b/deal.II/deal.II/include/fe/fe_values.h index eec716d7b3..3cab860c5d 100644 --- a/deal.II/deal.II/include/fe/fe_values.h +++ b/deal.II/deal.II/include/fe/fe_values.h @@ -165,6 +165,20 @@ class FEValuesData * 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 JxW_values; @@ -964,21 +978,27 @@ class FEValuesBase : protected FEValuesData const std::vector > & get_quadrature_points () const; /** - * Mapped quadrature weight. This - * is the Jacobi determinant - * times the weight of the - *ith 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 *ith 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 & get_JxW_values () const; @@ -1742,13 +1762,21 @@ class FEValues : public FEValuesBase /** - * 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 + * n.ds. + * * See FEValuesBase * * @author Wolfgang Bangerth, 1998, Guido Kanschat, 2000, 2001 -- 2.39.5