Element fields

The topology of the tetrahedral elements is stored in field kontet(1..4,*). This field is dynamically updated during mesh refinement. The next free entry in kontet is pointed to by ifreetet, the entries kontet(4,*) of entries in the field which have not been used yet point to a next free entry. The field kontet is used for the new refined mesh. Entries belonging to element numbers of the part of the mesh which is not refined are not available for the new tetrahedral elements since they are still part of the mesh after refinement. Also the element numbers of elements which are refined are kept (and are not available for the new, refined mesh) and considered as “parent” elements of the newly created elements. Therefore, at the start of the mesh refinement the tetrahedral elements in the part of the mesh to be refined are copied (and considered as the initial mesh in the refinement procedure) such that they occupy the lowest possible free element numbers, i.e. any numbers not used by any element of the unrefined mesh. The corresponding middle nodes of these elements, if any, are stored in field kontetor(1..6,*). The field kontetor is static, i.e. it only contains the middles nodes of the quadratic tetrahedral elements of the unrefined mesh. This field is used to calculate field ifacext and is discarded immediately afterwards.

**Figure 198:** Node, edge and face numbering within a tetrahedral element
$\begin{figure}\epsfig{file=tet.eps,width=10cm}\end{figure}$

Fields with the same number of lines as kontet are ifatet(1..4,*), bc(1..4,*), cg(1..3,*) and iedtet(1..6,*). They contain:

ifatet(1..4,*): the numbers of the faces belonging to the tetrahedral element. The order corresponds to Figure 198. The sign of the face number is the sign of the expression for the face equation in which the coordinates of the node opposite to the face (within the same element) were substituted.
bc(1..4,*): bc(1..3,*) contains the coordinates of the center of the circumscribed sphere of the element, bc(4,*) contains its radius.
cg(1..3,*): contains the coordinates of the center of gravity of the element.
iedtet(1..6,*): contains the number of the edges belonging to the element corresponding to the order in Figure 198.

All these fields are dynamic. The actual size used for allocation purposes is netet_.