Identification of the boundary curves in 2D finite elements codes

A simple algorithm for identification of the discretized curves bounding 2D regions is described. For a given FEM net defined by the (domain) nodal connectivity array, a boundary nodal connectivity array is generated. The latter contains subsequent boundary elements defined by nodes lying on the boundaries. Boundary elements are grouped into closed contours forming the curves bounding the region under consideration. The algorithm leads to substantial savings in data preparation time. It can also be used to check the consistency of the input connectivity array. A list of appropriate routines is included.