Generate element connectivity list (jtet) that gives neighbor information. Element connectivity is maintained by LaGriT, but can also be generated by the user with this command.
The jtet attribute contains for each facet of an element the neighboring element and its local face. For 3D grids the jtet relationship is reflexsive; each element-face pair has exactly one neighboring element-face pair. For 2D grids the jtet relationship can include cycles; a triangle or quad edge may have many edge neighbors. In this case the jtet is constructed as a closed cycle where the jtet of one element-edge pair will be a neighboring element-edge pair whose jtet wil be another neighboring element-edge pair and so on until all neighbors are included in the cycle exactly once.
The jtet is constructed by looking at matching node numbers and will use the parent nodes if they exist. Faces with matching node coordinates but different node numbers will not be matched.
For hybrid grids that contain degenerate elements there are two options. If the mesh object attribute jtet_reduce_nnd exists and is set to 1, then faces with repeated node numbers will be matched to faces with the same numbers but not repeated. For example if a degenerate hex has a face 1 1 2 3 and there is an element (prism, tet, pyramid) with face 1 2 3 and if jtet_reduce_nnd is 1, then these faces will be matched. Otherwise they will be marked as external boundary faces.