From: hartmann Date: Mon, 3 Sep 2001 16:33:48 +0000 (+0000) Subject: Report on higher order mapping functions. Documentation for MappingQ. X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=abd0065bb74c8b32cb975badc688f6a5ea402c6d;p=dealii-svn.git Report on higher order mapping functions. Documentation for MappingQ. git-svn-id: https://svn.dealii.org/trunk@4941 0785d39b-7218-0410-832d-ea1e28bc413d --- diff --git a/deal.II/doc/reports/mapping_q/img1.gif b/deal.II/doc/reports/mapping_q/img1.gif new file mode 100644 index 0000000000..3afa2db8d0 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img1.gif differ diff --git a/deal.II/doc/reports/mapping_q/img10.gif b/deal.II/doc/reports/mapping_q/img10.gif new file mode 100644 index 0000000000..f1b1253237 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img10.gif differ diff --git a/deal.II/doc/reports/mapping_q/img11.gif b/deal.II/doc/reports/mapping_q/img11.gif new file mode 100644 index 0000000000..f3a7034453 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img11.gif differ diff --git a/deal.II/doc/reports/mapping_q/img12.gif b/deal.II/doc/reports/mapping_q/img12.gif new file mode 100644 index 0000000000..7e40605864 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img12.gif differ diff --git a/deal.II/doc/reports/mapping_q/img13.gif b/deal.II/doc/reports/mapping_q/img13.gif new file mode 100644 index 0000000000..c7a3aeaac1 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img13.gif differ diff --git a/deal.II/doc/reports/mapping_q/img14.gif b/deal.II/doc/reports/mapping_q/img14.gif new file mode 100644 index 0000000000..e9c184cb6e Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img14.gif differ diff --git a/deal.II/doc/reports/mapping_q/img15.gif b/deal.II/doc/reports/mapping_q/img15.gif new file mode 100644 index 0000000000..0bab0d582f Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img15.gif differ diff --git a/deal.II/doc/reports/mapping_q/img16.gif b/deal.II/doc/reports/mapping_q/img16.gif new file mode 100644 index 0000000000..655453fbd7 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img16.gif differ diff --git a/deal.II/doc/reports/mapping_q/img17.gif b/deal.II/doc/reports/mapping_q/img17.gif new file mode 100644 index 0000000000..d16cfa2bcf Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img17.gif differ diff --git a/deal.II/doc/reports/mapping_q/img18.gif b/deal.II/doc/reports/mapping_q/img18.gif new file mode 100644 index 0000000000..273a7d4f6a Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img18.gif differ diff --git a/deal.II/doc/reports/mapping_q/img19.gif b/deal.II/doc/reports/mapping_q/img19.gif new file mode 100644 index 0000000000..7254199946 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img19.gif differ diff --git a/deal.II/doc/reports/mapping_q/img2.gif b/deal.II/doc/reports/mapping_q/img2.gif new file mode 100644 index 0000000000..91c5ff7155 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img2.gif differ diff --git a/deal.II/doc/reports/mapping_q/img20.gif b/deal.II/doc/reports/mapping_q/img20.gif new file mode 100644 index 0000000000..55356960d2 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img20.gif differ diff --git a/deal.II/doc/reports/mapping_q/img21.gif b/deal.II/doc/reports/mapping_q/img21.gif new file mode 100644 index 0000000000..0398f353ff Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img21.gif differ diff --git a/deal.II/doc/reports/mapping_q/img22.gif b/deal.II/doc/reports/mapping_q/img22.gif new file mode 100644 index 0000000000..de29603058 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img22.gif differ diff --git a/deal.II/doc/reports/mapping_q/img23.gif b/deal.II/doc/reports/mapping_q/img23.gif new file mode 100644 index 0000000000..b359f552c0 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img23.gif differ diff --git a/deal.II/doc/reports/mapping_q/img24.gif b/deal.II/doc/reports/mapping_q/img24.gif new file mode 100644 index 0000000000..dc96919673 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img24.gif differ diff --git a/deal.II/doc/reports/mapping_q/img25.gif b/deal.II/doc/reports/mapping_q/img25.gif new file mode 100644 index 0000000000..e7d03d09ac Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img25.gif differ diff --git a/deal.II/doc/reports/mapping_q/img26.gif b/deal.II/doc/reports/mapping_q/img26.gif new file mode 100644 index 0000000000..078c5eb10f Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img26.gif differ diff --git a/deal.II/doc/reports/mapping_q/img27.gif b/deal.II/doc/reports/mapping_q/img27.gif new file mode 100644 index 0000000000..99087f0b31 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img27.gif differ diff --git a/deal.II/doc/reports/mapping_q/img28.gif b/deal.II/doc/reports/mapping_q/img28.gif new file mode 100644 index 0000000000..707c7df44a Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img28.gif differ diff --git a/deal.II/doc/reports/mapping_q/img29.gif b/deal.II/doc/reports/mapping_q/img29.gif new file mode 100644 index 0000000000..edd5bfb79a Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img29.gif differ diff --git a/deal.II/doc/reports/mapping_q/img3.gif b/deal.II/doc/reports/mapping_q/img3.gif new file mode 100644 index 0000000000..55356960d2 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img3.gif differ diff --git a/deal.II/doc/reports/mapping_q/img30.gif b/deal.II/doc/reports/mapping_q/img30.gif new file mode 100644 index 0000000000..cd04d32788 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img30.gif differ diff --git a/deal.II/doc/reports/mapping_q/img31.gif b/deal.II/doc/reports/mapping_q/img31.gif new file mode 100644 index 0000000000..e9a9003034 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img31.gif differ diff --git a/deal.II/doc/reports/mapping_q/img32.gif b/deal.II/doc/reports/mapping_q/img32.gif new file mode 100644 index 0000000000..38306f0b72 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img32.gif differ diff --git a/deal.II/doc/reports/mapping_q/img33.gif b/deal.II/doc/reports/mapping_q/img33.gif new file mode 100644 index 0000000000..b8d2b5021c Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img33.gif differ diff --git a/deal.II/doc/reports/mapping_q/img34.gif b/deal.II/doc/reports/mapping_q/img34.gif new file mode 100644 index 0000000000..aea6c3eed7 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img34.gif differ diff --git a/deal.II/doc/reports/mapping_q/img35.gif b/deal.II/doc/reports/mapping_q/img35.gif new file mode 100644 index 0000000000..2dbcd8168b Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img35.gif differ diff --git a/deal.II/doc/reports/mapping_q/img36.gif b/deal.II/doc/reports/mapping_q/img36.gif new file mode 100644 index 0000000000..f8bfdf0abe Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img36.gif differ diff --git a/deal.II/doc/reports/mapping_q/img37.gif b/deal.II/doc/reports/mapping_q/img37.gif new file mode 100644 index 0000000000..65d5c0741f Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img37.gif differ diff --git a/deal.II/doc/reports/mapping_q/img38.gif b/deal.II/doc/reports/mapping_q/img38.gif new file mode 100644 index 0000000000..231b0e86a1 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img38.gif differ diff --git a/deal.II/doc/reports/mapping_q/img39.gif b/deal.II/doc/reports/mapping_q/img39.gif new file mode 100644 index 0000000000..ff944c6f4e Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img39.gif differ diff --git a/deal.II/doc/reports/mapping_q/img4.gif b/deal.II/doc/reports/mapping_q/img4.gif new file mode 100644 index 0000000000..3ebda319e9 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img4.gif differ diff --git a/deal.II/doc/reports/mapping_q/img40.gif b/deal.II/doc/reports/mapping_q/img40.gif new file mode 100644 index 0000000000..b4a8f2ab8f Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img40.gif differ diff --git a/deal.II/doc/reports/mapping_q/img41.gif b/deal.II/doc/reports/mapping_q/img41.gif new file mode 100644 index 0000000000..d95a0f01c1 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img41.gif differ diff --git a/deal.II/doc/reports/mapping_q/img42.gif b/deal.II/doc/reports/mapping_q/img42.gif new file mode 100644 index 0000000000..d28a084615 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img42.gif differ diff --git a/deal.II/doc/reports/mapping_q/img43.gif b/deal.II/doc/reports/mapping_q/img43.gif new file mode 100644 index 0000000000..b3d5a1a909 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img43.gif differ diff --git a/deal.II/doc/reports/mapping_q/img44.gif b/deal.II/doc/reports/mapping_q/img44.gif new file mode 100644 index 0000000000..86cc1179d7 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img44.gif differ diff --git a/deal.II/doc/reports/mapping_q/img45.gif b/deal.II/doc/reports/mapping_q/img45.gif new file mode 100644 index 0000000000..09dcfea500 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img45.gif differ diff --git a/deal.II/doc/reports/mapping_q/img46.gif b/deal.II/doc/reports/mapping_q/img46.gif new file mode 100644 index 0000000000..1e1590e8a6 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img46.gif differ diff --git a/deal.II/doc/reports/mapping_q/img47.gif b/deal.II/doc/reports/mapping_q/img47.gif new file mode 100644 index 0000000000..0239071c22 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img47.gif differ diff --git a/deal.II/doc/reports/mapping_q/img48.gif b/deal.II/doc/reports/mapping_q/img48.gif new file mode 100644 index 0000000000..15674c4a25 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img48.gif differ diff --git a/deal.II/doc/reports/mapping_q/img49.gif b/deal.II/doc/reports/mapping_q/img49.gif new file mode 100644 index 0000000000..ad5cc2d73e Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img49.gif differ diff --git a/deal.II/doc/reports/mapping_q/img5.gif b/deal.II/doc/reports/mapping_q/img5.gif new file mode 100644 index 0000000000..95d2ce653d Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img5.gif differ diff --git a/deal.II/doc/reports/mapping_q/img50.gif b/deal.II/doc/reports/mapping_q/img50.gif new file mode 100644 index 0000000000..6f0caf54da Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img50.gif differ diff --git a/deal.II/doc/reports/mapping_q/img51.gif b/deal.II/doc/reports/mapping_q/img51.gif new file mode 100644 index 0000000000..fd296a61dc Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img51.gif differ diff --git a/deal.II/doc/reports/mapping_q/img6.gif b/deal.II/doc/reports/mapping_q/img6.gif new file mode 100644 index 0000000000..2d477dab17 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img6.gif differ diff --git a/deal.II/doc/reports/mapping_q/img7.gif b/deal.II/doc/reports/mapping_q/img7.gif new file mode 100644 index 0000000000..18070cf724 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img7.gif differ diff --git a/deal.II/doc/reports/mapping_q/img8.gif b/deal.II/doc/reports/mapping_q/img8.gif new file mode 100644 index 0000000000..91c5ff7155 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img8.gif differ diff --git a/deal.II/doc/reports/mapping_q/img9.gif b/deal.II/doc/reports/mapping_q/img9.gif new file mode 100644 index 0000000000..5e6633a055 Binary files /dev/null and b/deal.II/doc/reports/mapping_q/img9.gif differ diff --git a/deal.II/doc/reports/mapping_q/index.html b/deal.II/doc/reports/mapping_q/index.html new file mode 100644 index 0000000000..a669c655b1 --- /dev/null +++ b/deal.II/doc/reports/mapping_q/index.html @@ -0,0 +1,863 @@ + + + + +No Title + + + + + + + + + +(Taken from the thesis (in preparation) of Ralf Hartmann) + +

+

+Higher order Boundary approximation + + +

+
+Ralf Hartmann, 2001 +
+University of Heidelberg +

+

+Introduction: In many numerical applications the domain + + +$\Omega\subset\mathbb R^d$, +$d\geq 2$ +is not a polygonal domain but includes +curved boundaries. For these cases the boundary cannot be represented +exactly by the discretised boundary. Approximating the boundary by a +piecewise linear boundary interpolation, i.e. by a polygonal boundary, +may in some applications not be sufficient. In these cases a higher +order boundary approximation, for example by piecewise quadratic or +cubic boundary interpolation, must be employed. In the finite element +framework this higher order boundary approximation is realized by +mapping the reference element $\hat K$ +to the element + + +$K=\sigma_K(\hat K)$ +in real space, whereas on cells K at the +boundary, i.e. + +$\partial K\cap\Gamma=\emptyset$, +the mappings +$\sigma_K$ +are given by polynomial functions of higher degree. + +

+Elements with general mapping functions $\sigma_K$. We begin +by first introducing some notation. Let $K\in T_h$ +be a cell of the +triangulation Th with + +$K=\sigma_K(\hat K)$, +where $\sigma_K$is a smooth bijective mapping of the reference element (unit square) +$\hat K$ +to the element K in real space, see Figure +1. +
+

   + + + +
Figure: +Mapping $\sigma $ +of reference element $\hat K$ +to the element K in real space.
+
+ + +\includegraphics[scale=0.3]{figures/m1.ps}
+
+
+

+In the following and for the sake of simplicity we suppress the letter +K in the subscript and write $\sigma $ +instead of $\sigma_K$. + +

+Mapping functions of higher polynomial degree. A mapping +function $\sigma $, +that maps the reference element $\hat K$ +to an +arbitrary quadrilateral cell K with straight boundaries, can in +general be represented by a bilinear function, i.e. by a +Q1-mapping. For the case that the cell K includes curved +boundaries it might be necessary to employ polynomial mapping +functions of higher degree. + +

+Given a degree p>0, a cell $K\in T_h$, +and (p+1)d mapping +support points $p_i\in K$, + + +$i=0,\ldots,(p+1)^d-1$, +we define a +Qp-mapping + +$\sigma\in [Q_p]^d$ +as follows +

+
+ + + + + + +
 \begin{displaymath} +\sigma(\hat x)=\sum_{i=0}^{(p+1)^d-1}p_i\phi_i(\hat x). +\end{displaymath} +(1)
+
+

+Here, $\phi_i$, + + +$i=0,\ldots,(p+1)^d-1$ +denote the Lagrange interpolation +basis functions, that satisfy +

+
+ + + +\begin{displaymath}\phi_i(\hat p_j)=\delta_{ij}, \quad i,j=0,\ldots,(p+1)^d-1, +\end{displaymath} +
+
+

+where $\hat p_i$, + + +$i=0,\ldots,(p+1)^d-1$ +denote the Lagrange support +points on the unit cell $\hat K$. +The definition of $\sigma $(1) ensures that each of the unit support points +$\hat p_i$ +is mapped onto the corresponding mapping support points +pi, i.e. +

+
+ + + + + + +
 \begin{displaymath} +\sigma(\hat p_i)=p_i, \quad i=0,\ldots,(p+1)^d-1 +\end{displaymath} +(2)
+
+

+Analogous to Lagrange finite elements the unit Lagrange support points +$\hat p_i$ +are equidistantly distributed on $\hat K$ +based on a tensor +product mesh. In the following we only consider the two-dimensional +case, d=2. For that case, Figure 2 +shows the distributions of the unit support points $\hat p_i$, + + +$i=0,\ldots,(p+1)^2-1$ +for degrees + +$p=1,\ldots ,4$. +
+
   + + + +
Figure: +Unit support points $\hat p_i$, + + +$0\leq i<(p+1)^2$, +for degrees + +$p=1,\ldots ,4$.
+
+ + +\includegraphics*[width=2.750cm]{../../../phd/figures/boundary_approximation/mapping/unit_points_q1_n.eps} + + +\includegraphics*[width=2.750cm]{../../../phd/figures/boundary_approximation/mapping/unit_points_q2_n.eps} + + +\includegraphics*[width=2.750cm]{../../../phd/figures/boundary_approximation/mapping/unit_points_q3_n.eps} + + +\includegraphics*[width=2.750cm]{../../../phd/figures/boundary_approximation/mapping/unit_points_q4_n.eps}
+
+
+Let the ordering and numbering of the unit support points be as +follows: first the corners, then the points on the edges and finally +the inner support points, see also Figure +2. Thus the first 4p points are placed +on the boundary + +$\partial\hat K$ +of the reference cell, i.e. +

+
+ + + +\begin{displaymath}\hat p_k\in\partial\hat K, \quad k=0,\ldots,4p-1. +\end{displaymath} +
+
+

+According to (2) these points are mapped to the +mapping support points pk, + +$k=0,\ldots,4p-1$ +that are chosen to be +placed on the boundary of the real cell in approximatively equal +distances, i.e. +

+
+ + + +\begin{displaymath}p_k\in\partial K, \quad k=0,\ldots,4p-1. +\end{displaymath} +
+
+

+While the support points pk, + +$k=0,\ldots,4p-1$ +on the boundary are +given by the boundary description of the real cell K, the inner + mapping support points +

+
+ + + +\begin{displaymath}p_i\in K\setminus\partial K, \quad i=4p,\ldots,(p+1)^2-1 +\end{displaymath} +
+
+

+are not uniquely determined. Numerical tests show that it is not a +trivial task to define the positions of the inner mapping support +points appropriately. If they are not chosen appropriately the +resulting mapping $\sigma $ +for a cell K may degenerate, i.e. the +mapping $\sigma $ +for some cell K may not be bijective. + +

+Computation of inner support points by smooth transformation. +In the following we will define the positions of the inner mapping +support points so that the mapping does - in all cases - not +degenerate. To this end, we employ an approach for the mapping of the +support points, that is in the style of the smooth transformations +that is used to transform structured triangulations to match complex +boundary discriptions. In the following, again for notational +convenience, we consider only the two-dimensional case. + +

+The smooth transformation mentioned above is based on solutions to the +Laplace equation that is solved on the reference cell $\hat K$. +Discrete boundary conditions are imposed that are given by the +coordinates of the mapping support points pk, + +$k=0,\ldots,4p-1$, +on +the boundary of the cell K in real space. + +

+To be more explicite we define a Laplace problem on the unit +cell $\hat K$ +

+
+ + + + + + +
 \begin{displaymath} +\begin{array}{rcll} +-\hat\Delta \sigma_l(\hat x)&=&0, \quad... +...l \hat K}(\hat x), \quad &\hat x\in \partial\hat K, +\end{array}\end{displaymath} +(3)
+
+

+for each component $\sigma_l$, +l=1,2, of the Qp mapping +$\sigma $. +Here, the discrete boundary function + +$g\in [Q_p]^2$ +is +given by +

+
+ + + + + + +
 \begin{displaymath} +g_l(\hat x)=\sum_{i=0}^{4p-1}(p_i)_l\phi_i(\hat x), \quad l=1,\ldots,d +\end{displaymath} +(4)
+
+

+where (pi)l denotes the lth component of the support point pi, +and $\phi_i$ +the corresponding Lagrangian interpolation basis +function. We recall that the numbering of the mapping support points +involves + +$p_k\in\partial K$ +for + +$k=0,\ldots,4p-1$. +Substituting +

+
+ + + + + + +
 \begin{displaymath} +\tilde \sigma_l:=\sigma_l-g_l, \quad l=1,2, +\end{displaymath} +(5)
+
+

+into the Laplace problem (3) yields the +zero boundary value problem, +

+
+ + + + + + +
 \begin{displaymath} +\begin{array}{rcll} +-\hat\Delta \tilde\sigma_l(\hat x)&=&\h... +...gma_l(\hat x)&=&0, \quad &\hat x\in \partial\hat K, +\end{array}\end{displaymath} +(6)
+
+

+that is equivalent to the following variational formulation +

+
+ + + +\begin{displaymath}\tilde\sigma_l\in H^1_0(\hat K):\qquad +(\hat\nabla \tilde\si... +...\hat\nabla \phi)_{\hat K} \quad \forall \phi\in H^1_0(\hat K). \end{displaymath} +
+
+

+Discretisation of this problem +

+
+ + + +\begin{displaymath}\tilde\sigma_l\in Q_p(\hat K):\qquad +(\hat\nabla \tilde\sigm... +...bla \phi_{4p+i})_{\hat K} \quad \forall i=0,\ldots, (p-1)^2-1, \end{displaymath} +
+
+

+and recalling definitions (1), (5) and (4) gives +

+
+ + + + + + +
 \begin{displaymath} +\sum_{j=1}^{(p-1)^2}S_{ij}(p_{4p+j})_l=-\sum_{k=0}^{4p-1}T_{ik}(p_k)_l, \quad i=0, \ldots, (p-1)^2-1, +\end{displaymath} +(7)
+
+

+with the matrices + +$S_{ij}\in\mathbb R^{(p-1)^2\times(p-1)^2}$ +and + +$T_{ik}\in\mathbb R^{(p-1)^2\times 4p}$ +given by +

+
+ + + +\begin{displaymath}S_{ij}=(\hat\nabla \phi_{4p+i}, \hat\nabla \phi_{4p+j})_{\hat K}, \quad i,j=0,\ldots,(p-1)^2-1, +\end{displaymath} +
+
+

+and +

+
+ + + +\begin{displaymath}T_{ik}=(\hat\nabla \phi_{4p+i}, \hat\nabla \phi_k)_{\hat K}, \quad i=0,\ldots,(p-1)^2-1,\quad k=0,\ldots,4p-1. +\end{displaymath} +
+
+

+The solutions to problem (7) for l=1,2 are +

+
+ + + +\begin{displaymath}(p_{4p+j})_l=-\sum_{i=0}^{(p-1)^2-1}\sum_{k=0}^{4p-1}S^{-1}_{ji}T_{ik}(p_k)_l, \quad j=0,\ldots,(p-1)^2-1, +\end{displaymath} +
+
+

+that may be written in compact form: +

+
+ + + + + + +
 \begin{displaymath} +p_{4p+j}=\sum_{k=0}^{4p-1}c_{jk}p_k, \quad j=0,\ldots,(p-1)^2-1, +\end{displaymath} +(8)
+
+

+where cjk represents the coefficient +

+
+ + + + + + +
 \begin{displaymath} +c_{jk}=-\sum_{i=0}^{(p-1)^2-1}S^{-1}_{ji}T_{ik}. +\end{displaymath} +(9)
+
+

+of the linear combination (8), that +represents the dependency of the jth inner mapping support point +p4p+j on the support points pk, + +$k=0,\ldots,4p-1$, +that are +placed on the boundary of the cell K. For a fixed degree p, these +coefficients cjk are the same for the mapping of all cells +K in real space because the cjk depend only on the reference +element $\hat K$. +Therefore the coefficients cjk can be +precomputed and result in following linear combinations: + +

+For p=2 the linear combination turns out to be +

+
+ + + +\begin{displaymath}p_8=\tfrac{1}{16}\sum_{k=0}^3p_k+\tfrac{3}{16}\sum_{k=4}^7p_k, +\end{displaymath} +
+
+

+see also Figure 3, left. +
+
   + + + +
Figure 3: +Left: Coefficients c8,k for Q2 mapping. Right: Coefficients c12,k for Q3 mapping.
+
+ + +\includegraphics*[scale=0.4]{figures/m2.ps}
+
+
+For the case that p=3, Figure 3, right, shows the coefficients c12,k of the linear combination for the inner mapping support point p12. The coefficents for the points p13, p14 and p15 can be obtain by rotation of the coefficients. + +

+Implementation in deal.II. The coefficients cjk, see +(9), are represented in the MappingQ +class by the laplace_on_quad_vector as follows +

+
+ + + +\begin{displaymath}\mbox{\textit{laplace\_on\_quad\_vector}[j][k]}=c_{jk} +\end{displaymath} +
+
+

+These coefficients are the same for the mapping of all cells +K in real space because the cjk depend only on the reference +element $\hat K$. +Hence for a given degree p the +laplace_on_quad_vector can be filled by the constructor of +the MappingQ class. This is done by calling the +MappingQ::set_laplace_on_quad_vector function that +includes the coefficients hardcoded for p=2 and p=3 in d=2dimensions, and a routine for computing the coefficients according to +(9) for all other cases. The mapping support +points $p_i\in K$, + + +$i=0,\ldots,(p+1)^d-1$ +are computed once for each +MappingQ object by the +MappingQ::compute_support_points_laplace that is invoked +by the virtual compute_mapping_support_points function of +the base Mapping class. In +MappingQ::compute_support_points_laplace, first the 4ppoints on the boundary of the cell are computed (by calling +MappingQ::add_line_support_points), then by calling +MappingQ::apply_laplace_vector the remaining (p-1)2inner mapping supports points are computed, where +MappingQ::apply_laplace_vector just performes the linear +combination given in (8). +
+ +
+Ralf Hartmann +
2001-09-03 +
+ +