In addition to the problem data described in Section 3, the user might also wish to specify the nonlinear element functions, and their derivatives, in a systematic way. A particular nonlinear element function is defined in terms of its problem variables and its type; both of these quantities are specified in Section 3. Thus, the only details which remain to be specified are the function and derivative values of the element types and the transformations between elemental and internal variables, if any.
In this section, we present one approach to this issue. As before, data is specified in a file. The file comprises an ordered mixture of indicator and data cards; the latter allow function and derivative definitions in appropriate high-level language statements.