Face fields

Figure 183: Node per face relationship

Faces are stored in field ifac(1..4,*). For a given node i ipofa(i) points to a face in ifac for which i is the lowest node number. The node numbers of this face are stored in entries ifac(1..3,ipofa(i)) in ascending order. The entry ifac(4,ipofa(i)) points to another face for which node i is also the lowest node, if any. If there exists no face for which i is the lowest node number ipofa(i)=0 (Figure 183). The scalar ifreefa points to a free entry in field ifac. For any line j in ifac which is not used yet ifac(4,j) points to the next free entry.

Other fields with a similar number of lines as ifac are itetfa, planfa and iexternfa. They contain:

• itetfa(1..2,i): the tetrahedral elements to which face i belongs. For an external face the second entry is zero.
• planfa(1..4,i): the equation of the face in the form ax+by+cz+d=0, with $\Vert(a,b,c)\Vert=1$.
• iexternfa(i): takes a nonzero value j for an external face, else zero. A nonzero value points to a parent external face (an external face belonging to the unrefined mesh) which is in the immediate neighborhood of face i. The parent external face information is stored in fields ifacext(1..6,*) and ifacexted(1..3,*). These fields are static and created at the start of the refinement. ifacext(1..6,j) contains the nodes belonging to face j, ifacexted(1..3,j) contains the external edges belonging to the face. Information on these external edges, e.g. external edge j, is stored in isharp(j), iedgext(1..3,j) and iedgeextfa(1..2,j). The reader is referred to the previous section for information on these fields. All of these fields are needed for the nodal projection at the end of the refinement.

All these fields (except the external ones) are dynamically adjusted during mesh refinement.