Fig. 4

Illustration of the \(\hbox {RT}_{0}\)shape functions in parametric space. The normal projections of the \(\hbox {RT}_{0}\) shape functions are constant along the edge of a finite element in the parametric space \({\mathcal {A}}\). The projection of the shape function associated with edge K onto the edge \(\mathcal {E}_K\) is given by and onto all other edges \(\widehat{\mathcal {E}}_L\) with \(L\ne K\) is . The factor 1/2 is due to the length of the element edge in the parametric space such that